URL
https://opencores.org/ocsvn/openrisc/openrisc/trunk
Subversion Repositories openrisc
[/] [openrisc/] [trunk/] [gnu-dev/] [or1k-gcc/] [gcc/] [tree-ssa-loop-niter.c] - Rev 824
Go to most recent revision | Compare with Previous | Blame | View Log
/* Functions to determine/estimate number of iterations of a loop. Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc. This file is part of GCC. GCC is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version. GCC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GCC; see the file COPYING3. If not see <http://www.gnu.org/licenses/>. */ #include "config.h" #include "system.h" #include "coretypes.h" #include "tm.h" #include "tree.h" #include "tm_p.h" #include "basic-block.h" #include "output.h" #include "tree-pretty-print.h" #include "gimple-pretty-print.h" #include "intl.h" #include "tree-flow.h" #include "tree-dump.h" #include "cfgloop.h" #include "tree-pass.h" #include "ggc.h" #include "tree-chrec.h" #include "tree-scalar-evolution.h" #include "tree-data-ref.h" #include "params.h" #include "flags.h" #include "diagnostic-core.h" #include "tree-inline.h" #include "gmp.h" #define SWAP(X, Y) do { affine_iv *tmp = (X); (X) = (Y); (Y) = tmp; } while (0) /* The maximum number of dominator BBs we search for conditions of loop header copies we use for simplifying a conditional expression. */ #define MAX_DOMINATORS_TO_WALK 8 /* Analysis of number of iterations of an affine exit test. */ /* Bounds on some value, BELOW <= X <= UP. */ typedef struct { mpz_t below, up; } bounds; /* Splits expression EXPR to a variable part VAR and constant OFFSET. */ static void split_to_var_and_offset (tree expr, tree *var, mpz_t offset) { tree type = TREE_TYPE (expr); tree op0, op1; double_int off; bool negate = false; *var = expr; mpz_set_ui (offset, 0); switch (TREE_CODE (expr)) { case MINUS_EXPR: negate = true; /* Fallthru. */ case PLUS_EXPR: case POINTER_PLUS_EXPR: op0 = TREE_OPERAND (expr, 0); op1 = TREE_OPERAND (expr, 1); if (TREE_CODE (op1) != INTEGER_CST) break; *var = op0; /* Always sign extend the offset. */ off = tree_to_double_int (op1); off = double_int_sext (off, TYPE_PRECISION (type)); mpz_set_double_int (offset, off, false); if (negate) mpz_neg (offset, offset); break; case INTEGER_CST: *var = build_int_cst_type (type, 0); off = tree_to_double_int (expr); mpz_set_double_int (offset, off, TYPE_UNSIGNED (type)); break; default: break; } } /* Stores estimate on the minimum/maximum value of the expression VAR + OFF in TYPE to MIN and MAX. */ static void determine_value_range (tree type, tree var, mpz_t off, mpz_t min, mpz_t max) { /* If the expression is a constant, we know its value exactly. */ if (integer_zerop (var)) { mpz_set (min, off); mpz_set (max, off); return; } /* If the computation may wrap, we know nothing about the value, except for the range of the type. */ get_type_static_bounds (type, min, max); if (!nowrap_type_p (type)) return; /* Since the addition of OFF does not wrap, if OFF is positive, then we may add it to MIN, otherwise to MAX. */ if (mpz_sgn (off) < 0) mpz_add (max, max, off); else mpz_add (min, min, off); } /* Stores the bounds on the difference of the values of the expressions (var + X) and (var + Y), computed in TYPE, to BNDS. */ static void bound_difference_of_offsetted_base (tree type, mpz_t x, mpz_t y, bounds *bnds) { int rel = mpz_cmp (x, y); bool may_wrap = !nowrap_type_p (type); mpz_t m; /* If X == Y, then the expressions are always equal. If X > Y, there are the following possibilities: a) neither of var + X and var + Y overflow or underflow, or both of them do. Then their difference is X - Y. b) var + X overflows, and var + Y does not. Then the values of the expressions are var + X - M and var + Y, where M is the range of the type, and their difference is X - Y - M. c) var + Y underflows and var + X does not. Their difference again is M - X + Y. Therefore, if the arithmetics in type does not overflow, then the bounds are (X - Y, X - Y), otherwise they are (X - Y - M, X - Y) Similarly, if X < Y, the bounds are either (X - Y, X - Y) or (X - Y, X - Y + M). */ if (rel == 0) { mpz_set_ui (bnds->below, 0); mpz_set_ui (bnds->up, 0); return; } mpz_init (m); mpz_set_double_int (m, double_int_mask (TYPE_PRECISION (type)), true); mpz_add_ui (m, m, 1); mpz_sub (bnds->up, x, y); mpz_set (bnds->below, bnds->up); if (may_wrap) { if (rel > 0) mpz_sub (bnds->below, bnds->below, m); else mpz_add (bnds->up, bnds->up, m); } mpz_clear (m); } /* From condition C0 CMP C1 derives information regarding the difference of values of VARX + OFFX and VARY + OFFY, computed in TYPE, and stores it to BNDS. */ static void refine_bounds_using_guard (tree type, tree varx, mpz_t offx, tree vary, mpz_t offy, tree c0, enum tree_code cmp, tree c1, bounds *bnds) { tree varc0, varc1, tmp, ctype; mpz_t offc0, offc1, loffx, loffy, bnd; bool lbound = false; bool no_wrap = nowrap_type_p (type); bool x_ok, y_ok; switch (cmp) { case LT_EXPR: case LE_EXPR: case GT_EXPR: case GE_EXPR: STRIP_SIGN_NOPS (c0); STRIP_SIGN_NOPS (c1); ctype = TREE_TYPE (c0); if (!useless_type_conversion_p (ctype, type)) return; break; case EQ_EXPR: /* We could derive quite precise information from EQ_EXPR, however, such a guard is unlikely to appear, so we do not bother with handling it. */ return; case NE_EXPR: /* NE_EXPR comparisons do not contain much of useful information, except for special case of comparing with the bounds of the type. */ if (TREE_CODE (c1) != INTEGER_CST || !INTEGRAL_TYPE_P (type)) return; /* Ensure that the condition speaks about an expression in the same type as X and Y. */ ctype = TREE_TYPE (c0); if (TYPE_PRECISION (ctype) != TYPE_PRECISION (type)) return; c0 = fold_convert (type, c0); c1 = fold_convert (type, c1); if (TYPE_MIN_VALUE (type) && operand_equal_p (c1, TYPE_MIN_VALUE (type), 0)) { cmp = GT_EXPR; break; } if (TYPE_MAX_VALUE (type) && operand_equal_p (c1, TYPE_MAX_VALUE (type), 0)) { cmp = LT_EXPR; break; } return; default: return; } mpz_init (offc0); mpz_init (offc1); split_to_var_and_offset (expand_simple_operations (c0), &varc0, offc0); split_to_var_and_offset (expand_simple_operations (c1), &varc1, offc1); /* We are only interested in comparisons of expressions based on VARX and VARY. TODO -- we might also be able to derive some bounds from expressions containing just one of the variables. */ if (operand_equal_p (varx, varc1, 0)) { tmp = varc0; varc0 = varc1; varc1 = tmp; mpz_swap (offc0, offc1); cmp = swap_tree_comparison (cmp); } if (!operand_equal_p (varx, varc0, 0) || !operand_equal_p (vary, varc1, 0)) goto end; mpz_init_set (loffx, offx); mpz_init_set (loffy, offy); if (cmp == GT_EXPR || cmp == GE_EXPR) { tmp = varx; varx = vary; vary = tmp; mpz_swap (offc0, offc1); mpz_swap (loffx, loffy); cmp = swap_tree_comparison (cmp); lbound = true; } /* If there is no overflow, the condition implies that (VARX + OFFX) cmp (VARY + OFFY) + (OFFX - OFFY + OFFC1 - OFFC0). The overflows and underflows may complicate things a bit; each overflow decreases the appropriate offset by M, and underflow increases it by M. The above inequality would not necessarily be true if -- VARX + OFFX underflows and VARX + OFFC0 does not, or VARX + OFFC0 overflows, but VARX + OFFX does not. This may only happen if OFFX < OFFC0. -- VARY + OFFY overflows and VARY + OFFC1 does not, or VARY + OFFC1 underflows and VARY + OFFY does not. This may only happen if OFFY > OFFC1. */ if (no_wrap) { x_ok = true; y_ok = true; } else { x_ok = (integer_zerop (varx) || mpz_cmp (loffx, offc0) >= 0); y_ok = (integer_zerop (vary) || mpz_cmp (loffy, offc1) <= 0); } if (x_ok && y_ok) { mpz_init (bnd); mpz_sub (bnd, loffx, loffy); mpz_add (bnd, bnd, offc1); mpz_sub (bnd, bnd, offc0); if (cmp == LT_EXPR) mpz_sub_ui (bnd, bnd, 1); if (lbound) { mpz_neg (bnd, bnd); if (mpz_cmp (bnds->below, bnd) < 0) mpz_set (bnds->below, bnd); } else { if (mpz_cmp (bnd, bnds->up) < 0) mpz_set (bnds->up, bnd); } mpz_clear (bnd); } mpz_clear (loffx); mpz_clear (loffy); end: mpz_clear (offc0); mpz_clear (offc1); } /* Stores the bounds on the value of the expression X - Y in LOOP to BNDS. The subtraction is considered to be performed in arbitrary precision, without overflows. We do not attempt to be too clever regarding the value ranges of X and Y; most of the time, they are just integers or ssa names offsetted by integer. However, we try to use the information contained in the comparisons before the loop (usually created by loop header copying). */ static void bound_difference (struct loop *loop, tree x, tree y, bounds *bnds) { tree type = TREE_TYPE (x); tree varx, vary; mpz_t offx, offy; mpz_t minx, maxx, miny, maxy; int cnt = 0; edge e; basic_block bb; tree c0, c1; gimple cond; enum tree_code cmp; /* Get rid of unnecessary casts, but preserve the value of the expressions. */ STRIP_SIGN_NOPS (x); STRIP_SIGN_NOPS (y); mpz_init (bnds->below); mpz_init (bnds->up); mpz_init (offx); mpz_init (offy); split_to_var_and_offset (x, &varx, offx); split_to_var_and_offset (y, &vary, offy); if (!integer_zerop (varx) && operand_equal_p (varx, vary, 0)) { /* Special case VARX == VARY -- we just need to compare the offsets. The matters are a bit more complicated in the case addition of offsets may wrap. */ bound_difference_of_offsetted_base (type, offx, offy, bnds); } else { /* Otherwise, use the value ranges to determine the initial estimates on below and up. */ mpz_init (minx); mpz_init (maxx); mpz_init (miny); mpz_init (maxy); determine_value_range (type, varx, offx, minx, maxx); determine_value_range (type, vary, offy, miny, maxy); mpz_sub (bnds->below, minx, maxy); mpz_sub (bnds->up, maxx, miny); mpz_clear (minx); mpz_clear (maxx); mpz_clear (miny); mpz_clear (maxy); } /* If both X and Y are constants, we cannot get any more precise. */ if (integer_zerop (varx) && integer_zerop (vary)) goto end; /* Now walk the dominators of the loop header and use the entry guards to refine the estimates. */ for (bb = loop->header; bb != ENTRY_BLOCK_PTR && cnt < MAX_DOMINATORS_TO_WALK; bb = get_immediate_dominator (CDI_DOMINATORS, bb)) { if (!single_pred_p (bb)) continue; e = single_pred_edge (bb); if (!(e->flags & (EDGE_TRUE_VALUE | EDGE_FALSE_VALUE))) continue; cond = last_stmt (e->src); c0 = gimple_cond_lhs (cond); cmp = gimple_cond_code (cond); c1 = gimple_cond_rhs (cond); if (e->flags & EDGE_FALSE_VALUE) cmp = invert_tree_comparison (cmp, false); refine_bounds_using_guard (type, varx, offx, vary, offy, c0, cmp, c1, bnds); ++cnt; } end: mpz_clear (offx); mpz_clear (offy); } /* Update the bounds in BNDS that restrict the value of X to the bounds that restrict the value of X + DELTA. X can be obtained as a difference of two values in TYPE. */ static void bounds_add (bounds *bnds, double_int delta, tree type) { mpz_t mdelta, max; mpz_init (mdelta); mpz_set_double_int (mdelta, delta, false); mpz_init (max); mpz_set_double_int (max, double_int_mask (TYPE_PRECISION (type)), true); mpz_add (bnds->up, bnds->up, mdelta); mpz_add (bnds->below, bnds->below, mdelta); if (mpz_cmp (bnds->up, max) > 0) mpz_set (bnds->up, max); mpz_neg (max, max); if (mpz_cmp (bnds->below, max) < 0) mpz_set (bnds->below, max); mpz_clear (mdelta); mpz_clear (max); } /* Update the bounds in BNDS that restrict the value of X to the bounds that restrict the value of -X. */ static void bounds_negate (bounds *bnds) { mpz_t tmp; mpz_init_set (tmp, bnds->up); mpz_neg (bnds->up, bnds->below); mpz_neg (bnds->below, tmp); mpz_clear (tmp); } /* Returns inverse of X modulo 2^s, where MASK = 2^s-1. */ static tree inverse (tree x, tree mask) { tree type = TREE_TYPE (x); tree rslt; unsigned ctr = tree_floor_log2 (mask); if (TYPE_PRECISION (type) <= HOST_BITS_PER_WIDE_INT) { unsigned HOST_WIDE_INT ix; unsigned HOST_WIDE_INT imask; unsigned HOST_WIDE_INT irslt = 1; gcc_assert (cst_and_fits_in_hwi (x)); gcc_assert (cst_and_fits_in_hwi (mask)); ix = int_cst_value (x); imask = int_cst_value (mask); for (; ctr; ctr--) { irslt *= ix; ix *= ix; } irslt &= imask; rslt = build_int_cst_type (type, irslt); } else { rslt = build_int_cst (type, 1); for (; ctr; ctr--) { rslt = int_const_binop (MULT_EXPR, rslt, x); x = int_const_binop (MULT_EXPR, x, x); } rslt = int_const_binop (BIT_AND_EXPR, rslt, mask); } return rslt; } /* Derives the upper bound BND on the number of executions of loop with exit condition S * i <> C. If NO_OVERFLOW is true, then the control variable of the loop does not overflow. EXIT_MUST_BE_TAKEN is true if we are guaranteed that the loop ends through this exit, i.e., the induction variable ever reaches the value of C. The value C is equal to final - base, where final and base are the final and initial value of the actual induction variable in the analysed loop. BNDS bounds the value of this difference when computed in signed type with unbounded range, while the computation of C is performed in an unsigned type with the range matching the range of the type of the induction variable. In particular, BNDS.up contains an upper bound on C in the following cases: -- if the iv must reach its final value without overflow, i.e., if NO_OVERFLOW && EXIT_MUST_BE_TAKEN is true, or -- if final >= base, which we know to hold when BNDS.below >= 0. */ static void number_of_iterations_ne_max (mpz_t bnd, bool no_overflow, tree c, tree s, bounds *bnds, bool exit_must_be_taken) { double_int max; mpz_t d; bool bnds_u_valid = ((no_overflow && exit_must_be_taken) || mpz_sgn (bnds->below) >= 0); if (multiple_of_p (TREE_TYPE (c), c, s)) { /* If C is an exact multiple of S, then its value will be reached before the induction variable overflows (unless the loop is exited in some other way before). Note that the actual induction variable in the loop (which ranges from base to final instead of from 0 to C) may overflow, in which case BNDS.up will not be giving a correct upper bound on C; thus, BNDS_U_VALID had to be computed in advance. */ no_overflow = true; exit_must_be_taken = true; } /* If the induction variable can overflow, the number of iterations is at most the period of the control variable (or infinite, but in that case the whole # of iterations analysis will fail). */ if (!no_overflow) { max = double_int_mask (TYPE_PRECISION (TREE_TYPE (c)) - tree_low_cst (num_ending_zeros (s), 1)); mpz_set_double_int (bnd, max, true); return; } /* Now we know that the induction variable does not overflow, so the loop iterates at most (range of type / S) times. */ mpz_set_double_int (bnd, double_int_mask (TYPE_PRECISION (TREE_TYPE (c))), true); /* If the induction variable is guaranteed to reach the value of C before overflow, ... */ if (exit_must_be_taken) { /* ... then we can strenghten this to C / S, and possibly we can use the upper bound on C given by BNDS. */ if (TREE_CODE (c) == INTEGER_CST) mpz_set_double_int (bnd, tree_to_double_int (c), true); else if (bnds_u_valid) mpz_set (bnd, bnds->up); } mpz_init (d); mpz_set_double_int (d, tree_to_double_int (s), true); mpz_fdiv_q (bnd, bnd, d); mpz_clear (d); } /* Determines number of iterations of loop whose ending condition is IV <> FINAL. TYPE is the type of the iv. The number of iterations is stored to NITER. EXIT_MUST_BE_TAKEN is true if we know that the exit must be taken eventually, i.e., that the IV ever reaches the value FINAL (we derived this earlier, and possibly set NITER->assumptions to make sure this is the case). BNDS contains the bounds on the difference FINAL - IV->base. */ static bool number_of_iterations_ne (tree type, affine_iv *iv, tree final, struct tree_niter_desc *niter, bool exit_must_be_taken, bounds *bnds) { tree niter_type = unsigned_type_for (type); tree s, c, d, bits, assumption, tmp, bound; mpz_t max; niter->control = *iv; niter->bound = final; niter->cmp = NE_EXPR; /* Rearrange the terms so that we get inequality S * i <> C, with S positive. Also cast everything to the unsigned type. If IV does not overflow, BNDS bounds the value of C. Also, this is the case if the computation |FINAL - IV->base| does not overflow, i.e., if BNDS->below in the result is nonnegative. */ if (tree_int_cst_sign_bit (iv->step)) { s = fold_convert (niter_type, fold_build1 (NEGATE_EXPR, type, iv->step)); c = fold_build2 (MINUS_EXPR, niter_type, fold_convert (niter_type, iv->base), fold_convert (niter_type, final)); bounds_negate (bnds); } else { s = fold_convert (niter_type, iv->step); c = fold_build2 (MINUS_EXPR, niter_type, fold_convert (niter_type, final), fold_convert (niter_type, iv->base)); } mpz_init (max); number_of_iterations_ne_max (max, iv->no_overflow, c, s, bnds, exit_must_be_taken); niter->max = mpz_get_double_int (niter_type, max, false); mpz_clear (max); /* First the trivial cases -- when the step is 1. */ if (integer_onep (s)) { niter->niter = c; return true; } /* Let nsd (step, size of mode) = d. If d does not divide c, the loop is infinite. Otherwise, the number of iterations is (inverse(s/d) * (c/d)) mod (size of mode/d). */ bits = num_ending_zeros (s); bound = build_low_bits_mask (niter_type, (TYPE_PRECISION (niter_type) - tree_low_cst (bits, 1))); d = fold_binary_to_constant (LSHIFT_EXPR, niter_type, build_int_cst (niter_type, 1), bits); s = fold_binary_to_constant (RSHIFT_EXPR, niter_type, s, bits); if (!exit_must_be_taken) { /* If we cannot assume that the exit is taken eventually, record the assumptions for divisibility of c. */ assumption = fold_build2 (FLOOR_MOD_EXPR, niter_type, c, d); assumption = fold_build2 (EQ_EXPR, boolean_type_node, assumption, build_int_cst (niter_type, 0)); if (!integer_nonzerop (assumption)) niter->assumptions = fold_build2 (TRUTH_AND_EXPR, boolean_type_node, niter->assumptions, assumption); } c = fold_build2 (EXACT_DIV_EXPR, niter_type, c, d); tmp = fold_build2 (MULT_EXPR, niter_type, c, inverse (s, bound)); niter->niter = fold_build2 (BIT_AND_EXPR, niter_type, tmp, bound); return true; } /* Checks whether we can determine the final value of the control variable of the loop with ending condition IV0 < IV1 (computed in TYPE). DELTA is the difference IV1->base - IV0->base, STEP is the absolute value of the step. The assumptions necessary to ensure that the computation of the final value does not overflow are recorded in NITER. If we find the final value, we adjust DELTA and return TRUE. Otherwise we return false. BNDS bounds the value of IV1->base - IV0->base, and will be updated by the same amount as DELTA. EXIT_MUST_BE_TAKEN is true if we know that the exit must be taken eventually. */ static bool number_of_iterations_lt_to_ne (tree type, affine_iv *iv0, affine_iv *iv1, struct tree_niter_desc *niter, tree *delta, tree step, bool exit_must_be_taken, bounds *bnds) { tree niter_type = TREE_TYPE (step); tree mod = fold_build2 (FLOOR_MOD_EXPR, niter_type, *delta, step); tree tmod; mpz_t mmod; tree assumption = boolean_true_node, bound, noloop; bool ret = false, fv_comp_no_overflow; tree type1 = type; if (POINTER_TYPE_P (type)) type1 = sizetype; if (TREE_CODE (mod) != INTEGER_CST) return false; if (integer_nonzerop (mod)) mod = fold_build2 (MINUS_EXPR, niter_type, step, mod); tmod = fold_convert (type1, mod); mpz_init (mmod); mpz_set_double_int (mmod, tree_to_double_int (mod), true); mpz_neg (mmod, mmod); /* If the induction variable does not overflow and the exit is taken, then the computation of the final value does not overflow. This is also obviously the case if the new final value is equal to the current one. Finally, we postulate this for pointer type variables, as the code cannot rely on the object to that the pointer points being placed at the end of the address space (and more pragmatically, TYPE_{MIN,MAX}_VALUE is not defined for pointers). */ if (integer_zerop (mod) || POINTER_TYPE_P (type)) fv_comp_no_overflow = true; else if (!exit_must_be_taken) fv_comp_no_overflow = false; else fv_comp_no_overflow = (iv0->no_overflow && integer_nonzerop (iv0->step)) || (iv1->no_overflow && integer_nonzerop (iv1->step)); if (integer_nonzerop (iv0->step)) { /* The final value of the iv is iv1->base + MOD, assuming that this computation does not overflow, and that iv0->base <= iv1->base + MOD. */ if (!fv_comp_no_overflow) { bound = fold_build2 (MINUS_EXPR, type1, TYPE_MAX_VALUE (type1), tmod); assumption = fold_build2 (LE_EXPR, boolean_type_node, iv1->base, bound); if (integer_zerop (assumption)) goto end; } if (mpz_cmp (mmod, bnds->below) < 0) noloop = boolean_false_node; else if (POINTER_TYPE_P (type)) noloop = fold_build2 (GT_EXPR, boolean_type_node, iv0->base, fold_build_pointer_plus (iv1->base, tmod)); else noloop = fold_build2 (GT_EXPR, boolean_type_node, iv0->base, fold_build2 (PLUS_EXPR, type1, iv1->base, tmod)); } else { /* The final value of the iv is iv0->base - MOD, assuming that this computation does not overflow, and that iv0->base - MOD <= iv1->base. */ if (!fv_comp_no_overflow) { bound = fold_build2 (PLUS_EXPR, type1, TYPE_MIN_VALUE (type1), tmod); assumption = fold_build2 (GE_EXPR, boolean_type_node, iv0->base, bound); if (integer_zerop (assumption)) goto end; } if (mpz_cmp (mmod, bnds->below) < 0) noloop = boolean_false_node; else if (POINTER_TYPE_P (type)) noloop = fold_build2 (GT_EXPR, boolean_type_node, fold_build_pointer_plus (iv0->base, fold_build1 (NEGATE_EXPR, type1, tmod)), iv1->base); else noloop = fold_build2 (GT_EXPR, boolean_type_node, fold_build2 (MINUS_EXPR, type1, iv0->base, tmod), iv1->base); } if (!integer_nonzerop (assumption)) niter->assumptions = fold_build2 (TRUTH_AND_EXPR, boolean_type_node, niter->assumptions, assumption); if (!integer_zerop (noloop)) niter->may_be_zero = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, niter->may_be_zero, noloop); bounds_add (bnds, tree_to_double_int (mod), type); *delta = fold_build2 (PLUS_EXPR, niter_type, *delta, mod); ret = true; end: mpz_clear (mmod); return ret; } /* Add assertions to NITER that ensure that the control variable of the loop with ending condition IV0 < IV1 does not overflow. Types of IV0 and IV1 are TYPE. Returns false if we can prove that there is an overflow, true otherwise. STEP is the absolute value of the step. */ static bool assert_no_overflow_lt (tree type, affine_iv *iv0, affine_iv *iv1, struct tree_niter_desc *niter, tree step) { tree bound, d, assumption, diff; tree niter_type = TREE_TYPE (step); if (integer_nonzerop (iv0->step)) { /* for (i = iv0->base; i < iv1->base; i += iv0->step) */ if (iv0->no_overflow) return true; /* If iv0->base is a constant, we can determine the last value before overflow precisely; otherwise we conservatively assume MAX - STEP + 1. */ if (TREE_CODE (iv0->base) == INTEGER_CST) { d = fold_build2 (MINUS_EXPR, niter_type, fold_convert (niter_type, TYPE_MAX_VALUE (type)), fold_convert (niter_type, iv0->base)); diff = fold_build2 (FLOOR_MOD_EXPR, niter_type, d, step); } else diff = fold_build2 (MINUS_EXPR, niter_type, step, build_int_cst (niter_type, 1)); bound = fold_build2 (MINUS_EXPR, type, TYPE_MAX_VALUE (type), fold_convert (type, diff)); assumption = fold_build2 (LE_EXPR, boolean_type_node, iv1->base, bound); } else { /* for (i = iv1->base; i > iv0->base; i += iv1->step) */ if (iv1->no_overflow) return true; if (TREE_CODE (iv1->base) == INTEGER_CST) { d = fold_build2 (MINUS_EXPR, niter_type, fold_convert (niter_type, iv1->base), fold_convert (niter_type, TYPE_MIN_VALUE (type))); diff = fold_build2 (FLOOR_MOD_EXPR, niter_type, d, step); } else diff = fold_build2 (MINUS_EXPR, niter_type, step, build_int_cst (niter_type, 1)); bound = fold_build2 (PLUS_EXPR, type, TYPE_MIN_VALUE (type), fold_convert (type, diff)); assumption = fold_build2 (GE_EXPR, boolean_type_node, iv0->base, bound); } if (integer_zerop (assumption)) return false; if (!integer_nonzerop (assumption)) niter->assumptions = fold_build2 (TRUTH_AND_EXPR, boolean_type_node, niter->assumptions, assumption); iv0->no_overflow = true; iv1->no_overflow = true; return true; } /* Add an assumption to NITER that a loop whose ending condition is IV0 < IV1 rolls. TYPE is the type of the control iv. BNDS bounds the value of IV1->base - IV0->base. */ static void assert_loop_rolls_lt (tree type, affine_iv *iv0, affine_iv *iv1, struct tree_niter_desc *niter, bounds *bnds) { tree assumption = boolean_true_node, bound, diff; tree mbz, mbzl, mbzr, type1; bool rolls_p, no_overflow_p; double_int dstep; mpz_t mstep, max; /* We are going to compute the number of iterations as (iv1->base - iv0->base + step - 1) / step, computed in the unsigned variant of TYPE. This formula only works if -step + 1 <= (iv1->base - iv0->base) <= MAX - step + 1 (where MAX is the maximum value of the unsigned variant of TYPE, and the computations in this formula are performed in full precision, i.e., without overflows). Usually, for loops with exit condition iv0->base + step * i < iv1->base, we have a condition of the form iv0->base - step < iv1->base before the loop, and for loops iv0->base < iv1->base - step * i the condition iv0->base < iv1->base + step, due to loop header copying, which enable us to prove the lower bound. The upper bound is more complicated. Unless the expressions for initial and final value themselves contain enough information, we usually cannot derive it from the context. */ /* First check whether the answer does not follow from the bounds we gathered before. */ if (integer_nonzerop (iv0->step)) dstep = tree_to_double_int (iv0->step); else { dstep = double_int_sext (tree_to_double_int (iv1->step), TYPE_PRECISION (type)); dstep = double_int_neg (dstep); } mpz_init (mstep); mpz_set_double_int (mstep, dstep, true); mpz_neg (mstep, mstep); mpz_add_ui (mstep, mstep, 1); rolls_p = mpz_cmp (mstep, bnds->below) <= 0; mpz_init (max); mpz_set_double_int (max, double_int_mask (TYPE_PRECISION (type)), true); mpz_add (max, max, mstep); no_overflow_p = (mpz_cmp (bnds->up, max) <= 0 /* For pointers, only values lying inside a single object can be compared or manipulated by pointer arithmetics. Gcc in general does not allow or handle objects larger than half of the address space, hence the upper bound is satisfied for pointers. */ || POINTER_TYPE_P (type)); mpz_clear (mstep); mpz_clear (max); if (rolls_p && no_overflow_p) return; type1 = type; if (POINTER_TYPE_P (type)) type1 = sizetype; /* Now the hard part; we must formulate the assumption(s) as expressions, and we must be careful not to introduce overflow. */ if (integer_nonzerop (iv0->step)) { diff = fold_build2 (MINUS_EXPR, type1, iv0->step, build_int_cst (type1, 1)); /* We need to know that iv0->base >= MIN + iv0->step - 1. Since 0 address never belongs to any object, we can assume this for pointers. */ if (!POINTER_TYPE_P (type)) { bound = fold_build2 (PLUS_EXPR, type1, TYPE_MIN_VALUE (type), diff); assumption = fold_build2 (GE_EXPR, boolean_type_node, iv0->base, bound); } /* And then we can compute iv0->base - diff, and compare it with iv1->base. */ mbzl = fold_build2 (MINUS_EXPR, type1, fold_convert (type1, iv0->base), diff); mbzr = fold_convert (type1, iv1->base); } else { diff = fold_build2 (PLUS_EXPR, type1, iv1->step, build_int_cst (type1, 1)); if (!POINTER_TYPE_P (type)) { bound = fold_build2 (PLUS_EXPR, type1, TYPE_MAX_VALUE (type), diff); assumption = fold_build2 (LE_EXPR, boolean_type_node, iv1->base, bound); } mbzl = fold_convert (type1, iv0->base); mbzr = fold_build2 (MINUS_EXPR, type1, fold_convert (type1, iv1->base), diff); } if (!integer_nonzerop (assumption)) niter->assumptions = fold_build2 (TRUTH_AND_EXPR, boolean_type_node, niter->assumptions, assumption); if (!rolls_p) { mbz = fold_build2 (GT_EXPR, boolean_type_node, mbzl, mbzr); niter->may_be_zero = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, niter->may_be_zero, mbz); } } /* Determines number of iterations of loop whose ending condition is IV0 < IV1. TYPE is the type of the iv. The number of iterations is stored to NITER. BNDS bounds the difference IV1->base - IV0->base. EXIT_MUST_BE_TAKEN is true if we know that the exit must be taken eventually. */ static bool number_of_iterations_lt (tree type, affine_iv *iv0, affine_iv *iv1, struct tree_niter_desc *niter, bool exit_must_be_taken, bounds *bnds) { tree niter_type = unsigned_type_for (type); tree delta, step, s; mpz_t mstep, tmp; if (integer_nonzerop (iv0->step)) { niter->control = *iv0; niter->cmp = LT_EXPR; niter->bound = iv1->base; } else { niter->control = *iv1; niter->cmp = GT_EXPR; niter->bound = iv0->base; } delta = fold_build2 (MINUS_EXPR, niter_type, fold_convert (niter_type, iv1->base), fold_convert (niter_type, iv0->base)); /* First handle the special case that the step is +-1. */ if ((integer_onep (iv0->step) && integer_zerop (iv1->step)) || (integer_all_onesp (iv1->step) && integer_zerop (iv0->step))) { /* for (i = iv0->base; i < iv1->base; i++) or for (i = iv1->base; i > iv0->base; i--). In both cases # of iterations is iv1->base - iv0->base, assuming that iv1->base >= iv0->base. First try to derive a lower bound on the value of iv1->base - iv0->base, computed in full precision. If the difference is nonnegative, we are done, otherwise we must record the condition. */ if (mpz_sgn (bnds->below) < 0) niter->may_be_zero = fold_build2 (LT_EXPR, boolean_type_node, iv1->base, iv0->base); niter->niter = delta; niter->max = mpz_get_double_int (niter_type, bnds->up, false); return true; } if (integer_nonzerop (iv0->step)) step = fold_convert (niter_type, iv0->step); else step = fold_convert (niter_type, fold_build1 (NEGATE_EXPR, type, iv1->step)); /* If we can determine the final value of the control iv exactly, we can transform the condition to != comparison. In particular, this will be the case if DELTA is constant. */ if (number_of_iterations_lt_to_ne (type, iv0, iv1, niter, &delta, step, exit_must_be_taken, bnds)) { affine_iv zps; zps.base = build_int_cst (niter_type, 0); zps.step = step; /* number_of_iterations_lt_to_ne will add assumptions that ensure that zps does not overflow. */ zps.no_overflow = true; return number_of_iterations_ne (type, &zps, delta, niter, true, bnds); } /* Make sure that the control iv does not overflow. */ if (!assert_no_overflow_lt (type, iv0, iv1, niter, step)) return false; /* We determine the number of iterations as (delta + step - 1) / step. For this to work, we must know that iv1->base >= iv0->base - step + 1, otherwise the loop does not roll. */ assert_loop_rolls_lt (type, iv0, iv1, niter, bnds); s = fold_build2 (MINUS_EXPR, niter_type, step, build_int_cst (niter_type, 1)); delta = fold_build2 (PLUS_EXPR, niter_type, delta, s); niter->niter = fold_build2 (FLOOR_DIV_EXPR, niter_type, delta, step); mpz_init (mstep); mpz_init (tmp); mpz_set_double_int (mstep, tree_to_double_int (step), true); mpz_add (tmp, bnds->up, mstep); mpz_sub_ui (tmp, tmp, 1); mpz_fdiv_q (tmp, tmp, mstep); niter->max = mpz_get_double_int (niter_type, tmp, false); mpz_clear (mstep); mpz_clear (tmp); return true; } /* Determines number of iterations of loop whose ending condition is IV0 <= IV1. TYPE is the type of the iv. The number of iterations is stored to NITER. EXIT_MUST_BE_TAKEN is true if we know that this condition must eventually become false (we derived this earlier, and possibly set NITER->assumptions to make sure this is the case). BNDS bounds the difference IV1->base - IV0->base. */ static bool number_of_iterations_le (tree type, affine_iv *iv0, affine_iv *iv1, struct tree_niter_desc *niter, bool exit_must_be_taken, bounds *bnds) { tree assumption; tree type1 = type; if (POINTER_TYPE_P (type)) type1 = sizetype; /* Say that IV0 is the control variable. Then IV0 <= IV1 iff IV0 < IV1 + 1, assuming that IV1 is not equal to the greatest value of the type. This we must know anyway, since if it is equal to this value, the loop rolls forever. We do not check this condition for pointer type ivs, as the code cannot rely on the object to that the pointer points being placed at the end of the address space (and more pragmatically, TYPE_{MIN,MAX}_VALUE is not defined for pointers). */ if (!exit_must_be_taken && !POINTER_TYPE_P (type)) { if (integer_nonzerop (iv0->step)) assumption = fold_build2 (NE_EXPR, boolean_type_node, iv1->base, TYPE_MAX_VALUE (type)); else assumption = fold_build2 (NE_EXPR, boolean_type_node, iv0->base, TYPE_MIN_VALUE (type)); if (integer_zerop (assumption)) return false; if (!integer_nonzerop (assumption)) niter->assumptions = fold_build2 (TRUTH_AND_EXPR, boolean_type_node, niter->assumptions, assumption); } if (integer_nonzerop (iv0->step)) { if (POINTER_TYPE_P (type)) iv1->base = fold_build_pointer_plus_hwi (iv1->base, 1); else iv1->base = fold_build2 (PLUS_EXPR, type1, iv1->base, build_int_cst (type1, 1)); } else if (POINTER_TYPE_P (type)) iv0->base = fold_build_pointer_plus_hwi (iv0->base, -1); else iv0->base = fold_build2 (MINUS_EXPR, type1, iv0->base, build_int_cst (type1, 1)); bounds_add (bnds, double_int_one, type1); return number_of_iterations_lt (type, iv0, iv1, niter, exit_must_be_taken, bnds); } /* Dumps description of affine induction variable IV to FILE. */ static void dump_affine_iv (FILE *file, affine_iv *iv) { if (!integer_zerop (iv->step)) fprintf (file, "["); print_generic_expr (dump_file, iv->base, TDF_SLIM); if (!integer_zerop (iv->step)) { fprintf (file, ", + , "); print_generic_expr (dump_file, iv->step, TDF_SLIM); fprintf (file, "]%s", iv->no_overflow ? "(no_overflow)" : ""); } } /* Determine the number of iterations according to condition (for staying inside loop) which compares two induction variables using comparison operator CODE. The induction variable on left side of the comparison is IV0, the right-hand side is IV1. Both induction variables must have type TYPE, which must be an integer or pointer type. The steps of the ivs must be constants (or NULL_TREE, which is interpreted as constant zero). LOOP is the loop whose number of iterations we are determining. ONLY_EXIT is true if we are sure this is the only way the loop could be exited (including possibly non-returning function calls, exceptions, etc.) -- in this case we can use the information whether the control induction variables can overflow or not in a more efficient way. The results (number of iterations and assumptions as described in comments at struct tree_niter_desc in tree-flow.h) are stored to NITER. Returns false if it fails to determine number of iterations, true if it was determined (possibly with some assumptions). */ static bool number_of_iterations_cond (struct loop *loop, tree type, affine_iv *iv0, enum tree_code code, affine_iv *iv1, struct tree_niter_desc *niter, bool only_exit) { bool exit_must_be_taken = false, ret; bounds bnds; /* The meaning of these assumptions is this: if !assumptions then the rest of information does not have to be valid if may_be_zero then the loop does not roll, even if niter != 0. */ niter->assumptions = boolean_true_node; niter->may_be_zero = boolean_false_node; niter->niter = NULL_TREE; niter->max = double_int_zero; niter->bound = NULL_TREE; niter->cmp = ERROR_MARK; /* Make < comparison from > ones, and for NE_EXPR comparisons, ensure that the control variable is on lhs. */ if (code == GE_EXPR || code == GT_EXPR || (code == NE_EXPR && integer_zerop (iv0->step))) { SWAP (iv0, iv1); code = swap_tree_comparison (code); } if (POINTER_TYPE_P (type)) { /* Comparison of pointers is undefined unless both iv0 and iv1 point to the same object. If they do, the control variable cannot wrap (as wrap around the bounds of memory will never return a pointer that would be guaranteed to point to the same object, even if we avoid undefined behavior by casting to size_t and back). */ iv0->no_overflow = true; iv1->no_overflow = true; } /* If the control induction variable does not overflow and the only exit from the loop is the one that we analyze, we know it must be taken eventually. */ if (only_exit) { if (!integer_zerop (iv0->step) && iv0->no_overflow) exit_must_be_taken = true; else if (!integer_zerop (iv1->step) && iv1->no_overflow) exit_must_be_taken = true; } /* We can handle the case when neither of the sides of the comparison is invariant, provided that the test is NE_EXPR. This rarely occurs in practice, but it is simple enough to manage. */ if (!integer_zerop (iv0->step) && !integer_zerop (iv1->step)) { if (code != NE_EXPR) return false; iv0->step = fold_binary_to_constant (MINUS_EXPR, type, iv0->step, iv1->step); iv0->no_overflow = false; iv1->step = build_int_cst (type, 0); iv1->no_overflow = true; } /* If the result of the comparison is a constant, the loop is weird. More precise handling would be possible, but the situation is not common enough to waste time on it. */ if (integer_zerop (iv0->step) && integer_zerop (iv1->step)) return false; /* Ignore loops of while (i-- < 10) type. */ if (code != NE_EXPR) { if (iv0->step && tree_int_cst_sign_bit (iv0->step)) return false; if (!integer_zerop (iv1->step) && !tree_int_cst_sign_bit (iv1->step)) return false; } /* If the loop exits immediately, there is nothing to do. */ if (integer_zerop (fold_build2 (code, boolean_type_node, iv0->base, iv1->base))) { niter->niter = build_int_cst (unsigned_type_for (type), 0); niter->max = double_int_zero; return true; } /* OK, now we know we have a senseful loop. Handle several cases, depending on what comparison operator is used. */ bound_difference (loop, iv1->base, iv0->base, &bnds); if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Analyzing # of iterations of loop %d\n", loop->num); fprintf (dump_file, " exit condition "); dump_affine_iv (dump_file, iv0); fprintf (dump_file, " %s ", code == NE_EXPR ? "!=" : code == LT_EXPR ? "<" : "<="); dump_affine_iv (dump_file, iv1); fprintf (dump_file, "\n"); fprintf (dump_file, " bounds on difference of bases: "); mpz_out_str (dump_file, 10, bnds.below); fprintf (dump_file, " ... "); mpz_out_str (dump_file, 10, bnds.up); fprintf (dump_file, "\n"); } switch (code) { case NE_EXPR: gcc_assert (integer_zerop (iv1->step)); ret = number_of_iterations_ne (type, iv0, iv1->base, niter, exit_must_be_taken, &bnds); break; case LT_EXPR: ret = number_of_iterations_lt (type, iv0, iv1, niter, exit_must_be_taken, &bnds); break; case LE_EXPR: ret = number_of_iterations_le (type, iv0, iv1, niter, exit_must_be_taken, &bnds); break; default: gcc_unreachable (); } mpz_clear (bnds.up); mpz_clear (bnds.below); if (dump_file && (dump_flags & TDF_DETAILS)) { if (ret) { fprintf (dump_file, " result:\n"); if (!integer_nonzerop (niter->assumptions)) { fprintf (dump_file, " under assumptions "); print_generic_expr (dump_file, niter->assumptions, TDF_SLIM); fprintf (dump_file, "\n"); } if (!integer_zerop (niter->may_be_zero)) { fprintf (dump_file, " zero if "); print_generic_expr (dump_file, niter->may_be_zero, TDF_SLIM); fprintf (dump_file, "\n"); } fprintf (dump_file, " # of iterations "); print_generic_expr (dump_file, niter->niter, TDF_SLIM); fprintf (dump_file, ", bounded by "); dump_double_int (dump_file, niter->max, true); fprintf (dump_file, "\n"); } else fprintf (dump_file, " failed\n\n"); } return ret; } /* Substitute NEW for OLD in EXPR and fold the result. */ static tree simplify_replace_tree (tree expr, tree old, tree new_tree) { unsigned i, n; tree ret = NULL_TREE, e, se; if (!expr) return NULL_TREE; /* Do not bother to replace constants. */ if (CONSTANT_CLASS_P (old)) return expr; if (expr == old || operand_equal_p (expr, old, 0)) return unshare_expr (new_tree); if (!EXPR_P (expr)) return expr; n = TREE_OPERAND_LENGTH (expr); for (i = 0; i < n; i++) { e = TREE_OPERAND (expr, i); se = simplify_replace_tree (e, old, new_tree); if (e == se) continue; if (!ret) ret = copy_node (expr); TREE_OPERAND (ret, i) = se; } return (ret ? fold (ret) : expr); } /* Expand definitions of ssa names in EXPR as long as they are simple enough, and return the new expression. */ tree expand_simple_operations (tree expr) { unsigned i, n; tree ret = NULL_TREE, e, ee, e1; enum tree_code code; gimple stmt; if (expr == NULL_TREE) return expr; if (is_gimple_min_invariant (expr)) return expr; code = TREE_CODE (expr); if (IS_EXPR_CODE_CLASS (TREE_CODE_CLASS (code))) { n = TREE_OPERAND_LENGTH (expr); for (i = 0; i < n; i++) { e = TREE_OPERAND (expr, i); ee = expand_simple_operations (e); if (e == ee) continue; if (!ret) ret = copy_node (expr); TREE_OPERAND (ret, i) = ee; } if (!ret) return expr; fold_defer_overflow_warnings (); ret = fold (ret); fold_undefer_and_ignore_overflow_warnings (); return ret; } if (TREE_CODE (expr) != SSA_NAME) return expr; stmt = SSA_NAME_DEF_STMT (expr); if (gimple_code (stmt) == GIMPLE_PHI) { basic_block src, dest; if (gimple_phi_num_args (stmt) != 1) return expr; e = PHI_ARG_DEF (stmt, 0); /* Avoid propagating through loop exit phi nodes, which could break loop-closed SSA form restrictions. */ dest = gimple_bb (stmt); src = single_pred (dest); if (TREE_CODE (e) == SSA_NAME && src->loop_father != dest->loop_father) return expr; return expand_simple_operations (e); } if (gimple_code (stmt) != GIMPLE_ASSIGN) return expr; e = gimple_assign_rhs1 (stmt); code = gimple_assign_rhs_code (stmt); if (get_gimple_rhs_class (code) == GIMPLE_SINGLE_RHS) { if (is_gimple_min_invariant (e)) return e; if (code == SSA_NAME) return expand_simple_operations (e); return expr; } switch (code) { CASE_CONVERT: /* Casts are simple. */ ee = expand_simple_operations (e); return fold_build1 (code, TREE_TYPE (expr), ee); case PLUS_EXPR: case MINUS_EXPR: case POINTER_PLUS_EXPR: /* And increments and decrements by a constant are simple. */ e1 = gimple_assign_rhs2 (stmt); if (!is_gimple_min_invariant (e1)) return expr; ee = expand_simple_operations (e); return fold_build2 (code, TREE_TYPE (expr), ee, e1); default: return expr; } } /* Tries to simplify EXPR using the condition COND. Returns the simplified expression (or EXPR unchanged, if no simplification was possible). */ static tree tree_simplify_using_condition_1 (tree cond, tree expr) { bool changed; tree e, te, e0, e1, e2, notcond; enum tree_code code = TREE_CODE (expr); if (code == INTEGER_CST) return expr; if (code == TRUTH_OR_EXPR || code == TRUTH_AND_EXPR || code == COND_EXPR) { changed = false; e0 = tree_simplify_using_condition_1 (cond, TREE_OPERAND (expr, 0)); if (TREE_OPERAND (expr, 0) != e0) changed = true; e1 = tree_simplify_using_condition_1 (cond, TREE_OPERAND (expr, 1)); if (TREE_OPERAND (expr, 1) != e1) changed = true; if (code == COND_EXPR) { e2 = tree_simplify_using_condition_1 (cond, TREE_OPERAND (expr, 2)); if (TREE_OPERAND (expr, 2) != e2) changed = true; } else e2 = NULL_TREE; if (changed) { if (code == COND_EXPR) expr = fold_build3 (code, boolean_type_node, e0, e1, e2); else expr = fold_build2 (code, boolean_type_node, e0, e1); } return expr; } /* In case COND is equality, we may be able to simplify EXPR by copy/constant propagation, and vice versa. Fold does not handle this, since it is considered too expensive. */ if (TREE_CODE (cond) == EQ_EXPR) { e0 = TREE_OPERAND (cond, 0); e1 = TREE_OPERAND (cond, 1); /* We know that e0 == e1. Check whether we cannot simplify expr using this fact. */ e = simplify_replace_tree (expr, e0, e1); if (integer_zerop (e) || integer_nonzerop (e)) return e; e = simplify_replace_tree (expr, e1, e0); if (integer_zerop (e) || integer_nonzerop (e)) return e; } if (TREE_CODE (expr) == EQ_EXPR) { e0 = TREE_OPERAND (expr, 0); e1 = TREE_OPERAND (expr, 1); /* If e0 == e1 (EXPR) implies !COND, then EXPR cannot be true. */ e = simplify_replace_tree (cond, e0, e1); if (integer_zerop (e)) return e; e = simplify_replace_tree (cond, e1, e0); if (integer_zerop (e)) return e; } if (TREE_CODE (expr) == NE_EXPR) { e0 = TREE_OPERAND (expr, 0); e1 = TREE_OPERAND (expr, 1); /* If e0 == e1 (!EXPR) implies !COND, then EXPR must be true. */ e = simplify_replace_tree (cond, e0, e1); if (integer_zerop (e)) return boolean_true_node; e = simplify_replace_tree (cond, e1, e0); if (integer_zerop (e)) return boolean_true_node; } te = expand_simple_operations (expr); /* Check whether COND ==> EXPR. */ notcond = invert_truthvalue (cond); e = fold_binary (TRUTH_OR_EXPR, boolean_type_node, notcond, te); if (e && integer_nonzerop (e)) return e; /* Check whether COND ==> not EXPR. */ e = fold_binary (TRUTH_AND_EXPR, boolean_type_node, cond, te); if (e && integer_zerop (e)) return e; return expr; } /* Tries to simplify EXPR using the condition COND. Returns the simplified expression (or EXPR unchanged, if no simplification was possible). Wrapper around tree_simplify_using_condition_1 that ensures that chains of simple operations in definitions of ssa names in COND are expanded, so that things like casts or incrementing the value of the bound before the loop do not cause us to fail. */ static tree tree_simplify_using_condition (tree cond, tree expr) { cond = expand_simple_operations (cond); return tree_simplify_using_condition_1 (cond, expr); } /* Tries to simplify EXPR using the conditions on entry to LOOP. Returns the simplified expression (or EXPR unchanged, if no simplification was possible).*/ static tree simplify_using_initial_conditions (struct loop *loop, tree expr) { edge e; basic_block bb; gimple stmt; tree cond; int cnt = 0; if (TREE_CODE (expr) == INTEGER_CST) return expr; /* Limit walking the dominators to avoid quadraticness in the number of BBs times the number of loops in degenerate cases. */ for (bb = loop->header; bb != ENTRY_BLOCK_PTR && cnt < MAX_DOMINATORS_TO_WALK; bb = get_immediate_dominator (CDI_DOMINATORS, bb)) { if (!single_pred_p (bb)) continue; e = single_pred_edge (bb); if (!(e->flags & (EDGE_TRUE_VALUE | EDGE_FALSE_VALUE))) continue; stmt = last_stmt (e->src); cond = fold_build2 (gimple_cond_code (stmt), boolean_type_node, gimple_cond_lhs (stmt), gimple_cond_rhs (stmt)); if (e->flags & EDGE_FALSE_VALUE) cond = invert_truthvalue (cond); expr = tree_simplify_using_condition (cond, expr); ++cnt; } return expr; } /* Tries to simplify EXPR using the evolutions of the loop invariants in the superloops of LOOP. Returns the simplified expression (or EXPR unchanged, if no simplification was possible). */ static tree simplify_using_outer_evolutions (struct loop *loop, tree expr) { enum tree_code code = TREE_CODE (expr); bool changed; tree e, e0, e1, e2; if (is_gimple_min_invariant (expr)) return expr; if (code == TRUTH_OR_EXPR || code == TRUTH_AND_EXPR || code == COND_EXPR) { changed = false; e0 = simplify_using_outer_evolutions (loop, TREE_OPERAND (expr, 0)); if (TREE_OPERAND (expr, 0) != e0) changed = true; e1 = simplify_using_outer_evolutions (loop, TREE_OPERAND (expr, 1)); if (TREE_OPERAND (expr, 1) != e1) changed = true; if (code == COND_EXPR) { e2 = simplify_using_outer_evolutions (loop, TREE_OPERAND (expr, 2)); if (TREE_OPERAND (expr, 2) != e2) changed = true; } else e2 = NULL_TREE; if (changed) { if (code == COND_EXPR) expr = fold_build3 (code, boolean_type_node, e0, e1, e2); else expr = fold_build2 (code, boolean_type_node, e0, e1); } return expr; } e = instantiate_parameters (loop, expr); if (is_gimple_min_invariant (e)) return e; return expr; } /* Returns true if EXIT is the only possible exit from LOOP. */ bool loop_only_exit_p (const struct loop *loop, const_edge exit) { basic_block *body; gimple_stmt_iterator bsi; unsigned i; gimple call; if (exit != single_exit (loop)) return false; body = get_loop_body (loop); for (i = 0; i < loop->num_nodes; i++) { for (bsi = gsi_start_bb (body[i]); !gsi_end_p (bsi); gsi_next (&bsi)) { call = gsi_stmt (bsi); if (gimple_code (call) != GIMPLE_CALL) continue; if (gimple_has_side_effects (call)) { free (body); return false; } } } free (body); return true; } /* Stores description of number of iterations of LOOP derived from EXIT (an exit edge of the LOOP) in NITER. Returns true if some useful information could be derived (and fields of NITER has meaning described in comments at struct tree_niter_desc declaration), false otherwise. If WARN is true and -Wunsafe-loop-optimizations was given, warn if the optimizer is going to use potentially unsafe assumptions. */ bool number_of_iterations_exit (struct loop *loop, edge exit, struct tree_niter_desc *niter, bool warn) { gimple stmt; tree type; tree op0, op1; enum tree_code code; affine_iv iv0, iv1; if (!dominated_by_p (CDI_DOMINATORS, loop->latch, exit->src)) return false; niter->assumptions = boolean_false_node; stmt = last_stmt (exit->src); if (!stmt || gimple_code (stmt) != GIMPLE_COND) return false; /* We want the condition for staying inside loop. */ code = gimple_cond_code (stmt); if (exit->flags & EDGE_TRUE_VALUE) code = invert_tree_comparison (code, false); switch (code) { case GT_EXPR: case GE_EXPR: case NE_EXPR: case LT_EXPR: case LE_EXPR: break; default: return false; } op0 = gimple_cond_lhs (stmt); op1 = gimple_cond_rhs (stmt); type = TREE_TYPE (op0); if (TREE_CODE (type) != INTEGER_TYPE && !POINTER_TYPE_P (type)) return false; if (!simple_iv (loop, loop_containing_stmt (stmt), op0, &iv0, false)) return false; if (!simple_iv (loop, loop_containing_stmt (stmt), op1, &iv1, false)) return false; /* We don't want to see undefined signed overflow warnings while computing the number of iterations. */ fold_defer_overflow_warnings (); iv0.base = expand_simple_operations (iv0.base); iv1.base = expand_simple_operations (iv1.base); if (!number_of_iterations_cond (loop, type, &iv0, code, &iv1, niter, loop_only_exit_p (loop, exit))) { fold_undefer_and_ignore_overflow_warnings (); return false; } if (optimize >= 3) { niter->assumptions = simplify_using_outer_evolutions (loop, niter->assumptions); niter->may_be_zero = simplify_using_outer_evolutions (loop, niter->may_be_zero); niter->niter = simplify_using_outer_evolutions (loop, niter->niter); } niter->assumptions = simplify_using_initial_conditions (loop, niter->assumptions); niter->may_be_zero = simplify_using_initial_conditions (loop, niter->may_be_zero); fold_undefer_and_ignore_overflow_warnings (); if (integer_onep (niter->assumptions)) return true; /* With -funsafe-loop-optimizations we assume that nothing bad can happen. But if we can prove that there is overflow or some other source of weird behavior, ignore the loop even with -funsafe-loop-optimizations. */ if (integer_zerop (niter->assumptions) || !single_exit (loop)) return false; if (flag_unsafe_loop_optimizations) niter->assumptions = boolean_true_node; if (warn) { const char *wording; location_t loc = gimple_location (stmt); /* We can provide a more specific warning if one of the operator is constant and the other advances by +1 or -1. */ if (!integer_zerop (iv1.step) ? (integer_zerop (iv0.step) && (integer_onep (iv1.step) || integer_all_onesp (iv1.step))) : (integer_onep (iv0.step) || integer_all_onesp (iv0.step))) wording = flag_unsafe_loop_optimizations ? N_("assuming that the loop is not infinite") : N_("cannot optimize possibly infinite loops"); else wording = flag_unsafe_loop_optimizations ? N_("assuming that the loop counter does not overflow") : N_("cannot optimize loop, the loop counter may overflow"); warning_at ((LOCATION_LINE (loc) > 0) ? loc : input_location, OPT_Wunsafe_loop_optimizations, "%s", gettext (wording)); } return flag_unsafe_loop_optimizations; } /* Try to determine the number of iterations of LOOP. If we succeed, expression giving number of iterations is returned and *EXIT is set to the edge from that the information is obtained. Otherwise chrec_dont_know is returned. */ tree find_loop_niter (struct loop *loop, edge *exit) { unsigned i; VEC (edge, heap) *exits = get_loop_exit_edges (loop); edge ex; tree niter = NULL_TREE, aniter; struct tree_niter_desc desc; *exit = NULL; FOR_EACH_VEC_ELT (edge, exits, i, ex) { if (!just_once_each_iteration_p (loop, ex->src)) continue; if (!number_of_iterations_exit (loop, ex, &desc, false)) continue; if (integer_nonzerop (desc.may_be_zero)) { /* We exit in the first iteration through this exit. We won't find anything better. */ niter = build_int_cst (unsigned_type_node, 0); *exit = ex; break; } if (!integer_zerop (desc.may_be_zero)) continue; aniter = desc.niter; if (!niter) { /* Nothing recorded yet. */ niter = aniter; *exit = ex; continue; } /* Prefer constants, the lower the better. */ if (TREE_CODE (aniter) != INTEGER_CST) continue; if (TREE_CODE (niter) != INTEGER_CST) { niter = aniter; *exit = ex; continue; } if (tree_int_cst_lt (aniter, niter)) { niter = aniter; *exit = ex; continue; } } VEC_free (edge, heap, exits); return niter ? niter : chrec_dont_know; } /* Return true if loop is known to have bounded number of iterations. */ bool finite_loop_p (struct loop *loop) { unsigned i; VEC (edge, heap) *exits; edge ex; struct tree_niter_desc desc; bool finite = false; int flags; if (flag_unsafe_loop_optimizations) return true; flags = flags_from_decl_or_type (current_function_decl); if ((flags & (ECF_CONST|ECF_PURE)) && !(flags & ECF_LOOPING_CONST_OR_PURE)) { if (dump_file && (dump_flags & TDF_DETAILS)) fprintf (dump_file, "Found loop %i to be finite: it is within pure or const function.\n", loop->num); return true; } exits = get_loop_exit_edges (loop); FOR_EACH_VEC_ELT (edge, exits, i, ex) { if (!just_once_each_iteration_p (loop, ex->src)) continue; if (number_of_iterations_exit (loop, ex, &desc, false)) { if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Found loop %i to be finite: iterating ", loop->num); print_generic_expr (dump_file, desc.niter, TDF_SLIM); fprintf (dump_file, " times\n"); } finite = true; break; } } VEC_free (edge, heap, exits); return finite; } /* Analysis of a number of iterations of a loop by a brute-force evaluation. */ /* Bound on the number of iterations we try to evaluate. */ #define MAX_ITERATIONS_TO_TRACK \ ((unsigned) PARAM_VALUE (PARAM_MAX_ITERATIONS_TO_TRACK)) /* Returns the loop phi node of LOOP such that ssa name X is derived from its result by a chain of operations such that all but exactly one of their operands are constants. */ static gimple chain_of_csts_start (struct loop *loop, tree x) { gimple stmt = SSA_NAME_DEF_STMT (x); tree use; basic_block bb = gimple_bb (stmt); enum tree_code code; if (!bb || !flow_bb_inside_loop_p (loop, bb)) return NULL; if (gimple_code (stmt) == GIMPLE_PHI) { if (bb == loop->header) return stmt; return NULL; } if (gimple_code (stmt) != GIMPLE_ASSIGN) return NULL; code = gimple_assign_rhs_code (stmt); if (gimple_references_memory_p (stmt) || TREE_CODE_CLASS (code) == tcc_reference || (code == ADDR_EXPR && !is_gimple_min_invariant (gimple_assign_rhs1 (stmt)))) return NULL; use = SINGLE_SSA_TREE_OPERAND (stmt, SSA_OP_USE); if (use == NULL_TREE) return NULL; return chain_of_csts_start (loop, use); } /* Determines whether the expression X is derived from a result of a phi node in header of LOOP such that * the derivation of X consists only from operations with constants * the initial value of the phi node is constant * the value of the phi node in the next iteration can be derived from the value in the current iteration by a chain of operations with constants. If such phi node exists, it is returned, otherwise NULL is returned. */ static gimple get_base_for (struct loop *loop, tree x) { gimple phi; tree init, next; if (is_gimple_min_invariant (x)) return NULL; phi = chain_of_csts_start (loop, x); if (!phi) return NULL; init = PHI_ARG_DEF_FROM_EDGE (phi, loop_preheader_edge (loop)); next = PHI_ARG_DEF_FROM_EDGE (phi, loop_latch_edge (loop)); if (TREE_CODE (next) != SSA_NAME) return NULL; if (!is_gimple_min_invariant (init)) return NULL; if (chain_of_csts_start (loop, next) != phi) return NULL; return phi; } /* Given an expression X, then * if X is NULL_TREE, we return the constant BASE. * otherwise X is a SSA name, whose value in the considered loop is derived by a chain of operations with constant from a result of a phi node in the header of the loop. Then we return value of X when the value of the result of this phi node is given by the constant BASE. */ static tree get_val_for (tree x, tree base) { gimple stmt; gcc_assert (is_gimple_min_invariant (base)); if (!x) return base; stmt = SSA_NAME_DEF_STMT (x); if (gimple_code (stmt) == GIMPLE_PHI) return base; gcc_assert (is_gimple_assign (stmt)); /* STMT must be either an assignment of a single SSA name or an expression involving an SSA name and a constant. Try to fold that expression using the value for the SSA name. */ if (gimple_assign_ssa_name_copy_p (stmt)) return get_val_for (gimple_assign_rhs1 (stmt), base); else if (gimple_assign_rhs_class (stmt) == GIMPLE_UNARY_RHS && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME) { return fold_build1 (gimple_assign_rhs_code (stmt), gimple_expr_type (stmt), get_val_for (gimple_assign_rhs1 (stmt), base)); } else if (gimple_assign_rhs_class (stmt) == GIMPLE_BINARY_RHS) { tree rhs1 = gimple_assign_rhs1 (stmt); tree rhs2 = gimple_assign_rhs2 (stmt); if (TREE_CODE (rhs1) == SSA_NAME) rhs1 = get_val_for (rhs1, base); else if (TREE_CODE (rhs2) == SSA_NAME) rhs2 = get_val_for (rhs2, base); else gcc_unreachable (); return fold_build2 (gimple_assign_rhs_code (stmt), gimple_expr_type (stmt), rhs1, rhs2); } else gcc_unreachable (); } /* Tries to count the number of iterations of LOOP till it exits by EXIT by brute force -- i.e. by determining the value of the operands of the condition at EXIT in first few iterations of the loop (assuming that these values are constant) and determining the first one in that the condition is not satisfied. Returns the constant giving the number of the iterations of LOOP if successful, chrec_dont_know otherwise. */ tree loop_niter_by_eval (struct loop *loop, edge exit) { tree acnd; tree op[2], val[2], next[2], aval[2]; gimple phi, cond; unsigned i, j; enum tree_code cmp; cond = last_stmt (exit->src); if (!cond || gimple_code (cond) != GIMPLE_COND) return chrec_dont_know; cmp = gimple_cond_code (cond); if (exit->flags & EDGE_TRUE_VALUE) cmp = invert_tree_comparison (cmp, false); switch (cmp) { case EQ_EXPR: case NE_EXPR: case GT_EXPR: case GE_EXPR: case LT_EXPR: case LE_EXPR: op[0] = gimple_cond_lhs (cond); op[1] = gimple_cond_rhs (cond); break; default: return chrec_dont_know; } for (j = 0; j < 2; j++) { if (is_gimple_min_invariant (op[j])) { val[j] = op[j]; next[j] = NULL_TREE; op[j] = NULL_TREE; } else { phi = get_base_for (loop, op[j]); if (!phi) return chrec_dont_know; val[j] = PHI_ARG_DEF_FROM_EDGE (phi, loop_preheader_edge (loop)); next[j] = PHI_ARG_DEF_FROM_EDGE (phi, loop_latch_edge (loop)); } } /* Don't issue signed overflow warnings. */ fold_defer_overflow_warnings (); for (i = 0; i < MAX_ITERATIONS_TO_TRACK; i++) { for (j = 0; j < 2; j++) aval[j] = get_val_for (op[j], val[j]); acnd = fold_binary (cmp, boolean_type_node, aval[0], aval[1]); if (acnd && integer_zerop (acnd)) { fold_undefer_and_ignore_overflow_warnings (); if (dump_file && (dump_flags & TDF_DETAILS)) fprintf (dump_file, "Proved that loop %d iterates %d times using brute force.\n", loop->num, i); return build_int_cst (unsigned_type_node, i); } for (j = 0; j < 2; j++) { val[j] = get_val_for (next[j], val[j]); if (!is_gimple_min_invariant (val[j])) { fold_undefer_and_ignore_overflow_warnings (); return chrec_dont_know; } } } fold_undefer_and_ignore_overflow_warnings (); return chrec_dont_know; } /* Finds the exit of the LOOP by that the loop exits after a constant number of iterations and stores the exit edge to *EXIT. The constant giving the number of iterations of LOOP is returned. The number of iterations is determined using loop_niter_by_eval (i.e. by brute force evaluation). If we are unable to find the exit for that loop_niter_by_eval determines the number of iterations, chrec_dont_know is returned. */ tree find_loop_niter_by_eval (struct loop *loop, edge *exit) { unsigned i; VEC (edge, heap) *exits = get_loop_exit_edges (loop); edge ex; tree niter = NULL_TREE, aniter; *exit = NULL; /* Loops with multiple exits are expensive to handle and less important. */ if (!flag_expensive_optimizations && VEC_length (edge, exits) > 1) return chrec_dont_know; FOR_EACH_VEC_ELT (edge, exits, i, ex) { if (!just_once_each_iteration_p (loop, ex->src)) continue; aniter = loop_niter_by_eval (loop, ex); if (chrec_contains_undetermined (aniter)) continue; if (niter && !tree_int_cst_lt (aniter, niter)) continue; niter = aniter; *exit = ex; } VEC_free (edge, heap, exits); return niter ? niter : chrec_dont_know; } /* Analysis of upper bounds on number of iterations of a loop. */ static double_int derive_constant_upper_bound_ops (tree, tree, enum tree_code, tree); /* Returns a constant upper bound on the value of the right-hand side of an assignment statement STMT. */ static double_int derive_constant_upper_bound_assign (gimple stmt) { enum tree_code code = gimple_assign_rhs_code (stmt); tree op0 = gimple_assign_rhs1 (stmt); tree op1 = gimple_assign_rhs2 (stmt); return derive_constant_upper_bound_ops (TREE_TYPE (gimple_assign_lhs (stmt)), op0, code, op1); } /* Returns a constant upper bound on the value of expression VAL. VAL is considered to be unsigned. If its type is signed, its value must be nonnegative. */ static double_int derive_constant_upper_bound (tree val) { enum tree_code code; tree op0, op1; extract_ops_from_tree (val, &code, &op0, &op1); return derive_constant_upper_bound_ops (TREE_TYPE (val), op0, code, op1); } /* Returns a constant upper bound on the value of expression OP0 CODE OP1, whose type is TYPE. The expression is considered to be unsigned. If its type is signed, its value must be nonnegative. */ static double_int derive_constant_upper_bound_ops (tree type, tree op0, enum tree_code code, tree op1) { tree subtype, maxt; double_int bnd, max, mmax, cst; gimple stmt; if (INTEGRAL_TYPE_P (type)) maxt = TYPE_MAX_VALUE (type); else maxt = upper_bound_in_type (type, type); max = tree_to_double_int (maxt); switch (code) { case INTEGER_CST: return tree_to_double_int (op0); CASE_CONVERT: subtype = TREE_TYPE (op0); if (!TYPE_UNSIGNED (subtype) /* If TYPE is also signed, the fact that VAL is nonnegative implies that OP0 is nonnegative. */ && TYPE_UNSIGNED (type) && !tree_expr_nonnegative_p (op0)) { /* If we cannot prove that the casted expression is nonnegative, we cannot establish more useful upper bound than the precision of the type gives us. */ return max; } /* We now know that op0 is an nonnegative value. Try deriving an upper bound for it. */ bnd = derive_constant_upper_bound (op0); /* If the bound does not fit in TYPE, max. value of TYPE could be attained. */ if (double_int_ucmp (max, bnd) < 0) return max; return bnd; case PLUS_EXPR: case POINTER_PLUS_EXPR: case MINUS_EXPR: if (TREE_CODE (op1) != INTEGER_CST || !tree_expr_nonnegative_p (op0)) return max; /* Canonicalize to OP0 - CST. Consider CST to be signed, in order to choose the most logical way how to treat this constant regardless of the signedness of the type. */ cst = tree_to_double_int (op1); cst = double_int_sext (cst, TYPE_PRECISION (type)); if (code != MINUS_EXPR) cst = double_int_neg (cst); bnd = derive_constant_upper_bound (op0); if (double_int_negative_p (cst)) { cst = double_int_neg (cst); /* Avoid CST == 0x80000... */ if (double_int_negative_p (cst)) return max;; /* OP0 + CST. We need to check that BND <= MAX (type) - CST. */ mmax = double_int_sub (max, cst); if (double_int_ucmp (bnd, mmax) > 0) return max; return double_int_add (bnd, cst); } else { /* OP0 - CST, where CST >= 0. If TYPE is signed, we have already verified that OP0 >= 0, and we know that the result is nonnegative. This implies that VAL <= BND - CST. If TYPE is unsigned, we must additionally know that OP0 >= CST, otherwise the operation underflows. */ /* This should only happen if the type is unsigned; however, for buggy programs that use overflowing signed arithmetics even with -fno-wrapv, this condition may also be true for signed values. */ if (double_int_ucmp (bnd, cst) < 0) return max; if (TYPE_UNSIGNED (type)) { tree tem = fold_binary (GE_EXPR, boolean_type_node, op0, double_int_to_tree (type, cst)); if (!tem || integer_nonzerop (tem)) return max; } bnd = double_int_sub (bnd, cst); } return bnd; case FLOOR_DIV_EXPR: case EXACT_DIV_EXPR: if (TREE_CODE (op1) != INTEGER_CST || tree_int_cst_sign_bit (op1)) return max; bnd = derive_constant_upper_bound (op0); return double_int_udiv (bnd, tree_to_double_int (op1), FLOOR_DIV_EXPR); case BIT_AND_EXPR: if (TREE_CODE (op1) != INTEGER_CST || tree_int_cst_sign_bit (op1)) return max; return tree_to_double_int (op1); case SSA_NAME: stmt = SSA_NAME_DEF_STMT (op0); if (gimple_code (stmt) != GIMPLE_ASSIGN || gimple_assign_lhs (stmt) != op0) return max; return derive_constant_upper_bound_assign (stmt); default: return max; } } /* Records that every statement in LOOP is executed I_BOUND times. REALISTIC is true if I_BOUND is expected to be close to the real number of iterations. UPPER is true if we are sure the loop iterates at most I_BOUND times. */ static void record_niter_bound (struct loop *loop, double_int i_bound, bool realistic, bool upper) { /* Update the bounds only when there is no previous estimation, or when the current estimation is smaller. */ if (upper && (!loop->any_upper_bound || double_int_ucmp (i_bound, loop->nb_iterations_upper_bound) < 0)) { loop->any_upper_bound = true; loop->nb_iterations_upper_bound = i_bound; } if (realistic && (!loop->any_estimate || double_int_ucmp (i_bound, loop->nb_iterations_estimate) < 0)) { loop->any_estimate = true; loop->nb_iterations_estimate = i_bound; } } /* Records that AT_STMT is executed at most BOUND + 1 times in LOOP. IS_EXIT is true if the loop is exited immediately after STMT, and this exit is taken at last when the STMT is executed BOUND + 1 times. REALISTIC is true if BOUND is expected to be close to the real number of iterations. UPPER is true if we are sure the loop iterates at most BOUND times. I_BOUND is an unsigned double_int upper estimate on BOUND. */ static void record_estimate (struct loop *loop, tree bound, double_int i_bound, gimple at_stmt, bool is_exit, bool realistic, bool upper) { double_int delta; edge exit; if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Statement %s", is_exit ? "(exit)" : ""); print_gimple_stmt (dump_file, at_stmt, 0, TDF_SLIM); fprintf (dump_file, " is %sexecuted at most ", upper ? "" : "probably "); print_generic_expr (dump_file, bound, TDF_SLIM); fprintf (dump_file, " (bounded by "); dump_double_int (dump_file, i_bound, true); fprintf (dump_file, ") + 1 times in loop %d.\n", loop->num); } /* If the I_BOUND is just an estimate of BOUND, it rarely is close to the real number of iterations. */ if (TREE_CODE (bound) != INTEGER_CST) realistic = false; if (!upper && !realistic) return; /* If we have a guaranteed upper bound, record it in the appropriate list. */ if (upper) { struct nb_iter_bound *elt = ggc_alloc_nb_iter_bound (); elt->bound = i_bound; elt->stmt = at_stmt; elt->is_exit = is_exit; elt->next = loop->bounds; loop->bounds = elt; } /* Update the number of iteration estimates according to the bound. If at_stmt is an exit or dominates the single exit from the loop, then the loop latch is executed at most BOUND times, otherwise it can be executed BOUND + 1 times. */ exit = single_exit (loop); if (is_exit || (exit != NULL && dominated_by_p (CDI_DOMINATORS, exit->src, gimple_bb (at_stmt)))) delta = double_int_zero; else delta = double_int_one; i_bound = double_int_add (i_bound, delta); /* If an overflow occurred, ignore the result. */ if (double_int_ucmp (i_bound, delta) < 0) return; record_niter_bound (loop, i_bound, realistic, upper); } /* Record the estimate on number of iterations of LOOP based on the fact that the induction variable BASE + STEP * i evaluated in STMT does not wrap and its values belong to the range <LOW, HIGH>. REALISTIC is true if the estimated number of iterations is expected to be close to the real one. UPPER is true if we are sure the induction variable does not wrap. */ static void record_nonwrapping_iv (struct loop *loop, tree base, tree step, gimple stmt, tree low, tree high, bool realistic, bool upper) { tree niter_bound, extreme, delta; tree type = TREE_TYPE (base), unsigned_type; double_int max; if (TREE_CODE (step) != INTEGER_CST || integer_zerop (step)) return; if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Induction variable ("); print_generic_expr (dump_file, TREE_TYPE (base), TDF_SLIM); fprintf (dump_file, ") "); print_generic_expr (dump_file, base, TDF_SLIM); fprintf (dump_file, " + "); print_generic_expr (dump_file, step, TDF_SLIM); fprintf (dump_file, " * iteration does not wrap in statement "); print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM); fprintf (dump_file, " in loop %d.\n", loop->num); } unsigned_type = unsigned_type_for (type); base = fold_convert (unsigned_type, base); step = fold_convert (unsigned_type, step); if (tree_int_cst_sign_bit (step)) { extreme = fold_convert (unsigned_type, low); if (TREE_CODE (base) != INTEGER_CST) base = fold_convert (unsigned_type, high); delta = fold_build2 (MINUS_EXPR, unsigned_type, base, extreme); step = fold_build1 (NEGATE_EXPR, unsigned_type, step); } else { extreme = fold_convert (unsigned_type, high); if (TREE_CODE (base) != INTEGER_CST) base = fold_convert (unsigned_type, low); delta = fold_build2 (MINUS_EXPR, unsigned_type, extreme, base); } /* STMT is executed at most NITER_BOUND + 1 times, since otherwise the value would get out of the range. */ niter_bound = fold_build2 (FLOOR_DIV_EXPR, unsigned_type, delta, step); max = derive_constant_upper_bound (niter_bound); record_estimate (loop, niter_bound, max, stmt, false, realistic, upper); } /* Returns true if REF is a reference to an array at the end of a dynamically allocated structure. If this is the case, the array may be allocated larger than its upper bound implies. */ bool array_at_struct_end_p (tree ref) { tree base = get_base_address (ref); tree parent, field; /* Unless the reference is through a pointer, the size of the array matches its declaration. */ if (!base || (!INDIRECT_REF_P (base) && TREE_CODE (base) != MEM_REF)) return false; for (;handled_component_p (ref); ref = parent) { parent = TREE_OPERAND (ref, 0); if (TREE_CODE (ref) == COMPONENT_REF) { /* All fields of a union are at its end. */ if (TREE_CODE (TREE_TYPE (parent)) == UNION_TYPE) continue; /* Unless the field is at the end of the struct, we are done. */ field = TREE_OPERAND (ref, 1); if (DECL_CHAIN (field)) return false; } /* The other options are ARRAY_REF, ARRAY_RANGE_REF, VIEW_CONVERT_EXPR. In all these cases, we might be accessing the last element, and although in practice this will probably never happen, it is legal for the indices of this last element to exceed the bounds of the array. Therefore, continue checking. */ } return true; } /* Determine information about number of iterations a LOOP from the index IDX of a data reference accessed in STMT. RELIABLE is true if STMT is guaranteed to be executed in every iteration of LOOP. Callback for for_each_index. */ struct ilb_data { struct loop *loop; gimple stmt; bool reliable; }; static bool idx_infer_loop_bounds (tree base, tree *idx, void *dta) { struct ilb_data *data = (struct ilb_data *) dta; tree ev, init, step; tree low, high, type, next; bool sign, upper = data->reliable, at_end = false; struct loop *loop = data->loop; if (TREE_CODE (base) != ARRAY_REF) return true; /* For arrays at the end of the structure, we are not guaranteed that they do not really extend over their declared size. However, for arrays of size greater than one, this is unlikely to be intended. */ if (array_at_struct_end_p (base)) { at_end = true; upper = false; } ev = instantiate_parameters (loop, analyze_scalar_evolution (loop, *idx)); init = initial_condition (ev); step = evolution_part_in_loop_num (ev, loop->num); if (!init || !step || TREE_CODE (step) != INTEGER_CST || integer_zerop (step) || tree_contains_chrecs (init, NULL) || chrec_contains_symbols_defined_in_loop (init, loop->num)) return true; low = array_ref_low_bound (base); high = array_ref_up_bound (base); /* The case of nonconstant bounds could be handled, but it would be complicated. */ if (TREE_CODE (low) != INTEGER_CST || !high || TREE_CODE (high) != INTEGER_CST) return true; sign = tree_int_cst_sign_bit (step); type = TREE_TYPE (step); /* The array of length 1 at the end of a structure most likely extends beyond its bounds. */ if (at_end && operand_equal_p (low, high, 0)) return true; /* In case the relevant bound of the array does not fit in type, or it does, but bound + step (in type) still belongs into the range of the array, the index may wrap and still stay within the range of the array (consider e.g. if the array is indexed by the full range of unsigned char). To make things simpler, we require both bounds to fit into type, although there are cases where this would not be strictly necessary. */ if (!int_fits_type_p (high, type) || !int_fits_type_p (low, type)) return true; low = fold_convert (type, low); high = fold_convert (type, high); if (sign) next = fold_binary (PLUS_EXPR, type, low, step); else next = fold_binary (PLUS_EXPR, type, high, step); if (tree_int_cst_compare (low, next) <= 0 && tree_int_cst_compare (next, high) <= 0) return true; record_nonwrapping_iv (loop, init, step, data->stmt, low, high, true, upper); return true; } /* Determine information about number of iterations a LOOP from the bounds of arrays in the data reference REF accessed in STMT. RELIABLE is true if STMT is guaranteed to be executed in every iteration of LOOP.*/ static void infer_loop_bounds_from_ref (struct loop *loop, gimple stmt, tree ref, bool reliable) { struct ilb_data data; data.loop = loop; data.stmt = stmt; data.reliable = reliable; for_each_index (&ref, idx_infer_loop_bounds, &data); } /* Determine information about number of iterations of a LOOP from the way arrays are used in STMT. RELIABLE is true if STMT is guaranteed to be executed in every iteration of LOOP. */ static void infer_loop_bounds_from_array (struct loop *loop, gimple stmt, bool reliable) { if (is_gimple_assign (stmt)) { tree op0 = gimple_assign_lhs (stmt); tree op1 = gimple_assign_rhs1 (stmt); /* For each memory access, analyze its access function and record a bound on the loop iteration domain. */ if (REFERENCE_CLASS_P (op0)) infer_loop_bounds_from_ref (loop, stmt, op0, reliable); if (REFERENCE_CLASS_P (op1)) infer_loop_bounds_from_ref (loop, stmt, op1, reliable); } else if (is_gimple_call (stmt)) { tree arg, lhs; unsigned i, n = gimple_call_num_args (stmt); lhs = gimple_call_lhs (stmt); if (lhs && REFERENCE_CLASS_P (lhs)) infer_loop_bounds_from_ref (loop, stmt, lhs, reliable); for (i = 0; i < n; i++) { arg = gimple_call_arg (stmt, i); if (REFERENCE_CLASS_P (arg)) infer_loop_bounds_from_ref (loop, stmt, arg, reliable); } } } /* Determine information about number of iterations of a LOOP from the fact that pointer arithmetics in STMT does not overflow. */ static void infer_loop_bounds_from_pointer_arith (struct loop *loop, gimple stmt) { tree def, base, step, scev, type, low, high; tree var, ptr; if (!is_gimple_assign (stmt) || gimple_assign_rhs_code (stmt) != POINTER_PLUS_EXPR) return; def = gimple_assign_lhs (stmt); if (TREE_CODE (def) != SSA_NAME) return; type = TREE_TYPE (def); if (!nowrap_type_p (type)) return; ptr = gimple_assign_rhs1 (stmt); if (!expr_invariant_in_loop_p (loop, ptr)) return; var = gimple_assign_rhs2 (stmt); if (TYPE_PRECISION (type) != TYPE_PRECISION (TREE_TYPE (var))) return; scev = instantiate_parameters (loop, analyze_scalar_evolution (loop, def)); if (chrec_contains_undetermined (scev)) return; base = initial_condition_in_loop_num (scev, loop->num); step = evolution_part_in_loop_num (scev, loop->num); if (!base || !step || TREE_CODE (step) != INTEGER_CST || tree_contains_chrecs (base, NULL) || chrec_contains_symbols_defined_in_loop (base, loop->num)) return; low = lower_bound_in_type (type, type); high = upper_bound_in_type (type, type); /* In C, pointer arithmetic p + 1 cannot use a NULL pointer, and p - 1 cannot produce a NULL pointer. The contrary would mean NULL points to an object, while NULL is supposed to compare unequal with the address of all objects. Furthermore, p + 1 cannot produce a NULL pointer and p - 1 cannot use a NULL pointer since that would mean wrapping, which we assume here not to happen. So, we can exclude NULL from the valid range of pointer arithmetic. */ if (flag_delete_null_pointer_checks && int_cst_value (low) == 0) low = build_int_cstu (TREE_TYPE (low), TYPE_ALIGN_UNIT (TREE_TYPE (type))); record_nonwrapping_iv (loop, base, step, stmt, low, high, false, true); } /* Determine information about number of iterations of a LOOP from the fact that signed arithmetics in STMT does not overflow. */ static void infer_loop_bounds_from_signedness (struct loop *loop, gimple stmt) { tree def, base, step, scev, type, low, high; if (gimple_code (stmt) != GIMPLE_ASSIGN) return; def = gimple_assign_lhs (stmt); if (TREE_CODE (def) != SSA_NAME) return; type = TREE_TYPE (def); if (!INTEGRAL_TYPE_P (type) || !TYPE_OVERFLOW_UNDEFINED (type)) return; scev = instantiate_parameters (loop, analyze_scalar_evolution (loop, def)); if (chrec_contains_undetermined (scev)) return; base = initial_condition_in_loop_num (scev, loop->num); step = evolution_part_in_loop_num (scev, loop->num); if (!base || !step || TREE_CODE (step) != INTEGER_CST || tree_contains_chrecs (base, NULL) || chrec_contains_symbols_defined_in_loop (base, loop->num)) return; low = lower_bound_in_type (type, type); high = upper_bound_in_type (type, type); record_nonwrapping_iv (loop, base, step, stmt, low, high, false, true); } /* The following analyzers are extracting informations on the bounds of LOOP from the following undefined behaviors: - data references should not access elements over the statically allocated size, - signed variables should not overflow when flag_wrapv is not set. */ static void infer_loop_bounds_from_undefined (struct loop *loop) { unsigned i; basic_block *bbs; gimple_stmt_iterator bsi; basic_block bb; bool reliable; bbs = get_loop_body (loop); for (i = 0; i < loop->num_nodes; i++) { bb = bbs[i]; /* If BB is not executed in each iteration of the loop, we cannot use the operations in it to infer reliable upper bound on the # of iterations of the loop. However, we can use it as a guess. */ reliable = dominated_by_p (CDI_DOMINATORS, loop->latch, bb); for (bsi = gsi_start_bb (bb); !gsi_end_p (bsi); gsi_next (&bsi)) { gimple stmt = gsi_stmt (bsi); infer_loop_bounds_from_array (loop, stmt, reliable); if (reliable) { infer_loop_bounds_from_signedness (loop, stmt); infer_loop_bounds_from_pointer_arith (loop, stmt); } } } free (bbs); } /* Converts VAL to double_int. */ static double_int gcov_type_to_double_int (gcov_type val) { double_int ret; ret.low = (unsigned HOST_WIDE_INT) val; /* If HOST_BITS_PER_WIDE_INT == HOST_BITS_PER_WIDEST_INT, avoid shifting by the size of type. */ val >>= HOST_BITS_PER_WIDE_INT - 1; val >>= 1; ret.high = (unsigned HOST_WIDE_INT) val; return ret; } /* Records estimates on numbers of iterations of LOOP. If USE_UNDEFINED_P is true also use estimates derived from undefined behavior. */ void estimate_numbers_of_iterations_loop (struct loop *loop, bool use_undefined_p) { VEC (edge, heap) *exits; tree niter, type; unsigned i; struct tree_niter_desc niter_desc; edge ex; double_int bound; /* Give up if we already have tried to compute an estimation. */ if (loop->estimate_state != EST_NOT_COMPUTED) return; loop->estimate_state = EST_AVAILABLE; loop->any_upper_bound = false; loop->any_estimate = false; exits = get_loop_exit_edges (loop); FOR_EACH_VEC_ELT (edge, exits, i, ex) { if (!number_of_iterations_exit (loop, ex, &niter_desc, false)) continue; niter = niter_desc.niter; type = TREE_TYPE (niter); if (TREE_CODE (niter_desc.may_be_zero) != INTEGER_CST) niter = build3 (COND_EXPR, type, niter_desc.may_be_zero, build_int_cst (type, 0), niter); record_estimate (loop, niter, niter_desc.max, last_stmt (ex->src), true, true, true); } VEC_free (edge, heap, exits); if (use_undefined_p) infer_loop_bounds_from_undefined (loop); /* If we have a measured profile, use it to estimate the number of iterations. */ if (loop->header->count != 0) { gcov_type nit = expected_loop_iterations_unbounded (loop) + 1; bound = gcov_type_to_double_int (nit); record_niter_bound (loop, bound, true, false); } /* If an upper bound is smaller than the realistic estimate of the number of iterations, use the upper bound instead. */ if (loop->any_upper_bound && loop->any_estimate && double_int_ucmp (loop->nb_iterations_upper_bound, loop->nb_iterations_estimate) < 0) loop->nb_iterations_estimate = loop->nb_iterations_upper_bound; } /* Sets NIT to the estimated number of executions of the latch of the LOOP. If CONSERVATIVE is true, we must be sure that NIT is at least as large as the number of iterations. If we have no reliable estimate, the function returns false, otherwise returns true. */ bool estimated_loop_iterations (struct loop *loop, bool conservative, double_int *nit) { estimate_numbers_of_iterations_loop (loop, true); if (conservative) { if (!loop->any_upper_bound) return false; *nit = loop->nb_iterations_upper_bound; } else { if (!loop->any_estimate) return false; *nit = loop->nb_iterations_estimate; } return true; } /* Similar to estimated_loop_iterations, but returns the estimate only if it fits to HOST_WIDE_INT. If this is not the case, or the estimate on the number of iterations of LOOP could not be derived, returns -1. */ HOST_WIDE_INT estimated_loop_iterations_int (struct loop *loop, bool conservative) { double_int nit; HOST_WIDE_INT hwi_nit; if (!estimated_loop_iterations (loop, conservative, &nit)) return -1; if (!double_int_fits_in_shwi_p (nit)) return -1; hwi_nit = double_int_to_shwi (nit); return hwi_nit < 0 ? -1 : hwi_nit; } /* Returns an upper bound on the number of executions of statements in the LOOP. For statements before the loop exit, this exceeds the number of execution of the latch by one. */ HOST_WIDE_INT max_stmt_executions_int (struct loop *loop, bool conservative) { HOST_WIDE_INT nit = estimated_loop_iterations_int (loop, conservative); HOST_WIDE_INT snit; if (nit == -1) return -1; snit = (HOST_WIDE_INT) ((unsigned HOST_WIDE_INT) nit + 1); /* If the computation overflows, return -1. */ return snit < 0 ? -1 : snit; } /* Sets NIT to the estimated number of executions of the latch of the LOOP, plus one. If CONSERVATIVE is true, we must be sure that NIT is at least as large as the number of iterations. If we have no reliable estimate, the function returns false, otherwise returns true. */ bool max_stmt_executions (struct loop *loop, bool conservative, double_int *nit) { double_int nit_minus_one; if (!estimated_loop_iterations (loop, conservative, nit)) return false; nit_minus_one = *nit; *nit = double_int_add (*nit, double_int_one); return double_int_ucmp (*nit, nit_minus_one) > 0; } /* Records estimates on numbers of iterations of loops. */ void estimate_numbers_of_iterations (bool use_undefined_p) { loop_iterator li; struct loop *loop; /* We don't want to issue signed overflow warnings while getting loop iteration estimates. */ fold_defer_overflow_warnings (); FOR_EACH_LOOP (li, loop, 0) { estimate_numbers_of_iterations_loop (loop, use_undefined_p); } fold_undefer_and_ignore_overflow_warnings (); } /* Returns true if statement S1 dominates statement S2. */ bool stmt_dominates_stmt_p (gimple s1, gimple s2) { basic_block bb1 = gimple_bb (s1), bb2 = gimple_bb (s2); if (!bb1 || s1 == s2) return true; if (bb1 == bb2) { gimple_stmt_iterator bsi; if (gimple_code (s2) == GIMPLE_PHI) return false; if (gimple_code (s1) == GIMPLE_PHI) return true; for (bsi = gsi_start_bb (bb1); gsi_stmt (bsi) != s2; gsi_next (&bsi)) if (gsi_stmt (bsi) == s1) return true; return false; } return dominated_by_p (CDI_DOMINATORS, bb2, bb1); } /* Returns true when we can prove that the number of executions of STMT in the loop is at most NITER, according to the bound on the number of executions of the statement NITER_BOUND->stmt recorded in NITER_BOUND. If STMT is NULL, we must prove this bound for all statements in the loop. */ static bool n_of_executions_at_most (gimple stmt, struct nb_iter_bound *niter_bound, tree niter) { double_int bound = niter_bound->bound; tree nit_type = TREE_TYPE (niter), e; enum tree_code cmp; gcc_assert (TYPE_UNSIGNED (nit_type)); /* If the bound does not even fit into NIT_TYPE, it cannot tell us that the number of iterations is small. */ if (!double_int_fits_to_tree_p (nit_type, bound)) return false; /* We know that NITER_BOUND->stmt is executed at most NITER_BOUND->bound + 1 times. This means that: -- if NITER_BOUND->is_exit is true, then everything before NITER_BOUND->stmt is executed at most NITER_BOUND->bound + 1 times, and everything after it at most NITER_BOUND->bound times. -- If NITER_BOUND->is_exit is false, then if we can prove that when STMT is executed, then NITER_BOUND->stmt is executed as well in the same iteration (we conclude that if both statements belong to the same basic block, or if STMT is after NITER_BOUND->stmt), then STMT is executed at most NITER_BOUND->bound + 1 times. Otherwise STMT is executed at most NITER_BOUND->bound + 2 times. */ if (niter_bound->is_exit) { if (stmt && stmt != niter_bound->stmt && stmt_dominates_stmt_p (niter_bound->stmt, stmt)) cmp = GE_EXPR; else cmp = GT_EXPR; } else { if (!stmt || (gimple_bb (stmt) != gimple_bb (niter_bound->stmt) && !stmt_dominates_stmt_p (niter_bound->stmt, stmt))) { bound = double_int_add (bound, double_int_one); if (double_int_zero_p (bound) || !double_int_fits_to_tree_p (nit_type, bound)) return false; } cmp = GT_EXPR; } e = fold_binary (cmp, boolean_type_node, niter, double_int_to_tree (nit_type, bound)); return e && integer_nonzerop (e); } /* Returns true if the arithmetics in TYPE can be assumed not to wrap. */ bool nowrap_type_p (tree type) { if (INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_UNDEFINED (type)) return true; if (POINTER_TYPE_P (type)) return true; return false; } /* Return false only when the induction variable BASE + STEP * I is known to not overflow: i.e. when the number of iterations is small enough with respect to the step and initial condition in order to keep the evolution confined in TYPEs bounds. Return true when the iv is known to overflow or when the property is not computable. USE_OVERFLOW_SEMANTICS is true if this function should assume that the rules for overflow of the given language apply (e.g., that signed arithmetics in C does not overflow). */ bool scev_probably_wraps_p (tree base, tree step, gimple at_stmt, struct loop *loop, bool use_overflow_semantics) { struct nb_iter_bound *bound; tree delta, step_abs; tree unsigned_type, valid_niter; tree type = TREE_TYPE (step); /* FIXME: We really need something like http://gcc.gnu.org/ml/gcc-patches/2005-06/msg02025.html. We used to test for the following situation that frequently appears during address arithmetics: D.1621_13 = (long unsigned intD.4) D.1620_12; D.1622_14 = D.1621_13 * 8; D.1623_15 = (doubleD.29 *) D.1622_14; And derived that the sequence corresponding to D_14 can be proved to not wrap because it is used for computing a memory access; however, this is not really the case -- for example, if D_12 = (unsigned char) [254,+,1], then D_14 has values 2032, 2040, 0, 8, ..., but the code is still legal. */ if (chrec_contains_undetermined (base) || chrec_contains_undetermined (step)) return true; if (integer_zerop (step)) return false; /* If we can use the fact that signed and pointer arithmetics does not wrap, we are done. */ if (use_overflow_semantics && nowrap_type_p (TREE_TYPE (base))) return false; /* To be able to use estimates on number of iterations of the loop, we must have an upper bound on the absolute value of the step. */ if (TREE_CODE (step) != INTEGER_CST) return true; /* Don't issue signed overflow warnings. */ fold_defer_overflow_warnings (); /* Otherwise, compute the number of iterations before we reach the bound of the type, and verify that the loop is exited before this occurs. */ unsigned_type = unsigned_type_for (type); base = fold_convert (unsigned_type, base); if (tree_int_cst_sign_bit (step)) { tree extreme = fold_convert (unsigned_type, lower_bound_in_type (type, type)); delta = fold_build2 (MINUS_EXPR, unsigned_type, base, extreme); step_abs = fold_build1 (NEGATE_EXPR, unsigned_type, fold_convert (unsigned_type, step)); } else { tree extreme = fold_convert (unsigned_type, upper_bound_in_type (type, type)); delta = fold_build2 (MINUS_EXPR, unsigned_type, extreme, base); step_abs = fold_convert (unsigned_type, step); } valid_niter = fold_build2 (FLOOR_DIV_EXPR, unsigned_type, delta, step_abs); estimate_numbers_of_iterations_loop (loop, true); for (bound = loop->bounds; bound; bound = bound->next) { if (n_of_executions_at_most (at_stmt, bound, valid_niter)) { fold_undefer_and_ignore_overflow_warnings (); return false; } } fold_undefer_and_ignore_overflow_warnings (); /* At this point we still don't have a proof that the iv does not overflow: give up. */ return true; } /* Frees the information on upper bounds on numbers of iterations of LOOP. */ void free_numbers_of_iterations_estimates_loop (struct loop *loop) { struct nb_iter_bound *bound, *next; loop->nb_iterations = NULL; loop->estimate_state = EST_NOT_COMPUTED; for (bound = loop->bounds; bound; bound = next) { next = bound->next; ggc_free (bound); } loop->bounds = NULL; } /* Frees the information on upper bounds on numbers of iterations of loops. */ void free_numbers_of_iterations_estimates (void) { loop_iterator li; struct loop *loop; FOR_EACH_LOOP (li, loop, 0) { free_numbers_of_iterations_estimates_loop (loop); } } /* Substitute value VAL for ssa name NAME inside expressions held at LOOP. */ void substitute_in_loop_info (struct loop *loop, tree name, tree val) { loop->nb_iterations = simplify_replace_tree (loop->nb_iterations, name, val); }
Go to most recent revision | Compare with Previous | Blame | View Log