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[/] [openrisc/] [trunk/] [gnu-old/] [gcc-4.2.2/] [gcc/] [tree-ssa-loop-niter.c] - Rev 856
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/* Functions to determine/estimate number of iterations of a loop. Copyright (C) 2004, 2005, 2006, 2007 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 "rtl.h" #include "tm_p.h" #include "hard-reg-set.h" #include "basic-block.h" #include "output.h" #include "diagnostic.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 "toplev.h" #include "tree-inline.h" #define SWAP(X, Y) do { void *tmp = (X); (X) = (Y); (Y) = tmp; } while (0) /* Analysis of number of iterations of an affine exit test. */ /* Returns true if ARG is either NULL_TREE or constant zero. Unlike integer_zerop, it does not care about overflow flags. */ bool zero_p (tree arg) { if (!arg) return true; if (TREE_CODE (arg) != INTEGER_CST) return false; return (TREE_INT_CST_LOW (arg) == 0 && TREE_INT_CST_HIGH (arg) == 0); } /* Returns true if ARG a nonzero constant. Unlike integer_nonzerop, it does not care about overflow flags. */ static bool nonzero_p (tree arg) { if (!arg) return false; if (TREE_CODE (arg) != INTEGER_CST) return false; return (TREE_INT_CST_LOW (arg) != 0 || TREE_INT_CST_HIGH (arg) != 0); } /* 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, 0); x = int_const_binop (MULT_EXPR, x, x, 0); } rslt = int_const_binop (BIT_AND_EXPR, rslt, mask, 0); } return rslt; } /* 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. NEVER_INFINITE 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). */ static bool number_of_iterations_ne (tree type, affine_iv *iv, tree final, struct tree_niter_desc *niter, bool never_infinite) { tree niter_type = unsigned_type_for (type); tree s, c, d, bits, assumption, tmp, bound; 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 (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)); } 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)); } /* 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 (!never_infinite) { /* If we cannot assume that the loop is not infinite, 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 (!nonzero_p (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. */ 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) { tree niter_type = TREE_TYPE (step); tree mod = fold_build2 (FLOOR_MOD_EXPR, niter_type, *delta, step); tree tmod; tree assumption = boolean_true_node, bound, noloop; if (TREE_CODE (mod) != INTEGER_CST) return false; if (nonzero_p (mod)) mod = fold_build2 (MINUS_EXPR, niter_type, step, mod); tmod = fold_convert (type, mod); if (nonzero_p (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 (!iv1->no_overflow && !zero_p (mod)) { bound = fold_build2 (MINUS_EXPR, type, TYPE_MAX_VALUE (type), tmod); assumption = fold_build2 (LE_EXPR, boolean_type_node, iv1->base, bound); if (zero_p (assumption)) return false; } noloop = fold_build2 (GT_EXPR, boolean_type_node, iv0->base, fold_build2 (PLUS_EXPR, type, 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 (!iv0->no_overflow && !zero_p (mod)) { bound = fold_build2 (PLUS_EXPR, type, TYPE_MIN_VALUE (type), tmod); assumption = fold_build2 (GE_EXPR, boolean_type_node, iv0->base, bound); if (zero_p (assumption)) return false; } noloop = fold_build2 (GT_EXPR, boolean_type_node, fold_build2 (MINUS_EXPR, type, iv0->base, tmod), iv1->base); } if (!nonzero_p (assumption)) niter->assumptions = fold_build2 (TRUTH_AND_EXPR, boolean_type_node, niter->assumptions, assumption); if (!zero_p (noloop)) niter->may_be_zero = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, niter->may_be_zero, noloop); *delta = fold_build2 (PLUS_EXPR, niter_type, *delta, mod); return true; } /* 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 (nonzero_p (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 (zero_p (assumption)) return false; if (!nonzero_p (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. */ static void assert_loop_rolls_lt (tree type, affine_iv *iv0, affine_iv *iv1, struct tree_niter_desc *niter) { tree assumption = boolean_true_node, bound, diff; tree mbz, mbzl, mbzr; if (nonzero_p (iv0->step)) { diff = fold_build2 (MINUS_EXPR, type, iv0->step, build_int_cst (type, 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, type, 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, type, iv0->base, diff); mbzr = iv1->base; } else { diff = fold_build2 (PLUS_EXPR, type, iv1->step, build_int_cst (type, 1)); if (!POINTER_TYPE_P (type)) { bound = fold_build2 (PLUS_EXPR, type, TYPE_MAX_VALUE (type), diff); assumption = fold_build2 (LE_EXPR, boolean_type_node, iv1->base, bound); } mbzl = iv0->base; mbzr = fold_build2 (MINUS_EXPR, type, iv1->base, diff); } mbz = fold_build2 (GT_EXPR, boolean_type_node, mbzl, mbzr); if (!nonzero_p (assumption)) niter->assumptions = fold_build2 (TRUTH_AND_EXPR, boolean_type_node, niter->assumptions, assumption); if (!zero_p (mbz)) 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. */ static bool number_of_iterations_lt (tree type, affine_iv *iv0, affine_iv *iv1, struct tree_niter_desc *niter, bool never_infinite ATTRIBUTE_UNUSED) { tree niter_type = unsigned_type_for (type); tree delta, step, s; if (nonzero_p (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 ((iv0->step && integer_onep (iv0->step) && zero_p (iv1->step)) || (iv1->step && integer_all_onesp (iv1->step) && zero_p (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. */ niter->may_be_zero = fold_build2 (LT_EXPR, boolean_type_node, iv1->base, iv0->base); niter->niter = delta; return true; } if (nonzero_p (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)) { 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); } /* 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); 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); 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. NEVER_INFINITE 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). */ static bool number_of_iterations_le (tree type, affine_iv *iv0, affine_iv *iv1, struct tree_niter_desc *niter, bool never_infinite) { tree assumption; /* 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. */ if (!never_infinite) { if (nonzero_p (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 (zero_p (assumption)) return false; if (!nonzero_p (assumption)) niter->assumptions = fold_build2 (TRUTH_AND_EXPR, boolean_type_node, niter->assumptions, assumption); } if (nonzero_p (iv0->step)) iv1->base = fold_build2 (PLUS_EXPR, type, iv1->base, build_int_cst (type, 1)); else iv0->base = fold_build2 (MINUS_EXPR, type, iv0->base, build_int_cst (type, 1)); return number_of_iterations_lt (type, iv0, iv1, niter, never_infinite); } /* 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). 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 (tree type, affine_iv *iv0, enum tree_code code, affine_iv *iv1, struct tree_niter_desc *niter, bool only_exit) { bool never_infinite; /* 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->additional_info = boolean_true_node; 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 && zero_p (iv0->step))) { SWAP (iv0, iv1); code = swap_tree_comparison (code); } if (!only_exit) { /* If this is not the only possible exit from the loop, the information that the induction variables cannot overflow as derived from signedness analysis cannot be relied upon. We use them e.g. in the following way: given loop for (i = 0; i <= n; i++), if i is signed, it cannot overflow, thus this loop is equivalent to for (i = 0; i < n + 1; i++); however, if n == MAX, but the loop is exited in some other way before i overflows, this transformation is incorrect (the new loop exits immediately). */ iv0->no_overflow = false; iv1->no_overflow = false; } 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). The restrictions on pointer arithmetics and comparisons of pointers ensure that using the no-overflow assumptions is correct in this case even if ONLY_EXIT is false. */ iv0->no_overflow = true; iv1->no_overflow = true; } /* If the control induction variable does not overflow, the loop obviously cannot be infinite. */ if (!zero_p (iv0->step) && iv0->no_overflow) never_infinite = true; else if (!zero_p (iv1->step) && iv1->no_overflow) never_infinite = true; else never_infinite = false; /* 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 (!zero_p (iv0->step) && !zero_p (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 = NULL_TREE; 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 (zero_p (iv0->step) && zero_p (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 (!zero_p (iv1->step) && !tree_int_cst_sign_bit (iv1->step)) return false; } /* If the loop exits immediately, there is nothing to do. */ if (zero_p (fold_build2 (code, boolean_type_node, iv0->base, iv1->base))) { niter->niter = build_int_cst (unsigned_type_for (type), 0); return true; } /* OK, now we know we have a senseful loop. Handle several cases, depending on what comparison operator is used. */ switch (code) { case NE_EXPR: gcc_assert (zero_p (iv1->step)); return number_of_iterations_ne (type, iv0, iv1->base, niter, never_infinite); case LT_EXPR: return number_of_iterations_lt (type, iv0, iv1, niter, never_infinite); case LE_EXPR: return number_of_iterations_le (type, iv0, iv1, niter, never_infinite); default: gcc_unreachable (); } } /* Substitute NEW for OLD in EXPR and fold the result. */ static tree simplify_replace_tree (tree expr, tree old, tree new) { unsigned i, n; tree ret = NULL_TREE, e, se; if (!expr) return NULL_TREE; if (expr == old || operand_equal_p (expr, old, 0)) return unshare_expr (new); if (!EXPR_P (expr)) return expr; n = TREE_CODE_LENGTH (TREE_CODE (expr)); for (i = 0; i < n; i++) { e = TREE_OPERAND (expr, i); se = simplify_replace_tree (e, old, new); 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, stmt; enum tree_code code; 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_CODE_LENGTH (code); 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 (TREE_CODE (stmt) != MODIFY_EXPR) return expr; e = TREE_OPERAND (stmt, 1); if (/* Casts are simple. */ TREE_CODE (e) != NOP_EXPR && TREE_CODE (e) != CONVERT_EXPR /* Copies are simple. */ && TREE_CODE (e) != SSA_NAME /* Assignments of invariants are simple. */ && !is_gimple_min_invariant (e) /* And increments and decrements by a constant are simple. */ && !((TREE_CODE (e) == PLUS_EXPR || TREE_CODE (e) == MINUS_EXPR) && is_gimple_min_invariant (TREE_OPERAND (e, 1)))) return expr; return expand_simple_operations (e); } /* 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 (zero_p (e) || nonzero_p (e)) return e; e = simplify_replace_tree (expr, e1, e0); if (zero_p (e) || nonzero_p (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 (zero_p (e)) return e; e = simplify_replace_tree (cond, e1, e0); if (zero_p (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 (zero_p (e)) return boolean_true_node; e = simplify_replace_tree (cond, e1, e0); if (zero_p (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 (nonzero_p (e)) return e; /* Check whether COND ==> not EXPR. */ e = fold_binary (TRUTH_AND_EXPR, boolean_type_node, cond, te); if (e && zero_p (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); } /* 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 /* Tries to simplify EXPR using the conditions on entry to LOOP. Record the conditions used for simplification to CONDS_USED. Returns the simplified expression (or EXPR unchanged, if no simplification was possible).*/ static tree simplify_using_initial_conditions (struct loop *loop, tree expr, tree *conds_used) { edge e; basic_block bb; tree exp, 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; cond = COND_EXPR_COND (last_stmt (e->src)); if (e->flags & EDGE_FALSE_VALUE) cond = invert_truthvalue (cond); exp = tree_simplify_using_condition (cond, expr); if (exp != expr) *conds_used = fold_build2 (TRUTH_AND_EXPR, boolean_type_node, *conds_used, cond); expr = exp; ++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. */ static bool loop_only_exit_p (struct loop *loop, edge exit) { basic_block *body; block_stmt_iterator bsi; unsigned i; tree call; if (exit != loop->single_exit) return false; body = get_loop_body (loop); for (i = 0; i < loop->num_nodes; i++) { for (bsi = bsi_start (body[0]); !bsi_end_p (bsi); bsi_next (&bsi)) { call = get_call_expr_in (bsi_stmt (bsi)); if (call && TREE_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) { tree stmt, cond, 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 || TREE_CODE (stmt) != COND_EXPR) return false; /* We want the condition for staying inside loop. */ cond = COND_EXPR_COND (stmt); if (exit->flags & EDGE_TRUE_VALUE) cond = invert_truthvalue (cond); code = TREE_CODE (cond); switch (code) { case GT_EXPR: case GE_EXPR: case NE_EXPR: case LT_EXPR: case LE_EXPR: break; default: return false; } op0 = TREE_OPERAND (cond, 0); op1 = TREE_OPERAND (cond, 1); type = TREE_TYPE (op0); if (TREE_CODE (type) != INTEGER_TYPE && !POINTER_TYPE_P (type)) return false; if (!simple_iv (loop, stmt, op0, &iv0, false)) return false; if (!simple_iv (loop, stmt, op1, &iv1, false)) return false; /* We don't want to see undefined signed overflow warnings while computing the nmber 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 (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->additional_info = boolean_true_node; niter->assumptions = simplify_using_initial_conditions (loop, niter->assumptions, &niter->additional_info); niter->may_be_zero = simplify_using_initial_conditions (loop, niter->may_be_zero, &niter->additional_info); 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)) return false; if (flag_unsafe_loop_optimizations) niter->assumptions = boolean_true_node; if (warn) { const char *wording; location_t loc = EXPR_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 (!zero_p (iv1.step) ? (zero_p (iv0.step) && (integer_onep (iv1.step) || integer_all_onesp (iv1.step))) : (iv0.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"); if (LOCATION_LINE (loc) > 0) warning (OPT_Wunsafe_loop_optimizations, "%H%s", &loc, gettext (wording)); else warning (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 n_exits, i; edge *exits = get_loop_exit_edges (loop, &n_exits); edge ex; tree niter = NULL_TREE, aniter; struct tree_niter_desc desc; *exit = NULL; for (i = 0; i < n_exits; i++) { ex = exits[i]; if (!just_once_each_iteration_p (loop, ex->src)) continue; if (!number_of_iterations_exit (loop, ex, &desc, false)) continue; if (nonzero_p (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 (!zero_p (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; } } free (exits); return niter ? niter : chrec_dont_know; } /* 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 tree chain_of_csts_start (struct loop *loop, tree x) { tree stmt = SSA_NAME_DEF_STMT (x); tree use; basic_block bb = bb_for_stmt (stmt); if (!bb || !flow_bb_inside_loop_p (loop, bb)) return NULL_TREE; if (TREE_CODE (stmt) == PHI_NODE) { if (bb == loop->header) return stmt; return NULL_TREE; } if (TREE_CODE (stmt) != MODIFY_EXPR) return NULL_TREE; if (!ZERO_SSA_OPERANDS (stmt, SSA_OP_ALL_VIRTUALS)) return NULL_TREE; if (SINGLE_SSA_DEF_OPERAND (stmt, SSA_OP_DEF) == NULL_DEF_OPERAND_P) return NULL_TREE; use = SINGLE_SSA_TREE_OPERAND (stmt, SSA_OP_USE); if (use == NULL_USE_OPERAND_P) return NULL_TREE; 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. If X is a constant, X is returned unchanged. Otherwise NULL_TREE is returned. */ static tree get_base_for (struct loop *loop, tree x) { tree phi, init, next; if (is_gimple_min_invariant (x)) return x; phi = chain_of_csts_start (loop, x); if (!phi) return NULL_TREE; 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_TREE; if (!is_gimple_min_invariant (init)) return NULL_TREE; if (chain_of_csts_start (loop, next) != phi) return NULL_TREE; 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) { tree stmt, nx, val; use_operand_p op; ssa_op_iter iter; gcc_assert (is_gimple_min_invariant (base)); if (!x) return base; stmt = SSA_NAME_DEF_STMT (x); if (TREE_CODE (stmt) == PHI_NODE) return base; FOR_EACH_SSA_USE_OPERAND (op, stmt, iter, SSA_OP_USE) { nx = USE_FROM_PTR (op); val = get_val_for (nx, base); SET_USE (op, val); val = fold (TREE_OPERAND (stmt, 1)); SET_USE (op, nx); /* only iterate loop once. */ return val; } /* Should never reach here. */ 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 cond, cnd, acnd; tree op[2], val[2], next[2], aval[2], phi[2]; unsigned i, j; enum tree_code cmp; cond = last_stmt (exit->src); if (!cond || TREE_CODE (cond) != COND_EXPR) return chrec_dont_know; cnd = COND_EXPR_COND (cond); if (exit->flags & EDGE_TRUE_VALUE) cnd = invert_truthvalue (cnd); cmp = TREE_CODE (cnd); switch (cmp) { case EQ_EXPR: case NE_EXPR: case GT_EXPR: case GE_EXPR: case LT_EXPR: case LE_EXPR: for (j = 0; j < 2; j++) op[j] = TREE_OPERAND (cnd, j); break; default: return chrec_dont_know; } for (j = 0; j < 2; j++) { phi[j] = get_base_for (loop, op[j]); if (!phi[j]) return chrec_dont_know; } for (j = 0; j < 2; j++) { if (TREE_CODE (phi[j]) == PHI_NODE) { val[j] = PHI_ARG_DEF_FROM_EDGE (phi[j], loop_preheader_edge (loop)); next[j] = PHI_ARG_DEF_FROM_EDGE (phi[j], loop_latch_edge (loop)); } else { val[j] = phi[j]; next[j] = NULL_TREE; op[j] = NULL_TREE; } } /* 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 && zero_p (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 n_exits, i; edge *exits = get_loop_exit_edges (loop, &n_exits); edge ex; tree niter = NULL_TREE, aniter; *exit = NULL; for (i = 0; i < n_exits; i++) { ex = exits[i]; 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; } free (exits); return niter ? niter : chrec_dont_know; } /* Analysis of upper bounds on number of iterations of a loop. */ /* Returns true if we can prove that COND ==> VAL >= 0. */ static bool implies_nonnegative_p (tree cond, tree val) { tree type = TREE_TYPE (val); tree compare; if (tree_expr_nonnegative_p (val)) return true; if (nonzero_p (cond)) return false; compare = fold_build2 (GE_EXPR, boolean_type_node, val, build_int_cst (type, 0)); compare = tree_simplify_using_condition_1 (cond, compare); return nonzero_p (compare); } /* Returns true if we can prove that COND ==> A >= B. */ static bool implies_ge_p (tree cond, tree a, tree b) { tree compare = fold_build2 (GE_EXPR, boolean_type_node, a, b); if (nonzero_p (compare)) return true; if (nonzero_p (cond)) return false; compare = tree_simplify_using_condition_1 (cond, compare); return nonzero_p (compare); } /* 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. The condition ADDITIONAL must be satisfied (for example, if VAL is "(unsigned) n" and ADDITIONAL is "n > 0", then we can derive that VAL is at most (unsigned) MAX_INT). */ static double_int derive_constant_upper_bound (tree val, tree additional) { tree type = TREE_TYPE (val); tree op0, op1, subtype, maxt; double_int bnd, max, mmax, cst; 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 (TREE_CODE (val)) { case INTEGER_CST: return tree_to_double_int (val); case NOP_EXPR: case CONVERT_EXPR: op0 = TREE_OPERAND (val, 0); 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) && !implies_nonnegative_p (additional, 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, additional); /* 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 MINUS_EXPR: op0 = TREE_OPERAND (val, 0); op1 = TREE_OPERAND (val, 1); if (TREE_CODE (op1) != INTEGER_CST || !implies_nonnegative_p (additional, 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 (TREE_CODE (val) == PLUS_EXPR) cst = double_int_neg (cst); bnd = derive_constant_upper_bound (op0, additional); 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_add (max, double_int_neg (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 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) && !implies_ge_p (additional, op0, double_int_to_tree (type, cst))) return max; bnd = double_int_add (bnd, double_int_neg (cst)); } return bnd; case FLOOR_DIV_EXPR: case EXACT_DIV_EXPR: op0 = TREE_OPERAND (val, 0); op1 = TREE_OPERAND (val, 1); if (TREE_CODE (op1) != INTEGER_CST || tree_int_cst_sign_bit (op1)) return max; bnd = derive_constant_upper_bound (op0, additional); return double_int_udiv (bnd, tree_to_double_int (op1), FLOOR_DIV_EXPR); default: return max; } } /* Records that AT_STMT is executed at most BOUND times in LOOP. The additional condition ADDITIONAL is recorded with the bound. */ void record_estimate (struct loop *loop, tree bound, tree additional, tree at_stmt) { struct nb_iter_bound *elt = xmalloc (sizeof (struct nb_iter_bound)); double_int i_bound = derive_constant_upper_bound (bound, additional); tree c_bound = double_int_to_tree (unsigned_type_for (TREE_TYPE (bound)), i_bound); if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Statements after "); print_generic_expr (dump_file, at_stmt, TDF_SLIM); fprintf (dump_file, " are executed at most "); print_generic_expr (dump_file, bound, TDF_SLIM); fprintf (dump_file, " (bounded by "); print_generic_expr (dump_file, c_bound, TDF_SLIM); fprintf (dump_file, ") times in loop %d.\n", loop->num); } elt->bound = c_bound; elt->at_stmt = at_stmt; elt->next = loop->bounds; loop->bounds = elt; } /* Initialize LOOP->ESTIMATED_NB_ITERATIONS with the lowest safe approximation of the number of iterations for LOOP. */ static void compute_estimated_nb_iterations (struct loop *loop) { struct nb_iter_bound *bound; for (bound = loop->bounds; bound; bound = bound->next) { if (TREE_CODE (bound->bound) != INTEGER_CST) continue; /* Update only when there is no previous estimation, or when the current estimation is smaller. */ if (chrec_contains_undetermined (loop->estimated_nb_iterations) || tree_int_cst_lt (bound->bound, loop->estimated_nb_iterations)) loop->estimated_nb_iterations = bound->bound; } } /* 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 bb, *bbs; block_stmt_iterator bsi; 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. */ if (!dominated_by_p (CDI_DOMINATORS, loop->latch, bb)) continue; for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi)) { tree stmt = bsi_stmt (bsi); switch (TREE_CODE (stmt)) { case MODIFY_EXPR: { tree op0 = TREE_OPERAND (stmt, 0); tree op1 = TREE_OPERAND (stmt, 1); /* For each array access, analyze its access function and record a bound on the loop iteration domain. */ if (TREE_CODE (op1) == ARRAY_REF && !array_ref_contains_indirect_ref (op1)) estimate_iters_using_array (stmt, op1); if (TREE_CODE (op0) == ARRAY_REF && !array_ref_contains_indirect_ref (op0)) estimate_iters_using_array (stmt, op0); /* For each signed type variable in LOOP, analyze its scalar evolution and record a bound of the loop based on the type's ranges. */ else if (!flag_wrapv && TREE_CODE (op0) == SSA_NAME) { tree init, step, diff, estimation; tree scev = instantiate_parameters (loop, analyze_scalar_evolution (loop, op0)); tree type = chrec_type (scev); if (chrec_contains_undetermined (scev) || TYPE_OVERFLOW_WRAPS (type)) break; init = initial_condition_in_loop_num (scev, loop->num); step = evolution_part_in_loop_num (scev, loop->num); if (init == NULL_TREE || step == NULL_TREE || TREE_CODE (init) != INTEGER_CST || TREE_CODE (step) != INTEGER_CST || TYPE_MIN_VALUE (type) == NULL_TREE || TYPE_MAX_VALUE (type) == NULL_TREE) break; if (integer_nonzerop (step)) { tree utype; if (tree_int_cst_lt (step, integer_zero_node)) diff = fold_build2 (MINUS_EXPR, type, init, TYPE_MIN_VALUE (type)); else diff = fold_build2 (MINUS_EXPR, type, TYPE_MAX_VALUE (type), init); utype = unsigned_type_for (type); estimation = fold_build2 (CEIL_DIV_EXPR, type, diff, step); record_estimate (loop, fold_convert (utype, estimation), boolean_true_node, stmt); } } break; } case CALL_EXPR: { tree args; for (args = TREE_OPERAND (stmt, 1); args; args = TREE_CHAIN (args)) if (TREE_CODE (TREE_VALUE (args)) == ARRAY_REF && !array_ref_contains_indirect_ref (TREE_VALUE (args))) estimate_iters_using_array (stmt, TREE_VALUE (args)); break; } default: break; } } } compute_estimated_nb_iterations (loop); free (bbs); } /* Records estimates on numbers of iterations of LOOP. */ static void estimate_numbers_of_iterations_loop (struct loop *loop) { edge *exits; tree niter, type; unsigned i, n_exits; struct tree_niter_desc niter_desc; /* Give up if we already have tried to compute an estimation. */ if (loop->estimated_nb_iterations == chrec_dont_know /* Or when we already have an estimation. */ || (loop->estimated_nb_iterations != NULL_TREE && TREE_CODE (loop->estimated_nb_iterations) == INTEGER_CST)) return; else loop->estimated_nb_iterations = chrec_dont_know; exits = get_loop_exit_edges (loop, &n_exits); for (i = 0; i < n_exits; i++) { if (!number_of_iterations_exit (loop, exits[i], &niter_desc, false)) continue; niter = niter_desc.niter; type = TREE_TYPE (niter); if (!zero_p (niter_desc.may_be_zero) && !nonzero_p (niter_desc.may_be_zero)) niter = build3 (COND_EXPR, type, niter_desc.may_be_zero, build_int_cst (type, 0), niter); record_estimate (loop, niter, niter_desc.additional_info, last_stmt (exits[i]->src)); } free (exits); if (chrec_contains_undetermined (loop->estimated_nb_iterations)) infer_loop_bounds_from_undefined (loop); } /* Records estimates on numbers of iterations of LOOPS. */ void estimate_numbers_of_iterations (struct loops *loops) { unsigned i; struct loop *loop; /* We don't want to issue signed overflow warnings while getting loop iteration estimates. */ fold_defer_overflow_warnings (); for (i = 1; i < loops->num; i++) { loop = loops->parray[i]; if (loop) estimate_numbers_of_iterations_loop (loop); } fold_undefer_and_ignore_overflow_warnings (); } /* Returns true if statement S1 dominates statement S2. */ static bool stmt_dominates_stmt_p (tree s1, tree s2) { basic_block bb1 = bb_for_stmt (s1), bb2 = bb_for_stmt (s2); if (!bb1 || s1 == s2) return true; if (bb1 == bb2) { block_stmt_iterator bsi; for (bsi = bsi_start (bb1); bsi_stmt (bsi) != s2; bsi_next (&bsi)) if (bsi_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 fact that the statement NITER_BOUND->at_stmt is executed at most NITER_BOUND->bound times. */ static bool n_of_executions_at_most (tree stmt, struct nb_iter_bound *niter_bound, tree niter) { tree cond; tree bound = niter_bound->bound; tree bound_type = TREE_TYPE (bound); tree nit_type = TREE_TYPE (niter); enum tree_code cmp; gcc_assert (TYPE_UNSIGNED (bound_type) && TYPE_UNSIGNED (nit_type) && is_gimple_min_invariant (bound)); if (TYPE_PRECISION (nit_type) > TYPE_PRECISION (bound_type)) bound = fold_convert (nit_type, bound); else niter = fold_convert (bound_type, niter); /* After the statement niter_bound->at_stmt we know that anything is executed at most BOUND times. */ if (stmt && stmt_dominates_stmt_p (niter_bound->at_stmt, stmt)) cmp = GE_EXPR; /* Before the statement niter_bound->at_stmt we know that anything is executed at most BOUND + 1 times. */ else cmp = GT_EXPR; cond = fold_binary (cmp, boolean_type_node, niter, bound); return nonzero_p (cond); } /* 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, tree 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) || TREE_CODE (step) != INTEGER_CST) return true; if (zero_p (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 (type)) return false; /* 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); 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->estimated_nb_iterations = NULL; for (bound = loop->bounds; bound; bound = next) { next = bound->next; free (bound); } loop->bounds = NULL; } /* Frees the information on upper bounds on numbers of iterations of LOOPS. */ void free_numbers_of_iterations_estimates (struct loops *loops) { unsigned i; struct loop *loop; for (i = 1; i < loops->num; i++) { loop = loops->parray[i]; if (loop) 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); loop->estimated_nb_iterations = simplify_replace_tree (loop->estimated_nb_iterations, name, val); }
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