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/* Predicate aware uninitialized variable warning. Copyright (C) 2001, 2002, 2003, 2004, 2005, 2007, 2008, 2010 Free Software Foundation, Inc. Contributed by Xinliang David Li <davidxl@google.com> 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 "flags.h" #include "tm_p.h" #include "langhooks.h" #include "basic-block.h" #include "output.h" #include "function.h" #include "gimple-pretty-print.h" #include "bitmap.h" #include "pointer-set.h" #include "tree-flow.h" #include "gimple.h" #include "tree-inline.h" #include "timevar.h" #include "hashtab.h" #include "tree-dump.h" #include "tree-pass.h" #include "diagnostic-core.h" #include "timevar.h" /* This implements the pass that does predicate aware warning on uses of possibly uninitialized variables. The pass first collects the set of possibly uninitialized SSA names. For each such name, it walks through all its immediate uses. For each immediate use, it rebuilds the condition expression (the predicate) that guards the use. The predicate is then examined to see if the variable is always defined under that same condition. This is done either by pruning the unrealizable paths that lead to the default definitions or by checking if the predicate set that guards the defining paths is a superset of the use predicate. */ /* Pointer set of potentially undefined ssa names, i.e., ssa names that are defined by phi with operands that are not defined or potentially undefined. */ static struct pointer_set_t *possibly_undefined_names = 0; /* Bit mask handling macros. */ #define MASK_SET_BIT(mask, pos) mask |= (1 << pos) #define MASK_TEST_BIT(mask, pos) (mask & (1 << pos)) #define MASK_EMPTY(mask) (mask == 0) /* Returns the first bit position (starting from LSB) in mask that is non zero. Returns -1 if the mask is empty. */ static int get_mask_first_set_bit (unsigned mask) { int pos = 0; if (mask == 0) return -1; while ((mask & (1 << pos)) == 0) pos++; return pos; } #define MASK_FIRST_SET_BIT(mask) get_mask_first_set_bit (mask) /* Return true if T, an SSA_NAME, has an undefined value. */ bool ssa_undefined_value_p (tree t) { tree var = SSA_NAME_VAR (t); /* Parameters get their initial value from the function entry. */ if (TREE_CODE (var) == PARM_DECL) return false; /* When returning by reference the return address is actually a hidden parameter. */ if (TREE_CODE (SSA_NAME_VAR (t)) == RESULT_DECL && DECL_BY_REFERENCE (SSA_NAME_VAR (t))) return false; /* Hard register variables get their initial value from the ether. */ if (TREE_CODE (var) == VAR_DECL && DECL_HARD_REGISTER (var)) return false; /* The value is undefined iff its definition statement is empty. */ return (gimple_nop_p (SSA_NAME_DEF_STMT (t)) || (possibly_undefined_names && pointer_set_contains (possibly_undefined_names, t))); } /* Checks if the operand OPND of PHI is defined by another phi with one operand defined by this PHI, but the rest operands are all defined. If yes, returns true to skip this this operand as being redundant. Can be enhanced to be more general. */ static bool can_skip_redundant_opnd (tree opnd, gimple phi) { gimple op_def; tree phi_def; int i, n; phi_def = gimple_phi_result (phi); op_def = SSA_NAME_DEF_STMT (opnd); if (gimple_code (op_def) != GIMPLE_PHI) return false; n = gimple_phi_num_args (op_def); for (i = 0; i < n; ++i) { tree op = gimple_phi_arg_def (op_def, i); if (TREE_CODE (op) != SSA_NAME) continue; if (op != phi_def && ssa_undefined_value_p (op)) return false; } return true; } /* Returns a bit mask holding the positions of arguments in PHI that have empty (or possibly empty) definitions. */ static unsigned compute_uninit_opnds_pos (gimple phi) { size_t i, n; unsigned uninit_opnds = 0; n = gimple_phi_num_args (phi); /* Bail out for phi with too many args. */ if (n > 32) return 0; for (i = 0; i < n; ++i) { tree op = gimple_phi_arg_def (phi, i); if (TREE_CODE (op) == SSA_NAME && ssa_undefined_value_p (op) && !can_skip_redundant_opnd (op, phi)) MASK_SET_BIT (uninit_opnds, i); } return uninit_opnds; } /* Find the immediate postdominator PDOM of the specified basic block BLOCK. */ static inline basic_block find_pdom (basic_block block) { if (block == EXIT_BLOCK_PTR) return EXIT_BLOCK_PTR; else { basic_block bb = get_immediate_dominator (CDI_POST_DOMINATORS, block); if (! bb) return EXIT_BLOCK_PTR; return bb; } } /* Find the immediate DOM of the specified basic block BLOCK. */ static inline basic_block find_dom (basic_block block) { if (block == ENTRY_BLOCK_PTR) return ENTRY_BLOCK_PTR; else { basic_block bb = get_immediate_dominator (CDI_DOMINATORS, block); if (! bb) return ENTRY_BLOCK_PTR; return bb; } } /* Returns true if BB1 is postdominating BB2 and BB1 is not a loop exit bb. The loop exit bb check is simple and does not cover all cases. */ static bool is_non_loop_exit_postdominating (basic_block bb1, basic_block bb2) { if (!dominated_by_p (CDI_POST_DOMINATORS, bb2, bb1)) return false; if (single_pred_p (bb1) && !single_succ_p (bb2)) return false; return true; } /* Find the closest postdominator of a specified BB, which is control equivalent to BB. */ static inline basic_block find_control_equiv_block (basic_block bb) { basic_block pdom; pdom = find_pdom (bb); /* Skip the postdominating bb that is also loop exit. */ if (!is_non_loop_exit_postdominating (pdom, bb)) return NULL; if (dominated_by_p (CDI_DOMINATORS, pdom, bb)) return pdom; return NULL; } #define MAX_NUM_CHAINS 8 #define MAX_CHAIN_LEN 5 /* Computes the control dependence chains (paths of edges) for DEP_BB up to the dominating basic block BB (the head node of a chain should be dominated by it). CD_CHAINS is pointer to a dynamic array holding the result chains. CUR_CD_CHAIN is the current chain being computed. *NUM_CHAINS is total number of chains. The function returns true if the information is successfully computed, return false if there is no control dependence or not computed. */ static bool compute_control_dep_chain (basic_block bb, basic_block dep_bb, VEC(edge, heap) **cd_chains, size_t *num_chains, VEC(edge, heap) **cur_cd_chain) { edge_iterator ei; edge e; size_t i; bool found_cd_chain = false; size_t cur_chain_len = 0; if (EDGE_COUNT (bb->succs) < 2) return false; /* Could use a set instead. */ cur_chain_len = VEC_length (edge, *cur_cd_chain); if (cur_chain_len > MAX_CHAIN_LEN) return false; for (i = 0; i < cur_chain_len; i++) { edge e = VEC_index (edge, *cur_cd_chain, i); /* cycle detected. */ if (e->src == bb) return false; } FOR_EACH_EDGE (e, ei, bb->succs) { basic_block cd_bb; if (e->flags & (EDGE_FAKE | EDGE_ABNORMAL)) continue; cd_bb = e->dest; VEC_safe_push (edge, heap, *cur_cd_chain, e); while (!is_non_loop_exit_postdominating (cd_bb, bb)) { if (cd_bb == dep_bb) { /* Found a direct control dependence. */ if (*num_chains < MAX_NUM_CHAINS) { cd_chains[*num_chains] = VEC_copy (edge, heap, *cur_cd_chain); (*num_chains)++; } found_cd_chain = true; /* check path from next edge. */ break; } /* Now check if DEP_BB is indirectly control dependent on BB. */ if (compute_control_dep_chain (cd_bb, dep_bb, cd_chains, num_chains, cur_cd_chain)) { found_cd_chain = true; break; } cd_bb = find_pdom (cd_bb); if (cd_bb == EXIT_BLOCK_PTR) break; } VEC_pop (edge, *cur_cd_chain); gcc_assert (VEC_length (edge, *cur_cd_chain) == cur_chain_len); } gcc_assert (VEC_length (edge, *cur_cd_chain) == cur_chain_len); return found_cd_chain; } typedef struct use_pred_info { gimple cond; bool invert; } *use_pred_info_t; DEF_VEC_P(use_pred_info_t); DEF_VEC_ALLOC_P(use_pred_info_t, heap); /* Converts the chains of control dependence edges into a set of predicates. A control dependence chain is represented by a vector edges. DEP_CHAINS points to an array of dependence chains. NUM_CHAINS is the size of the chain array. One edge in a dependence chain is mapped to predicate expression represented by use_pred_info_t type. One dependence chain is converted to a composite predicate that is the result of AND operation of use_pred_info_t mapped to each edge. A composite predicate is presented by a vector of use_pred_info_t. On return, *PREDS points to the resulting array of composite predicates. *NUM_PREDS is the number of composite predictes. */ static bool convert_control_dep_chain_into_preds (VEC(edge, heap) **dep_chains, size_t num_chains, VEC(use_pred_info_t, heap) ***preds, size_t *num_preds) { bool has_valid_pred = false; size_t i, j; if (num_chains == 0 || num_chains >= MAX_NUM_CHAINS) return false; /* Now convert the control dep chain into a set of predicates. */ *preds = XCNEWVEC (VEC(use_pred_info_t, heap) *, num_chains); *num_preds = num_chains; for (i = 0; i < num_chains; i++) { VEC(edge, heap) *one_cd_chain = dep_chains[i]; has_valid_pred = false; for (j = 0; j < VEC_length (edge, one_cd_chain); j++) { gimple cond_stmt; gimple_stmt_iterator gsi; basic_block guard_bb; use_pred_info_t one_pred; edge e; e = VEC_index (edge, one_cd_chain, j); guard_bb = e->src; gsi = gsi_last_bb (guard_bb); if (gsi_end_p (gsi)) { has_valid_pred = false; break; } cond_stmt = gsi_stmt (gsi); if (gimple_code (cond_stmt) == GIMPLE_CALL && EDGE_COUNT (e->src->succs) >= 2) { /* Ignore EH edge. Can add assertion on the other edge's flag. */ continue; } /* Skip if there is essentially one succesor. */ if (EDGE_COUNT (e->src->succs) == 2) { edge e1; edge_iterator ei1; bool skip = false; FOR_EACH_EDGE (e1, ei1, e->src->succs) { if (EDGE_COUNT (e1->dest->succs) == 0) { skip = true; break; } } if (skip) continue; } if (gimple_code (cond_stmt) != GIMPLE_COND) { has_valid_pred = false; break; } one_pred = XNEW (struct use_pred_info); one_pred->cond = cond_stmt; one_pred->invert = !!(e->flags & EDGE_FALSE_VALUE); VEC_safe_push (use_pred_info_t, heap, (*preds)[i], one_pred); has_valid_pred = true; } if (!has_valid_pred) break; } return has_valid_pred; } /* Computes all control dependence chains for USE_BB. The control dependence chains are then converted to an array of composite predicates pointed to by PREDS. PHI_BB is the basic block of the phi whose result is used in USE_BB. */ static bool find_predicates (VEC(use_pred_info_t, heap) ***preds, size_t *num_preds, basic_block phi_bb, basic_block use_bb) { size_t num_chains = 0, i; VEC(edge, heap) **dep_chains = 0; VEC(edge, heap) *cur_chain = 0; bool has_valid_pred = false; basic_block cd_root = 0; dep_chains = XCNEWVEC (VEC(edge, heap) *, MAX_NUM_CHAINS); /* First find the closest bb that is control equivalent to PHI_BB that also dominates USE_BB. */ cd_root = phi_bb; while (dominated_by_p (CDI_DOMINATORS, use_bb, cd_root)) { basic_block ctrl_eq_bb = find_control_equiv_block (cd_root); if (ctrl_eq_bb && dominated_by_p (CDI_DOMINATORS, use_bb, ctrl_eq_bb)) cd_root = ctrl_eq_bb; else break; } compute_control_dep_chain (cd_root, use_bb, dep_chains, &num_chains, &cur_chain); has_valid_pred = convert_control_dep_chain_into_preds (dep_chains, num_chains, preds, num_preds); /* Free individual chain */ VEC_free (edge, heap, cur_chain); for (i = 0; i < num_chains; i++) VEC_free (edge, heap, dep_chains[i]); free (dep_chains); return has_valid_pred; } /* Computes the set of incoming edges of PHI that have non empty definitions of a phi chain. The collection will be done recursively on operands that are defined by phis. CD_ROOT is the control dependence root. *EDGES holds the result, and VISITED_PHIS is a pointer set for detecting cycles. */ static void collect_phi_def_edges (gimple phi, basic_block cd_root, VEC(edge, heap) **edges, struct pointer_set_t *visited_phis) { size_t i, n; edge opnd_edge; tree opnd; if (pointer_set_insert (visited_phis, phi)) return; n = gimple_phi_num_args (phi); for (i = 0; i < n; i++) { opnd_edge = gimple_phi_arg_edge (phi, i); opnd = gimple_phi_arg_def (phi, i); if (TREE_CODE (opnd) != SSA_NAME) { if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "\n[CHECK] Found def edge %d in ", (int)i); print_gimple_stmt (dump_file, phi, 0, 0); } VEC_safe_push (edge, heap, *edges, opnd_edge); } else { gimple def = SSA_NAME_DEF_STMT (opnd); if (gimple_code (def) == GIMPLE_PHI && dominated_by_p (CDI_DOMINATORS, gimple_bb (def), cd_root)) collect_phi_def_edges (def, cd_root, edges, visited_phis); else if (!ssa_undefined_value_p (opnd)) { if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "\n[CHECK] Found def edge %d in ", (int)i); print_gimple_stmt (dump_file, phi, 0, 0); } VEC_safe_push (edge, heap, *edges, opnd_edge); } } } } /* For each use edge of PHI, computes all control dependence chains. The control dependence chains are then converted to an array of composite predicates pointed to by PREDS. */ static bool find_def_preds (VEC(use_pred_info_t, heap) ***preds, size_t *num_preds, gimple phi) { size_t num_chains = 0, i, n; VEC(edge, heap) **dep_chains = 0; VEC(edge, heap) *cur_chain = 0; VEC(edge, heap) *def_edges = 0; bool has_valid_pred = false; basic_block phi_bb, cd_root = 0; struct pointer_set_t *visited_phis; dep_chains = XCNEWVEC (VEC(edge, heap) *, MAX_NUM_CHAINS); phi_bb = gimple_bb (phi); /* First find the closest dominating bb to be the control dependence root */ cd_root = find_dom (phi_bb); if (!cd_root) return false; visited_phis = pointer_set_create (); collect_phi_def_edges (phi, cd_root, &def_edges, visited_phis); pointer_set_destroy (visited_phis); n = VEC_length (edge, def_edges); if (n == 0) return false; for (i = 0; i < n; i++) { size_t prev_nc, j; edge opnd_edge; opnd_edge = VEC_index (edge, def_edges, i); prev_nc = num_chains; compute_control_dep_chain (cd_root, opnd_edge->src, dep_chains, &num_chains, &cur_chain); /* Free individual chain */ VEC_free (edge, heap, cur_chain); cur_chain = 0; /* Now update the newly added chains with the phi operand edge: */ if (EDGE_COUNT (opnd_edge->src->succs) > 1) { if (prev_nc == num_chains && num_chains < MAX_NUM_CHAINS) num_chains++; for (j = prev_nc; j < num_chains; j++) { VEC_safe_push (edge, heap, dep_chains[j], opnd_edge); } } } has_valid_pred = convert_control_dep_chain_into_preds (dep_chains, num_chains, preds, num_preds); for (i = 0; i < num_chains; i++) VEC_free (edge, heap, dep_chains[i]); free (dep_chains); return has_valid_pred; } /* Dumps the predicates (PREDS) for USESTMT. */ static void dump_predicates (gimple usestmt, size_t num_preds, VEC(use_pred_info_t, heap) **preds, const char* msg) { size_t i, j; VEC(use_pred_info_t, heap) *one_pred_chain; fprintf (dump_file, msg); print_gimple_stmt (dump_file, usestmt, 0, 0); fprintf (dump_file, "is guarded by :\n"); /* do some dumping here: */ for (i = 0; i < num_preds; i++) { size_t np; one_pred_chain = preds[i]; np = VEC_length (use_pred_info_t, one_pred_chain); for (j = 0; j < np; j++) { use_pred_info_t one_pred = VEC_index (use_pred_info_t, one_pred_chain, j); if (one_pred->invert) fprintf (dump_file, " (.NOT.) "); print_gimple_stmt (dump_file, one_pred->cond, 0, 0); if (j < np - 1) fprintf (dump_file, "(.AND.)\n"); } if (i < num_preds - 1) fprintf (dump_file, "(.OR.)\n"); } } /* Destroys the predicate set *PREDS. */ static void destroy_predicate_vecs (size_t n, VEC(use_pred_info_t, heap) ** preds) { size_t i, j; for (i = 0; i < n; i++) { for (j = 0; j < VEC_length (use_pred_info_t, preds[i]); j++) free (VEC_index (use_pred_info_t, preds[i], j)); VEC_free (use_pred_info_t, heap, preds[i]); } free (preds); } /* Computes the 'normalized' conditional code with operand swapping and condition inversion. */ static enum tree_code get_cmp_code (enum tree_code orig_cmp_code, bool swap_cond, bool invert) { enum tree_code tc = orig_cmp_code; if (swap_cond) tc = swap_tree_comparison (orig_cmp_code); if (invert) tc = invert_tree_comparison (tc, false); switch (tc) { case LT_EXPR: case LE_EXPR: case GT_EXPR: case GE_EXPR: case EQ_EXPR: case NE_EXPR: break; default: return ERROR_MARK; } return tc; } /* Returns true if VAL falls in the range defined by BOUNDARY and CMPC, i.e. all values in the range satisfies (x CMPC BOUNDARY) == true. */ static bool is_value_included_in (tree val, tree boundary, enum tree_code cmpc) { bool inverted = false; bool is_unsigned; bool result; /* Only handle integer constant here. */ if (TREE_CODE (val) != INTEGER_CST || TREE_CODE (boundary) != INTEGER_CST) return true; is_unsigned = TYPE_UNSIGNED (TREE_TYPE (val)); if (cmpc == GE_EXPR || cmpc == GT_EXPR || cmpc == NE_EXPR) { cmpc = invert_tree_comparison (cmpc, false); inverted = true; } if (is_unsigned) { if (cmpc == EQ_EXPR) result = tree_int_cst_equal (val, boundary); else if (cmpc == LT_EXPR) result = INT_CST_LT_UNSIGNED (val, boundary); else { gcc_assert (cmpc == LE_EXPR); result = (tree_int_cst_equal (val, boundary) || INT_CST_LT_UNSIGNED (val, boundary)); } } else { if (cmpc == EQ_EXPR) result = tree_int_cst_equal (val, boundary); else if (cmpc == LT_EXPR) result = INT_CST_LT (val, boundary); else { gcc_assert (cmpc == LE_EXPR); result = (tree_int_cst_equal (val, boundary) || INT_CST_LT (val, boundary)); } } if (inverted) result ^= 1; return result; } /* Returns true if PRED is common among all the predicate chains (PREDS) (and therefore can be factored out). NUM_PRED_CHAIN is the size of array PREDS. */ static bool find_matching_predicate_in_rest_chains (use_pred_info_t pred, VEC(use_pred_info_t, heap) **preds, size_t num_pred_chains) { size_t i, j, n; /* trival case */ if (num_pred_chains == 1) return true; for (i = 1; i < num_pred_chains; i++) { bool found = false; VEC(use_pred_info_t, heap) *one_chain = preds[i]; n = VEC_length (use_pred_info_t, one_chain); for (j = 0; j < n; j++) { use_pred_info_t pred2 = VEC_index (use_pred_info_t, one_chain, j); /* can relax the condition comparison to not use address comparison. However, the most common case is that multiple control dependent paths share a common path prefix, so address comparison should be ok. */ if (pred2->cond == pred->cond && pred2->invert == pred->invert) { found = true; break; } } if (!found) return false; } return true; } /* Forward declaration. */ static bool is_use_properly_guarded (gimple use_stmt, basic_block use_bb, gimple phi, unsigned uninit_opnds, struct pointer_set_t *visited_phis); /* Returns true if all uninitialized opnds are pruned. Returns false otherwise. PHI is the phi node with uninitialized operands, UNINIT_OPNDS is the bitmap of the uninitialize operand positions, FLAG_DEF is the statement defining the flag guarding the use of the PHI output, BOUNDARY_CST is the const value used in the predicate associated with the flag, CMP_CODE is the comparison code used in the predicate, VISITED_PHIS is the pointer set of phis visited, and VISITED_FLAG_PHIS is the pointer to the pointer set of flag definitions that are also phis. Example scenario: BB1: flag_1 = phi <0, 1> // (1) var_1 = phi <undef, some_val> BB2: flag_2 = phi <0, flag_1, flag_1> // (2) var_2 = phi <undef, var_1, var_1> if (flag_2 == 1) goto BB3; BB3: use of var_2 // (3) Because some flag arg in (1) is not constant, if we do not look into the flag phis recursively, it is conservatively treated as unknown and var_1 is thought to be flowed into use at (3). Since var_1 is potentially uninitialized a false warning will be emitted. Checking recursively into (1), the compiler can find out that only some_val (which is defined) can flow into (3) which is OK. */ static bool prune_uninit_phi_opnds_in_unrealizable_paths ( gimple phi, unsigned uninit_opnds, gimple flag_def, tree boundary_cst, enum tree_code cmp_code, struct pointer_set_t *visited_phis, bitmap *visited_flag_phis) { unsigned i; for (i = 0; i < MIN (32, gimple_phi_num_args (flag_def)); i++) { tree flag_arg; if (!MASK_TEST_BIT (uninit_opnds, i)) continue; flag_arg = gimple_phi_arg_def (flag_def, i); if (!is_gimple_constant (flag_arg)) { gimple flag_arg_def, phi_arg_def; tree phi_arg; unsigned uninit_opnds_arg_phi; if (TREE_CODE (flag_arg) != SSA_NAME) return false; flag_arg_def = SSA_NAME_DEF_STMT (flag_arg); if (gimple_code (flag_arg_def) != GIMPLE_PHI) return false; phi_arg = gimple_phi_arg_def (phi, i); if (TREE_CODE (phi_arg) != SSA_NAME) return false; phi_arg_def = SSA_NAME_DEF_STMT (phi_arg); if (gimple_code (phi_arg_def) != GIMPLE_PHI) return false; if (gimple_bb (phi_arg_def) != gimple_bb (flag_arg_def)) return false; if (!*visited_flag_phis) *visited_flag_phis = BITMAP_ALLOC (NULL); if (bitmap_bit_p (*visited_flag_phis, SSA_NAME_VERSION (gimple_phi_result (flag_arg_def)))) return false; bitmap_set_bit (*visited_flag_phis, SSA_NAME_VERSION (gimple_phi_result (flag_arg_def))); /* Now recursively prune the uninitialized phi args. */ uninit_opnds_arg_phi = compute_uninit_opnds_pos (phi_arg_def); if (!prune_uninit_phi_opnds_in_unrealizable_paths ( phi_arg_def, uninit_opnds_arg_phi, flag_arg_def, boundary_cst, cmp_code, visited_phis, visited_flag_phis)) return false; bitmap_clear_bit (*visited_flag_phis, SSA_NAME_VERSION (gimple_phi_result (flag_arg_def))); continue; } /* Now check if the constant is in the guarded range. */ if (is_value_included_in (flag_arg, boundary_cst, cmp_code)) { tree opnd; gimple opnd_def; /* Now that we know that this undefined edge is not pruned. If the operand is defined by another phi, we can further prune the incoming edges of that phi by checking the predicates of this operands. */ opnd = gimple_phi_arg_def (phi, i); opnd_def = SSA_NAME_DEF_STMT (opnd); if (gimple_code (opnd_def) == GIMPLE_PHI) { edge opnd_edge; unsigned uninit_opnds2 = compute_uninit_opnds_pos (opnd_def); gcc_assert (!MASK_EMPTY (uninit_opnds2)); opnd_edge = gimple_phi_arg_edge (phi, i); if (!is_use_properly_guarded (phi, opnd_edge->src, opnd_def, uninit_opnds2, visited_phis)) return false; } else return false; } } return true; } /* A helper function that determines if the predicate set of the use is not overlapping with that of the uninit paths. The most common senario of guarded use is in Example 1: Example 1: if (some_cond) { x = ...; flag = true; } ... some code ... if (flag) use (x); The real world examples are usually more complicated, but similar and usually result from inlining: bool init_func (int * x) { if (some_cond) return false; *x = .. return true; } void foo(..) { int x; if (!init_func(&x)) return; .. some_code ... use (x); } Another possible use scenario is in the following trivial example: Example 2: if (n > 0) x = 1; ... if (n > 0) { if (m < 2) .. = x; } Predicate analysis needs to compute the composite predicate: 1) 'x' use predicate: (n > 0) .AND. (m < 2) 2) 'x' default value (non-def) predicate: .NOT. (n > 0) (the predicate chain for phi operand defs can be computed starting from a bb that is control equivalent to the phi's bb and is dominating the operand def.) and check overlapping: (n > 0) .AND. (m < 2) .AND. (.NOT. (n > 0)) <==> false This implementation provides framework that can handle scenarios. (Note that many simple cases are handled properly without the predicate analysis -- this is due to jump threading transformation which eliminates the merge point thus makes path sensitive analysis unnecessary.) NUM_PREDS is the number is the number predicate chains, PREDS is the array of chains, PHI is the phi node whose incoming (undefined) paths need to be pruned, and UNINIT_OPNDS is the bitmap holding uninit operand positions. VISITED_PHIS is the pointer set of phi stmts being checked. */ static bool use_pred_not_overlap_with_undef_path_pred ( size_t num_preds, VEC(use_pred_info_t, heap) **preds, gimple phi, unsigned uninit_opnds, struct pointer_set_t *visited_phis) { unsigned int i, n; gimple flag_def = 0; tree boundary_cst = 0; enum tree_code cmp_code; bool swap_cond = false; bool invert = false; VEC(use_pred_info_t, heap) *the_pred_chain; bitmap visited_flag_phis = NULL; bool all_pruned = false; gcc_assert (num_preds > 0); /* Find within the common prefix of multiple predicate chains a predicate that is a comparison of a flag variable against a constant. */ the_pred_chain = preds[0]; n = VEC_length (use_pred_info_t, the_pred_chain); for (i = 0; i < n; i++) { gimple cond; tree cond_lhs, cond_rhs, flag = 0; use_pred_info_t the_pred = VEC_index (use_pred_info_t, the_pred_chain, i); cond = the_pred->cond; invert = the_pred->invert; cond_lhs = gimple_cond_lhs (cond); cond_rhs = gimple_cond_rhs (cond); cmp_code = gimple_cond_code (cond); if (cond_lhs != NULL_TREE && TREE_CODE (cond_lhs) == SSA_NAME && cond_rhs != NULL_TREE && is_gimple_constant (cond_rhs)) { boundary_cst = cond_rhs; flag = cond_lhs; } else if (cond_rhs != NULL_TREE && TREE_CODE (cond_rhs) == SSA_NAME && cond_lhs != NULL_TREE && is_gimple_constant (cond_lhs)) { boundary_cst = cond_lhs; flag = cond_rhs; swap_cond = true; } if (!flag) continue; flag_def = SSA_NAME_DEF_STMT (flag); if (!flag_def) continue; if ((gimple_code (flag_def) == GIMPLE_PHI) && (gimple_bb (flag_def) == gimple_bb (phi)) && find_matching_predicate_in_rest_chains ( the_pred, preds, num_preds)) break; flag_def = 0; } if (!flag_def) return false; /* Now check all the uninit incoming edge has a constant flag value that is in conflict with the use guard/predicate. */ cmp_code = get_cmp_code (cmp_code, swap_cond, invert); if (cmp_code == ERROR_MARK) return false; all_pruned = prune_uninit_phi_opnds_in_unrealizable_paths (phi, uninit_opnds, flag_def, boundary_cst, cmp_code, visited_phis, &visited_flag_phis); if (visited_flag_phis) BITMAP_FREE (visited_flag_phis); return all_pruned; } /* Returns true if TC is AND or OR */ static inline bool is_and_or_or (enum tree_code tc, tree typ) { return (tc == BIT_IOR_EXPR || (tc == BIT_AND_EXPR && (typ == 0 || TREE_CODE (typ) == BOOLEAN_TYPE))); } typedef struct norm_cond { VEC(gimple, heap) *conds; enum tree_code cond_code; bool invert; } *norm_cond_t; /* Normalizes gimple condition COND. The normalization follows UD chains to form larger condition expression trees. NORM_COND holds the normalized result. COND_CODE is the logical opcode (AND or OR) of the normalized tree. */ static void normalize_cond_1 (gimple cond, norm_cond_t norm_cond, enum tree_code cond_code) { enum gimple_code gc; enum tree_code cur_cond_code; tree rhs1, rhs2; gc = gimple_code (cond); if (gc != GIMPLE_ASSIGN) { VEC_safe_push (gimple, heap, norm_cond->conds, cond); return; } cur_cond_code = gimple_assign_rhs_code (cond); rhs1 = gimple_assign_rhs1 (cond); rhs2 = gimple_assign_rhs2 (cond); if (cur_cond_code == NE_EXPR) { if (integer_zerop (rhs2) && (TREE_CODE (rhs1) == SSA_NAME)) normalize_cond_1 ( SSA_NAME_DEF_STMT (rhs1), norm_cond, cond_code); else if (integer_zerop (rhs1) && (TREE_CODE (rhs2) == SSA_NAME)) normalize_cond_1 ( SSA_NAME_DEF_STMT (rhs2), norm_cond, cond_code); else VEC_safe_push (gimple, heap, norm_cond->conds, cond); return; } if (is_and_or_or (cur_cond_code, TREE_TYPE (rhs1)) && (cond_code == cur_cond_code || cond_code == ERROR_MARK) && (TREE_CODE (rhs1) == SSA_NAME && TREE_CODE (rhs2) == SSA_NAME)) { normalize_cond_1 (SSA_NAME_DEF_STMT (rhs1), norm_cond, cur_cond_code); normalize_cond_1 (SSA_NAME_DEF_STMT (rhs2), norm_cond, cur_cond_code); norm_cond->cond_code = cur_cond_code; } else VEC_safe_push (gimple, heap, norm_cond->conds, cond); } /* See normalize_cond_1 for details. INVERT is a flag to indicate if COND needs to be inverted or not. */ static void normalize_cond (gimple cond, norm_cond_t norm_cond, bool invert) { enum tree_code cond_code; norm_cond->cond_code = ERROR_MARK; norm_cond->invert = false; norm_cond->conds = NULL; gcc_assert (gimple_code (cond) == GIMPLE_COND); cond_code = gimple_cond_code (cond); if (invert) cond_code = invert_tree_comparison (cond_code, false); if (cond_code == NE_EXPR) { if (integer_zerop (gimple_cond_rhs (cond)) && (TREE_CODE (gimple_cond_lhs (cond)) == SSA_NAME)) normalize_cond_1 ( SSA_NAME_DEF_STMT (gimple_cond_lhs (cond)), norm_cond, ERROR_MARK); else if (integer_zerop (gimple_cond_lhs (cond)) && (TREE_CODE (gimple_cond_rhs (cond)) == SSA_NAME)) normalize_cond_1 ( SSA_NAME_DEF_STMT (gimple_cond_rhs (cond)), norm_cond, ERROR_MARK); else { VEC_safe_push (gimple, heap, norm_cond->conds, cond); norm_cond->invert = invert; } } else { VEC_safe_push (gimple, heap, norm_cond->conds, cond); norm_cond->invert = invert; } gcc_assert (VEC_length (gimple, norm_cond->conds) == 1 || is_and_or_or (norm_cond->cond_code, NULL)); } /* Returns true if the domain for condition COND1 is a subset of COND2. REVERSE is a flag. when it is true the function checks if COND1 is a superset of COND2. INVERT1 and INVERT2 are flags to indicate if COND1 and COND2 need to be inverted or not. */ static bool is_gcond_subset_of (gimple cond1, bool invert1, gimple cond2, bool invert2, bool reverse) { enum gimple_code gc1, gc2; enum tree_code cond1_code, cond2_code; gimple tmp; tree cond1_lhs, cond1_rhs, cond2_lhs, cond2_rhs; /* Take the short cut. */ if (cond1 == cond2) return true; if (reverse) { tmp = cond1; cond1 = cond2; cond2 = tmp; } gc1 = gimple_code (cond1); gc2 = gimple_code (cond2); if ((gc1 != GIMPLE_ASSIGN && gc1 != GIMPLE_COND) || (gc2 != GIMPLE_ASSIGN && gc2 != GIMPLE_COND)) return cond1 == cond2; cond1_code = ((gc1 == GIMPLE_ASSIGN) ? gimple_assign_rhs_code (cond1) : gimple_cond_code (cond1)); cond2_code = ((gc2 == GIMPLE_ASSIGN) ? gimple_assign_rhs_code (cond2) : gimple_cond_code (cond2)); if (TREE_CODE_CLASS (cond1_code) != tcc_comparison || TREE_CODE_CLASS (cond2_code) != tcc_comparison) return false; if (invert1) cond1_code = invert_tree_comparison (cond1_code, false); if (invert2) cond2_code = invert_tree_comparison (cond2_code, false); cond1_lhs = ((gc1 == GIMPLE_ASSIGN) ? gimple_assign_rhs1 (cond1) : gimple_cond_lhs (cond1)); cond1_rhs = ((gc1 == GIMPLE_ASSIGN) ? gimple_assign_rhs2 (cond1) : gimple_cond_rhs (cond1)); cond2_lhs = ((gc2 == GIMPLE_ASSIGN) ? gimple_assign_rhs1 (cond2) : gimple_cond_lhs (cond2)); cond2_rhs = ((gc2 == GIMPLE_ASSIGN) ? gimple_assign_rhs2 (cond2) : gimple_cond_rhs (cond2)); /* Assuming const operands have been swapped to the rhs at this point of the analysis. */ if (cond1_lhs != cond2_lhs) return false; if (!is_gimple_constant (cond1_rhs) || TREE_CODE (cond1_rhs) != INTEGER_CST) return (cond1_rhs == cond2_rhs); if (!is_gimple_constant (cond2_rhs) || TREE_CODE (cond2_rhs) != INTEGER_CST) return (cond1_rhs == cond2_rhs); if (cond1_code == EQ_EXPR) return is_value_included_in (cond1_rhs, cond2_rhs, cond2_code); if (cond1_code == NE_EXPR || cond2_code == EQ_EXPR) return ((cond2_code == cond1_code) && tree_int_cst_equal (cond1_rhs, cond2_rhs)); if (((cond1_code == GE_EXPR || cond1_code == GT_EXPR) && (cond2_code == LE_EXPR || cond2_code == LT_EXPR)) || ((cond1_code == LE_EXPR || cond1_code == LT_EXPR) && (cond2_code == GE_EXPR || cond2_code == GT_EXPR))) return false; if (cond1_code != GE_EXPR && cond1_code != GT_EXPR && cond1_code != LE_EXPR && cond1_code != LT_EXPR) return false; if (cond1_code == GT_EXPR) { cond1_code = GE_EXPR; cond1_rhs = fold_binary (PLUS_EXPR, TREE_TYPE (cond1_rhs), cond1_rhs, fold_convert (TREE_TYPE (cond1_rhs), integer_one_node)); } else if (cond1_code == LT_EXPR) { cond1_code = LE_EXPR; cond1_rhs = fold_binary (MINUS_EXPR, TREE_TYPE (cond1_rhs), cond1_rhs, fold_convert (TREE_TYPE (cond1_rhs), integer_one_node)); } if (!cond1_rhs) return false; gcc_assert (cond1_code == GE_EXPR || cond1_code == LE_EXPR); if (cond2_code == GE_EXPR || cond2_code == GT_EXPR || cond2_code == LE_EXPR || cond2_code == LT_EXPR) return is_value_included_in (cond1_rhs, cond2_rhs, cond2_code); else if (cond2_code == NE_EXPR) return (is_value_included_in (cond1_rhs, cond2_rhs, cond2_code) && !is_value_included_in (cond2_rhs, cond1_rhs, cond1_code)); return false; } /* Returns true if the domain of the condition expression in COND is a subset of any of the sub-conditions of the normalized condtion NORM_COND. INVERT is a flag to indicate of the COND needs to be inverted. REVERSE is a flag. When it is true, the check is reversed -- it returns true if COND is a superset of any of the subconditions of NORM_COND. */ static bool is_subset_of_any (gimple cond, bool invert, norm_cond_t norm_cond, bool reverse) { size_t i; size_t len = VEC_length (gimple, norm_cond->conds); for (i = 0; i < len; i++) { if (is_gcond_subset_of (cond, invert, VEC_index (gimple, norm_cond->conds, i), false, reverse)) return true; } return false; } /* NORM_COND1 and NORM_COND2 are normalized logical/BIT OR expressions (formed by following UD chains not control dependence chains). The function returns true of domain of and expression NORM_COND1 is a subset of NORM_COND2's. The implementation is conservative, and it returns false if it the inclusion relationship may not hold. */ static bool is_or_set_subset_of (norm_cond_t norm_cond1, norm_cond_t norm_cond2) { size_t i; size_t len = VEC_length (gimple, norm_cond1->conds); for (i = 0; i < len; i++) { if (!is_subset_of_any (VEC_index (gimple, norm_cond1->conds, i), false, norm_cond2, false)) return false; } return true; } /* NORM_COND1 and NORM_COND2 are normalized logical AND expressions (formed by following UD chains not control dependence chains). The function returns true of domain of and expression NORM_COND1 is a subset of NORM_COND2's. */ static bool is_and_set_subset_of (norm_cond_t norm_cond1, norm_cond_t norm_cond2) { size_t i; size_t len = VEC_length (gimple, norm_cond2->conds); for (i = 0; i < len; i++) { if (!is_subset_of_any (VEC_index (gimple, norm_cond2->conds, i), false, norm_cond1, true)) return false; } return true; } /* Returns true of the domain if NORM_COND1 is a subset of that of NORM_COND2. Returns false if it can not be proved to be so. */ static bool is_norm_cond_subset_of (norm_cond_t norm_cond1, norm_cond_t norm_cond2) { size_t i; enum tree_code code1, code2; code1 = norm_cond1->cond_code; code2 = norm_cond2->cond_code; if (code1 == BIT_AND_EXPR) { /* Both conditions are AND expressions. */ if (code2 == BIT_AND_EXPR) return is_and_set_subset_of (norm_cond1, norm_cond2); /* NORM_COND1 is an AND expression, and NORM_COND2 is an OR expression. In this case, returns true if any subexpression of NORM_COND1 is a subset of any subexpression of NORM_COND2. */ else if (code2 == BIT_IOR_EXPR) { size_t len1; len1 = VEC_length (gimple, norm_cond1->conds); for (i = 0; i < len1; i++) { gimple cond1 = VEC_index (gimple, norm_cond1->conds, i); if (is_subset_of_any (cond1, false, norm_cond2, false)) return true; } return false; } else { gcc_assert (code2 == ERROR_MARK); gcc_assert (VEC_length (gimple, norm_cond2->conds) == 1); return is_subset_of_any (VEC_index (gimple, norm_cond2->conds, 0), norm_cond2->invert, norm_cond1, true); } } /* NORM_COND1 is an OR expression */ else if (code1 == BIT_IOR_EXPR) { if (code2 != code1) return false; return is_or_set_subset_of (norm_cond1, norm_cond2); } else { gcc_assert (code1 == ERROR_MARK); gcc_assert (VEC_length (gimple, norm_cond1->conds) == 1); /* Conservatively returns false if NORM_COND1 is non-decomposible and NORM_COND2 is an AND expression. */ if (code2 == BIT_AND_EXPR) return false; if (code2 == BIT_IOR_EXPR) return is_subset_of_any (VEC_index (gimple, norm_cond1->conds, 0), norm_cond1->invert, norm_cond2, false); gcc_assert (code2 == ERROR_MARK); gcc_assert (VEC_length (gimple, norm_cond2->conds) == 1); return is_gcond_subset_of (VEC_index (gimple, norm_cond1->conds, 0), norm_cond1->invert, VEC_index (gimple, norm_cond2->conds, 0), norm_cond2->invert, false); } } /* Returns true of the domain of single predicate expression EXPR1 is a subset of that of EXPR2. Returns false if it can not be proved. */ static bool is_pred_expr_subset_of (use_pred_info_t expr1, use_pred_info_t expr2) { gimple cond1, cond2; enum tree_code code1, code2; struct norm_cond norm_cond1, norm_cond2; bool is_subset = false; cond1 = expr1->cond; cond2 = expr2->cond; code1 = gimple_cond_code (cond1); code2 = gimple_cond_code (cond2); if (expr1->invert) code1 = invert_tree_comparison (code1, false); if (expr2->invert) code2 = invert_tree_comparison (code2, false); /* Fast path -- match exactly */ if ((gimple_cond_lhs (cond1) == gimple_cond_lhs (cond2)) && (gimple_cond_rhs (cond1) == gimple_cond_rhs (cond2)) && (code1 == code2)) return true; /* Normalize conditions. To keep NE_EXPR, do not invert with both need inversion. */ normalize_cond (cond1, &norm_cond1, (expr1->invert)); normalize_cond (cond2, &norm_cond2, (expr2->invert)); is_subset = is_norm_cond_subset_of (&norm_cond1, &norm_cond2); /* Free memory */ VEC_free (gimple, heap, norm_cond1.conds); VEC_free (gimple, heap, norm_cond2.conds); return is_subset ; } /* Returns true if the domain of PRED1 is a subset of that of PRED2. Returns false if it can not be proved so. */ static bool is_pred_chain_subset_of (VEC(use_pred_info_t, heap) *pred1, VEC(use_pred_info_t, heap) *pred2) { size_t np1, np2, i1, i2; np1 = VEC_length (use_pred_info_t, pred1); np2 = VEC_length (use_pred_info_t, pred2); for (i2 = 0; i2 < np2; i2++) { bool found = false; use_pred_info_t info2 = VEC_index (use_pred_info_t, pred2, i2); for (i1 = 0; i1 < np1; i1++) { use_pred_info_t info1 = VEC_index (use_pred_info_t, pred1, i1); if (is_pred_expr_subset_of (info1, info2)) { found = true; break; } } if (!found) return false; } return true; } /* Returns true if the domain defined by one pred chain ONE_PRED is a subset of the domain of *PREDS. It returns false if ONE_PRED's domain is not a subset of any of the sub-domains of PREDS ( corresponding to each individual chains in it), even though it may be still be a subset of whole domain of PREDS which is the union (ORed) of all its subdomains. In other words, the result is conservative. */ static bool is_included_in (VEC(use_pred_info_t, heap) *one_pred, VEC(use_pred_info_t, heap) **preds, size_t n) { size_t i; for (i = 0; i < n; i++) { if (is_pred_chain_subset_of (one_pred, preds[i])) return true; } return false; } /* compares two predicate sets PREDS1 and PREDS2 and returns true if the domain defined by PREDS1 is a superset of PREDS2's domain. N1 and N2 are array sizes of PREDS1 and PREDS2 respectively. The implementation chooses not to build generic trees (and relying on the folding capability of the compiler), but instead performs brute force comparison of individual predicate chains (won't be a compile time problem as the chains are pretty short). When the function returns false, it does not necessarily mean *PREDS1 is not a superset of *PREDS2, but mean it may not be so since the analysis can not prove it. In such cases, false warnings may still be emitted. */ static bool is_superset_of (VEC(use_pred_info_t, heap) **preds1, size_t n1, VEC(use_pred_info_t, heap) **preds2, size_t n2) { size_t i; VEC(use_pred_info_t, heap) *one_pred_chain; for (i = 0; i < n2; i++) { one_pred_chain = preds2[i]; if (!is_included_in (one_pred_chain, preds1, n1)) return false; } return true; } /* Comparison function used by qsort. It is used to sort predicate chains to allow predicate simplification. */ static int pred_chain_length_cmp (const void *p1, const void *p2) { use_pred_info_t i1, i2; VEC(use_pred_info_t, heap) * const *chain1 = (VEC(use_pred_info_t, heap) * const *)p1; VEC(use_pred_info_t, heap) * const *chain2 = (VEC(use_pred_info_t, heap) * const *)p2; if (VEC_length (use_pred_info_t, *chain1) != VEC_length (use_pred_info_t, *chain2)) return (VEC_length (use_pred_info_t, *chain1) - VEC_length (use_pred_info_t, *chain2)); i1 = VEC_index (use_pred_info_t, *chain1, 0); i2 = VEC_index (use_pred_info_t, *chain2, 0); /* Allow predicates with similar prefix come together. */ if (!i1->invert && i2->invert) return -1; else if (i1->invert && !i2->invert) return 1; return gimple_uid (i1->cond) - gimple_uid (i2->cond); } /* x OR (!x AND y) is equivalent to x OR y. This function normalizes x1 OR (!x1 AND x2) OR (!x1 AND !x2 AND x3) into x1 OR x2 OR x3. PREDS is the predicate chains, and N is the number of chains. Returns true if normalization happens. */ static bool normalize_preds (VEC(use_pred_info_t, heap) **preds, size_t *n) { size_t i, j, ll; VEC(use_pred_info_t, heap) *pred_chain; VEC(use_pred_info_t, heap) *x = 0; use_pred_info_t xj = 0, nxj = 0; if (*n < 2) return false; /* First sort the chains in ascending order of lengths. */ qsort (preds, *n, sizeof (void *), pred_chain_length_cmp); pred_chain = preds[0]; ll = VEC_length (use_pred_info_t, pred_chain); if (ll != 1) { if (ll == 2) { use_pred_info_t xx, yy, xx2, nyy; VEC(use_pred_info_t, heap) *pred_chain2 = preds[1]; if (VEC_length (use_pred_info_t, pred_chain2) != 2) return false; /* See if simplification x AND y OR x AND !y is possible. */ xx = VEC_index (use_pred_info_t, pred_chain, 0); yy = VEC_index (use_pred_info_t, pred_chain, 1); xx2 = VEC_index (use_pred_info_t, pred_chain2, 0); nyy = VEC_index (use_pred_info_t, pred_chain2, 1); if (gimple_cond_lhs (xx->cond) != gimple_cond_lhs (xx2->cond) || gimple_cond_rhs (xx->cond) != gimple_cond_rhs (xx2->cond) || gimple_cond_code (xx->cond) != gimple_cond_code (xx2->cond) || (xx->invert != xx2->invert)) return false; if (gimple_cond_lhs (yy->cond) != gimple_cond_lhs (nyy->cond) || gimple_cond_rhs (yy->cond) != gimple_cond_rhs (nyy->cond) || gimple_cond_code (yy->cond) != gimple_cond_code (nyy->cond) || (yy->invert == nyy->invert)) return false; /* Now merge the first two chains. */ free (yy); free (nyy); free (xx2); VEC_free (use_pred_info_t, heap, pred_chain); VEC_free (use_pred_info_t, heap, pred_chain2); pred_chain = 0; VEC_safe_push (use_pred_info_t, heap, pred_chain, xx); preds[0] = pred_chain; for (i = 1; i < *n - 1; i++) preds[i] = preds[i + 1]; preds[*n - 1] = 0; *n = *n - 1; } else return false; } VEC_safe_push (use_pred_info_t, heap, x, VEC_index (use_pred_info_t, pred_chain, 0)); /* The loop extracts x1, x2, x3, etc from chains x1 OR (!x1 AND x2) OR (!x1 AND !x2 AND x3) OR ... */ for (i = 1; i < *n; i++) { pred_chain = preds[i]; if (VEC_length (use_pred_info_t, pred_chain) != i + 1) return false; for (j = 0; j < i; j++) { xj = VEC_index (use_pred_info_t, x, j); nxj = VEC_index (use_pred_info_t, pred_chain, j); /* Check if nxj is !xj */ if (gimple_cond_lhs (xj->cond) != gimple_cond_lhs (nxj->cond) || gimple_cond_rhs (xj->cond) != gimple_cond_rhs (nxj->cond) || gimple_cond_code (xj->cond) != gimple_cond_code (nxj->cond) || (xj->invert == nxj->invert)) return false; } VEC_safe_push (use_pred_info_t, heap, x, VEC_index (use_pred_info_t, pred_chain, i)); } /* Now normalize the pred chains using the extraced x1, x2, x3 etc. */ for (j = 0; j < *n; j++) { use_pred_info_t t; xj = VEC_index (use_pred_info_t, x, j); t = XNEW (struct use_pred_info); *t = *xj; VEC_replace (use_pred_info_t, x, j, t); } for (i = 0; i < *n; i++) { pred_chain = preds[i]; for (j = 0; j < VEC_length (use_pred_info_t, pred_chain); j++) free (VEC_index (use_pred_info_t, pred_chain, j)); VEC_free (use_pred_info_t, heap, pred_chain); pred_chain = 0; /* A new chain. */ VEC_safe_push (use_pred_info_t, heap, pred_chain, VEC_index (use_pred_info_t, x, i)); preds[i] = pred_chain; } return true; } /* Computes the predicates that guard the use and checks if the incoming paths that have empty (or possibly empty) defintion can be pruned/filtered. The function returns true if it can be determined that the use of PHI's def in USE_STMT is guarded with a predicate set not overlapping with predicate sets of all runtime paths that do not have a definition. Returns false if it is not or it can not be determined. USE_BB is the bb of the use (for phi operand use, the bb is not the bb of the phi stmt, but the src bb of the operand edge). UNINIT_OPNDS is a bit vector. If an operand of PHI is uninitialized, the correponding bit in the vector is 1. VISIED_PHIS is a pointer set of phis being visted. */ static bool is_use_properly_guarded (gimple use_stmt, basic_block use_bb, gimple phi, unsigned uninit_opnds, struct pointer_set_t *visited_phis) { basic_block phi_bb; VEC(use_pred_info_t, heap) **preds = 0; VEC(use_pred_info_t, heap) **def_preds = 0; size_t num_preds = 0, num_def_preds = 0; bool has_valid_preds = false; bool is_properly_guarded = false; if (pointer_set_insert (visited_phis, phi)) return false; phi_bb = gimple_bb (phi); if (is_non_loop_exit_postdominating (use_bb, phi_bb)) return false; has_valid_preds = find_predicates (&preds, &num_preds, phi_bb, use_bb); if (!has_valid_preds) { destroy_predicate_vecs (num_preds, preds); return false; } if (dump_file) dump_predicates (use_stmt, num_preds, preds, "\nUse in stmt "); has_valid_preds = find_def_preds (&def_preds, &num_def_preds, phi); if (has_valid_preds) { bool normed; if (dump_file) dump_predicates (phi, num_def_preds, def_preds, "Operand defs of phi "); normed = normalize_preds (def_preds, &num_def_preds); if (normed && dump_file) { fprintf (dump_file, "\nNormalized to\n"); dump_predicates (phi, num_def_preds, def_preds, "Operand defs of phi "); } is_properly_guarded = is_superset_of (def_preds, num_def_preds, preds, num_preds); } /* further prune the dead incoming phi edges. */ if (!is_properly_guarded) is_properly_guarded = use_pred_not_overlap_with_undef_path_pred ( num_preds, preds, phi, uninit_opnds, visited_phis); destroy_predicate_vecs (num_preds, preds); destroy_predicate_vecs (num_def_preds, def_preds); return is_properly_guarded; } /* Searches through all uses of a potentially uninitialized variable defined by PHI and returns a use statement if the use is not properly guarded. It returns NULL if all uses are guarded. UNINIT_OPNDS is a bitvector holding the position(s) of uninit PHI operands. WORKLIST is the vector of candidate phis that may be updated by this function. ADDED_TO_WORKLIST is the pointer set tracking if the new phi is already in the worklist. */ static gimple find_uninit_use (gimple phi, unsigned uninit_opnds, VEC(gimple, heap) **worklist, struct pointer_set_t *added_to_worklist) { tree phi_result; use_operand_p use_p; gimple use_stmt; imm_use_iterator iter; phi_result = gimple_phi_result (phi); FOR_EACH_IMM_USE_FAST (use_p, iter, phi_result) { struct pointer_set_t *visited_phis; basic_block use_bb; use_stmt = USE_STMT (use_p); if (is_gimple_debug (use_stmt)) continue; visited_phis = pointer_set_create (); if (gimple_code (use_stmt) == GIMPLE_PHI) use_bb = gimple_phi_arg_edge (use_stmt, PHI_ARG_INDEX_FROM_USE (use_p))->src; else use_bb = gimple_bb (use_stmt); if (is_use_properly_guarded (use_stmt, use_bb, phi, uninit_opnds, visited_phis)) { pointer_set_destroy (visited_phis); continue; } pointer_set_destroy (visited_phis); if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "[CHECK]: Found unguarded use: "); print_gimple_stmt (dump_file, use_stmt, 0, 0); } /* Found one real use, return. */ if (gimple_code (use_stmt) != GIMPLE_PHI) return use_stmt; /* Found a phi use that is not guarded, add the phi to the worklist. */ if (!pointer_set_insert (added_to_worklist, use_stmt)) { if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "[WORKLIST]: Update worklist with phi: "); print_gimple_stmt (dump_file, use_stmt, 0, 0); } VEC_safe_push (gimple, heap, *worklist, use_stmt); pointer_set_insert (possibly_undefined_names, phi_result); } } return NULL; } /* Look for inputs to PHI that are SSA_NAMEs that have empty definitions and gives warning if there exists a runtime path from the entry to a use of the PHI def that does not contain a definition. In other words, the warning is on the real use. The more dead paths that can be pruned by the compiler, the fewer false positives the warning is. WORKLIST is a vector of candidate phis to be examined. ADDED_TO_WORKLIST is a pointer set tracking if the new phi is added to the worklist or not. */ static void warn_uninitialized_phi (gimple phi, VEC(gimple, heap) **worklist, struct pointer_set_t *added_to_worklist) { unsigned uninit_opnds; gimple uninit_use_stmt = 0; tree uninit_op; /* Don't look at memory tags. */ if (!is_gimple_reg (gimple_phi_result (phi))) return; uninit_opnds = compute_uninit_opnds_pos (phi); if (MASK_EMPTY (uninit_opnds)) return; if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "[CHECK]: examining phi: "); print_gimple_stmt (dump_file, phi, 0, 0); } /* Now check if we have any use of the value without proper guard. */ uninit_use_stmt = find_uninit_use (phi, uninit_opnds, worklist, added_to_worklist); /* All uses are properly guarded. */ if (!uninit_use_stmt) return; uninit_op = gimple_phi_arg_def (phi, MASK_FIRST_SET_BIT (uninit_opnds)); warn_uninit (OPT_Wmaybe_uninitialized, uninit_op, SSA_NAME_VAR (uninit_op), SSA_NAME_VAR (uninit_op), "%qD may be used uninitialized in this function", uninit_use_stmt); } /* Entry point to the late uninitialized warning pass. */ static unsigned int execute_late_warn_uninitialized (void) { basic_block bb; gimple_stmt_iterator gsi; VEC(gimple, heap) *worklist = 0; struct pointer_set_t *added_to_worklist; calculate_dominance_info (CDI_DOMINATORS); calculate_dominance_info (CDI_POST_DOMINATORS); /* Re-do the plain uninitialized variable check, as optimization may have straightened control flow. Do this first so that we don't accidentally get a "may be" warning when we'd have seen an "is" warning later. */ warn_uninitialized_vars (/*warn_possibly_uninitialized=*/1); timevar_push (TV_TREE_UNINIT); possibly_undefined_names = pointer_set_create (); added_to_worklist = pointer_set_create (); /* Initialize worklist */ FOR_EACH_BB (bb) for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) { gimple phi = gsi_stmt (gsi); size_t n, i; n = gimple_phi_num_args (phi); /* Don't look at memory tags. */ if (!is_gimple_reg (gimple_phi_result (phi))) continue; for (i = 0; i < n; ++i) { tree op = gimple_phi_arg_def (phi, i); if (TREE_CODE (op) == SSA_NAME && ssa_undefined_value_p (op)) { VEC_safe_push (gimple, heap, worklist, phi); pointer_set_insert (added_to_worklist, phi); if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "[WORKLIST]: add to initial list: "); print_gimple_stmt (dump_file, phi, 0, 0); } break; } } } while (VEC_length (gimple, worklist) != 0) { gimple cur_phi = 0; cur_phi = VEC_pop (gimple, worklist); warn_uninitialized_phi (cur_phi, &worklist, added_to_worklist); } VEC_free (gimple, heap, worklist); pointer_set_destroy (added_to_worklist); pointer_set_destroy (possibly_undefined_names); possibly_undefined_names = NULL; free_dominance_info (CDI_POST_DOMINATORS); timevar_pop (TV_TREE_UNINIT); return 0; } static bool gate_warn_uninitialized (void) { return warn_uninitialized != 0; } struct gimple_opt_pass pass_late_warn_uninitialized = { { GIMPLE_PASS, "uninit", /* name */ gate_warn_uninitialized, /* gate */ execute_late_warn_uninitialized, /* execute */ NULL, /* sub */ NULL, /* next */ 0, /* static_pass_number */ TV_NONE, /* tv_id */ PROP_ssa, /* properties_required */ 0, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ 0 /* todo_flags_finish */ } };
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