/* Utilities for ipa analysis. Copyright (C) 2005-2023 Free Software Foundation, Inc. Contributed by Kenneth Zadeck 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 . */ #include "config.h" #include "system.h" #include "coretypes.h" #include "backend.h" #include "tree.h" #include "gimple.h" #include "predict.h" #include "alloc-pool.h" #include "cgraph.h" #include "lto-streamer.h" #include "dumpfile.h" #include "splay-tree.h" #include "ipa-utils.h" #include "symbol-summary.h" #include "tree-vrp.h" #include "ipa-prop.h" #include "ipa-fnsummary.h" #include "tree-eh.h" #include "gimple-iterator.h" #include "ipa-modref-tree.h" #include "ipa-modref.h" #include "tree-ssa-loop-niter.h" #include "calls.h" #include "cfgloop.h" #include "cfganal.h" /* Debugging function for postorder and inorder code. NOTE is a string that is printed before the nodes are printed. ORDER is an array of cgraph_nodes that has COUNT useful nodes in it. */ void ipa_print_order (FILE* out, const char * note, struct cgraph_node** order, int count) { int i; fprintf (out, "\n\n ordered call graph: %s\n", note); for (i = count - 1; i >= 0; i--) order[i]->dump (out); fprintf (out, "\n"); fflush (out); } struct searchc_env { struct cgraph_node **stack; struct cgraph_node **result; int stack_size; int order_pos; splay_tree nodes_marked_new; bool reduce; int count; }; /* This is an implementation of Tarjan's strongly connected region finder as reprinted in Aho Hopcraft and Ullman's The Design and Analysis of Computer Programs (1975) pages 192-193. This version has been customized for cgraph_nodes. The env parameter is because it is recursive and there are no nested functions here. This function should only be called from itself or ipa_reduced_postorder. ENV is a stack env and would be unnecessary if C had nested functions. V is the node to start searching from. */ static void searchc (struct searchc_env* env, struct cgraph_node *v, bool (*ignore_edge) (struct cgraph_edge *)) { struct cgraph_edge *edge; struct ipa_dfs_info *v_info = (struct ipa_dfs_info *) v->aux; /* mark node as old */ v_info->new_node = false; splay_tree_remove (env->nodes_marked_new, v->get_uid ()); v_info->dfn_number = env->count; v_info->low_link = env->count; env->count++; env->stack[(env->stack_size)++] = v; v_info->on_stack = true; for (edge = v->callees; edge; edge = edge->next_callee) { struct ipa_dfs_info * w_info; enum availability avail; struct cgraph_node *w = edge->callee->ultimate_alias_target (&avail); if (!w || (ignore_edge && ignore_edge (edge))) continue; if (w->aux && (avail >= AVAIL_INTERPOSABLE)) { w_info = (struct ipa_dfs_info *) w->aux; if (w_info->new_node) { searchc (env, w, ignore_edge); v_info->low_link = (v_info->low_link < w_info->low_link) ? v_info->low_link : w_info->low_link; } else if ((w_info->dfn_number < v_info->dfn_number) && (w_info->on_stack)) v_info->low_link = (w_info->dfn_number < v_info->low_link) ? w_info->dfn_number : v_info->low_link; } } if (v_info->low_link == v_info->dfn_number) { struct cgraph_node *last = NULL; struct cgraph_node *x; struct ipa_dfs_info *x_info; do { x = env->stack[--(env->stack_size)]; x_info = (struct ipa_dfs_info *) x->aux; x_info->on_stack = false; x_info->scc_no = v_info->dfn_number; if (env->reduce) { x_info->next_cycle = last; last = x; } else env->result[env->order_pos++] = x; } while (v != x); if (env->reduce) env->result[env->order_pos++] = v; } } /* Topsort the call graph by caller relation. Put the result in ORDER. The REDUCE flag is true if you want the cycles reduced to single nodes. You can use ipa_get_nodes_in_cycle to obtain a vector containing all real call graph nodes in a reduced node. Set ALLOW_OVERWRITABLE if nodes with such availability should be included. IGNORE_EDGE, if non-NULL is a hook that may make some edges insignificant for the topological sort. */ int ipa_reduced_postorder (struct cgraph_node **order, bool reduce, bool (*ignore_edge) (struct cgraph_edge *)) { struct cgraph_node *node; struct searchc_env env; splay_tree_node result; env.stack = XCNEWVEC (struct cgraph_node *, symtab->cgraph_count); env.stack_size = 0; env.result = order; env.order_pos = 0; env.nodes_marked_new = splay_tree_new (splay_tree_compare_ints, 0, 0); env.count = 1; env.reduce = reduce; FOR_EACH_DEFINED_FUNCTION (node) { enum availability avail = node->get_availability (); if (avail > AVAIL_INTERPOSABLE || avail == AVAIL_INTERPOSABLE) { /* Reuse the info if it is already there. */ struct ipa_dfs_info *info = (struct ipa_dfs_info *) node->aux; if (!info) info = XCNEW (struct ipa_dfs_info); info->new_node = true; info->on_stack = false; info->next_cycle = NULL; node->aux = info; splay_tree_insert (env.nodes_marked_new, (splay_tree_key)node->get_uid (), (splay_tree_value)node); } else node->aux = NULL; } result = splay_tree_min (env.nodes_marked_new); while (result) { node = (struct cgraph_node *)result->value; searchc (&env, node, ignore_edge); result = splay_tree_min (env.nodes_marked_new); } splay_tree_delete (env.nodes_marked_new); free (env.stack); return env.order_pos; } /* Deallocate all ipa_dfs_info structures pointed to by the aux pointer of call graph nodes. */ void ipa_free_postorder_info (void) { struct cgraph_node *node; FOR_EACH_DEFINED_FUNCTION (node) { /* Get rid of the aux information. */ if (node->aux) { free (node->aux); node->aux = NULL; } } } /* Get the set of nodes for the cycle in the reduced call graph starting from NODE. */ vec ipa_get_nodes_in_cycle (struct cgraph_node *node) { vec v = vNULL; struct ipa_dfs_info *node_dfs_info; while (node) { v.safe_push (node); node_dfs_info = (struct ipa_dfs_info *) node->aux; node = node_dfs_info->next_cycle; } return v; } /* Return true iff the CS is an edge within a strongly connected component as computed by ipa_reduced_postorder. */ bool ipa_edge_within_scc (struct cgraph_edge *cs) { struct ipa_dfs_info *caller_dfs = (struct ipa_dfs_info *) cs->caller->aux; struct ipa_dfs_info *callee_dfs; struct cgraph_node *callee = cs->callee->function_symbol (); callee_dfs = (struct ipa_dfs_info *) callee->aux; return (caller_dfs && callee_dfs && caller_dfs->scc_no == callee_dfs->scc_no); } struct postorder_stack { struct cgraph_node *node; struct cgraph_edge *edge; int ref; }; /* Fill array order with all nodes with output flag set in the reverse topological order. Return the number of elements in the array. FIXME: While walking, consider aliases, too. */ int ipa_reverse_postorder (struct cgraph_node **order) { struct cgraph_node *node, *node2; int stack_size = 0; int order_pos = 0; struct cgraph_edge *edge; int pass; struct ipa_ref *ref = NULL; struct postorder_stack *stack = XCNEWVEC (struct postorder_stack, symtab->cgraph_count); /* We have to deal with cycles nicely, so use a depth first traversal output algorithm. Ignore the fact that some functions won't need to be output and put them into order as well, so we get dependencies right through inline functions. */ FOR_EACH_FUNCTION (node) node->aux = NULL; for (pass = 0; pass < 2; pass++) FOR_EACH_FUNCTION (node) if (!node->aux && (pass || (!node->address_taken && !node->inlined_to && !node->alias && !node->thunk && !node->only_called_directly_p ()))) { stack_size = 0; stack[stack_size].node = node; stack[stack_size].edge = node->callers; stack[stack_size].ref = 0; node->aux = (void *)(size_t)1; while (stack_size >= 0) { while (true) { node2 = NULL; while (stack[stack_size].edge && !node2) { edge = stack[stack_size].edge; node2 = edge->caller; stack[stack_size].edge = edge->next_caller; /* Break possible cycles involving always-inline functions by ignoring edges from always-inline functions to non-always-inline functions. */ if (DECL_DISREGARD_INLINE_LIMITS (edge->caller->decl) && !DECL_DISREGARD_INLINE_LIMITS (edge->callee->function_symbol ()->decl)) node2 = NULL; } for (; stack[stack_size].node->iterate_referring ( stack[stack_size].ref, ref) && !node2; stack[stack_size].ref++) { if (ref->use == IPA_REF_ALIAS) node2 = dyn_cast (ref->referring); } if (!node2) break; if (!node2->aux) { stack[++stack_size].node = node2; stack[stack_size].edge = node2->callers; stack[stack_size].ref = 0; node2->aux = (void *)(size_t)1; } } order[order_pos++] = stack[stack_size--].node; } } free (stack); FOR_EACH_FUNCTION (node) node->aux = NULL; return order_pos; } /* Given a memory reference T, will return the variable at the bottom of the access. Unlike get_base_address, this will recurse through INDIRECT_REFS. */ tree get_base_var (tree t) { while (!SSA_VAR_P (t) && (!CONSTANT_CLASS_P (t)) && TREE_CODE (t) != LABEL_DECL && TREE_CODE (t) != FUNCTION_DECL && TREE_CODE (t) != CONST_DECL && TREE_CODE (t) != CONSTRUCTOR) { t = TREE_OPERAND (t, 0); } return t; } /* Scale function of calls in NODE by ratio ORIG_COUNT/NODE->count. */ void scale_ipa_profile_for_fn (struct cgraph_node *node, profile_count orig_count) { profile_count to = node->count; profile_count::adjust_for_ipa_scaling (&to, &orig_count); struct cgraph_edge *e; for (e = node->callees; e; e = e->next_callee) e->count = e->count.apply_scale (to, orig_count); for (e = node->indirect_calls; e; e = e->next_callee) e->count = e->count.apply_scale (to, orig_count); } /* SRC and DST are going to be merged. Take SRC's profile and merge it into DST so it is not going to be lost. Possibly destroy SRC's body on the way unless PRESERVE_BODY is set. */ void ipa_merge_profiles (struct cgraph_node *dst, struct cgraph_node *src, bool preserve_body) { tree oldsrcdecl = src->decl; struct function *srccfun, *dstcfun; bool match = true; bool copy_counts = false; if (!src->definition || !dst->definition) return; if (src->frequency < dst->frequency) src->frequency = dst->frequency; /* Time profiles are merged. */ if (dst->tp_first_run > src->tp_first_run && src->tp_first_run) dst->tp_first_run = src->tp_first_run; if (src->profile_id && !dst->profile_id) dst->profile_id = src->profile_id; /* Merging zero profile to dst is no-op. */ if (src->count.ipa () == profile_count::zero ()) return; /* FIXME when we merge in unknown profile, we ought to set counts as unsafe. */ if (!src->count.initialized_p () || !(src->count.ipa () == src->count)) return; profile_count orig_count = dst->count; /* Either sum the profiles if both are IPA and not global0, or pick more informative one (that is nonzero IPA if other is uninitialized, guessed or global0). */ if ((dst->count.ipa ().nonzero_p () || src->count.ipa ().nonzero_p ()) && dst->count.ipa ().initialized_p () && src->count.ipa ().initialized_p ()) dst->count = dst->count.ipa () + src->count.ipa (); else if (dst->count.ipa ().initialized_p ()) ; else if (src->count.ipa ().initialized_p ()) { copy_counts = true; dst->count = src->count.ipa (); } /* If no updating needed return early. */ if (dst->count == orig_count) return; if (symtab->dump_file) { fprintf (symtab->dump_file, "Merging profiles of %s count:", src->dump_name ()); src->count.dump (symtab->dump_file); fprintf (symtab->dump_file, " to %s count:", dst->dump_name ()); orig_count.dump (symtab->dump_file); fprintf (symtab->dump_file, " resulting count:"); dst->count.dump (symtab->dump_file); fprintf (symtab->dump_file, "\n"); } /* First handle functions with no gimple body. */ if (dst->thunk || dst->alias || src->thunk || src->alias) { scale_ipa_profile_for_fn (dst, orig_count); return; } /* This is ugly. We need to get both function bodies into memory. If declaration is merged, we need to duplicate it to be able to load body that is being replaced. This makes symbol table temporarily inconsistent. */ if (src->decl == dst->decl) { struct lto_in_decl_state temp; struct lto_in_decl_state *state; /* We are going to move the decl, we want to remove its file decl data. and link these with the new decl. */ temp.fn_decl = src->decl; lto_in_decl_state **slot = src->lto_file_data->function_decl_states->find_slot (&temp, NO_INSERT); state = *slot; src->lto_file_data->function_decl_states->clear_slot (slot); gcc_assert (state); /* Duplicate the decl and be sure it does not link into body of DST. */ src->decl = copy_node (src->decl); DECL_STRUCT_FUNCTION (src->decl) = NULL; DECL_ARGUMENTS (src->decl) = NULL; DECL_INITIAL (src->decl) = NULL; DECL_RESULT (src->decl) = NULL; /* Associate the decl state with new declaration, so LTO streamer can look it up. */ state->fn_decl = src->decl; slot = src->lto_file_data->function_decl_states->find_slot (state, INSERT); gcc_assert (!*slot); *slot = state; } src->get_untransformed_body (); dst->get_untransformed_body (); srccfun = DECL_STRUCT_FUNCTION (src->decl); dstcfun = DECL_STRUCT_FUNCTION (dst->decl); if (n_basic_blocks_for_fn (srccfun) != n_basic_blocks_for_fn (dstcfun)) { if (symtab->dump_file) fprintf (symtab->dump_file, "Giving up; number of basic block mismatch.\n"); match = false; } else if (last_basic_block_for_fn (srccfun) != last_basic_block_for_fn (dstcfun)) { if (symtab->dump_file) fprintf (symtab->dump_file, "Giving up; last block mismatch.\n"); match = false; } else { basic_block srcbb, dstbb; struct cgraph_edge *e, *e2; for (e = dst->callees, e2 = src->callees; e && e2 && match; e2 = e2->next_callee, e = e->next_callee) { if (gimple_bb (e->call_stmt)->index != gimple_bb (e2->call_stmt)->index) { if (symtab->dump_file) fprintf (symtab->dump_file, "Giving up; call stmt mismatch.\n"); match = false; } } if (e || e2) { if (symtab->dump_file) fprintf (symtab->dump_file, "Giving up; number of calls differs.\n"); match = false; } for (e = dst->indirect_calls, e2 = src->indirect_calls; e && e2 && match; e2 = e2->next_callee, e = e->next_callee) { if (gimple_bb (e->call_stmt)->index != gimple_bb (e2->call_stmt)->index) { if (symtab->dump_file) fprintf (symtab->dump_file, "Giving up; indirect call stmt mismatch.\n"); match = false; } } if (e || e2) { if (symtab->dump_file) fprintf (symtab->dump_file, "Giving up; number of indirect calls differs.\n"); match=false; } if (match) FOR_ALL_BB_FN (srcbb, srccfun) { unsigned int i; dstbb = BASIC_BLOCK_FOR_FN (dstcfun, srcbb->index); if (dstbb == NULL) { if (symtab->dump_file) fprintf (symtab->dump_file, "No matching block for bb %i.\n", srcbb->index); match = false; break; } if (EDGE_COUNT (srcbb->succs) != EDGE_COUNT (dstbb->succs)) { if (symtab->dump_file) fprintf (symtab->dump_file, "Edge count mismatch for bb %i.\n", srcbb->index); match = false; break; } for (i = 0; i < EDGE_COUNT (srcbb->succs); i++) { edge srce = EDGE_SUCC (srcbb, i); edge dste = EDGE_SUCC (dstbb, i); if (srce->dest->index != dste->dest->index) { if (symtab->dump_file) fprintf (symtab->dump_file, "Succ edge mismatch for bb %i.\n", srce->dest->index); match = false; break; } } } } if (match) { struct cgraph_edge *e, *e2; basic_block srcbb, dstbb; /* Function and global profile may be out of sync. First scale it same way as fixup_cfg would. */ profile_count srcnum = src->count; profile_count srcden = ENTRY_BLOCK_PTR_FOR_FN (srccfun)->count; bool srcscale = srcnum.initialized_p () && !(srcnum == srcden); profile_count dstnum = orig_count; profile_count dstden = ENTRY_BLOCK_PTR_FOR_FN (dstcfun)->count; bool dstscale = !copy_counts && dstnum.initialized_p () && !(dstnum == dstden); /* TODO: merge also statement histograms. */ FOR_ALL_BB_FN (srcbb, srccfun) { unsigned int i; dstbb = BASIC_BLOCK_FOR_FN (dstcfun, srcbb->index); profile_count srccount = srcbb->count; if (srcscale) srccount = srccount.apply_scale (srcnum, srcden); if (dstscale) dstbb->count = dstbb->count.apply_scale (dstnum, dstden); if (copy_counts) { dstbb->count = srccount; for (i = 0; i < EDGE_COUNT (srcbb->succs); i++) { edge srce = EDGE_SUCC (srcbb, i); edge dste = EDGE_SUCC (dstbb, i); if (srce->probability.initialized_p ()) dste->probability = srce->probability; } } else { for (i = 0; i < EDGE_COUNT (srcbb->succs); i++) { edge srce = EDGE_SUCC (srcbb, i); edge dste = EDGE_SUCC (dstbb, i); dste->probability = dste->probability * dstbb->count.ipa ().probability_in (dstbb->count.ipa () + srccount.ipa ()) + srce->probability * srcbb->count.ipa ().probability_in (dstbb->count.ipa () + srccount.ipa ()); } dstbb->count = dstbb->count.ipa () + srccount.ipa (); } } push_cfun (dstcfun); update_max_bb_count (); compute_function_frequency (); pop_cfun (); for (e = dst->callees; e; e = e->next_callee) { if (e->speculative) continue; e->count = gimple_bb (e->call_stmt)->count; } for (e = dst->indirect_calls, e2 = src->indirect_calls; e; e2 = (e2 ? e2->next_callee : NULL), e = e->next_callee) { if (!e->speculative && !e2->speculative) { /* FIXME: we need to also merge ipa-profile histograms because with LTO merging happens from lto-symtab before these are converted to indirect edges. */ e->count = gimple_bb (e->call_stmt)->count; continue; } /* When copying just remove all speuclations on dst and then copy one from src. */ if (copy_counts) { while (e->speculative) cgraph_edge::resolve_speculation (e, NULL); e->count = gimple_bb (e->call_stmt)->count; if (e2->speculative) { for (cgraph_edge *e3 = e2->first_speculative_call_target (); e3; e3 = e3->next_speculative_call_target ()) { cgraph_edge *ns; ns = e->make_speculative (dyn_cast (e3->speculative_call_target_ref ()->referred), e3->count, e3->speculative_id); /* Target may differ from ref (for example it may be redirected to local alias. */ ns->redirect_callee (e3->callee); } } continue; } /* Iterate all speculations in SRC, see if corresponding ones exist int DST and if so, sum the counts. Otherwise create new speculation. */ int max_spec = 0; for (cgraph_edge *e3 = e->first_speculative_call_target (); e3; e3 = e3->next_speculative_call_target ()) if (e3->speculative_id > max_spec) max_spec = e3->speculative_id; for (cgraph_edge *e3 = e2->first_speculative_call_target (); e3; e3 = e3->next_speculative_call_target ()) { cgraph_edge *te = e->speculative_call_for_target (dyn_cast (e3->speculative_call_target_ref ()->referred)); if (te) te->count = te->count + e3->count; else { e->count = e->count + e3->count; cgraph_edge *ns; ns = e->make_speculative (dyn_cast (e3->speculative_call_target_ref () ->referred), e3->count, e3->speculative_id + max_spec + 1); /* Target may differ from ref (for example it may be redirected to local alias. */ ns->redirect_callee (e3->callee); } } } if (!preserve_body) src->release_body (); /* Update summary. */ compute_fn_summary (dst, 0); } /* We can't update CFG profile, but we can scale IPA profile. CFG will be scaled according to dst->count after IPA passes. */ else scale_ipa_profile_for_fn (dst, orig_count); src->decl = oldsrcdecl; } /* Return true if call to DEST is known to be self-recusive call withing FUNC. */ bool recursive_call_p (tree func, tree dest) { struct cgraph_node *dest_node = cgraph_node::get_create (dest); struct cgraph_node *cnode = cgraph_node::get_create (func); ipa_ref *alias; enum availability avail; gcc_assert (!cnode->alias); if (cnode != dest_node->ultimate_alias_target (&avail)) return false; if (avail >= AVAIL_AVAILABLE) return true; if (!dest_node->semantically_equivalent_p (cnode)) return false; /* If there is only one way to call the fuction or we know all of them are semantically equivalent, we still can consider call recursive. */ FOR_EACH_ALIAS (cnode, alias) if (!dest_node->semantically_equivalent_p (alias->referring)) return false; return true; } /* Return true if stmt may terminate execution of function. If assume_return_or_eh we can further assume that the function ends either by retrn statement or EH (no trapping or infinite loops). */ bool stmt_may_terminate_function_p (function *fun, gimple *stmt, bool assume_return_or_eh) { if (stmt_can_throw_external (fun, stmt)) return true; if (assume_return_or_eh) return false; gasm *astmt = dyn_cast (stmt); if (astmt && gimple_asm_volatile_p (astmt)) return true; if (gimple_could_trap_p (stmt)) return true; if (gcall *call = dyn_cast (stmt)) { int flags = gimple_call_flags (call); if (flags & (ECF_PURE | ECF_CONST) && ! (flags & ECF_LOOPING_CONST_OR_PURE)) return false; modref_summary *s = get_modref_function_summary (call, NULL); if (s && !s->side_effects) return false; return true; } return false; } /* Return bitmap of all basic blocks whose first statements are known to execute on every invocation of the function. If assume_return_or_eh we can further assume that the function ends either by retrn statement or EH (no trapping or infinite loops). This is useful when sumarizing function in passes like ipa-modref. Seeing assume_return_or_eh to false is used to prove that given statmeent will be executed even if the function gets into infinite loop or trap. */ bitmap find_always_executed_bbs (function *fun, bool assume_return_or_eh) { auto_vec stack; auto_vec terminating_bbs; hash_set visited; hash_set terminating_bbs_set; edge e; edge_iterator ei; int flags = flags_from_decl_or_type (fun->decl); /* PUre and const functions always return. */ assume_return_or_eh |= (flags & (ECF_CONST|ECF_PURE)) && !(flags & ECF_LOOPING_CONST_OR_PURE); if (!assume_return_or_eh) mark_dfs_back_edges (fun); /* First walk all BBs reachable from entry stopping on statements that may terminate execution. Everything past this statement is not going to be executed each invocation. */ stack.safe_push (ENTRY_BLOCK_PTR_FOR_FN (fun)); while (!stack.is_empty ()) { basic_block bb = stack.pop (); bool found = false, found_exit = false; if (bb->index == EXIT_BLOCK) continue; FOR_EACH_EDGE (e, ei, bb->succs) { if (e->dest == EXIT_BLOCK_PTR_FOR_FN (fun)) { found_exit = true; break; } /* Watch for infinite loops. */ if (!found && !assume_return_or_eh && (e->flags & EDGE_DFS_BACK)) { if (!dom_info_available_p (CDI_DOMINATORS)) calculate_dominance_info (CDI_DOMINATORS); /* If this is not a loop latch edge it is an irreducible region. Assume that it is infinite. TODO: with C++ forced progression we can still walk the irreducible region and see if it contains any side effects. Similarly for loops. -ffinite-loops does not really imply this since we allow inlining across -ffinite-loops bondary and thus it can be used only as a loop flag. */ if (e->dest->loop_father->header != e->dest || !dominated_by_p (CDI_DOMINATORS, bb, e->dest)) found = true; else if (!finite_loop_p (e->dest->loop_father)) found = true; } } if (!assume_return_or_eh && (EDGE_COUNT (bb->succs) == 0 || (bb->flags & BB_IRREDUCIBLE_LOOP))) found = true; for (gimple_stmt_iterator si = gsi_start_nondebug_after_labels_bb (bb); !gsi_end_p (si) && !found; gsi_next_nondebug (&si)) if (stmt_may_terminate_function_p (fun, gsi_stmt (si), assume_return_or_eh)) { found = true; break; } if (found) { visited.add (EXIT_BLOCK_PTR_FOR_FN (fun)); if (!found_exit) { terminating_bbs.safe_push (bb); terminating_bbs_set.add (bb); } } else FOR_EACH_EDGE (e, ei, bb->succs) if (!visited.add (e->dest)) stack.safe_push (e->dest); } /* Next walk from exit block and find all articulations in the CFG. Add all terminating basic blocks as "fake" predecessors of the exit block. */ bitmap ret = BITMAP_ALLOC (NULL); /* A degenerated case when there is no path to exit. */ if (!visited.contains (EXIT_BLOCK_PTR_FOR_FN (fun))) { bitmap_set_bit (ret, single_succ_edge (ENTRY_BLOCK_PTR_FOR_FN (fun))->dest->index); return ret; } struct astate { unsigned int dfs_preorder; unsigned int dfs_postorder; unsigned int low, high; }; struct worklist { basic_block bb; astate *cstate; }; struct obstack state_obstack; gcc_obstack_init (&state_obstack); hash_map state; auto_vec worklist_vec; unsigned int next_dfs_num = 1; /* Always executed blocks are blocks that are on every path from entry to exit. We proceed in two steps. First we do backward DFS walk (so we know that entry is always reached) and record preorder and postorder visiting times. In second step we proceed in postorder and for every block A we compute minimal preorder (A.low) and maximal postorder (A.high) of block reachable from the BBs in DFS subtree of A. If A is always executed there are no edges out of this subtree. This can be tested by checking that A.low == A.preorder and B.high == A.postorder. This is first step. Do backward DFS walk and record preorder, postorder and predecessor info. Initialize stack in postorder. */ worklist we = {EXIT_BLOCK_PTR_FOR_FN (fun), NULL}; worklist_vec.safe_push (we); while (!worklist_vec.is_empty ()) { worklist &w = worklist_vec.last (); basic_block bb = w.bb; astate *cstate = w.cstate; if (!cstate) { astate **slot = &state.get_or_insert (bb); cstate = *slot; /* Already processed by DFS? */ if (cstate) { worklist_vec.pop (); continue; } /* DFS is visiting BB for first time. */ *slot = cstate = XOBNEW (&state_obstack, struct astate); cstate->low = cstate->high = cstate->dfs_preorder = next_dfs_num++; w.cstate = cstate; /* Exit block is special; process all fake edges we identified. */ if (bb == EXIT_BLOCK_PTR_FOR_FN (fun)) for (basic_block bb2 : terminating_bbs) { worklist we = {bb2, NULL}; worklist_vec.safe_push (we); } FOR_EACH_EDGE (e, ei, bb->preds) if (visited.contains (e->src)) { worklist we = {e->src, NULL}; worklist_vec.safe_push (we); } /* Keep BB on worklist so we process it last time. */ continue; } /* We are finished with processing reachable BBs, see if we have articulation. */ worklist_vec.pop (); cstate->high = cstate->dfs_postorder = next_dfs_num++; stack.safe_push (bb); } /* This is the final postorder walk. Determine low and high values and mark always executed blocks. */ for (basic_block bb : stack) { astate *cstate = *state.get (bb); FOR_EACH_EDGE (e, ei, bb->preds) { astate **cstate2 = state.get (e->src); /* We skip walking part of CFG reached only after first edge to exit. No BB reachable from the skipped part is always executed */ if (!cstate2) { if (e->src != ENTRY_BLOCK_PTR_FOR_FN (fun)) cstate->low = 0; continue; } cstate->low = MIN (cstate->low, (*cstate2)->low); cstate->high = MAX (cstate->high, (*cstate2)->high); } if (dump_file && (dump_flags & TDF_DETAILS) && bb != EXIT_BLOCK_PTR_FOR_FN (fun)) fprintf (dump_file, "BB %i %s preorder %i posorder %i low %i high %i\n", bb->index, terminating_bbs_set.contains (bb) ? "(terminating)": "", cstate->dfs_preorder, cstate->dfs_postorder, cstate->low, cstate->high); if (cstate->low == cstate->dfs_preorder && cstate->high == cstate->dfs_postorder && bb != EXIT_BLOCK_PTR_FOR_FN (fun)) bitmap_set_bit (ret, bb->index); if (terminating_bbs_set.contains (bb)) cstate->low = 0; else FOR_EACH_EDGE (e, ei, bb->succs) { astate **cstate2 = state.get (e->dest); if (!cstate2) continue; cstate->low = MIN (cstate->low, (*cstate2)->low); cstate->high = MAX (cstate->high, (*cstate2)->high); } } obstack_free (&state_obstack, NULL); if (dump_file) { fprintf (dump_file, "Always executed bbbs %s: ", assume_return_or_eh ? "(assuming return or EH)": ""); bitmap_print (dump_file, ret, "", "\n"); } return ret; }