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/* Rewrite a program in Normal form into SSA. Copyright (C) 2001, 2002, 2003, 2004, 2005, 2007, 2008, 2009, 2010 Free Software Foundation, Inc. Contributed by Diego Novillo <dnovillo@redhat.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 "rtl.h" #include "tm_p.h" #include "langhooks.h" #include "hard-reg-set.h" #include "basic-block.h" #include "output.h" #include "expr.h" #include "function.h" #include "diagnostic.h" #include "bitmap.h" #include "tree-flow.h" #include "gimple.h" #include "tree-inline.h" #include "varray.h" #include "timevar.h" #include "hashtab.h" #include "tree-dump.h" #include "tree-pass.h" #include "cfgloop.h" #include "domwalk.h" #include "ggc.h" #include "params.h" #include "vecprim.h" /* This file builds the SSA form for a function as described in: R. Cytron, J. Ferrante, B. Rosen, M. Wegman, and K. Zadeck. Efficiently Computing Static Single Assignment Form and the Control Dependence Graph. ACM Transactions on Programming Languages and Systems, 13(4):451-490, October 1991. */ /* Structure to map a variable VAR to the set of blocks that contain definitions for VAR. */ struct def_blocks_d { /* The variable. */ tree var; /* Blocks that contain definitions of VAR. Bit I will be set if the Ith block contains a definition of VAR. */ bitmap def_blocks; /* Blocks that contain a PHI node for VAR. */ bitmap phi_blocks; /* Blocks where VAR is live-on-entry. Similar semantics as DEF_BLOCKS. */ bitmap livein_blocks; }; /* Each entry in DEF_BLOCKS contains an element of type STRUCT DEF_BLOCKS_D, mapping a variable VAR to a bitmap describing all the basic blocks where VAR is defined (assigned a new value). It also contains a bitmap of all the blocks where VAR is live-on-entry (i.e., there is a use of VAR in block B without a preceding definition in B). The live-on-entry information is used when computing PHI pruning heuristics. */ static htab_t def_blocks; /* Stack of trees used to restore the global currdefs to its original state after completing rewriting of a block and its dominator children. Its elements have the following properties: - An SSA_NAME (N) indicates that the current definition of the underlying variable should be set to the given SSA_NAME. If the symbol associated with the SSA_NAME is not a GIMPLE register, the next slot in the stack must be a _DECL node (SYM). In this case, the name N in the previous slot is the current reaching definition for SYM. - A _DECL node indicates that the underlying variable has no current definition. - A NULL node at the top entry is used to mark the last slot associated with the current block. */ static VEC(tree,heap) *block_defs_stack; /* Set of existing SSA names being replaced by update_ssa. */ static sbitmap old_ssa_names; /* Set of new SSA names being added by update_ssa. Note that both NEW_SSA_NAMES and OLD_SSA_NAMES are dense bitmaps because most of the operations done on them are presence tests. */ static sbitmap new_ssa_names; sbitmap interesting_blocks; /* Set of SSA names that have been marked to be released after they were registered in the replacement table. They will be finally released after we finish updating the SSA web. */ static bitmap names_to_release; static VEC(gimple_vec, heap) *phis_to_rewrite; /* The bitmap of non-NULL elements of PHIS_TO_REWRITE. */ static bitmap blocks_with_phis_to_rewrite; /* Growth factor for NEW_SSA_NAMES and OLD_SSA_NAMES. These sets need to grow as the callers to register_new_name_mapping will typically create new names on the fly. FIXME. Currently set to 1/3 to avoid frequent reallocations but still need to find a reasonable growth strategy. */ #define NAME_SETS_GROWTH_FACTOR (MAX (3, num_ssa_names / 3)) /* Tuple used to represent replacement mappings. */ struct repl_map_d { tree name; bitmap set; }; /* NEW -> OLD_SET replacement table. If we are replacing several existing SSA names O_1, O_2, ..., O_j with a new name N_i, then REPL_TBL[N_i] = { O_1, O_2, ..., O_j }. */ static htab_t repl_tbl; /* The function the SSA updating data structures have been initialized for. NULL if they need to be initialized by register_new_name_mapping. */ static struct function *update_ssa_initialized_fn = NULL; /* Statistics kept by update_ssa to use in the virtual mapping heuristic. If the number of virtual mappings is beyond certain threshold, the updater will switch from using the mappings into renaming the virtual symbols from scratch. In some cases, the large number of name mappings for virtual names causes significant slowdowns in the PHI insertion code. */ struct update_ssa_stats_d { unsigned num_virtual_mappings; unsigned num_total_mappings; bitmap virtual_symbols; unsigned num_virtual_symbols; }; static struct update_ssa_stats_d update_ssa_stats; /* Global data to attach to the main dominator walk structure. */ struct mark_def_sites_global_data { /* This bitmap contains the variables which are set before they are used in a basic block. */ bitmap kills; }; /* Information stored for SSA names. */ struct ssa_name_info { /* The current reaching definition replacing this SSA name. */ tree current_def; /* This field indicates whether or not the variable may need PHI nodes. See the enum's definition for more detailed information about the states. */ ENUM_BITFIELD (need_phi_state) need_phi_state : 2; /* Age of this record (so that info_for_ssa_name table can be cleared quickly); if AGE < CURRENT_INFO_FOR_SSA_NAME_AGE, then the fields are assumed to be null. */ unsigned age; }; /* The information associated with names. */ typedef struct ssa_name_info *ssa_name_info_p; DEF_VEC_P (ssa_name_info_p); DEF_VEC_ALLOC_P (ssa_name_info_p, heap); static VEC(ssa_name_info_p, heap) *info_for_ssa_name; static unsigned current_info_for_ssa_name_age; /* The set of blocks affected by update_ssa. */ static bitmap blocks_to_update; /* The main entry point to the SSA renamer (rewrite_blocks) may be called several times to do different, but related, tasks. Initially, we need it to rename the whole program into SSA form. At other times, we may need it to only rename into SSA newly exposed symbols. Finally, we can also call it to incrementally fix an already built SSA web. */ enum rewrite_mode { /* Convert the whole function into SSA form. */ REWRITE_ALL, /* Incrementally update the SSA web by replacing existing SSA names with new ones. See update_ssa for details. */ REWRITE_UPDATE }; /* Prototypes for debugging functions. */ extern void dump_tree_ssa (FILE *); extern void debug_tree_ssa (void); extern void debug_def_blocks (void); extern void dump_tree_ssa_stats (FILE *); extern void debug_tree_ssa_stats (void); extern void dump_update_ssa (FILE *); extern void debug_update_ssa (void); extern void dump_names_replaced_by (FILE *, tree); extern void debug_names_replaced_by (tree); extern void dump_def_blocks (FILE *); extern void debug_def_blocks (void); extern void dump_defs_stack (FILE *, int); extern void debug_defs_stack (int); extern void dump_currdefs (FILE *); extern void debug_currdefs (void); /* Return true if STMT needs to be rewritten. When renaming a subset of the variables, not all statements will be processed. This is decided in mark_def_sites. */ static inline bool rewrite_uses_p (gimple stmt) { return gimple_visited_p (stmt); } /* Set the rewrite marker on STMT to the value given by REWRITE_P. */ static inline void set_rewrite_uses (gimple stmt, bool rewrite_p) { gimple_set_visited (stmt, rewrite_p); } /* Return true if the DEFs created by statement STMT should be registered when marking new definition sites. This is slightly different than rewrite_uses_p: it's used by update_ssa to distinguish statements that need to have both uses and defs processed from those that only need to have their defs processed. Statements that define new SSA names only need to have their defs registered, but they don't need to have their uses renamed. */ static inline bool register_defs_p (gimple stmt) { return gimple_plf (stmt, GF_PLF_1) != 0; } /* If REGISTER_DEFS_P is true, mark STMT to have its DEFs registered. */ static inline void set_register_defs (gimple stmt, bool register_defs_p) { gimple_set_plf (stmt, GF_PLF_1, register_defs_p); } /* Get the information associated with NAME. */ static inline ssa_name_info_p get_ssa_name_ann (tree name) { unsigned ver = SSA_NAME_VERSION (name); unsigned len = VEC_length (ssa_name_info_p, info_for_ssa_name); struct ssa_name_info *info; if (ver >= len) { unsigned new_len = num_ssa_names; VEC_reserve (ssa_name_info_p, heap, info_for_ssa_name, new_len); while (len++ < new_len) { struct ssa_name_info *info = XCNEW (struct ssa_name_info); info->age = current_info_for_ssa_name_age; VEC_quick_push (ssa_name_info_p, info_for_ssa_name, info); } } info = VEC_index (ssa_name_info_p, info_for_ssa_name, ver); if (info->age < current_info_for_ssa_name_age) { info->need_phi_state = NEED_PHI_STATE_UNKNOWN; info->current_def = NULL_TREE; info->age = current_info_for_ssa_name_age; } return info; } /* Clears info for SSA names. */ static void clear_ssa_name_info (void) { current_info_for_ssa_name_age++; } /* Get phi_state field for VAR. */ static inline enum need_phi_state get_phi_state (tree var) { if (TREE_CODE (var) == SSA_NAME) return get_ssa_name_ann (var)->need_phi_state; else return var_ann (var)->need_phi_state; } /* Sets phi_state field for VAR to STATE. */ static inline void set_phi_state (tree var, enum need_phi_state state) { if (TREE_CODE (var) == SSA_NAME) get_ssa_name_ann (var)->need_phi_state = state; else var_ann (var)->need_phi_state = state; } /* Return the current definition for VAR. */ tree get_current_def (tree var) { if (TREE_CODE (var) == SSA_NAME) return get_ssa_name_ann (var)->current_def; else return var_ann (var)->current_def; } /* Sets current definition of VAR to DEF. */ void set_current_def (tree var, tree def) { if (TREE_CODE (var) == SSA_NAME) get_ssa_name_ann (var)->current_def = def; else var_ann (var)->current_def = def; } /* Compute global livein information given the set of blocks where an object is locally live at the start of the block (LIVEIN) and the set of blocks where the object is defined (DEF_BLOCKS). Note: This routine augments the existing local livein information to include global livein (i.e., it modifies the underlying bitmap for LIVEIN). */ void compute_global_livein (bitmap livein ATTRIBUTE_UNUSED, bitmap def_blocks ATTRIBUTE_UNUSED) { basic_block bb, *worklist, *tos; unsigned i; bitmap_iterator bi; tos = worklist = (basic_block *) xmalloc (sizeof (basic_block) * (last_basic_block + 1)); EXECUTE_IF_SET_IN_BITMAP (livein, 0, i, bi) *tos++ = BASIC_BLOCK (i); /* Iterate until the worklist is empty. */ while (tos != worklist) { edge e; edge_iterator ei; /* Pull a block off the worklist. */ bb = *--tos; /* For each predecessor block. */ FOR_EACH_EDGE (e, ei, bb->preds) { basic_block pred = e->src; int pred_index = pred->index; /* None of this is necessary for the entry block. */ if (pred != ENTRY_BLOCK_PTR && ! bitmap_bit_p (livein, pred_index) && ! bitmap_bit_p (def_blocks, pred_index)) { *tos++ = pred; bitmap_set_bit (livein, pred_index); } } } free (worklist); } /* Cleans up the REWRITE_THIS_STMT and REGISTER_DEFS_IN_THIS_STMT flags for all statements in basic block BB. */ static void initialize_flags_in_bb (basic_block bb) { gimple stmt; gimple_stmt_iterator gsi; for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) { gimple phi = gsi_stmt (gsi); set_rewrite_uses (phi, false); set_register_defs (phi, false); } for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) { stmt = gsi_stmt (gsi); /* We are going to use the operand cache API, such as SET_USE, SET_DEF, and FOR_EACH_IMM_USE_FAST. The operand cache for each statement should be up-to-date. */ gcc_assert (!gimple_modified_p (stmt)); set_rewrite_uses (stmt, false); set_register_defs (stmt, false); } } /* Mark block BB as interesting for update_ssa. */ static void mark_block_for_update (basic_block bb) { gcc_assert (blocks_to_update != NULL); if (bitmap_bit_p (blocks_to_update, bb->index)) return; bitmap_set_bit (blocks_to_update, bb->index); initialize_flags_in_bb (bb); } /* Return the set of blocks where variable VAR is defined and the blocks where VAR is live on entry (livein). If no entry is found in DEF_BLOCKS, a new one is created and returned. */ static inline struct def_blocks_d * get_def_blocks_for (tree var) { struct def_blocks_d db, *db_p; void **slot; db.var = var; slot = htab_find_slot (def_blocks, (void *) &db, INSERT); if (*slot == NULL) { db_p = XNEW (struct def_blocks_d); db_p->var = var; db_p->def_blocks = BITMAP_ALLOC (NULL); db_p->phi_blocks = BITMAP_ALLOC (NULL); db_p->livein_blocks = BITMAP_ALLOC (NULL); *slot = (void *) db_p; } else db_p = (struct def_blocks_d *) *slot; return db_p; } /* Mark block BB as the definition site for variable VAR. PHI_P is true if VAR is defined by a PHI node. */ static void set_def_block (tree var, basic_block bb, bool phi_p) { struct def_blocks_d *db_p; enum need_phi_state state; state = get_phi_state (var); db_p = get_def_blocks_for (var); /* Set the bit corresponding to the block where VAR is defined. */ bitmap_set_bit (db_p->def_blocks, bb->index); if (phi_p) bitmap_set_bit (db_p->phi_blocks, bb->index); /* Keep track of whether or not we may need to insert PHI nodes. If we are in the UNKNOWN state, then this is the first definition of VAR. Additionally, we have not seen any uses of VAR yet, so we do not need a PHI node for this variable at this time (i.e., transition to NEED_PHI_STATE_NO). If we are in any other state, then we either have multiple definitions of this variable occurring in different blocks or we saw a use of the variable which was not dominated by the block containing the definition(s). In this case we may need a PHI node, so enter state NEED_PHI_STATE_MAYBE. */ if (state == NEED_PHI_STATE_UNKNOWN) set_phi_state (var, NEED_PHI_STATE_NO); else set_phi_state (var, NEED_PHI_STATE_MAYBE); } /* Mark block BB as having VAR live at the entry to BB. */ static void set_livein_block (tree var, basic_block bb) { struct def_blocks_d *db_p; enum need_phi_state state = get_phi_state (var); db_p = get_def_blocks_for (var); /* Set the bit corresponding to the block where VAR is live in. */ bitmap_set_bit (db_p->livein_blocks, bb->index); /* Keep track of whether or not we may need to insert PHI nodes. If we reach here in NEED_PHI_STATE_NO, see if this use is dominated by the single block containing the definition(s) of this variable. If it is, then we remain in NEED_PHI_STATE_NO, otherwise we transition to NEED_PHI_STATE_MAYBE. */ if (state == NEED_PHI_STATE_NO) { int def_block_index = bitmap_first_set_bit (db_p->def_blocks); if (def_block_index == -1 || ! dominated_by_p (CDI_DOMINATORS, bb, BASIC_BLOCK (def_block_index))) set_phi_state (var, NEED_PHI_STATE_MAYBE); } else set_phi_state (var, NEED_PHI_STATE_MAYBE); } /* Return true if symbol SYM is marked for renaming. */ static inline bool symbol_marked_for_renaming (tree sym) { return bitmap_bit_p (SYMS_TO_RENAME (cfun), DECL_UID (sym)); } /* Return true if NAME is in OLD_SSA_NAMES. */ static inline bool is_old_name (tree name) { unsigned ver = SSA_NAME_VERSION (name); if (!new_ssa_names) return false; return ver < new_ssa_names->n_bits && TEST_BIT (old_ssa_names, ver); } /* Return true if NAME is in NEW_SSA_NAMES. */ static inline bool is_new_name (tree name) { unsigned ver = SSA_NAME_VERSION (name); if (!new_ssa_names) return false; return ver < new_ssa_names->n_bits && TEST_BIT (new_ssa_names, ver); } /* Hashing and equality functions for REPL_TBL. */ static hashval_t repl_map_hash (const void *p) { return htab_hash_pointer ((const void *)((const struct repl_map_d *)p)->name); } static int repl_map_eq (const void *p1, const void *p2) { return ((const struct repl_map_d *)p1)->name == ((const struct repl_map_d *)p2)->name; } static void repl_map_free (void *p) { BITMAP_FREE (((struct repl_map_d *)p)->set); free (p); } /* Return the names replaced by NEW_TREE (i.e., REPL_TBL[NEW_TREE].SET). */ static inline bitmap names_replaced_by (tree new_tree) { struct repl_map_d m; void **slot; m.name = new_tree; slot = htab_find_slot (repl_tbl, (void *) &m, NO_INSERT); /* If N was not registered in the replacement table, return NULL. */ if (slot == NULL || *slot == NULL) return NULL; return ((struct repl_map_d *) *slot)->set; } /* Add OLD to REPL_TBL[NEW_TREE].SET. */ static inline void add_to_repl_tbl (tree new_tree, tree old) { struct repl_map_d m, *mp; void **slot; m.name = new_tree; slot = htab_find_slot (repl_tbl, (void *) &m, INSERT); if (*slot == NULL) { mp = XNEW (struct repl_map_d); mp->name = new_tree; mp->set = BITMAP_ALLOC (NULL); *slot = (void *) mp; } else mp = (struct repl_map_d *) *slot; bitmap_set_bit (mp->set, SSA_NAME_VERSION (old)); } /* Add a new mapping NEW_TREE -> OLD REPL_TBL. Every entry N_i in REPL_TBL represents the set of names O_1 ... O_j replaced by N_i. This is used by update_ssa and its helpers to introduce new SSA names in an already formed SSA web. */ static void add_new_name_mapping (tree new_tree, tree old) { timevar_push (TV_TREE_SSA_INCREMENTAL); /* OLD and NEW_TREE must be different SSA names for the same symbol. */ gcc_assert (new_tree != old && SSA_NAME_VAR (new_tree) == SSA_NAME_VAR (old)); /* If this mapping is for virtual names, we will need to update virtual operands. If this is a mapping for .MEM, then we gather the symbols associated with each name. */ if (!is_gimple_reg (new_tree)) { tree sym; update_ssa_stats.num_virtual_mappings++; update_ssa_stats.num_virtual_symbols++; /* Keep counts of virtual mappings and symbols to use in the virtual mapping heuristic. If we have large numbers of virtual mappings for a relatively low number of symbols, it will make more sense to rename the symbols from scratch. Otherwise, the insertion of PHI nodes for each of the old names in these mappings will be very slow. */ sym = SSA_NAME_VAR (new_tree); bitmap_set_bit (update_ssa_stats.virtual_symbols, DECL_UID (sym)); } /* We may need to grow NEW_SSA_NAMES and OLD_SSA_NAMES because our caller may have created new names since the set was created. */ if (new_ssa_names->n_bits <= num_ssa_names - 1) { unsigned int new_sz = num_ssa_names + NAME_SETS_GROWTH_FACTOR; new_ssa_names = sbitmap_resize (new_ssa_names, new_sz, 0); old_ssa_names = sbitmap_resize (old_ssa_names, new_sz, 0); } /* Update the REPL_TBL table. */ add_to_repl_tbl (new_tree, old); /* If OLD had already been registered as a new name, then all the names that OLD replaces should also be replaced by NEW_TREE. */ if (is_new_name (old)) bitmap_ior_into (names_replaced_by (new_tree), names_replaced_by (old)); /* Register NEW_TREE and OLD in NEW_SSA_NAMES and OLD_SSA_NAMES, respectively. */ SET_BIT (new_ssa_names, SSA_NAME_VERSION (new_tree)); SET_BIT (old_ssa_names, SSA_NAME_VERSION (old)); /* Update mapping counter to use in the virtual mapping heuristic. */ update_ssa_stats.num_total_mappings++; timevar_pop (TV_TREE_SSA_INCREMENTAL); } /* Call back for walk_dominator_tree used to collect definition sites for every variable in the function. For every statement S in block BB: 1- Variables defined by S in the DEFS of S are marked in the bitmap KILLS. 2- If S uses a variable VAR and there is no preceding kill of VAR, then it is marked in the LIVEIN_BLOCKS bitmap associated with VAR. This information is used to determine which variables are live across block boundaries to reduce the number of PHI nodes we create. */ static void mark_def_sites (basic_block bb, gimple stmt, bitmap kills) { tree def; use_operand_p use_p; ssa_op_iter iter; /* Since this is the first time that we rewrite the program into SSA form, force an operand scan on every statement. */ update_stmt (stmt); gcc_assert (blocks_to_update == NULL); set_register_defs (stmt, false); set_rewrite_uses (stmt, false); if (is_gimple_debug (stmt)) return; /* If a variable is used before being set, then the variable is live across a block boundary, so mark it live-on-entry to BB. */ FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_USE) { tree sym = USE_FROM_PTR (use_p); gcc_assert (DECL_P (sym)); if (!bitmap_bit_p (kills, DECL_UID (sym))) set_livein_block (sym, bb); set_rewrite_uses (stmt, true); } /* Now process the defs. Mark BB as the definition block and add each def to the set of killed symbols. */ FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_DEF) { gcc_assert (DECL_P (def)); set_def_block (def, bb, false); bitmap_set_bit (kills, DECL_UID (def)); set_register_defs (stmt, true); } /* If we found the statement interesting then also mark the block BB as interesting. */ if (rewrite_uses_p (stmt) || register_defs_p (stmt)) SET_BIT (interesting_blocks, bb->index); } /* Structure used by prune_unused_phi_nodes to record bounds of the intervals in the dfs numbering of the dominance tree. */ struct dom_dfsnum { /* Basic block whose index this entry corresponds to. */ unsigned bb_index; /* The dfs number of this node. */ unsigned dfs_num; }; /* Compares two entries of type struct dom_dfsnum by dfs_num field. Callback for qsort. */ static int cmp_dfsnum (const void *a, const void *b) { const struct dom_dfsnum *const da = (const struct dom_dfsnum *) a; const struct dom_dfsnum *const db = (const struct dom_dfsnum *) b; return (int) da->dfs_num - (int) db->dfs_num; } /* Among the intervals starting at the N points specified in DEFS, find the one that contains S, and return its bb_index. */ static unsigned find_dfsnum_interval (struct dom_dfsnum *defs, unsigned n, unsigned s) { unsigned f = 0, t = n, m; while (t > f + 1) { m = (f + t) / 2; if (defs[m].dfs_num <= s) f = m; else t = m; } return defs[f].bb_index; } /* Clean bits from PHIS for phi nodes whose value cannot be used in USES. KILLS is a bitmap of blocks where the value is defined before any use. */ static void prune_unused_phi_nodes (bitmap phis, bitmap kills, bitmap uses) { VEC(int, heap) *worklist; bitmap_iterator bi; unsigned i, b, p, u, top; bitmap live_phis; basic_block def_bb, use_bb; edge e; edge_iterator ei; bitmap to_remove; struct dom_dfsnum *defs; unsigned n_defs, adef; if (bitmap_empty_p (uses)) { bitmap_clear (phis); return; } /* The phi must dominate a use, or an argument of a live phi. Also, we do not create any phi nodes in def blocks, unless they are also livein. */ to_remove = BITMAP_ALLOC (NULL); bitmap_and_compl (to_remove, kills, uses); bitmap_and_compl_into (phis, to_remove); if (bitmap_empty_p (phis)) { BITMAP_FREE (to_remove); return; } /* We want to remove the unnecessary phi nodes, but we do not want to compute liveness information, as that may be linear in the size of CFG, and if there are lot of different variables to rewrite, this may lead to quadratic behavior. Instead, we basically emulate standard dce. We put all uses to worklist, then for each of them find the nearest def that dominates them. If this def is a phi node, we mark it live, and if it was not live before, we add the predecessors of its basic block to the worklist. To quickly locate the nearest def that dominates use, we use dfs numbering of the dominance tree (that is already available in order to speed up queries). For each def, we have the interval given by the dfs number on entry to and on exit from the corresponding subtree in the dominance tree. The nearest dominator for a given use is the smallest of these intervals that contains entry and exit dfs numbers for the basic block with the use. If we store the bounds for all the uses to an array and sort it, we can locate the nearest dominating def in logarithmic time by binary search.*/ bitmap_ior (to_remove, kills, phis); n_defs = bitmap_count_bits (to_remove); defs = XNEWVEC (struct dom_dfsnum, 2 * n_defs + 1); defs[0].bb_index = 1; defs[0].dfs_num = 0; adef = 1; EXECUTE_IF_SET_IN_BITMAP (to_remove, 0, i, bi) { def_bb = BASIC_BLOCK (i); defs[adef].bb_index = i; defs[adef].dfs_num = bb_dom_dfs_in (CDI_DOMINATORS, def_bb); defs[adef + 1].bb_index = i; defs[adef + 1].dfs_num = bb_dom_dfs_out (CDI_DOMINATORS, def_bb); adef += 2; } BITMAP_FREE (to_remove); gcc_assert (adef == 2 * n_defs + 1); qsort (defs, adef, sizeof (struct dom_dfsnum), cmp_dfsnum); gcc_assert (defs[0].bb_index == 1); /* Now each DEFS entry contains the number of the basic block to that the dfs number corresponds. Change them to the number of basic block that corresponds to the interval following the dfs number. Also, for the dfs_out numbers, increase the dfs number by one (so that it corresponds to the start of the following interval, not to the end of the current one). We use WORKLIST as a stack. */ worklist = VEC_alloc (int, heap, n_defs + 1); VEC_quick_push (int, worklist, 1); top = 1; n_defs = 1; for (i = 1; i < adef; i++) { b = defs[i].bb_index; if (b == top) { /* This is a closing element. Interval corresponding to the top of the stack after removing it follows. */ VEC_pop (int, worklist); top = VEC_index (int, worklist, VEC_length (int, worklist) - 1); defs[n_defs].bb_index = top; defs[n_defs].dfs_num = defs[i].dfs_num + 1; } else { /* Opening element. Nothing to do, just push it to the stack and move it to the correct position. */ defs[n_defs].bb_index = defs[i].bb_index; defs[n_defs].dfs_num = defs[i].dfs_num; VEC_quick_push (int, worklist, b); top = b; } /* If this interval starts at the same point as the previous one, cancel the previous one. */ if (defs[n_defs].dfs_num == defs[n_defs - 1].dfs_num) defs[n_defs - 1].bb_index = defs[n_defs].bb_index; else n_defs++; } VEC_pop (int, worklist); gcc_assert (VEC_empty (int, worklist)); /* Now process the uses. */ live_phis = BITMAP_ALLOC (NULL); EXECUTE_IF_SET_IN_BITMAP (uses, 0, i, bi) { VEC_safe_push (int, heap, worklist, i); } while (!VEC_empty (int, worklist)) { b = VEC_pop (int, worklist); if (b == ENTRY_BLOCK) continue; /* If there is a phi node in USE_BB, it is made live. Otherwise, find the def that dominates the immediate dominator of USE_BB (the kill in USE_BB does not dominate the use). */ if (bitmap_bit_p (phis, b)) p = b; else { use_bb = get_immediate_dominator (CDI_DOMINATORS, BASIC_BLOCK (b)); p = find_dfsnum_interval (defs, n_defs, bb_dom_dfs_in (CDI_DOMINATORS, use_bb)); if (!bitmap_bit_p (phis, p)) continue; } /* If the phi node is already live, there is nothing to do. */ if (bitmap_bit_p (live_phis, p)) continue; /* Mark the phi as live, and add the new uses to the worklist. */ bitmap_set_bit (live_phis, p); def_bb = BASIC_BLOCK (p); FOR_EACH_EDGE (e, ei, def_bb->preds) { u = e->src->index; if (bitmap_bit_p (uses, u)) continue; /* In case there is a kill directly in the use block, do not record the use (this is also necessary for correctness, as we assume that uses dominated by a def directly in their block have been filtered out before). */ if (bitmap_bit_p (kills, u)) continue; bitmap_set_bit (uses, u); VEC_safe_push (int, heap, worklist, u); } } VEC_free (int, heap, worklist); bitmap_copy (phis, live_phis); BITMAP_FREE (live_phis); free (defs); } /* Return the set of blocks where variable VAR is defined and the blocks where VAR is live on entry (livein). Return NULL, if no entry is found in DEF_BLOCKS. */ static inline struct def_blocks_d * find_def_blocks_for (tree var) { struct def_blocks_d dm; dm.var = var; return (struct def_blocks_d *) htab_find (def_blocks, &dm); } /* Retrieve or create a default definition for symbol SYM. */ static inline tree get_default_def_for (tree sym) { tree ddef = gimple_default_def (cfun, sym); if (ddef == NULL_TREE) { ddef = make_ssa_name (sym, gimple_build_nop ()); set_default_def (sym, ddef); } return ddef; } /* Marks phi node PHI in basic block BB for rewrite. */ static void mark_phi_for_rewrite (basic_block bb, gimple phi) { gimple_vec phis; unsigned i, idx = bb->index; if (rewrite_uses_p (phi)) return; set_rewrite_uses (phi, true); if (!blocks_with_phis_to_rewrite) return; bitmap_set_bit (blocks_with_phis_to_rewrite, idx); VEC_reserve (gimple_vec, heap, phis_to_rewrite, last_basic_block + 1); for (i = VEC_length (gimple_vec, phis_to_rewrite); i <= idx; i++) VEC_quick_push (gimple_vec, phis_to_rewrite, NULL); phis = VEC_index (gimple_vec, phis_to_rewrite, idx); if (!phis) phis = VEC_alloc (gimple, heap, 10); VEC_safe_push (gimple, heap, phis, phi); VEC_replace (gimple_vec, phis_to_rewrite, idx, phis); } /* Insert PHI nodes for variable VAR using the iterated dominance frontier given in PHI_INSERTION_POINTS. If UPDATE_P is true, this function assumes that the caller is incrementally updating the existing SSA form, in which case VAR may be an SSA name instead of a symbol. PHI_INSERTION_POINTS is updated to reflect nodes that already had a PHI node for VAR. On exit, only the nodes that received a PHI node for VAR will be present in PHI_INSERTION_POINTS. */ static void insert_phi_nodes_for (tree var, bitmap phi_insertion_points, bool update_p) { unsigned bb_index; edge e; gimple phi; basic_block bb; bitmap_iterator bi; struct def_blocks_d *def_map; def_map = find_def_blocks_for (var); gcc_assert (def_map); /* Remove the blocks where we already have PHI nodes for VAR. */ bitmap_and_compl_into (phi_insertion_points, def_map->phi_blocks); /* Remove obviously useless phi nodes. */ prune_unused_phi_nodes (phi_insertion_points, def_map->def_blocks, def_map->livein_blocks); /* And insert the PHI nodes. */ EXECUTE_IF_SET_IN_BITMAP (phi_insertion_points, 0, bb_index, bi) { bb = BASIC_BLOCK (bb_index); if (update_p) mark_block_for_update (bb); phi = NULL; if (TREE_CODE (var) == SSA_NAME) { /* If we are rewriting SSA names, create the LHS of the PHI node by duplicating VAR. This is useful in the case of pointers, to also duplicate pointer attributes (alias information, in particular). */ edge_iterator ei; tree new_lhs; gcc_assert (update_p); phi = create_phi_node (var, bb); new_lhs = duplicate_ssa_name (var, phi); gimple_phi_set_result (phi, new_lhs); add_new_name_mapping (new_lhs, var); /* Add VAR to every argument slot of PHI. We need VAR in every argument so that rewrite_update_phi_arguments knows which name is this PHI node replacing. If VAR is a symbol marked for renaming, this is not necessary, the renamer will use the symbol on the LHS to get its reaching definition. */ FOR_EACH_EDGE (e, ei, bb->preds) add_phi_arg (phi, var, e, UNKNOWN_LOCATION); } else { tree tracked_var; gcc_assert (DECL_P (var)); phi = create_phi_node (var, bb); tracked_var = target_for_debug_bind (var); if (tracked_var) { gimple note = gimple_build_debug_bind (tracked_var, PHI_RESULT (phi), phi); gimple_stmt_iterator si = gsi_after_labels (bb); gsi_insert_before (&si, note, GSI_SAME_STMT); } } /* Mark this PHI node as interesting for update_ssa. */ set_register_defs (phi, true); mark_phi_for_rewrite (bb, phi); } } /* Insert PHI nodes at the dominance frontier of blocks with variable definitions. DFS contains the dominance frontier information for the flowgraph. */ static void insert_phi_nodes (bitmap *dfs) { referenced_var_iterator rvi; bitmap_iterator bi; tree var; bitmap vars; unsigned uid; timevar_push (TV_TREE_INSERT_PHI_NODES); /* Do two stages to avoid code generation differences for UID differences but no UID ordering differences. */ vars = BITMAP_ALLOC (NULL); FOR_EACH_REFERENCED_VAR (var, rvi) { struct def_blocks_d *def_map; def_map = find_def_blocks_for (var); if (def_map == NULL) continue; if (get_phi_state (var) != NEED_PHI_STATE_NO) bitmap_set_bit (vars, DECL_UID (var)); } EXECUTE_IF_SET_IN_BITMAP (vars, 0, uid, bi) { tree var = referenced_var (uid); struct def_blocks_d *def_map; bitmap idf; def_map = find_def_blocks_for (var); idf = compute_idf (def_map->def_blocks, dfs); insert_phi_nodes_for (var, idf, false); BITMAP_FREE (idf); } BITMAP_FREE (vars); timevar_pop (TV_TREE_INSERT_PHI_NODES); } /* Push SYM's current reaching definition into BLOCK_DEFS_STACK and register DEF (an SSA_NAME) to be a new definition for SYM. */ static void register_new_def (tree def, tree sym) { tree currdef; /* If this variable is set in a single basic block and all uses are dominated by the set(s) in that single basic block, then there is no reason to record anything for this variable in the block local definition stacks. Doing so just wastes time and memory. This is the same test to prune the set of variables which may need PHI nodes. So we just use that information since it's already computed and available for us to use. */ if (get_phi_state (sym) == NEED_PHI_STATE_NO) { set_current_def (sym, def); return; } currdef = get_current_def (sym); /* If SYM is not a GIMPLE register, then CURRDEF may be a name whose SSA_NAME_VAR is not necessarily SYM. In this case, also push SYM in the stack so that we know which symbol is being defined by this SSA name when we unwind the stack. */ if (currdef && !is_gimple_reg (sym)) VEC_safe_push (tree, heap, block_defs_stack, sym); /* Push the current reaching definition into BLOCK_DEFS_STACK. This stack is later used by the dominator tree callbacks to restore the reaching definitions for all the variables defined in the block after a recursive visit to all its immediately dominated blocks. If there is no current reaching definition, then just record the underlying _DECL node. */ VEC_safe_push (tree, heap, block_defs_stack, currdef ? currdef : sym); /* Set the current reaching definition for SYM to be DEF. */ set_current_def (sym, def); } /* Perform a depth-first traversal of the dominator tree looking for variables to rename. BB is the block where to start searching. Renaming is a five step process: 1- Every definition made by PHI nodes at the start of the blocks is registered as the current definition for the corresponding variable. 2- Every statement in BB is rewritten. USE and VUSE operands are rewritten with their corresponding reaching definition. DEF and VDEF targets are registered as new definitions. 3- All the PHI nodes in successor blocks of BB are visited. The argument corresponding to BB is replaced with its current reaching definition. 4- Recursively rewrite every dominator child block of BB. 5- Restore (in reverse order) the current reaching definition for every new definition introduced in this block. This is done so that when we return from the recursive call, all the current reaching definitions are restored to the names that were valid in the dominator parent of BB. */ /* Return the current definition for variable VAR. If none is found, create a new SSA name to act as the zeroth definition for VAR. */ static tree get_reaching_def (tree var) { tree currdef; /* Lookup the current reaching definition for VAR. */ currdef = get_current_def (var); /* If there is no reaching definition for VAR, create and register a default definition for it (if needed). */ if (currdef == NULL_TREE) { tree sym = DECL_P (var) ? var : SSA_NAME_VAR (var); currdef = get_default_def_for (sym); set_current_def (var, currdef); } /* Return the current reaching definition for VAR, or the default definition, if we had to create one. */ return currdef; } /* SSA Rewriting Step 2. Rewrite every variable used in each statement in the block with its immediate reaching definitions. Update the current definition of a variable when a new real or virtual definition is found. */ static void rewrite_stmt (gimple_stmt_iterator si) { use_operand_p use_p; def_operand_p def_p; ssa_op_iter iter; gimple stmt = gsi_stmt (si); /* If mark_def_sites decided that we don't need to rewrite this statement, ignore it. */ gcc_assert (blocks_to_update == NULL); if (!rewrite_uses_p (stmt) && !register_defs_p (stmt)) return; if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Renaming statement "); print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM); fprintf (dump_file, "\n"); } /* Step 1. Rewrite USES in the statement. */ if (rewrite_uses_p (stmt)) FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_USE) { tree var = USE_FROM_PTR (use_p); gcc_assert (DECL_P (var)); SET_USE (use_p, get_reaching_def (var)); } /* Step 2. Register the statement's DEF operands. */ if (register_defs_p (stmt)) FOR_EACH_SSA_DEF_OPERAND (def_p, stmt, iter, SSA_OP_DEF) { tree var = DEF_FROM_PTR (def_p); tree name = make_ssa_name (var, stmt); tree tracked_var; gcc_assert (DECL_P (var)); SET_DEF (def_p, name); register_new_def (DEF_FROM_PTR (def_p), var); tracked_var = target_for_debug_bind (var); if (tracked_var) { gimple note = gimple_build_debug_bind (tracked_var, name, stmt); gsi_insert_after (&si, note, GSI_SAME_STMT); } } } /* SSA Rewriting Step 3. Visit all the successor blocks of BB looking for PHI nodes. For every PHI node found, add a new argument containing the current reaching definition for the variable and the edge through which that definition is reaching the PHI node. */ static void rewrite_add_phi_arguments (basic_block bb) { edge e; edge_iterator ei; FOR_EACH_EDGE (e, ei, bb->succs) { gimple phi; gimple_stmt_iterator gsi; for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi)) { tree currdef; gimple stmt; phi = gsi_stmt (gsi); currdef = get_reaching_def (SSA_NAME_VAR (gimple_phi_result (phi))); stmt = SSA_NAME_DEF_STMT (currdef); add_phi_arg (phi, currdef, e, gimple_location (stmt)); } } } /* SSA Rewriting Step 1. Initialization, create a block local stack of reaching definitions for new SSA names produced in this block (BLOCK_DEFS). Register new definitions for every PHI node in the block. */ static void rewrite_enter_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED, basic_block bb) { gimple phi; gimple_stmt_iterator gsi; if (dump_file && (dump_flags & TDF_DETAILS)) fprintf (dump_file, "\n\nRenaming block #%d\n\n", bb->index); /* Mark the unwind point for this block. */ VEC_safe_push (tree, heap, block_defs_stack, NULL_TREE); /* Step 1. Register new definitions for every PHI node in the block. Conceptually, all the PHI nodes are executed in parallel and each PHI node introduces a new version for the associated variable. */ for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) { tree result; phi = gsi_stmt (gsi); result = gimple_phi_result (phi); gcc_assert (is_gimple_reg (result)); register_new_def (result, SSA_NAME_VAR (result)); } /* Step 2. Rewrite every variable used in each statement in the block with its immediate reaching definitions. Update the current definition of a variable when a new real or virtual definition is found. */ if (TEST_BIT (interesting_blocks, bb->index)) for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) rewrite_stmt (gsi); /* Step 3. Visit all the successor blocks of BB looking for PHI nodes. For every PHI node found, add a new argument containing the current reaching definition for the variable and the edge through which that definition is reaching the PHI node. */ rewrite_add_phi_arguments (bb); } /* Called after visiting all the statements in basic block BB and all of its dominator children. Restore CURRDEFS to its original value. */ static void rewrite_leave_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED, basic_block bb ATTRIBUTE_UNUSED) { /* Restore CURRDEFS to its original state. */ while (VEC_length (tree, block_defs_stack) > 0) { tree tmp = VEC_pop (tree, block_defs_stack); tree saved_def, var; if (tmp == NULL_TREE) break; if (TREE_CODE (tmp) == SSA_NAME) { /* If we recorded an SSA_NAME, then make the SSA_NAME the current definition of its underlying variable. Note that if the SSA_NAME is not for a GIMPLE register, the symbol being defined is stored in the next slot in the stack. This mechanism is needed because an SSA name for a non-register symbol may be the definition for more than one symbol (e.g., SFTs, aliased variables, etc). */ saved_def = tmp; var = SSA_NAME_VAR (saved_def); if (!is_gimple_reg (var)) var = VEC_pop (tree, block_defs_stack); } else { /* If we recorded anything else, it must have been a _DECL node and its current reaching definition must have been NULL. */ saved_def = NULL; var = tmp; } set_current_def (var, saved_def); } } /* Dump bitmap SET (assumed to contain VAR_DECLs) to FILE. */ void dump_decl_set (FILE *file, bitmap set) { if (set) { bitmap_iterator bi; unsigned i; fprintf (file, "{ "); EXECUTE_IF_SET_IN_BITMAP (set, 0, i, bi) { print_generic_expr (file, referenced_var (i), 0); fprintf (file, " "); } fprintf (file, "}"); } else fprintf (file, "NIL"); } /* Dump bitmap SET (assumed to contain VAR_DECLs) to FILE. */ void debug_decl_set (bitmap set) { dump_decl_set (stderr, set); fprintf (stderr, "\n"); } /* Dump the renaming stack (block_defs_stack) to FILE. Traverse the stack up to a maximum of N levels. If N is -1, the whole stack is dumped. New levels are created when the dominator tree traversal used for renaming enters a new sub-tree. */ void dump_defs_stack (FILE *file, int n) { int i, j; fprintf (file, "\n\nRenaming stack"); if (n > 0) fprintf (file, " (up to %d levels)", n); fprintf (file, "\n\n"); i = 1; fprintf (file, "Level %d (current level)\n", i); for (j = (int) VEC_length (tree, block_defs_stack) - 1; j >= 0; j--) { tree name, var; name = VEC_index (tree, block_defs_stack, j); if (name == NULL_TREE) { i++; if (n > 0 && i > n) break; fprintf (file, "\nLevel %d\n", i); continue; } if (DECL_P (name)) { var = name; name = NULL_TREE; } else { var = SSA_NAME_VAR (name); if (!is_gimple_reg (var)) { j--; var = VEC_index (tree, block_defs_stack, j); } } fprintf (file, " Previous CURRDEF ("); print_generic_expr (file, var, 0); fprintf (file, ") = "); if (name) print_generic_expr (file, name, 0); else fprintf (file, "<NIL>"); fprintf (file, "\n"); } } /* Dump the renaming stack (block_defs_stack) to stderr. Traverse the stack up to a maximum of N levels. If N is -1, the whole stack is dumped. New levels are created when the dominator tree traversal used for renaming enters a new sub-tree. */ void debug_defs_stack (int n) { dump_defs_stack (stderr, n); } /* Dump the current reaching definition of every symbol to FILE. */ void dump_currdefs (FILE *file) { referenced_var_iterator i; tree var; fprintf (file, "\n\nCurrent reaching definitions\n\n"); FOR_EACH_REFERENCED_VAR (var, i) if (SYMS_TO_RENAME (cfun) == NULL || bitmap_bit_p (SYMS_TO_RENAME (cfun), DECL_UID (var))) { fprintf (file, "CURRDEF ("); print_generic_expr (file, var, 0); fprintf (file, ") = "); if (get_current_def (var)) print_generic_expr (file, get_current_def (var), 0); else fprintf (file, "<NIL>"); fprintf (file, "\n"); } } /* Dump the current reaching definition of every symbol to stderr. */ void debug_currdefs (void) { dump_currdefs (stderr); } /* Dump SSA information to FILE. */ void dump_tree_ssa (FILE *file) { const char *funcname = lang_hooks.decl_printable_name (current_function_decl, 2); fprintf (file, "SSA renaming information for %s\n\n", funcname); dump_def_blocks (file); dump_defs_stack (file, -1); dump_currdefs (file); dump_tree_ssa_stats (file); } /* Dump SSA information to stderr. */ void debug_tree_ssa (void) { dump_tree_ssa (stderr); } /* Dump statistics for the hash table HTAB. */ static void htab_statistics (FILE *file, htab_t htab) { fprintf (file, "size %ld, %ld elements, %f collision/search ratio\n", (long) htab_size (htab), (long) htab_elements (htab), htab_collisions (htab)); } /* Dump SSA statistics on FILE. */ void dump_tree_ssa_stats (FILE *file) { if (def_blocks || repl_tbl) fprintf (file, "\nHash table statistics:\n"); if (def_blocks) { fprintf (file, " def_blocks: "); htab_statistics (file, def_blocks); } if (repl_tbl) { fprintf (file, " repl_tbl: "); htab_statistics (file, repl_tbl); } if (def_blocks || repl_tbl) fprintf (file, "\n"); } /* Dump SSA statistics on stderr. */ void debug_tree_ssa_stats (void) { dump_tree_ssa_stats (stderr); } /* Hashing and equality functions for DEF_BLOCKS. */ static hashval_t def_blocks_hash (const void *p) { return htab_hash_pointer ((const void *)((const struct def_blocks_d *)p)->var); } static int def_blocks_eq (const void *p1, const void *p2) { return ((const struct def_blocks_d *)p1)->var == ((const struct def_blocks_d *)p2)->var; } /* Free memory allocated by one entry in DEF_BLOCKS. */ static void def_blocks_free (void *p) { struct def_blocks_d *entry = (struct def_blocks_d *) p; BITMAP_FREE (entry->def_blocks); BITMAP_FREE (entry->phi_blocks); BITMAP_FREE (entry->livein_blocks); free (entry); } /* Callback for htab_traverse to dump the DEF_BLOCKS hash table. */ static int debug_def_blocks_r (void **slot, void *data) { FILE *file = (FILE *) data; struct def_blocks_d *db_p = (struct def_blocks_d *) *slot; fprintf (file, "VAR: "); print_generic_expr (file, db_p->var, dump_flags); bitmap_print (file, db_p->def_blocks, ", DEF_BLOCKS: { ", "}"); bitmap_print (file, db_p->livein_blocks, ", LIVEIN_BLOCKS: { ", "}"); bitmap_print (file, db_p->phi_blocks, ", PHI_BLOCKS: { ", "}\n"); return 1; } /* Dump the DEF_BLOCKS hash table on FILE. */ void dump_def_blocks (FILE *file) { fprintf (file, "\n\nDefinition and live-in blocks:\n\n"); if (def_blocks) htab_traverse (def_blocks, debug_def_blocks_r, file); } /* Dump the DEF_BLOCKS hash table on stderr. */ void debug_def_blocks (void) { dump_def_blocks (stderr); } /* Register NEW_NAME to be the new reaching definition for OLD_NAME. */ static inline void register_new_update_single (tree new_name, tree old_name) { tree currdef = get_current_def (old_name); /* Push the current reaching definition into BLOCK_DEFS_STACK. This stack is later used by the dominator tree callbacks to restore the reaching definitions for all the variables defined in the block after a recursive visit to all its immediately dominated blocks. */ VEC_reserve (tree, heap, block_defs_stack, 2); VEC_quick_push (tree, block_defs_stack, currdef); VEC_quick_push (tree, block_defs_stack, old_name); /* Set the current reaching definition for OLD_NAME to be NEW_NAME. */ set_current_def (old_name, new_name); } /* Register NEW_NAME to be the new reaching definition for all the names in OLD_NAMES. Used by the incremental SSA update routines to replace old SSA names with new ones. */ static inline void register_new_update_set (tree new_name, bitmap old_names) { bitmap_iterator bi; unsigned i; EXECUTE_IF_SET_IN_BITMAP (old_names, 0, i, bi) register_new_update_single (new_name, ssa_name (i)); } /* If the operand pointed to by USE_P is a name in OLD_SSA_NAMES or it is a symbol marked for renaming, replace it with USE_P's current reaching definition. */ static inline void maybe_replace_use (use_operand_p use_p) { tree rdef = NULL_TREE; tree use = USE_FROM_PTR (use_p); tree sym = DECL_P (use) ? use : SSA_NAME_VAR (use); if (symbol_marked_for_renaming (sym)) rdef = get_reaching_def (sym); else if (is_old_name (use)) rdef = get_reaching_def (use); if (rdef && rdef != use) SET_USE (use_p, rdef); } /* Same as maybe_replace_use, but without introducing default stmts, returning false to indicate a need to do so. */ static inline bool maybe_replace_use_in_debug_stmt (use_operand_p use_p) { tree rdef = NULL_TREE; tree use = USE_FROM_PTR (use_p); tree sym = DECL_P (use) ? use : SSA_NAME_VAR (use); if (symbol_marked_for_renaming (sym)) rdef = get_current_def (sym); else if (is_old_name (use)) { rdef = get_current_def (use); /* We can't assume that, if there's no current definition, the default one should be used. It could be the case that we've rearranged blocks so that the earlier definition no longer dominates the use. */ if (!rdef && SSA_NAME_IS_DEFAULT_DEF (use)) rdef = use; } else rdef = use; if (rdef && rdef != use) SET_USE (use_p, rdef); return rdef != NULL_TREE; } /* If the operand pointed to by DEF_P is an SSA name in NEW_SSA_NAMES or OLD_SSA_NAMES, or if it is a symbol marked for renaming, register it as the current definition for the names replaced by DEF_P. */ static inline void maybe_register_def (def_operand_p def_p, gimple stmt, gimple_stmt_iterator gsi) { tree def = DEF_FROM_PTR (def_p); tree sym = DECL_P (def) ? def : SSA_NAME_VAR (def); /* If DEF is a naked symbol that needs renaming, create a new name for it. */ if (symbol_marked_for_renaming (sym)) { if (DECL_P (def)) { tree tracked_var; def = make_ssa_name (def, stmt); SET_DEF (def_p, def); tracked_var = target_for_debug_bind (sym); if (tracked_var) { gimple note = gimple_build_debug_bind (tracked_var, def, stmt); /* If stmt ends the bb, insert the debug stmt on the single non-EH edge from the stmt. */ if (gsi_one_before_end_p (gsi) && stmt_ends_bb_p (stmt)) { basic_block bb = gsi_bb (gsi); edge_iterator ei; edge e, ef = NULL; FOR_EACH_EDGE (e, ei, bb->succs) if (!(e->flags & EDGE_EH)) { gcc_assert (!ef); ef = e; } gcc_assert (ef && single_pred_p (ef->dest) && !phi_nodes (ef->dest) && ef->dest != EXIT_BLOCK_PTR); gsi_insert_on_edge_immediate (ef, note); } else gsi_insert_after (&gsi, note, GSI_SAME_STMT); } } register_new_update_single (def, sym); } else { /* If DEF is a new name, register it as a new definition for all the names replaced by DEF. */ if (is_new_name (def)) register_new_update_set (def, names_replaced_by (def)); /* If DEF is an old name, register DEF as a new definition for itself. */ if (is_old_name (def)) register_new_update_single (def, def); } } /* Update every variable used in the statement pointed-to by SI. The statement is assumed to be in SSA form already. Names in OLD_SSA_NAMES used by SI will be updated to their current reaching definition. Names in OLD_SSA_NAMES or NEW_SSA_NAMES defined by SI will be registered as a new definition for their corresponding name in OLD_SSA_NAMES. */ static void rewrite_update_stmt (gimple stmt, gimple_stmt_iterator gsi) { use_operand_p use_p; def_operand_p def_p; ssa_op_iter iter; /* Only update marked statements. */ if (!rewrite_uses_p (stmt) && !register_defs_p (stmt)) return; if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Updating SSA information for statement "); print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM); fprintf (dump_file, "\n"); } /* Rewrite USES included in OLD_SSA_NAMES and USES whose underlying symbol is marked for renaming. */ if (rewrite_uses_p (stmt)) { if (is_gimple_debug (stmt)) { bool failed = false; FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_USE) if (!maybe_replace_use_in_debug_stmt (use_p)) { failed = true; break; } if (failed) { /* DOM sometimes threads jumps in such a way that a debug stmt ends up referencing a SSA variable that no longer dominates the debug stmt, but such that all incoming definitions refer to the same definition in an earlier dominator. We could try to recover that definition somehow, but this will have to do for now. Introducing a default definition, which is what maybe_replace_use() would do in such cases, may modify code generation, for the otherwise-unused default definition would never go away, modifying SSA version numbers all over. */ gimple_debug_bind_reset_value (stmt); update_stmt (stmt); } } else { FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_ALL_USES) maybe_replace_use (use_p); } } /* Register definitions of names in NEW_SSA_NAMES and OLD_SSA_NAMES. Also register definitions for names whose underlying symbol is marked for renaming. */ if (register_defs_p (stmt)) FOR_EACH_SSA_DEF_OPERAND (def_p, stmt, iter, SSA_OP_ALL_DEFS) maybe_register_def (def_p, stmt, gsi); } /* Visit all the successor blocks of BB looking for PHI nodes. For every PHI node found, check if any of its arguments is in OLD_SSA_NAMES. If so, and if the argument has a current reaching definition, replace it. */ static void rewrite_update_phi_arguments (basic_block bb) { edge e; edge_iterator ei; unsigned i; FOR_EACH_EDGE (e, ei, bb->succs) { gimple phi; gimple_vec phis; if (!bitmap_bit_p (blocks_with_phis_to_rewrite, e->dest->index)) continue; phis = VEC_index (gimple_vec, phis_to_rewrite, e->dest->index); for (i = 0; VEC_iterate (gimple, phis, i, phi); i++) { tree arg, lhs_sym, reaching_def = NULL; use_operand_p arg_p; gcc_assert (rewrite_uses_p (phi)); arg_p = PHI_ARG_DEF_PTR_FROM_EDGE (phi, e); arg = USE_FROM_PTR (arg_p); if (arg && !DECL_P (arg) && TREE_CODE (arg) != SSA_NAME) continue; lhs_sym = SSA_NAME_VAR (gimple_phi_result (phi)); if (arg == NULL_TREE) { /* When updating a PHI node for a recently introduced symbol we may find NULL arguments. That's why we take the symbol from the LHS of the PHI node. */ reaching_def = get_reaching_def (lhs_sym); } else { tree sym = DECL_P (arg) ? arg : SSA_NAME_VAR (arg); if (symbol_marked_for_renaming (sym)) reaching_def = get_reaching_def (sym); else if (is_old_name (arg)) reaching_def = get_reaching_def (arg); } /* Update the argument if there is a reaching def. */ if (reaching_def) { gimple stmt; source_location locus; int arg_i = PHI_ARG_INDEX_FROM_USE (arg_p); SET_USE (arg_p, reaching_def); stmt = SSA_NAME_DEF_STMT (reaching_def); /* Single element PHI nodes behave like copies, so get the location from the phi argument. */ if (gimple_code (stmt) == GIMPLE_PHI && gimple_phi_num_args (stmt) == 1) locus = gimple_phi_arg_location (stmt, 0); else locus = gimple_location (stmt); gimple_phi_arg_set_location (phi, arg_i, locus); } if (e->flags & EDGE_ABNORMAL) SSA_NAME_OCCURS_IN_ABNORMAL_PHI (USE_FROM_PTR (arg_p)) = 1; } } } /* Initialization of block data structures for the incremental SSA update pass. Create a block local stack of reaching definitions for new SSA names produced in this block (BLOCK_DEFS). Register new definitions for every PHI node in the block. */ static void rewrite_update_enter_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED, basic_block bb) { edge e; edge_iterator ei; bool is_abnormal_phi; gimple_stmt_iterator gsi; if (dump_file && (dump_flags & TDF_DETAILS)) fprintf (dump_file, "\n\nRegistering new PHI nodes in block #%d\n\n", bb->index); /* Mark the unwind point for this block. */ VEC_safe_push (tree, heap, block_defs_stack, NULL_TREE); if (!bitmap_bit_p (blocks_to_update, bb->index)) return; /* Mark the LHS if any of the arguments flows through an abnormal edge. */ is_abnormal_phi = false; FOR_EACH_EDGE (e, ei, bb->preds) if (e->flags & EDGE_ABNORMAL) { is_abnormal_phi = true; break; } /* If any of the PHI nodes is a replacement for a name in OLD_SSA_NAMES or it's one of the names in NEW_SSA_NAMES, then register it as a new definition for its corresponding name. Also register definitions for names whose underlying symbols are marked for renaming. */ for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) { tree lhs, lhs_sym; gimple phi = gsi_stmt (gsi); if (!register_defs_p (phi)) continue; lhs = gimple_phi_result (phi); lhs_sym = SSA_NAME_VAR (lhs); if (symbol_marked_for_renaming (lhs_sym)) register_new_update_single (lhs, lhs_sym); else { /* If LHS is a new name, register a new definition for all the names replaced by LHS. */ if (is_new_name (lhs)) register_new_update_set (lhs, names_replaced_by (lhs)); /* If LHS is an OLD name, register it as a new definition for itself. */ if (is_old_name (lhs)) register_new_update_single (lhs, lhs); } if (is_abnormal_phi) SSA_NAME_OCCURS_IN_ABNORMAL_PHI (lhs) = 1; } /* Step 2. Rewrite every variable used in each statement in the block. */ if (TEST_BIT (interesting_blocks, bb->index)) { gcc_assert (bitmap_bit_p (blocks_to_update, bb->index)); for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) rewrite_update_stmt (gsi_stmt (gsi), gsi); } /* Step 3. Update PHI nodes. */ rewrite_update_phi_arguments (bb); } /* Called after visiting block BB. Unwind BLOCK_DEFS_STACK to restore the current reaching definition of every name re-written in BB to the original reaching definition before visiting BB. This unwinding must be done in the opposite order to what is done in register_new_update_set. */ static void rewrite_update_leave_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED, basic_block bb ATTRIBUTE_UNUSED) { while (VEC_length (tree, block_defs_stack) > 0) { tree var = VEC_pop (tree, block_defs_stack); tree saved_def; /* NULL indicates the unwind stop point for this block (see rewrite_update_enter_block). */ if (var == NULL) return; saved_def = VEC_pop (tree, block_defs_stack); set_current_def (var, saved_def); } } /* Rewrite the actual blocks, statements, and PHI arguments, to be in SSA form. ENTRY indicates the block where to start. Every block dominated by ENTRY will be rewritten. WHAT indicates what actions will be taken by the renamer (see enum rewrite_mode). BLOCKS are the set of interesting blocks for the dominator walker to process. If this set is NULL, then all the nodes dominated by ENTRY are walked. Otherwise, blocks dominated by ENTRY that are not present in BLOCKS are ignored. */ static void rewrite_blocks (basic_block entry, enum rewrite_mode what) { struct dom_walk_data walk_data; /* Rewrite all the basic blocks in the program. */ timevar_push (TV_TREE_SSA_REWRITE_BLOCKS); /* Setup callbacks for the generic dominator tree walker. */ memset (&walk_data, 0, sizeof (walk_data)); walk_data.dom_direction = CDI_DOMINATORS; if (what == REWRITE_ALL) { walk_data.before_dom_children = rewrite_enter_block; walk_data.after_dom_children = rewrite_leave_block; } else if (what == REWRITE_UPDATE) { walk_data.before_dom_children = rewrite_update_enter_block; walk_data.after_dom_children = rewrite_update_leave_block; } else gcc_unreachable (); block_defs_stack = VEC_alloc (tree, heap, 10); /* Initialize the dominator walker. */ init_walk_dominator_tree (&walk_data); /* Recursively walk the dominator tree rewriting each statement in each basic block. */ walk_dominator_tree (&walk_data, entry); /* Finalize the dominator walker. */ fini_walk_dominator_tree (&walk_data); /* Debugging dumps. */ if (dump_file && (dump_flags & TDF_STATS)) { dump_dfa_stats (dump_file); if (def_blocks) dump_tree_ssa_stats (dump_file); } VEC_free (tree, heap, block_defs_stack); timevar_pop (TV_TREE_SSA_REWRITE_BLOCKS); } /* Block processing routine for mark_def_sites. Clear the KILLS bitmap at the start of each block, and call mark_def_sites for each statement. */ static void mark_def_sites_block (struct dom_walk_data *walk_data, basic_block bb) { struct mark_def_sites_global_data *gd; bitmap kills; gimple_stmt_iterator gsi; gd = (struct mark_def_sites_global_data *) walk_data->global_data; kills = gd->kills; bitmap_clear (kills); for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) mark_def_sites (bb, gsi_stmt (gsi), kills); } /* Mark the definition site blocks for each variable, so that we know where the variable is actually live. The INTERESTING_BLOCKS global will be filled in with all the blocks that should be processed by the renamer. It is assumed that the caller has already initialized and zeroed it. */ static void mark_def_site_blocks (void) { struct dom_walk_data walk_data; struct mark_def_sites_global_data mark_def_sites_global_data; /* Setup callbacks for the generic dominator tree walker to find and mark definition sites. */ walk_data.dom_direction = CDI_DOMINATORS; walk_data.initialize_block_local_data = NULL; walk_data.before_dom_children = mark_def_sites_block; walk_data.after_dom_children = NULL; /* Notice that this bitmap is indexed using variable UIDs, so it must be large enough to accommodate all the variables referenced in the function, not just the ones we are renaming. */ mark_def_sites_global_data.kills = BITMAP_ALLOC (NULL); walk_data.global_data = &mark_def_sites_global_data; /* We do not have any local data. */ walk_data.block_local_data_size = 0; /* Initialize the dominator walker. */ init_walk_dominator_tree (&walk_data); /* Recursively walk the dominator tree. */ walk_dominator_tree (&walk_data, ENTRY_BLOCK_PTR); /* Finalize the dominator walker. */ fini_walk_dominator_tree (&walk_data); /* We no longer need this bitmap, clear and free it. */ BITMAP_FREE (mark_def_sites_global_data.kills); } /* Initialize internal data needed during renaming. */ static void init_ssa_renamer (void) { tree var; referenced_var_iterator rvi; cfun->gimple_df->in_ssa_p = false; /* Allocate memory for the DEF_BLOCKS hash table. */ gcc_assert (def_blocks == NULL); def_blocks = htab_create (num_referenced_vars, def_blocks_hash, def_blocks_eq, def_blocks_free); FOR_EACH_REFERENCED_VAR(var, rvi) set_current_def (var, NULL_TREE); } /* Deallocate internal data structures used by the renamer. */ static void fini_ssa_renamer (void) { if (def_blocks) { htab_delete (def_blocks); def_blocks = NULL; } cfun->gimple_df->in_ssa_p = true; } /* Main entry point into the SSA builder. The renaming process proceeds in four main phases: 1- Compute dominance frontier and immediate dominators, needed to insert PHI nodes and rename the function in dominator tree order. 2- Find and mark all the blocks that define variables (mark_def_site_blocks). 3- Insert PHI nodes at dominance frontiers (insert_phi_nodes). 4- Rename all the blocks (rewrite_blocks) and statements in the program. Steps 3 and 4 are done using the dominator tree walker (walk_dominator_tree). */ static unsigned int rewrite_into_ssa (void) { bitmap *dfs; basic_block bb; timevar_push (TV_TREE_SSA_OTHER); /* Initialize operand data structures. */ init_ssa_operands (); /* Initialize internal data needed by the renamer. */ init_ssa_renamer (); /* Initialize the set of interesting blocks. The callback mark_def_sites will add to this set those blocks that the renamer should process. */ interesting_blocks = sbitmap_alloc (last_basic_block); sbitmap_zero (interesting_blocks); /* Initialize dominance frontier. */ dfs = XNEWVEC (bitmap, last_basic_block); FOR_EACH_BB (bb) dfs[bb->index] = BITMAP_ALLOC (NULL); /* 1- Compute dominance frontiers. */ calculate_dominance_info (CDI_DOMINATORS); compute_dominance_frontiers (dfs); /* 2- Find and mark definition sites. */ mark_def_site_blocks (); /* 3- Insert PHI nodes at dominance frontiers of definition blocks. */ insert_phi_nodes (dfs); /* 4- Rename all the blocks. */ rewrite_blocks (ENTRY_BLOCK_PTR, REWRITE_ALL); /* Free allocated memory. */ FOR_EACH_BB (bb) BITMAP_FREE (dfs[bb->index]); free (dfs); sbitmap_free (interesting_blocks); fini_ssa_renamer (); timevar_pop (TV_TREE_SSA_OTHER); return 0; } struct gimple_opt_pass pass_build_ssa = { { GIMPLE_PASS, "ssa", /* name */ NULL, /* gate */ rewrite_into_ssa, /* execute */ NULL, /* sub */ NULL, /* next */ 0, /* static_pass_number */ TV_NONE, /* tv_id */ PROP_cfg | PROP_referenced_vars, /* properties_required */ PROP_ssa, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ TODO_dump_func | TODO_update_ssa_only_virtuals | TODO_verify_ssa | TODO_remove_unused_locals /* todo_flags_finish */ } }; /* Mark the definition of VAR at STMT and BB as interesting for the renamer. BLOCKS is the set of blocks that need updating. */ static void mark_def_interesting (tree var, gimple stmt, basic_block bb, bool insert_phi_p) { gcc_assert (bitmap_bit_p (blocks_to_update, bb->index)); set_register_defs (stmt, true); if (insert_phi_p) { bool is_phi_p = gimple_code (stmt) == GIMPLE_PHI; set_def_block (var, bb, is_phi_p); /* If VAR is an SSA name in NEW_SSA_NAMES, this is a definition site for both itself and all the old names replaced by it. */ if (TREE_CODE (var) == SSA_NAME && is_new_name (var)) { bitmap_iterator bi; unsigned i; bitmap set = names_replaced_by (var); if (set) EXECUTE_IF_SET_IN_BITMAP (set, 0, i, bi) set_def_block (ssa_name (i), bb, is_phi_p); } } } /* Mark the use of VAR at STMT and BB as interesting for the renamer. INSERT_PHI_P is true if we are going to insert new PHI nodes. */ static inline void mark_use_interesting (tree var, gimple stmt, basic_block bb, bool insert_phi_p) { basic_block def_bb = gimple_bb (stmt); mark_block_for_update (def_bb); mark_block_for_update (bb); if (gimple_code (stmt) == GIMPLE_PHI) mark_phi_for_rewrite (def_bb, stmt); else { set_rewrite_uses (stmt, true); if (is_gimple_debug (stmt)) return; } /* If VAR has not been defined in BB, then it is live-on-entry to BB. Note that we cannot just use the block holding VAR's definition because if VAR is one of the names in OLD_SSA_NAMES, it will have several definitions (itself and all the names that replace it). */ if (insert_phi_p) { struct def_blocks_d *db_p = get_def_blocks_for (var); if (!bitmap_bit_p (db_p->def_blocks, bb->index)) set_livein_block (var, bb); } } /* Do a dominator walk starting at BB processing statements that reference symbols in SYMS_TO_RENAME. This is very similar to mark_def_sites, but the scan handles statements whose operands may already be SSA names. If INSERT_PHI_P is true, mark those uses as live in the corresponding block. This is later used by the PHI placement algorithm to make PHI pruning decisions. FIXME. Most of this would be unnecessary if we could associate a symbol to all the SSA names that reference it. But that sounds like it would be expensive to maintain. Still, it would be interesting to see if it makes better sense to do that. */ static void prepare_block_for_update (basic_block bb, bool insert_phi_p) { basic_block son; gimple_stmt_iterator si; edge e; edge_iterator ei; mark_block_for_update (bb); /* Process PHI nodes marking interesting those that define or use the symbols that we are interested in. */ for (si = gsi_start_phis (bb); !gsi_end_p (si); gsi_next (&si)) { gimple phi = gsi_stmt (si); tree lhs_sym, lhs = gimple_phi_result (phi); lhs_sym = DECL_P (lhs) ? lhs : SSA_NAME_VAR (lhs); if (!symbol_marked_for_renaming (lhs_sym)) continue; mark_def_interesting (lhs_sym, phi, bb, insert_phi_p); /* Mark the uses in phi nodes as interesting. It would be more correct to process the arguments of the phi nodes of the successor edges of BB at the end of prepare_block_for_update, however, that turns out to be significantly more expensive. Doing it here is conservatively correct -- it may only cause us to believe a value to be live in a block that also contains its definition, and thus insert a few more phi nodes for it. */ FOR_EACH_EDGE (e, ei, bb->preds) mark_use_interesting (lhs_sym, phi, e->src, insert_phi_p); } /* Process the statements. */ for (si = gsi_start_bb (bb); !gsi_end_p (si); gsi_next (&si)) { gimple stmt; ssa_op_iter i; use_operand_p use_p; def_operand_p def_p; stmt = gsi_stmt (si); FOR_EACH_SSA_USE_OPERAND (use_p, stmt, i, SSA_OP_ALL_USES) { tree use = USE_FROM_PTR (use_p); tree sym = DECL_P (use) ? use : SSA_NAME_VAR (use); if (symbol_marked_for_renaming (sym)) mark_use_interesting (sym, stmt, bb, insert_phi_p); } FOR_EACH_SSA_DEF_OPERAND (def_p, stmt, i, SSA_OP_ALL_DEFS) { tree def = DEF_FROM_PTR (def_p); tree sym = DECL_P (def) ? def : SSA_NAME_VAR (def); if (symbol_marked_for_renaming (sym)) mark_def_interesting (sym, stmt, bb, insert_phi_p); } } /* Now visit all the blocks dominated by BB. */ for (son = first_dom_son (CDI_DOMINATORS, bb); son; son = next_dom_son (CDI_DOMINATORS, son)) prepare_block_for_update (son, insert_phi_p); } /* Helper for prepare_names_to_update. Mark all the use sites for NAME as interesting. BLOCKS and INSERT_PHI_P are as in prepare_names_to_update. */ static void prepare_use_sites_for (tree name, bool insert_phi_p) { use_operand_p use_p; imm_use_iterator iter; FOR_EACH_IMM_USE_FAST (use_p, iter, name) { gimple stmt = USE_STMT (use_p); basic_block bb = gimple_bb (stmt); if (gimple_code (stmt) == GIMPLE_PHI) { int ix = PHI_ARG_INDEX_FROM_USE (use_p); edge e = gimple_phi_arg_edge (stmt, ix); mark_use_interesting (name, stmt, e->src, insert_phi_p); } else { /* For regular statements, mark this as an interesting use for NAME. */ mark_use_interesting (name, stmt, bb, insert_phi_p); } } } /* Helper for prepare_names_to_update. Mark the definition site for NAME as interesting. BLOCKS and INSERT_PHI_P are as in prepare_names_to_update. */ static void prepare_def_site_for (tree name, bool insert_phi_p) { gimple stmt; basic_block bb; gcc_assert (names_to_release == NULL || !bitmap_bit_p (names_to_release, SSA_NAME_VERSION (name))); stmt = SSA_NAME_DEF_STMT (name); bb = gimple_bb (stmt); if (bb) { gcc_assert (bb->index < last_basic_block); mark_block_for_update (bb); mark_def_interesting (name, stmt, bb, insert_phi_p); } } /* Mark definition and use sites of names in NEW_SSA_NAMES and OLD_SSA_NAMES. INSERT_PHI_P is true if the caller wants to insert PHI nodes for newly created names. */ static void prepare_names_to_update (bool insert_phi_p) { unsigned i = 0; bitmap_iterator bi; sbitmap_iterator sbi; /* If a name N from NEW_SSA_NAMES is also marked to be released, remove it from NEW_SSA_NAMES so that we don't try to visit its defining basic block (which most likely doesn't exist). Notice that we cannot do the same with names in OLD_SSA_NAMES because we want to replace existing instances. */ if (names_to_release) EXECUTE_IF_SET_IN_BITMAP (names_to_release, 0, i, bi) RESET_BIT (new_ssa_names, i); /* First process names in NEW_SSA_NAMES. Otherwise, uses of old names may be considered to be live-in on blocks that contain definitions for their replacements. */ EXECUTE_IF_SET_IN_SBITMAP (new_ssa_names, 0, i, sbi) prepare_def_site_for (ssa_name (i), insert_phi_p); /* If an old name is in NAMES_TO_RELEASE, we cannot remove it from OLD_SSA_NAMES, but we have to ignore its definition site. */ EXECUTE_IF_SET_IN_SBITMAP (old_ssa_names, 0, i, sbi) { if (names_to_release == NULL || !bitmap_bit_p (names_to_release, i)) prepare_def_site_for (ssa_name (i), insert_phi_p); prepare_use_sites_for (ssa_name (i), insert_phi_p); } } /* Dump all the names replaced by NAME to FILE. */ void dump_names_replaced_by (FILE *file, tree name) { unsigned i; bitmap old_set; bitmap_iterator bi; print_generic_expr (file, name, 0); fprintf (file, " -> { "); old_set = names_replaced_by (name); EXECUTE_IF_SET_IN_BITMAP (old_set, 0, i, bi) { print_generic_expr (file, ssa_name (i), 0); fprintf (file, " "); } fprintf (file, "}\n"); } /* Dump all the names replaced by NAME to stderr. */ void debug_names_replaced_by (tree name) { dump_names_replaced_by (stderr, name); } /* Dump SSA update information to FILE. */ void dump_update_ssa (FILE *file) { unsigned i = 0; bitmap_iterator bi; if (!need_ssa_update_p (cfun)) return; if (new_ssa_names && sbitmap_first_set_bit (new_ssa_names) >= 0) { sbitmap_iterator sbi; fprintf (file, "\nSSA replacement table\n"); fprintf (file, "N_i -> { O_1 ... O_j } means that N_i replaces " "O_1, ..., O_j\n\n"); EXECUTE_IF_SET_IN_SBITMAP (new_ssa_names, 0, i, sbi) dump_names_replaced_by (file, ssa_name (i)); fprintf (file, "\n"); fprintf (file, "Number of virtual NEW -> OLD mappings: %7u\n", update_ssa_stats.num_virtual_mappings); fprintf (file, "Number of real NEW -> OLD mappings: %7u\n", update_ssa_stats.num_total_mappings - update_ssa_stats.num_virtual_mappings); fprintf (file, "Number of total NEW -> OLD mappings: %7u\n", update_ssa_stats.num_total_mappings); fprintf (file, "\nNumber of virtual symbols: %u\n", update_ssa_stats.num_virtual_symbols); } if (!bitmap_empty_p (SYMS_TO_RENAME (cfun))) { fprintf (file, "\n\nSymbols to be put in SSA form\n\n"); dump_decl_set (file, SYMS_TO_RENAME (cfun)); fprintf (file, "\n"); } if (names_to_release && !bitmap_empty_p (names_to_release)) { fprintf (file, "\n\nSSA names to release after updating the SSA web\n\n"); EXECUTE_IF_SET_IN_BITMAP (names_to_release, 0, i, bi) { print_generic_expr (file, ssa_name (i), 0); fprintf (file, " "); } } fprintf (file, "\n\n"); } /* Dump SSA update information to stderr. */ void debug_update_ssa (void) { dump_update_ssa (stderr); } /* Initialize data structures used for incremental SSA updates. */ static void init_update_ssa (struct function *fn) { /* Reserve more space than the current number of names. The calls to add_new_name_mapping are typically done after creating new SSA names, so we'll need to reallocate these arrays. */ old_ssa_names = sbitmap_alloc (num_ssa_names + NAME_SETS_GROWTH_FACTOR); sbitmap_zero (old_ssa_names); new_ssa_names = sbitmap_alloc (num_ssa_names + NAME_SETS_GROWTH_FACTOR); sbitmap_zero (new_ssa_names); repl_tbl = htab_create (20, repl_map_hash, repl_map_eq, repl_map_free); names_to_release = NULL; memset (&update_ssa_stats, 0, sizeof (update_ssa_stats)); update_ssa_stats.virtual_symbols = BITMAP_ALLOC (NULL); update_ssa_initialized_fn = fn; } /* Deallocate data structures used for incremental SSA updates. */ void delete_update_ssa (void) { unsigned i; bitmap_iterator bi; sbitmap_free (old_ssa_names); old_ssa_names = NULL; sbitmap_free (new_ssa_names); new_ssa_names = NULL; htab_delete (repl_tbl); repl_tbl = NULL; bitmap_clear (SYMS_TO_RENAME (update_ssa_initialized_fn)); BITMAP_FREE (update_ssa_stats.virtual_symbols); if (names_to_release) { EXECUTE_IF_SET_IN_BITMAP (names_to_release, 0, i, bi) release_ssa_name (ssa_name (i)); BITMAP_FREE (names_to_release); } clear_ssa_name_info (); fini_ssa_renamer (); if (blocks_with_phis_to_rewrite) EXECUTE_IF_SET_IN_BITMAP (blocks_with_phis_to_rewrite, 0, i, bi) { gimple_vec phis = VEC_index (gimple_vec, phis_to_rewrite, i); VEC_free (gimple, heap, phis); VEC_replace (gimple_vec, phis_to_rewrite, i, NULL); } BITMAP_FREE (blocks_with_phis_to_rewrite); BITMAP_FREE (blocks_to_update); update_ssa_initialized_fn = NULL; } /* Create a new name for OLD_NAME in statement STMT and replace the operand pointed to by DEF_P with the newly created name. Return the new name and register the replacement mapping <NEW, OLD> in update_ssa's tables. */ tree create_new_def_for (tree old_name, gimple stmt, def_operand_p def) { tree new_name = duplicate_ssa_name (old_name, stmt); SET_DEF (def, new_name); if (gimple_code (stmt) == GIMPLE_PHI) { edge e; edge_iterator ei; basic_block bb = gimple_bb (stmt); /* If needed, mark NEW_NAME as occurring in an abnormal PHI node. */ FOR_EACH_EDGE (e, ei, bb->preds) if (e->flags & EDGE_ABNORMAL) { SSA_NAME_OCCURS_IN_ABNORMAL_PHI (new_name) = 1; break; } } register_new_name_mapping (new_name, old_name); /* For the benefit of passes that will be updating the SSA form on their own, set the current reaching definition of OLD_NAME to be NEW_NAME. */ set_current_def (old_name, new_name); return new_name; } /* Register name NEW to be a replacement for name OLD. This function must be called for every replacement that should be performed by update_ssa. */ void register_new_name_mapping (tree new_tree, tree old) { if (!update_ssa_initialized_fn) init_update_ssa (cfun); gcc_assert (update_ssa_initialized_fn == cfun); add_new_name_mapping (new_tree, old); } /* Register symbol SYM to be renamed by update_ssa. */ void mark_sym_for_renaming (tree sym) { bitmap_set_bit (SYMS_TO_RENAME (cfun), DECL_UID (sym)); } /* Register all the symbols in SET to be renamed by update_ssa. */ void mark_set_for_renaming (bitmap set) { bitmap_iterator bi; unsigned i; if (set == NULL || bitmap_empty_p (set)) return; EXECUTE_IF_SET_IN_BITMAP (set, 0, i, bi) mark_sym_for_renaming (referenced_var (i)); } /* Return true if there is any work to be done by update_ssa for function FN. */ bool need_ssa_update_p (struct function *fn) { gcc_assert (fn != NULL); return (update_ssa_initialized_fn == fn || (fn->gimple_df && !bitmap_empty_p (SYMS_TO_RENAME (fn)))); } /* Return true if SSA name mappings have been registered for SSA updating. */ bool name_mappings_registered_p (void) { if (!update_ssa_initialized_fn) return false; gcc_assert (update_ssa_initialized_fn == cfun); return repl_tbl && htab_elements (repl_tbl) > 0; } /* Return true if name N has been registered in the replacement table. */ bool name_registered_for_update_p (tree n ATTRIBUTE_UNUSED) { if (!update_ssa_initialized_fn) return false; gcc_assert (update_ssa_initialized_fn == cfun); return is_new_name (n) || is_old_name (n); } /* Return the set of all the SSA names marked to be replaced. */ bitmap ssa_names_to_replace (void) { unsigned i = 0; bitmap ret; sbitmap_iterator sbi; gcc_assert (update_ssa_initialized_fn == NULL || update_ssa_initialized_fn == cfun); ret = BITMAP_ALLOC (NULL); EXECUTE_IF_SET_IN_SBITMAP (old_ssa_names, 0, i, sbi) bitmap_set_bit (ret, i); return ret; } /* Mark NAME to be released after update_ssa has finished. */ void release_ssa_name_after_update_ssa (tree name) { gcc_assert (cfun && update_ssa_initialized_fn == cfun); if (names_to_release == NULL) names_to_release = BITMAP_ALLOC (NULL); bitmap_set_bit (names_to_release, SSA_NAME_VERSION (name)); } /* Insert new PHI nodes to replace VAR. DFS contains dominance frontier information. BLOCKS is the set of blocks to be updated. This is slightly different than the regular PHI insertion algorithm. The value of UPDATE_FLAGS controls how PHI nodes for real names (i.e., GIMPLE registers) are inserted: - If UPDATE_FLAGS == TODO_update_ssa, we are only interested in PHI nodes inside the region affected by the block that defines VAR and the blocks that define all its replacements. All these definition blocks are stored in DEF_BLOCKS[VAR]->DEF_BLOCKS. First, we compute the entry point to the region (ENTRY). This is given by the nearest common dominator to all the definition blocks. When computing the iterated dominance frontier (IDF), any block not strictly dominated by ENTRY is ignored. We then call the standard PHI insertion algorithm with the pruned IDF. - If UPDATE_FLAGS == TODO_update_ssa_full_phi, the IDF for real names is not pruned. PHI nodes are inserted at every IDF block. */ static void insert_updated_phi_nodes_for (tree var, bitmap *dfs, bitmap blocks, unsigned update_flags) { basic_block entry; struct def_blocks_d *db; bitmap idf, pruned_idf; bitmap_iterator bi; unsigned i; #if defined ENABLE_CHECKING if (TREE_CODE (var) == SSA_NAME) gcc_assert (is_old_name (var)); else gcc_assert (symbol_marked_for_renaming (var)); #endif /* Get all the definition sites for VAR. */ db = find_def_blocks_for (var); /* No need to do anything if there were no definitions to VAR. */ if (db == NULL || bitmap_empty_p (db->def_blocks)) return; /* Compute the initial iterated dominance frontier. */ idf = compute_idf (db->def_blocks, dfs); pruned_idf = BITMAP_ALLOC (NULL); if (TREE_CODE (var) == SSA_NAME) { if (update_flags == TODO_update_ssa) { /* If doing regular SSA updates for GIMPLE registers, we are only interested in IDF blocks dominated by the nearest common dominator of all the definition blocks. */ entry = nearest_common_dominator_for_set (CDI_DOMINATORS, db->def_blocks); if (entry != ENTRY_BLOCK_PTR) EXECUTE_IF_SET_IN_BITMAP (idf, 0, i, bi) if (BASIC_BLOCK (i) != entry && dominated_by_p (CDI_DOMINATORS, BASIC_BLOCK (i), entry)) bitmap_set_bit (pruned_idf, i); } else { /* Otherwise, do not prune the IDF for VAR. */ gcc_assert (update_flags == TODO_update_ssa_full_phi); bitmap_copy (pruned_idf, idf); } } else { /* Otherwise, VAR is a symbol that needs to be put into SSA form for the first time, so we need to compute the full IDF for it. */ bitmap_copy (pruned_idf, idf); } if (!bitmap_empty_p (pruned_idf)) { /* Make sure that PRUNED_IDF blocks and all their feeding blocks are included in the region to be updated. The feeding blocks are important to guarantee that the PHI arguments are renamed properly. */ /* FIXME, this is not needed if we are updating symbols. We are already starting at the ENTRY block anyway. */ bitmap_ior_into (blocks, pruned_idf); EXECUTE_IF_SET_IN_BITMAP (pruned_idf, 0, i, bi) { edge e; edge_iterator ei; basic_block bb = BASIC_BLOCK (i); FOR_EACH_EDGE (e, ei, bb->preds) if (e->src->index >= 0) bitmap_set_bit (blocks, e->src->index); } insert_phi_nodes_for (var, pruned_idf, true); } BITMAP_FREE (pruned_idf); BITMAP_FREE (idf); } /* Heuristic to determine whether SSA name mappings for virtual names should be discarded and their symbols rewritten from scratch. When there is a large number of mappings for virtual names, the insertion of PHI nodes for the old names in the mappings takes considerable more time than if we inserted PHI nodes for the symbols instead. Currently the heuristic takes these stats into account: - Number of mappings for virtual SSA names. - Number of distinct virtual symbols involved in those mappings. If the number of virtual mappings is much larger than the number of virtual symbols, then it will be faster to compute PHI insertion spots for the symbols. Even if this involves traversing the whole CFG, which is what happens when symbols are renamed from scratch. */ static bool switch_virtuals_to_full_rewrite_p (void) { if (update_ssa_stats.num_virtual_mappings < (unsigned) MIN_VIRTUAL_MAPPINGS) return false; if (update_ssa_stats.num_virtual_mappings > (unsigned) VIRTUAL_MAPPINGS_TO_SYMS_RATIO * update_ssa_stats.num_virtual_symbols) return true; return false; } /* Remove every virtual mapping and mark all the affected virtual symbols for renaming. */ static void switch_virtuals_to_full_rewrite (void) { unsigned i = 0; sbitmap_iterator sbi; if (dump_file) { fprintf (dump_file, "\nEnabled virtual name mapping heuristic.\n"); fprintf (dump_file, "\tNumber of virtual mappings: %7u\n", update_ssa_stats.num_virtual_mappings); fprintf (dump_file, "\tNumber of unique virtual symbols: %7u\n", update_ssa_stats.num_virtual_symbols); fprintf (dump_file, "Updating FUD-chains from top of CFG will be " "faster than processing\nthe name mappings.\n\n"); } /* Remove all virtual names from NEW_SSA_NAMES and OLD_SSA_NAMES. Note that it is not really necessary to remove the mappings from REPL_TBL, that would only waste time. */ EXECUTE_IF_SET_IN_SBITMAP (new_ssa_names, 0, i, sbi) if (!is_gimple_reg (ssa_name (i))) RESET_BIT (new_ssa_names, i); EXECUTE_IF_SET_IN_SBITMAP (old_ssa_names, 0, i, sbi) if (!is_gimple_reg (ssa_name (i))) RESET_BIT (old_ssa_names, i); mark_set_for_renaming (update_ssa_stats.virtual_symbols); } /* Given a set of newly created SSA names (NEW_SSA_NAMES) and a set of existing SSA names (OLD_SSA_NAMES), update the SSA form so that: 1- The names in OLD_SSA_NAMES dominated by the definitions of NEW_SSA_NAMES are all re-written to be reached by the appropriate definition from NEW_SSA_NAMES. 2- If needed, new PHI nodes are added to the iterated dominance frontier of the blocks where each of NEW_SSA_NAMES are defined. The mapping between OLD_SSA_NAMES and NEW_SSA_NAMES is setup by calling register_new_name_mapping for every pair of names that the caller wants to replace. The caller identifies the new names that have been inserted and the names that need to be replaced by calling register_new_name_mapping for every pair <NEW, OLD>. Note that the function assumes that the new names have already been inserted in the IL. For instance, given the following code: 1 L0: 2 x_1 = PHI (0, x_5) 3 if (x_1 < 10) 4 if (x_1 > 7) 5 y_2 = 0 6 else 7 y_3 = x_1 + x_7 8 endif 9 x_5 = x_1 + 1 10 goto L0; 11 endif Suppose that we insert new names x_10 and x_11 (lines 4 and 8). 1 L0: 2 x_1 = PHI (0, x_5) 3 if (x_1 < 10) 4 x_10 = ... 5 if (x_1 > 7) 6 y_2 = 0 7 else 8 x_11 = ... 9 y_3 = x_1 + x_7 10 endif 11 x_5 = x_1 + 1 12 goto L0; 13 endif We want to replace all the uses of x_1 with the new definitions of x_10 and x_11. Note that the only uses that should be replaced are those at lines 5, 9 and 11. Also, the use of x_7 at line 9 should *not* be replaced (this is why we cannot just mark symbol 'x' for renaming). Additionally, we may need to insert a PHI node at line 11 because that is a merge point for x_10 and x_11. So the use of x_1 at line 11 will be replaced with the new PHI node. The insertion of PHI nodes is optional. They are not strictly necessary to preserve the SSA form, and depending on what the caller inserted, they may not even be useful for the optimizers. UPDATE_FLAGS controls various aspects of how update_ssa operates, see the documentation for TODO_update_ssa*. */ void update_ssa (unsigned update_flags) { basic_block bb, start_bb; bitmap_iterator bi; unsigned i = 0; bool insert_phi_p; sbitmap_iterator sbi; if (!need_ssa_update_p (cfun)) return; timevar_push (TV_TREE_SSA_INCREMENTAL); if (!update_ssa_initialized_fn) init_update_ssa (cfun); gcc_assert (update_ssa_initialized_fn == cfun); blocks_with_phis_to_rewrite = BITMAP_ALLOC (NULL); if (!phis_to_rewrite) phis_to_rewrite = VEC_alloc (gimple_vec, heap, last_basic_block); blocks_to_update = BITMAP_ALLOC (NULL); /* Ensure that the dominance information is up-to-date. */ calculate_dominance_info (CDI_DOMINATORS); /* Only one update flag should be set. */ gcc_assert (update_flags == TODO_update_ssa || update_flags == TODO_update_ssa_no_phi || update_flags == TODO_update_ssa_full_phi || update_flags == TODO_update_ssa_only_virtuals); /* If we only need to update virtuals, remove all the mappings for real names before proceeding. The caller is responsible for having dealt with the name mappings before calling update_ssa. */ if (update_flags == TODO_update_ssa_only_virtuals) { sbitmap_zero (old_ssa_names); sbitmap_zero (new_ssa_names); htab_empty (repl_tbl); } insert_phi_p = (update_flags != TODO_update_ssa_no_phi); if (insert_phi_p) { /* If the caller requested PHI nodes to be added, initialize live-in information data structures (DEF_BLOCKS). */ /* For each SSA name N, the DEF_BLOCKS table describes where the name is defined, which blocks have PHI nodes for N, and which blocks have uses of N (i.e., N is live-on-entry in those blocks). */ def_blocks = htab_create (num_ssa_names, def_blocks_hash, def_blocks_eq, def_blocks_free); } else { def_blocks = NULL; } /* Heuristic to avoid massive slow downs when the replacement mappings include lots of virtual names. */ if (insert_phi_p && switch_virtuals_to_full_rewrite_p ()) switch_virtuals_to_full_rewrite (); /* If there are names defined in the replacement table, prepare definition and use sites for all the names in NEW_SSA_NAMES and OLD_SSA_NAMES. */ if (sbitmap_first_set_bit (new_ssa_names) >= 0) { prepare_names_to_update (insert_phi_p); /* If all the names in NEW_SSA_NAMES had been marked for removal, and there are no symbols to rename, then there's nothing else to do. */ if (sbitmap_first_set_bit (new_ssa_names) < 0 && bitmap_empty_p (SYMS_TO_RENAME (cfun))) goto done; } /* Next, determine the block at which to start the renaming process. */ if (!bitmap_empty_p (SYMS_TO_RENAME (cfun))) { /* If we have to rename some symbols from scratch, we need to start the process at the root of the CFG. FIXME, it should be possible to determine the nearest block that had a definition for each of the symbols that are marked for updating. For now this seems more work than it's worth. */ start_bb = ENTRY_BLOCK_PTR; /* Traverse the CFG looking for existing definitions and uses of symbols in SYMS_TO_RENAME. Mark interesting blocks and statements and set local live-in information for the PHI placement heuristics. */ prepare_block_for_update (start_bb, insert_phi_p); } else { /* Otherwise, the entry block to the region is the nearest common dominator for the blocks in BLOCKS. */ start_bb = nearest_common_dominator_for_set (CDI_DOMINATORS, blocks_to_update); } /* If requested, insert PHI nodes at the iterated dominance frontier of every block, creating new definitions for names in OLD_SSA_NAMES and for symbols in SYMS_TO_RENAME. */ if (insert_phi_p) { bitmap *dfs; /* If the caller requested PHI nodes to be added, compute dominance frontiers. */ dfs = XNEWVEC (bitmap, last_basic_block); FOR_EACH_BB (bb) dfs[bb->index] = BITMAP_ALLOC (NULL); compute_dominance_frontiers (dfs); if (sbitmap_first_set_bit (old_ssa_names) >= 0) { sbitmap_iterator sbi; /* insert_update_phi_nodes_for will call add_new_name_mapping when inserting new PHI nodes, so the set OLD_SSA_NAMES will grow while we are traversing it (but it will not gain any new members). Copy OLD_SSA_NAMES to a temporary for traversal. */ sbitmap tmp = sbitmap_alloc (old_ssa_names->n_bits); sbitmap_copy (tmp, old_ssa_names); EXECUTE_IF_SET_IN_SBITMAP (tmp, 0, i, sbi) insert_updated_phi_nodes_for (ssa_name (i), dfs, blocks_to_update, update_flags); sbitmap_free (tmp); } EXECUTE_IF_SET_IN_BITMAP (SYMS_TO_RENAME (cfun), 0, i, bi) insert_updated_phi_nodes_for (referenced_var (i), dfs, blocks_to_update, update_flags); FOR_EACH_BB (bb) BITMAP_FREE (dfs[bb->index]); free (dfs); /* Insertion of PHI nodes may have added blocks to the region. We need to re-compute START_BB to include the newly added blocks. */ if (start_bb != ENTRY_BLOCK_PTR) start_bb = nearest_common_dominator_for_set (CDI_DOMINATORS, blocks_to_update); } /* Reset the current definition for name and symbol before renaming the sub-graph. */ EXECUTE_IF_SET_IN_SBITMAP (old_ssa_names, 0, i, sbi) set_current_def (ssa_name (i), NULL_TREE); EXECUTE_IF_SET_IN_BITMAP (SYMS_TO_RENAME (cfun), 0, i, bi) set_current_def (referenced_var (i), NULL_TREE); /* Now start the renaming process at START_BB. */ interesting_blocks = sbitmap_alloc (last_basic_block); sbitmap_zero (interesting_blocks); EXECUTE_IF_SET_IN_BITMAP (blocks_to_update, 0, i, bi) SET_BIT (interesting_blocks, i); rewrite_blocks (start_bb, REWRITE_UPDATE); sbitmap_free (interesting_blocks); /* Debugging dumps. */ if (dump_file) { int c; unsigned i; dump_update_ssa (dump_file); fprintf (dump_file, "Incremental SSA update started at block: %d\n\n", start_bb->index); c = 0; EXECUTE_IF_SET_IN_BITMAP (blocks_to_update, 0, i, bi) c++; fprintf (dump_file, "Number of blocks in CFG: %d\n", last_basic_block); fprintf (dump_file, "Number of blocks to update: %d (%3.0f%%)\n\n", c, PERCENT (c, last_basic_block)); if (dump_flags & TDF_DETAILS) { fprintf (dump_file, "Affected blocks: "); EXECUTE_IF_SET_IN_BITMAP (blocks_to_update, 0, i, bi) fprintf (dump_file, "%u ", i); fprintf (dump_file, "\n"); } fprintf (dump_file, "\n\n"); } /* Free allocated memory. */ done: delete_update_ssa (); timevar_pop (TV_TREE_SSA_INCREMENTAL); }