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Diffstat (limited to 'gcc/tree-ssa-copyrename.c')
| -rw-r--r-- | gcc/tree-ssa-copyrename.c | 388 |
1 files changed, 388 insertions, 0 deletions
diff --git a/gcc/tree-ssa-copyrename.c b/gcc/tree-ssa-copyrename.c new file mode 100644 index 00000000000..91c0f74ac55 --- /dev/null +++ b/gcc/tree-ssa-copyrename.c @@ -0,0 +1,388 @@ +/* Rename SSA copies. + Copyright (C) 2004 Free Software Foundation, Inc. + Contributed by Andrew MacLeod <amacleod@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 2, 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 COPYING. If not, write to +the Free Software Foundation, 59 Temple Place - Suite 330, +Boston, MA 02111-1307, USA. */ + +#include "config.h" +#include "system.h" +#include "coretypes.h" +#include "tm.h" +#include "tree.h" +#include "flags.h" +#include "basic-block.h" +#include "function.h" +#include "diagnostic.h" +#include "bitmap.h" +#include "tree-flow.h" +#include "tree-simple.h" +#include "tree-inline.h" +#include "timevar.h" +#include "tree-alias-common.h" +#include "hashtab.h" +#include "tree-dump.h" +#include "tree-ssa-live.h" +#include "tree-pass.h" + +extern void rename_ssa_copies (void); + +/* The following routines implement the SSA copy renaming phase. + + This optimization looks for copies between 2 SSA_NAMES, either through a + direct copy, or an implicit one via a PHI node result and its arguments. + + Each copy is examined to determine if it is possible to rename the base + variable of one of the operands to the same variable as the other operand. + ie. + T.3_5 = <blah> + a_1 = T.3_5 + + If this copy couldn't be copy propagated, it could possibly remain in the + program throughout the optimization phases. After SSA->normal, it would + become: + + T.3 = <blah> + a = T.3 + + Since T.3_5 is distinct from all other SSA versions of T.3, there is no + fundamental reason why the base variable needs to be T.3, subject to + certain restrictions. This optimization attempts to determine if we can + change the base variable on copies like this, and result in code such as: + + a_5 = <blah> + a_1 = a_5 + + This gives the SSA->normal pass a shot at coalescing a_1 and a_5. If it is + possible, the copy goes away completely. If it isn't possible, a new temp + will be created for a_5, and you will end up with the exact same code: + + a.8 = <blah> + a = a.8 + + The other benefit of performing this optimization relates to what variables + are chosen in copies. Gimplification of the program uses temporaries for + a lot of things. expressions like + + a_1 = <blah> + <blah2> = a_1 + + get turned into + + T.3_5 = <blah> + a_1 = T.3_5 + <blah2> = a_1 + + Copy propagation is done in a forward direction, and if we can propagate + through the copy, we end up with: + + T.3_5 = <blah> + <blah2> = T.3_5 + + The copy is gone, but so is all reference to the user variable 'a'. By + performing this optimization, we would see the sequence: + + a_5 = <blah> + a_1 = a_5 + <blah2> = a_1 + + which copy propagation would then turn into: + + a_5 = <blah> + <blah2> = a_5 + + and so we still retain the user variable whenever possible. */ + + +/* Coalesce the partitions in MAP representing VAR1 and VAR2 if it is valid. + Choose a representative for the partition, and send debug info to DEBUG. */ + +static void +copy_rename_partition_coalesce (var_map map, tree var1, tree var2, FILE *debug) +{ + int p1, p2, p3; + tree root1, root2; + var_ann_t ann1, ann2, ann3; + bool gimp1, gimp2; + +#ifdef ENABLE_CHECKING + if (TREE_CODE (var1) != SSA_NAME || TREE_CODE (var2) != SSA_NAME) + abort (); +#endif + + register_ssa_partition (map, var1, false); + register_ssa_partition (map, var2, true); + + p1 = partition_find (map->var_partition, SSA_NAME_VERSION (var1)); + p2 = partition_find (map->var_partition, SSA_NAME_VERSION (var2)); + + if (debug) + { + fprintf (debug, "Try : "); + print_generic_expr (debug, var1, TDF_SLIM); + fprintf (debug, "(P%d) & ", p1); + print_generic_expr (debug, var2, TDF_SLIM); + fprintf (debug, "(P%d)", p2); + } + +#ifdef ENABLE_CHECKING + if (p1 == NO_PARTITION || p2 == NO_PARTITION) + abort (); +#endif + + root1 = SSA_NAME_VAR (partition_to_var (map, p1)); + root2 = SSA_NAME_VAR (partition_to_var (map, p2)); + + if (DECL_HARD_REGISTER (root1) || DECL_HARD_REGISTER (root2)) + { + if (debug) + { + if (DECL_HARD_REGISTER (root1)) + print_generic_expr (debug, var1, TDF_SLIM); + else + print_generic_expr (debug, var2, TDF_SLIM); + fprintf (debug, " is a hardware register. No Coalescing.\n"); + } + return; + } + + ann1 = var_ann (root1); + ann2 = var_ann (root2); + + if (p1 == p2) + { + if (debug) + fprintf (debug, " : Already coalesced.\n"); + return; + } + + /* Partitions already have the same root, simply merge them. */ + if (root1 == root2) + { + p1 = partition_union (map->var_partition, p1, p2); + if (debug) + fprintf (debug, " : Same root, coalesced --> P%d.\n", p1); + return; + } + + /* Never attempt to coalesce 2 difference parameters. */ + if (TREE_CODE (root1) == PARM_DECL && TREE_CODE (root2) == PARM_DECL) + { + if (debug) + fprintf (debug, " : 2 different PARM_DECLS. No coalesce.\n"); + return; + } + + gimp1 = is_gimple_tmp_var (root1); + gimp2 = is_gimple_tmp_var (root2); + + /* Never attempt to coalesce 2 user variables unless one is an inline + variable. */ + if (!gimp1 && !gimp2) + { + if (DECL_FROM_INLINE (root2)) + gimp2 = true; + else + if (DECL_FROM_INLINE (root1)) + gimp1 = true; + else + { + if (debug) + fprintf (debug, " : 2 different USER vars. No coalesce.\n"); + return; + } + } + + + /* Don't coalesce if there are two different memory tags. */ + if (ann1->type_mem_tag && ann2->type_mem_tag + && ann1->type_mem_tag != ann2->type_mem_tag) + { + if (debug) + fprintf (debug, " : 2 memory tags. No coalesce.\n"); + return; + } + + /* If both values have default defs, we can't coalesce. If only one has a + tag, make sure that variable is the new root partition. */ + if (default_def (root1)) + { + if (default_def (root2)) + { + if (debug) + fprintf (debug, " : 2 default defs. No coalesce.\n"); + return; + } + else + { + gimp2 = true; + gimp1 = false; + } + } + else + if (default_def (root2)) + { + gimp1 = true; + gimp2 = false; + } + + /* Merge the two partitions. */ + p3 = partition_union (map->var_partition, p1, p2); + + /* Set the root variable of the partition to the better choice, if there is + one. */ + if (!gimp2) + SSA_NAME_VAR (partition_to_var (map, p3)) = root2; + else + if (!gimp1) + SSA_NAME_VAR (partition_to_var (map, p3)) = root1; + + /* Update the various flag widgitry of the current base representative. */ + ann3 = var_ann (SSA_NAME_VAR (partition_to_var (map, p3))); + if (ann1->type_mem_tag) + ann3->type_mem_tag = ann1->type_mem_tag; + else + ann3->type_mem_tag = ann2->type_mem_tag; + + if (debug) + { + fprintf (debug, " --> P%d ", p3); + print_generic_expr (debug, SSA_NAME_VAR (partition_to_var (map, p3)), + TDF_SLIM); + fprintf (debug, "\n"); + } +} + + +/* This function will make a pass through the IL, and attempt to coalesce any + SSA versions which occur in PHI's or copies. Coalescing is accomplished by + changing the underlying root variable of all coalesced version. This will + then cause the SSA->normal pass to attempt to coalesce them all to the same + variable. */ + +void +rename_ssa_copies (void) +{ + var_map map; + basic_block bb; + block_stmt_iterator bsi; + tree phi, stmt, var, part_var; + unsigned x; + FILE *debug; + + if (dump_file && (dump_flags & TDF_DETAILS)) + debug = dump_file; + else + debug = NULL; + + map = init_var_map (highest_ssa_version + 1); + + FOR_EACH_BB (bb) + { + /* Scan for real copies. */ + for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi)) + { + stmt = bsi_stmt (bsi); + if (TREE_CODE (stmt) == MODIFY_EXPR) + { + tree lhs = TREE_OPERAND (stmt, 0); + tree rhs = TREE_OPERAND (stmt, 1); + + if (TREE_CODE (lhs) == SSA_NAME + && !has_hidden_use (SSA_NAME_VAR (lhs)) + && TREE_CODE (rhs) == SSA_NAME) + copy_rename_partition_coalesce (map, lhs, rhs, debug); + } + } + } + + FOR_EACH_BB (bb) + { + /* Treat PHI nodes as copies between the result and each argument. */ + for (phi = phi_nodes (bb); phi; phi = TREE_CHAIN (phi)) + { + int i; + tree res = PHI_RESULT (phi); + + /* Do not process virtual SSA_NAMES or variables which have + hidden uses. */ + if (!is_gimple_reg (SSA_NAME_VAR (res)) + || has_hidden_use (SSA_NAME_VAR (res))) + continue; + + for (i = 0; i < PHI_NUM_ARGS (phi); i++) + { + tree arg = PHI_ARG_DEF (phi, i); + if (TREE_CODE (arg) == SSA_NAME) + copy_rename_partition_coalesce (map, res, arg, debug); + } + } + } + + if (debug) + dump_var_map (debug, map); + + /* Now one more pass to make all elements of a partition share the same + root variable. */ + + for (x = 1; x <= highest_ssa_version; x++) + { + part_var = partition_to_var (map, x); + if (!part_var) + continue; + var = map->partition_to_var[x]; + if (debug) + { + if (SSA_NAME_VAR (var) != SSA_NAME_VAR (part_var)) + { + fprintf (debug, "Coalesced "); + print_generic_expr (debug, var, TDF_SLIM); + fprintf (debug, " to "); + print_generic_expr (debug, part_var, TDF_SLIM); + fprintf (debug, "\n"); + } + } + SSA_NAME_VAR (var) = SSA_NAME_VAR (part_var); + } + + delete_var_map (map); +} + +/* Return true if copy rename is to be performed. */ + +static bool +gate_copyrename (void) +{ + return flag_tree_copyrename != 0; +} + +struct tree_opt_pass pass_rename_ssa_copies = +{ + "copyrename", /* name */ + gate_copyrename, /* gate */ + rename_ssa_copies, /* execute */ + NULL, /* sub */ + NULL, /* next */ + 0, /* static_pass_number */ + TV_TREE_COPY_RENAME, /* tv_id */ + PROP_cfg | PROP_ssa, /* properties_required */ + 0, /* properties_provided */ + 0, /* properties_destroyed */ + 0, /* todo_flags_start */ + TODO_dump_func | TODO_verify_ssa /* todo_flags_finish */ +}; + |