diff options
author | law <law@138bc75d-0d04-0410-961f-82ee72b054a4> | 2005-04-13 04:29:40 +0000 |
---|---|---|
committer | law <law@138bc75d-0d04-0410-961f-82ee72b054a4> | 2005-04-13 04:29:40 +0000 |
commit | 5f718c29c69b083f07d3d234c7e79502c2d1547b (patch) | |
tree | 6045fae43be21a314688da828dfd1010938a5ab4 /gcc/tree-ssa-uncprop.c | |
parent | 3bcf2cd545426aea123eaec3aab7417b569a6cc3 (diff) | |
download | gcc-5f718c29c69b083f07d3d234c7e79502c2d1547b.tar.gz |
* Makefile.in (OBJS-common): Add tree-ssa-uncprop.o.
(tree-ssa-uncprop.o): Add dependencies.
* tree-cfg.c (remove_useless_stmts_bb, remove_useless_stmts): Remove.
* tree-flow.h (remove_useless_stmts): Remove prototype.
* tree-outof-ssa.c (rewrite_out_of_ssa): Remove call to
remove_useless_stmts.
* timevar.def (TV_TREE_SSA_UNCPROP): New timevar.
* tree-optimize.c (init_tree_optimization_passes): Add uncprop pass.
* tree-pass.h (pass_uncprop): Declare.
* tree-ssa-uncprop.c: New file.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@98066 138bc75d-0d04-0410-961f-82ee72b054a4
Diffstat (limited to 'gcc/tree-ssa-uncprop.c')
-rw-r--r-- | gcc/tree-ssa-uncprop.c | 614 |
1 files changed, 614 insertions, 0 deletions
diff --git a/gcc/tree-ssa-uncprop.c b/gcc/tree-ssa-uncprop.c new file mode 100644 index 00000000000..4400ee78003 --- /dev/null +++ b/gcc/tree-ssa-uncprop.c @@ -0,0 +1,614 @@ +/* Routines for discovering and unpropagating edge equivalences. + Copyright (C) 2005 Free Software Foundation, Inc. + +This file is part of GCC. + +GCC is free software; you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation; either version 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 "rtl.h" +#include "tm_p.h" +#include "ggc.h" +#include "basic-block.h" +#include "output.h" +#include "errors.h" +#include "expr.h" +#include "function.h" +#include "diagnostic.h" +#include "timevar.h" +#include "tree-dump.h" +#include "tree-flow.h" +#include "domwalk.h" +#include "real.h" +#include "tree-pass.h" +#include "tree-ssa-propagate.h" +#include "langhooks.h" + +/* The basic structure describing an equivalency created by traversing + an edge. Traversing the edge effectively means that we can assume + that we've seen an assignment LHS = RHS. */ +struct edge_equivalency +{ + tree rhs; + tree lhs; +}; + +/* This routine finds and records edge equivalences for every edge + in the CFG. + + When complete, each edge that creates an equivalency will have an + EDGE_EQUIVALENCY structure hanging off the edge's AUX field. + The caller is responsible for freeing the AUX fields. */ + +static void +associate_equivalences_with_edges (void) +{ + basic_block bb; + + /* Walk over each block. If the block ends with a control statement, + then it might create a useful equivalence. */ + FOR_EACH_BB (bb) + { + block_stmt_iterator bsi = bsi_last (bb); + tree stmt; + + /* If the block does not end with a COND_EXPR or SWITCH_EXPR + then there is nothing to do. */ + if (bsi_end_p (bsi)) + continue; + + stmt = bsi_stmt (bsi); + + if (!stmt) + continue; + + /* A COND_EXPR may create an equivalency in a variety of different + ways. */ + if (TREE_CODE (stmt) == COND_EXPR) + { + tree cond = COND_EXPR_COND (stmt); + edge true_edge; + edge false_edge; + struct edge_equivalency *equivalency; + + extract_true_false_edges_from_block (bb, &true_edge, &false_edge); + + /* If the conditional is a single variable 'X', record 'X = 1' + for the true edge and 'X = 0' on the false edge. */ + if (TREE_CODE (cond) == SSA_NAME) + { + equivalency = xmalloc (sizeof (struct edge_equivalency)); + equivalency->rhs = constant_boolean_node (1, TREE_TYPE (cond)); + equivalency->lhs = cond; + true_edge->aux = equivalency; + + equivalency = xmalloc (sizeof (struct edge_equivalency)); + equivalency->rhs = constant_boolean_node (0, TREE_TYPE (cond)); + equivalency->lhs = cond; + false_edge->aux = equivalency; + } + /* Equality tests may create one or two equivalences. */ + else if (TREE_CODE (cond) == EQ_EXPR || TREE_CODE (cond) == NE_EXPR) + { + tree op0 = TREE_OPERAND (cond, 0); + tree op1 = TREE_OPERAND (cond, 1); + + /* Special case comparing booleans against a constant as we + know the value of OP0 on both arms of the branch. i.e., we + can record an equivalence for OP0 rather than COND. */ + if (TREE_CODE (op0) == SSA_NAME + && TREE_CODE (TREE_TYPE (op0)) == BOOLEAN_TYPE + && is_gimple_min_invariant (op1)) + { + if (TREE_CODE (cond) == EQ_EXPR) + { + equivalency = xmalloc (sizeof (struct edge_equivalency)); + equivalency->lhs = op0; + equivalency->rhs = (integer_zerop (op1) + ? boolean_false_node + : boolean_true_node); + true_edge->aux = equivalency; + + equivalency = xmalloc (sizeof (struct edge_equivalency)); + equivalency->lhs = op0; + equivalency->rhs = (integer_zerop (op1) + ? boolean_true_node + : boolean_false_node); + false_edge->aux = equivalency; + } + else + { + equivalency = xmalloc (sizeof (struct edge_equivalency)); + equivalency->lhs = op0; + equivalency->rhs = (integer_zerop (op1) + ? boolean_true_node + : boolean_false_node); + true_edge->aux = equivalency; + + equivalency = xmalloc (sizeof (struct edge_equivalency)); + equivalency->lhs = op0; + equivalency->rhs = (integer_zerop (op1) + ? boolean_false_node + : boolean_true_node); + false_edge->aux = equivalency; + } + } + + if (TREE_CODE (op0) == SSA_NAME + && (is_gimple_min_invariant (op1) + || TREE_CODE (op1) == SSA_NAME)) + { + /* For IEEE, -0.0 == 0.0, so we don't necessarily know + the sign of a variable compared against zero. If + we're honoring signed zeros, then we cannot record + this value unless we know that the value is nonzero. */ + if (HONOR_SIGNED_ZEROS (TYPE_MODE (TREE_TYPE (op0))) + && (TREE_CODE (op1) != REAL_CST + || REAL_VALUES_EQUAL (dconst0, TREE_REAL_CST (op1)))) + continue; + + equivalency = xmalloc (sizeof (struct edge_equivalency)); + equivalency->lhs = op0; + equivalency->rhs = op1; + if (TREE_CODE (cond) == EQ_EXPR) + true_edge->aux = equivalency; + else + false_edge->aux = equivalency; + + } + } + + /* ??? TRUTH_NOT_EXPR can create an equivalence too. */ + } + + /* For a SWITCH_EXPR, a case label which represents a single + value and which is the only case label which reaches the + target block creates an equivalence. */ + if (TREE_CODE (stmt) == SWITCH_EXPR) + { + tree cond = SWITCH_COND (stmt); + + if (TREE_CODE (cond) == SSA_NAME) + { + tree labels = SWITCH_LABELS (stmt); + int i, n_labels = TREE_VEC_LENGTH (labels); + tree *info = xcalloc (n_basic_blocks, sizeof (tree)); + + /* Walk over the case label vector. Record blocks + which are reached by a single case label which represents + a single value. */ + for (i = 0; i < n_labels; i++) + { + tree label = TREE_VEC_ELT (labels, i); + basic_block bb = label_to_block (CASE_LABEL (label)); + + + if (CASE_HIGH (label) + || !CASE_LOW (label) + || info[bb->index]) + info[bb->index] = error_mark_node; + else + info[bb->index] = label; + } + + /* Now walk over the blocks to determine which ones were + marked as being reached by a useful case label. */ + for (i = 0; i < n_basic_blocks; i++) + { + tree node = info[i]; + + if (node != NULL + && node != error_mark_node) + { + tree x = fold_convert (TREE_TYPE (cond), CASE_LOW (node)); + struct edge_equivalency *equivalency; + + /* Record an equivalency on the edge from BB to basic + block I. */ + equivalency = xmalloc (sizeof (struct edge_equivalency)); + equivalency->rhs = x; + equivalency->lhs = cond; + find_edge (bb, BASIC_BLOCK (i))->aux = equivalency; + } + } + free (info); + } + } + + } +} + + +/* Translating out of SSA sometimes requires inserting copies and + constant initializations on edges to eliminate PHI nodes. + + In some cases those copies and constant initializations are + redundant because the target already has the value on the + RHS of the assignment. + + We previously tried to catch these cases after translating + out of SSA form. However, that code often missed cases. Worse + yet, the cases it missed were also often missed by the RTL + optimizers. Thus the resulting code had redundant instructions. + + This pass attempts to detect these situations before translating + out of SSA form. + + The key concept that this pass is built upon is that these + redundant copies and constant initializations often occur + due to constant/copy propagating equivalences resulting from + COND_EXPRs and SWITCH_EXPRs. + + We want to do those propagations as they can sometimes allow + the SSA optimziers to do a better job. However, in the cases + where such propagations do not result in further optimization, + we would like to "undo" the propagation to avoid the redundant + copies and constant initializations. + + This pass works by first associating equivalences with edges in + the CFG. For example, the edge leading from a SWITCH_EXPR to + its associated CASE_LABEL will have an equivalency between + SWITCH_COND and the value in the case label. + + Once we have found the edge equivalences, we proceed to walk + the CFG in dominator order. As we traverse edges we record + equivalences associated with those edges we traverse. + + When we encounter a PHI node, we walk its arguments to see if we + have an equivalence for the PHI argument. If so, then we replace + the argument. + + Equivalences are looked up based on their value (think of it as + the RHS of an assignment). A value may be an SSA_NAME or an + invariant. We may have several SSA_NAMEs with the same value, + so with each value we have a list of SSA_NAMEs that have the + same value. */ + +/* As we enter each block we record the value for any edge equivalency + leading to this block. If no such edge equivalency exists, then we + record NULL. These equivalences are live until we leave the dominator + subtree rooted at the block where we record the equivalency. */ +static varray_type equiv_stack; + +/* Global hash table implementing a mapping from invariant values + to a list of SSA_NAMEs which have the same value. We might be + able to reuse tree-vn for this code. */ +static htab_t equiv; + +/* Main structure for recording equivalences into our hash table. */ +struct equiv_hash_elt +{ + /* The value/key of this entry. */ + tree value; + + /* List of SSA_NAMEs which have the same value/key. */ + varray_type equivalences; +}; + +static void uncprop_initialize_block (struct dom_walk_data *, basic_block); +static void uncprop_finalize_block (struct dom_walk_data *, basic_block); +static void uncprop_into_successor_phis (struct dom_walk_data *, basic_block); + +/* Hashing and equality routines for the hash table. */ + +static hashval_t +equiv_hash (const void *p) +{ + tree value = ((struct equiv_hash_elt *)p)->value; + return iterative_hash_expr (value, 0); +} + +static int +equiv_eq (const void *p1, const void *p2) +{ + tree value1 = ((struct equiv_hash_elt *)p1)->value; + tree value2 = ((struct equiv_hash_elt *)p2)->value; + + return operand_equal_p (value1, value2, 0); +} + +/* Remove the most recently recorded equivalency for VALUE. */ + +static void +remove_equivalence (tree value) +{ + struct equiv_hash_elt equiv_hash_elt, *equiv_hash_elt_p; + void **slot; + + equiv_hash_elt.value = value; + equiv_hash_elt.equivalences = NULL; + + slot = htab_find_slot (equiv, &equiv_hash_elt, NO_INSERT); + + equiv_hash_elt_p = (struct equiv_hash_elt *) *slot; + VARRAY_POP (equiv_hash_elt_p->equivalences); +} + +/* Record EQUIVALENCE = VALUE into our hash table. */ + +static void +record_equiv (tree value, tree equivalence) +{ + struct equiv_hash_elt *equiv_hash_elt; + void **slot; + + equiv_hash_elt = xmalloc (sizeof (struct equiv_hash_elt)); + equiv_hash_elt->value = value; + equiv_hash_elt->equivalences = NULL; + + slot = htab_find_slot (equiv, equiv_hash_elt, INSERT); + + if (*slot == NULL) + *slot = (void *) equiv_hash_elt; + else + free (equiv_hash_elt); + + equiv_hash_elt = (struct equiv_hash_elt *) *slot; + + if (!equiv_hash_elt->equivalences) + VARRAY_TREE_INIT (equiv_hash_elt->equivalences, 10, "value equivs"); + VARRAY_PUSH_TREE (equiv_hash_elt->equivalences, equivalence); +} + +/* Main driver for un-cprop. */ + +static void +tree_ssa_uncprop (void) +{ + struct dom_walk_data walk_data; + basic_block bb; + + associate_equivalences_with_edges (); + + /* Create our global data structures. */ + equiv = htab_create (1024, equiv_hash, equiv_eq, free); + VARRAY_TREE_INIT (equiv_stack, 2, "Block equiv stack"); + + /* We're going to do a dominator walk, so ensure that we have + dominance information. */ + calculate_dominance_info (CDI_DOMINATORS); + + /* Setup callbacks for the generic dominator tree walker. */ + walk_data.walk_stmts_backward = false; + walk_data.dom_direction = CDI_DOMINATORS; + walk_data.initialize_block_local_data = NULL; + walk_data.before_dom_children_before_stmts = uncprop_initialize_block; + walk_data.before_dom_children_walk_stmts = NULL; + walk_data.before_dom_children_after_stmts = uncprop_into_successor_phis; + walk_data.after_dom_children_before_stmts = NULL; + walk_data.after_dom_children_walk_stmts = NULL; + walk_data.after_dom_children_after_stmts = uncprop_finalize_block; + walk_data.global_data = NULL; + walk_data.block_local_data_size = 0; + walk_data.interesting_blocks = NULL; + + /* Now initialize the dominator walker. */ + init_walk_dominator_tree (&walk_data); + + /* Recursively walk the dominator tree undoing unprofitable + constant/copy propagations. */ + walk_dominator_tree (&walk_data, ENTRY_BLOCK_PTR); + + /* Finalize and clean up. */ + fini_walk_dominator_tree (&walk_data); + + /* EQUIV_STACK should already be empty at this point, so we just need + to empty elements out of the hash table and cleanup the AUX field + on the edges. */ + htab_delete (equiv); + FOR_EACH_BB (bb) + { + edge e; + edge_iterator ei; + + FOR_EACH_EDGE (e, ei, bb->succs) + { + if (e->aux) + { + free (e->aux); + e->aux = NULL; + } + } + } + +} + + +/* We have finished processing the dominator children of BB, perform + any finalization actions in preparation for leaving this node in + the dominator tree. */ + +static void +uncprop_finalize_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED, + basic_block bb ATTRIBUTE_UNUSED) +{ + tree value = VARRAY_TOP_TREE (equiv_stack); + + /* Pop the topmost value off the equiv stack. */ + VARRAY_POP (equiv_stack); + + /* If that value was non-null, then pop the topmost equivalency off + its equivalency stack. */ + if (value != NULL) + remove_equivalence (value); +} + +/* Unpropagate values from PHI nodes in successor blocks of BB. */ + +static void +uncprop_into_successor_phis (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED, + basic_block bb) +{ + edge e; + edge_iterator ei; + + /* For each successor edge, first temporarily record any equivalence + on that edge. Then unpropagate values in any PHI nodes at the + destination of the edge. Then remove the temporary equivalence. */ + FOR_EACH_EDGE (e, ei, bb->succs) + { + tree phi = phi_nodes (e->dest); + + /* If there are no PHI nodes in this destination, then there is + no sense in recording any equivalences. */ + if (!phi) + continue; + + /* Record any equivalency associated with E. */ + if (e->aux) + { + struct edge_equivalency *equiv = e->aux; + record_equiv (equiv->rhs, equiv->lhs); + } + + /* Walk over the PHI nodes, unpropagating values. */ + for ( ; phi; phi = PHI_CHAIN (phi)) + { + /* Sigh. We'll have more efficient access to this one day. */ + tree arg = PHI_ARG_DEF (phi, e->dest_idx); + struct equiv_hash_elt equiv_hash_elt; + void **slot; + + /* If the argument is not an invariant, or refers to the same + underlying variable as the PHI result, then there's no + point in un-propagating the argument. */ + if (!is_gimple_min_invariant (arg) + && SSA_NAME_VAR (arg) != SSA_NAME_VAR (PHI_RESULT (phi))) + continue; + + /* Lookup this argument's value in the hash table. */ + equiv_hash_elt.value = arg; + equiv_hash_elt.equivalences = NULL; + slot = htab_find_slot (equiv, &equiv_hash_elt, NO_INSERT); + + if (slot) + { + struct equiv_hash_elt *elt = *slot; + int j; + + /* Walk every equivalence with the same value. If we find + one with the same underlying variable as the PHI result, + then replace the value in the argument with its equivalent + SSA_NAME. Use the most recent equivlance as hopefully + that results in shortest lifetimes. */ + for (j = VARRAY_ACTIVE_SIZE (elt->equivalences) - 1; j >= 0; j--) + { + tree equiv = VARRAY_TREE (elt->equivalences, j); + + if (SSA_NAME_VAR (equiv) == SSA_NAME_VAR (PHI_RESULT (phi))) + { + SET_PHI_ARG_DEF (phi, e->dest_idx, equiv); + break; + } + } + } + } + + /* If we had an equivalence associated with this edge, remove it. */ + if (e->aux) + { + struct edge_equivalency *equiv = e->aux; + remove_equivalence (equiv->rhs); + } + } +} + +/* Ignoring loop backedges, if BB has precisely one incoming edge then + return that edge. Otherwise return NULL. */ +static edge +single_incoming_edge_ignoring_loop_edges (basic_block bb) +{ + edge retval = NULL; + edge e; + edge_iterator ei; + + FOR_EACH_EDGE (e, ei, bb->preds) + { + /* A loop back edge can be identified by the destination of + the edge dominating the source of the edge. */ + if (dominated_by_p (CDI_DOMINATORS, e->src, e->dest)) + continue; + + /* If we have already seen a non-loop edge, then we must have + multiple incoming non-loop edges and thus we return NULL. */ + if (retval) + return NULL; + + /* This is the first non-loop incoming edge we have found. Record + it. */ + retval = e; + } + + return retval; +} + +static void +uncprop_initialize_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED, + basic_block bb) +{ + basic_block parent; + edge e; + bool recorded = false; + + /* If this block is dominated by a single incoming edge and that edge + has an equivalency, then record the equivalency and push the + VALUE onto EQUIV_STACK. Else push a NULL entry on EQUIV_STACK. */ + parent = get_immediate_dominator (CDI_DOMINATORS, bb); + if (parent) + { + e = single_incoming_edge_ignoring_loop_edges (bb); + + if (e && e->src == parent && e->aux) + { + struct edge_equivalency *equiv = e->aux; + + record_equiv (equiv->rhs, equiv->lhs); + VARRAY_PUSH_TREE (equiv_stack, equiv->rhs); + recorded = true; + } + } + + if (!recorded) + VARRAY_PUSH_TREE (equiv_stack, NULL_TREE); +} + +static bool +gate_uncprop (void) +{ + return flag_tree_dom != 0; +} + +struct tree_opt_pass pass_uncprop = +{ + "uncprop", /* name */ + gate_uncprop, /* gate */ + tree_ssa_uncprop, /* execute */ + NULL, /* sub */ + NULL, /* next */ + 0, /* static_pass_number */ + TV_TREE_SSA_UNCPROP, /* 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 */ + 0 /* letter */ +}; |