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author | Ben Cheng <bccheng@google.com> | 2014-03-25 22:37:19 -0700 |
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committer | Ben Cheng <bccheng@google.com> | 2014-03-25 22:37:19 -0700 |
commit | 1bc5aee63eb72b341f506ad058502cd0361f0d10 (patch) | |
tree | c607e8252f3405424ff15bc2d00aa38dadbb2518 /gcc-4.9/gcc/tree-ssa-uncprop.c | |
parent | 283a0bf58fcf333c58a2a92c3ebbc41fb9eb1fdb (diff) | |
download | toolchain_gcc-1bc5aee63eb72b341f506ad058502cd0361f0d10.tar.gz toolchain_gcc-1bc5aee63eb72b341f506ad058502cd0361f0d10.tar.bz2 toolchain_gcc-1bc5aee63eb72b341f506ad058502cd0361f0d10.zip |
Initial checkin of GCC 4.9.0 from trunk (r208799).
Change-Id: I48a3c08bb98542aa215912a75f03c0890e497dba
Diffstat (limited to 'gcc-4.9/gcc/tree-ssa-uncprop.c')
-rw-r--r-- | gcc-4.9/gcc/tree-ssa-uncprop.c | 627 |
1 files changed, 627 insertions, 0 deletions
diff --git a/gcc-4.9/gcc/tree-ssa-uncprop.c b/gcc-4.9/gcc/tree-ssa-uncprop.c new file mode 100644 index 000000000..a43dd1a84 --- /dev/null +++ b/gcc-4.9/gcc/tree-ssa-uncprop.c @@ -0,0 +1,627 @@ +/* Routines for discovering and unpropagating edge equivalences. + Copyright (C) 2005-2014 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 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 "stor-layout.h" +#include "flags.h" +#include "tm_p.h" +#include "basic-block.h" +#include "function.h" +#include "hash-table.h" +#include "tree-ssa-alias.h" +#include "internal-fn.h" +#include "gimple-expr.h" +#include "is-a.h" +#include "gimple.h" +#include "gimple-iterator.h" +#include "gimple-ssa.h" +#include "tree-cfg.h" +#include "tree-phinodes.h" +#include "ssa-iterators.h" +#include "domwalk.h" +#include "tree-pass.h" +#include "tree-ssa-propagate.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_FN (bb, cfun) + { + gimple_stmt_iterator gsi = gsi_last_bb (bb); + gimple stmt; + + /* If the block does not end with a COND_EXPR or SWITCH_EXPR + then there is nothing to do. */ + if (gsi_end_p (gsi)) + continue; + + stmt = gsi_stmt (gsi); + + if (!stmt) + continue; + + /* A COND_EXPR may create an equivalency in a variety of different + ways. */ + if (gimple_code (stmt) == GIMPLE_COND) + { + edge true_edge; + edge false_edge; + struct edge_equivalency *equivalency; + enum tree_code code = gimple_cond_code (stmt); + + extract_true_false_edges_from_block (bb, &true_edge, &false_edge); + + /* Equality tests may create one or two equivalences. */ + if (code == EQ_EXPR || code == NE_EXPR) + { + tree op0 = gimple_cond_lhs (stmt); + tree op1 = gimple_cond_rhs (stmt); + + /* 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 + && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op0) + && TREE_CODE (TREE_TYPE (op0)) == BOOLEAN_TYPE + && is_gimple_min_invariant (op1)) + { + if (code == EQ_EXPR) + { + equivalency = XNEW (struct edge_equivalency); + equivalency->lhs = op0; + equivalency->rhs = (integer_zerop (op1) + ? boolean_false_node + : boolean_true_node); + true_edge->aux = equivalency; + + equivalency = XNEW (struct edge_equivalency); + equivalency->lhs = op0; + equivalency->rhs = (integer_zerop (op1) + ? boolean_true_node + : boolean_false_node); + false_edge->aux = equivalency; + } + else + { + equivalency = XNEW (struct edge_equivalency); + equivalency->lhs = op0; + equivalency->rhs = (integer_zerop (op1) + ? boolean_true_node + : boolean_false_node); + true_edge->aux = equivalency; + + equivalency = XNEW (struct edge_equivalency); + equivalency->lhs = op0; + equivalency->rhs = (integer_zerop (op1) + ? boolean_false_node + : boolean_true_node); + false_edge->aux = equivalency; + } + } + + else if (TREE_CODE (op0) == SSA_NAME + && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op0) + && (is_gimple_min_invariant (op1) + || (TREE_CODE (op1) == SSA_NAME + && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op1)))) + { + /* 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 = XNEW (struct edge_equivalency); + equivalency->lhs = op0; + equivalency->rhs = op1; + if (code == 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. */ + else if (gimple_code (stmt) == GIMPLE_SWITCH) + { + tree cond = gimple_switch_index (stmt); + + if (TREE_CODE (cond) == SSA_NAME + && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (cond)) + { + int i, n_labels = gimple_switch_num_labels (stmt); + tree *info = XCNEWVEC (tree, last_basic_block_for_fn (cfun)); + + /* 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 = gimple_switch_label (stmt, 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_for_fn (cfun); 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 = XNEW (struct edge_equivalency); + equivalency->rhs = x; + equivalency->lhs = cond; + find_edge (bb, BASIC_BLOCK_FOR_FN (cfun, 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 optimizers 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. */ + + +/* 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. */ + vec<tree> equivalences; +}; + +/* Value to ssa name equivalence hashtable helpers. */ + +struct val_ssa_equiv_hasher +{ + typedef equiv_hash_elt value_type; + typedef equiv_hash_elt compare_type; + static inline hashval_t hash (const value_type *); + static inline bool equal (const value_type *, const compare_type *); + static inline void remove (value_type *); +}; + +inline hashval_t +val_ssa_equiv_hasher::hash (const value_type *p) +{ + tree const value = p->value; + return iterative_hash_expr (value, 0); +} + +inline bool +val_ssa_equiv_hasher::equal (const value_type *p1, const compare_type *p2) +{ + tree value1 = p1->value; + tree value2 = p2->value; + + return operand_equal_p (value1, value2, 0); +} + +/* Free an instance of equiv_hash_elt. */ + +inline void +val_ssa_equiv_hasher::remove (value_type *elt) +{ + elt->equivalences.release (); + free (elt); +} + +/* 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 hash_table <val_ssa_equiv_hasher> val_ssa_equiv; + +static void uncprop_into_successor_phis (basic_block); + +/* Remove the most recently recorded equivalency for VALUE. */ + +static void +remove_equivalence (tree value) +{ + struct equiv_hash_elt an_equiv_elt, *an_equiv_elt_p; + equiv_hash_elt **slot; + + an_equiv_elt.value = value; + an_equiv_elt.equivalences.create (0); + + slot = val_ssa_equiv.find_slot (&an_equiv_elt, NO_INSERT); + + an_equiv_elt_p = *slot; + an_equiv_elt_p->equivalences.pop (); +} + +/* Record EQUIVALENCE = VALUE into our hash table. */ + +static void +record_equiv (tree value, tree equivalence) +{ + equiv_hash_elt *an_equiv_elt_p; + equiv_hash_elt **slot; + + an_equiv_elt_p = XNEW (struct equiv_hash_elt); + an_equiv_elt_p->value = value; + an_equiv_elt_p->equivalences.create (0); + + slot = val_ssa_equiv.find_slot (an_equiv_elt_p, INSERT); + + if (*slot == NULL) + *slot = an_equiv_elt_p; + else + free (an_equiv_elt_p); + + an_equiv_elt_p = *slot; + + an_equiv_elt_p->equivalences.safe_push (equivalence); +} + +class uncprop_dom_walker : public dom_walker +{ +public: + uncprop_dom_walker (cdi_direction direction) : dom_walker (direction) {} + + virtual void before_dom_children (basic_block); + virtual void after_dom_children (basic_block); + +private: + + /* 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. */ + auto_vec<tree, 2> m_equiv_stack; +}; + +/* Main driver for un-cprop. */ + +static unsigned int +tree_ssa_uncprop (void) +{ + basic_block bb; + + associate_equivalences_with_edges (); + + /* Create our global data structures. */ + val_ssa_equiv.create (1024); + + /* We're going to do a dominator walk, so ensure that we have + dominance information. */ + calculate_dominance_info (CDI_DOMINATORS); + + /* Recursively walk the dominator tree undoing unprofitable + constant/copy propagations. */ + uncprop_dom_walker (CDI_DOMINATORS).walk (cfun->cfg->x_entry_block_ptr); + + /* we just need to empty elements out of the hash table, and cleanup the + AUX field on the edges. */ + val_ssa_equiv.dispose (); + FOR_EACH_BB_FN (bb, cfun) + { + edge e; + edge_iterator ei; + + FOR_EACH_EDGE (e, ei, bb->succs) + { + if (e->aux) + { + free (e->aux); + e->aux = NULL; + } + } + } + return 0; +} + + +/* We have finished processing the dominator children of BB, perform + any finalization actions in preparation for leaving this node in + the dominator tree. */ + +void +uncprop_dom_walker::after_dom_children (basic_block bb ATTRIBUTE_UNUSED) +{ + /* Pop the topmost value off the equiv stack. */ + tree value = m_equiv_stack.pop (); + + /* 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 (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) + { + gimple_seq phis = phi_nodes (e->dest); + gimple_stmt_iterator gsi; + + /* If there are no PHI nodes in this destination, then there is + no sense in recording any equivalences. */ + if (gimple_seq_empty_p (phis)) + continue; + + /* Record any equivalency associated with E. */ + if (e->aux) + { + struct edge_equivalency *equiv = (struct edge_equivalency *) e->aux; + record_equiv (equiv->rhs, equiv->lhs); + } + + /* Walk over the PHI nodes, unpropagating values. */ + for (gsi = gsi_start (phis) ; !gsi_end_p (gsi); gsi_next (&gsi)) + { + gimple phi = gsi_stmt (gsi); + tree arg = PHI_ARG_DEF (phi, e->dest_idx); + tree res = PHI_RESULT (phi); + equiv_hash_elt an_equiv_elt; + equiv_hash_elt **slot; + + /* If the argument is not an invariant and can be potentially + coalesced with the result, then there's no point in + un-propagating the argument. */ + if (!is_gimple_min_invariant (arg) + && gimple_can_coalesce_p (arg, res)) + continue; + + /* Lookup this argument's value in the hash table. */ + an_equiv_elt.value = arg; + an_equiv_elt.equivalences.create (0); + slot = val_ssa_equiv.find_slot (&an_equiv_elt, NO_INSERT); + + if (slot) + { + struct equiv_hash_elt *elt = *slot; + int j; + + /* Walk every equivalence with the same value. If we find + one that can potentially coalesce with the PHI rsult, + then replace the value in the argument with its equivalent + SSA_NAME. Use the most recent equivalence as hopefully + that results in shortest lifetimes. */ + for (j = elt->equivalences.length () - 1; j >= 0; j--) + { + tree equiv = elt->equivalences[j]; + + if (gimple_can_coalesce_p (equiv, res)) + { + 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 = (struct edge_equivalency *) 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; +} + +void +uncprop_dom_walker::before_dom_children (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 = (struct edge_equivalency *) e->aux; + + record_equiv (equiv->rhs, equiv->lhs); + m_equiv_stack.safe_push (equiv->rhs); + recorded = true; + } + } + + if (!recorded) + m_equiv_stack.safe_push (NULL_TREE); + + uncprop_into_successor_phis (bb); +} + +static bool +gate_uncprop (void) +{ + return flag_tree_dom != 0; +} + +namespace { + +const pass_data pass_data_uncprop = +{ + GIMPLE_PASS, /* type */ + "uncprop", /* name */ + OPTGROUP_NONE, /* optinfo_flags */ + true, /* has_gate */ + true, /* has_execute */ + TV_TREE_SSA_UNCPROP, /* tv_id */ + ( PROP_cfg | PROP_ssa ), /* properties_required */ + 0, /* properties_provided */ + 0, /* properties_destroyed */ + 0, /* todo_flags_start */ + TODO_verify_ssa, /* todo_flags_finish */ +}; + +class pass_uncprop : public gimple_opt_pass +{ +public: + pass_uncprop (gcc::context *ctxt) + : gimple_opt_pass (pass_data_uncprop, ctxt) + {} + + /* opt_pass methods: */ + opt_pass * clone () { return new pass_uncprop (m_ctxt); } + bool gate () { return gate_uncprop (); } + unsigned int execute () { return tree_ssa_uncprop (); } + +}; // class pass_uncprop + +} // anon namespace + +gimple_opt_pass * +make_pass_uncprop (gcc::context *ctxt) +{ + return new pass_uncprop (ctxt); +} |