/* Dead code elimination pass for the GNU compiler.
- Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007
+ Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011
Free Software Foundation, Inc.
Contributed by Ben Elliston <bje@redhat.com>
and Andrew MacLeod <amacleod@redhat.com>
Adapted to use control dependence by Steven Bosscher, SUSE Labs.
-
+
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 "system.h"
#include "coretypes.h"
#include "tm.h"
-#include "ggc.h"
-
-/* These RTL headers are needed for basic-block.h. */
-#include "rtl.h"
-#include "tm_p.h"
-#include "hard-reg-set.h"
-#include "obstack.h"
-#include "basic-block.h"
#include "tree.h"
-#include "diagnostic.h"
+#include "tree-pretty-print.h"
+#include "gimple-pretty-print.h"
+#include "basic-block.h"
#include "tree-flow.h"
-#include "tree-gimple.h"
+#include "gimple.h"
#include "tree-dump.h"
#include "tree-pass.h"
#include "timevar.h"
#include "flags.h"
#include "cfgloop.h"
#include "tree-scalar-evolution.h"
-\f
+
static struct stmt_stats
{
int total;
int removed_phis;
} stats;
-static VEC(tree,heap) *worklist;
+#define STMT_NECESSARY GF_PLF_1
+
+static VEC(gimple,heap) *worklist;
/* Vector indicating an SSA name has already been processed and marked
as necessary. */
static sbitmap processed;
-/* Vector indicating that last_stmt if a basic block has already been
- marked as necessary. */
+/* Vector indicating that the last statement of a basic block has already
+ been marked as necessary. */
static sbitmap last_stmt_necessary;
+/* Vector indicating that BB contains statements that are live. */
+static sbitmap bb_contains_live_stmts;
+
/* Before we can determine whether a control branch is dead, we need to
compute which blocks are control dependent on which edges.
find_control_dependence (el, i);
}
-
-#define NECESSARY(stmt) stmt->base.asm_written_flag
-
/* If STMT is not already marked necessary, mark it, and add it to the
worklist if ADD_TO_WORKLIST is true. */
+
static inline void
-mark_stmt_necessary (tree stmt, bool add_to_worklist)
+mark_stmt_necessary (gimple stmt, bool add_to_worklist)
{
gcc_assert (stmt);
- gcc_assert (!DECL_P (stmt));
- if (NECESSARY (stmt))
+ if (gimple_plf (stmt, STMT_NECESSARY))
return;
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "Marking useful stmt: ");
- print_generic_stmt (dump_file, stmt, TDF_SLIM);
+ print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
fprintf (dump_file, "\n");
}
- NECESSARY (stmt) = 1;
+ gimple_set_plf (stmt, STMT_NECESSARY, true);
if (add_to_worklist)
- VEC_safe_push (tree, heap, worklist, stmt);
+ VEC_safe_push (gimple, heap, worklist, stmt);
+ if (bb_contains_live_stmts && !is_gimple_debug (stmt))
+ SET_BIT (bb_contains_live_stmts, gimple_bb (stmt)->index);
}
static inline void
mark_operand_necessary (tree op)
{
- tree stmt;
+ gimple stmt;
int ver;
gcc_assert (op);
ver = SSA_NAME_VERSION (op);
if (TEST_BIT (processed, ver))
- return;
+ {
+ stmt = SSA_NAME_DEF_STMT (op);
+ gcc_assert (gimple_nop_p (stmt)
+ || gimple_plf (stmt, STMT_NECESSARY));
+ return;
+ }
SET_BIT (processed, ver);
stmt = SSA_NAME_DEF_STMT (op);
gcc_assert (stmt);
- if (NECESSARY (stmt) || IS_EMPTY_STMT (stmt))
+ if (gimple_plf (stmt, STMT_NECESSARY) || gimple_nop_p (stmt))
return;
- NECESSARY (stmt) = 1;
- VEC_safe_push (tree, heap, worklist, stmt);
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "marking necessary through ");
+ print_generic_expr (dump_file, op, 0);
+ fprintf (dump_file, " stmt ");
+ print_gimple_stmt (dump_file, stmt, 0, 0);
+ }
+
+ gimple_set_plf (stmt, STMT_NECESSARY, true);
+ if (bb_contains_live_stmts)
+ SET_BIT (bb_contains_live_stmts, gimple_bb (stmt)->index);
+ VEC_safe_push (gimple, heap, worklist, stmt);
}
necessary. */
static void
-mark_stmt_if_obviously_necessary (tree stmt, bool aggressive)
+mark_stmt_if_obviously_necessary (gimple stmt, bool aggressive)
{
- stmt_ann_t ann;
- tree op;
-
/* With non-call exceptions, we have to assume that all statements could
throw. If a statement may throw, it is inherently necessary. */
- if (flag_non_call_exceptions
- && tree_could_throw_p (stmt))
+ if (cfun->can_throw_non_call_exceptions && stmt_could_throw_p (stmt))
{
mark_stmt_necessary (stmt, true);
return;
}
- /* Statements that are implicitly live. Most function calls, asm and return
- statements are required. Labels and BIND_EXPR nodes are kept because
- they are control flow, and we have no way of knowing whether they can be
- removed. DCE can eliminate all the other statements in a block, and CFG
- can then remove the block and labels. */
- switch (TREE_CODE (stmt))
+ /* Statements that are implicitly live. Most function calls, asm
+ and return statements are required. Labels and GIMPLE_BIND nodes
+ are kept because they are control flow, and we have no way of
+ knowing whether they can be removed. DCE can eliminate all the
+ other statements in a block, and CFG can then remove the block
+ and labels. */
+ switch (gimple_code (stmt))
{
- case PREDICT_EXPR:
- case LABEL_EXPR:
- case CASE_LABEL_EXPR:
+ case GIMPLE_PREDICT:
+ case GIMPLE_LABEL:
mark_stmt_necessary (stmt, false);
return;
- case ASM_EXPR:
- case RESX_EXPR:
- case RETURN_EXPR:
- case CHANGE_DYNAMIC_TYPE_EXPR:
+ case GIMPLE_ASM:
+ case GIMPLE_RESX:
+ case GIMPLE_RETURN:
mark_stmt_necessary (stmt, true);
return;
- case CALL_EXPR:
- /* Most, but not all function calls are required. Function calls that
- produce no result and have no side effects (i.e. const pure
- functions) are unnecessary. */
- if (TREE_SIDE_EFFECTS (stmt))
- mark_stmt_necessary (stmt, true);
- return;
-
- case GIMPLE_MODIFY_STMT:
- op = get_call_expr_in (stmt);
- if (op && TREE_SIDE_EFFECTS (op))
- {
- mark_stmt_necessary (stmt, true);
- return;
- }
+ case GIMPLE_CALL:
+ {
+ tree callee = gimple_call_fndecl (stmt);
+ if (callee != NULL_TREE
+ && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL)
+ switch (DECL_FUNCTION_CODE (callee))
+ {
+ case BUILT_IN_MALLOC:
+ case BUILT_IN_CALLOC:
+ case BUILT_IN_ALLOCA:
+ case BUILT_IN_ALLOCA_WITH_ALIGN:
+ return;
- /* These values are mildly magic bits of the EH runtime. We can't
- see the entire lifetime of these values until landing pads are
- generated. */
- if (TREE_CODE (GIMPLE_STMT_OPERAND (stmt, 0)) == EXC_PTR_EXPR
- || TREE_CODE (GIMPLE_STMT_OPERAND (stmt, 0)) == FILTER_EXPR)
- {
- mark_stmt_necessary (stmt, true);
+ default:;
+ }
+ /* Most, but not all function calls are required. Function calls that
+ produce no result and have no side effects (i.e. const pure
+ functions) are unnecessary. */
+ if (gimple_has_side_effects (stmt))
+ {
+ mark_stmt_necessary (stmt, true);
+ return;
+ }
+ if (!gimple_call_lhs (stmt))
return;
- }
- break;
+ break;
+ }
+
+ case GIMPLE_DEBUG:
+ /* Debug temps without a value are not useful. ??? If we could
+ easily locate the debug temp bind stmt for a use thereof,
+ would could refrain from marking all debug temps here, and
+ mark them only if they're used. */
+ if (!gimple_debug_bind_p (stmt)
+ || gimple_debug_bind_has_value_p (stmt)
+ || TREE_CODE (gimple_debug_bind_get_var (stmt)) != DEBUG_EXPR_DECL)
+ mark_stmt_necessary (stmt, false);
+ return;
- case GOTO_EXPR:
+ case GIMPLE_GOTO:
gcc_assert (!simple_goto_p (stmt));
mark_stmt_necessary (stmt, true);
return;
- case COND_EXPR:
- gcc_assert (EDGE_COUNT (bb_for_stmt (stmt)->succs) == 2);
+ case GIMPLE_COND:
+ gcc_assert (EDGE_COUNT (gimple_bb (stmt)->succs) == 2);
/* Fall through. */
- case SWITCH_EXPR:
+ case GIMPLE_SWITCH:
if (! aggressive)
mark_stmt_necessary (stmt, true);
break;
+ case GIMPLE_ASSIGN:
+ if (TREE_CODE (gimple_assign_lhs (stmt)) == SSA_NAME
+ && TREE_CLOBBER_P (gimple_assign_rhs1 (stmt)))
+ return;
+ break;
+
default:
break;
}
- ann = stmt_ann (stmt);
-
/* If the statement has volatile operands, it needs to be preserved.
Same for statements that can alter control flow in unpredictable
ways. */
- if (ann->has_volatile_ops || is_ctrl_altering_stmt (stmt))
+ if (gimple_has_volatile_ops (stmt) || is_ctrl_altering_stmt (stmt))
{
mark_stmt_necessary (stmt, true);
return;
}
-/* Make corresponding control dependent edges necessary. We only
- have to do this once for each basic block, so we clear the bitmap
- after we're done. */
+/* Mark the last statement of BB as necessary. */
+
static void
-mark_control_dependent_edges_necessary (basic_block bb, struct edge_list *el)
+mark_last_stmt_necessary (basic_block bb)
+{
+ gimple stmt = last_stmt (bb);
+
+ SET_BIT (last_stmt_necessary, bb->index);
+ SET_BIT (bb_contains_live_stmts, bb->index);
+
+ /* We actually mark the statement only if it is a control statement. */
+ if (stmt && is_ctrl_stmt (stmt))
+ mark_stmt_necessary (stmt, true);
+}
+
+
+/* Mark control dependent edges of BB as necessary. We have to do this only
+ once for each basic block so we set the appropriate bit after we're done.
+
+ When IGNORE_SELF is true, ignore BB in the list of control dependences. */
+
+static void
+mark_control_dependent_edges_necessary (basic_block bb, struct edge_list *el,
+ bool ignore_self)
{
bitmap_iterator bi;
unsigned edge_number;
+ bool skipped = false;
gcc_assert (bb != EXIT_BLOCK_PTR);
EXECUTE_IF_CONTROL_DEPENDENT (bi, bb->index, edge_number)
{
- tree t;
basic_block cd_bb = INDEX_EDGE_PRED_BB (el, edge_number);
- if (TEST_BIT (last_stmt_necessary, cd_bb->index))
- continue;
- SET_BIT (last_stmt_necessary, cd_bb->index);
+ if (ignore_self && cd_bb == bb)
+ {
+ skipped = true;
+ continue;
+ }
- t = last_stmt (cd_bb);
- if (t && is_ctrl_stmt (t))
- mark_stmt_necessary (t, true);
+ if (!TEST_BIT (last_stmt_necessary, cd_bb->index))
+ mark_last_stmt_necessary (cd_bb);
}
+
+ if (!skipped)
+ SET_BIT (visited_control_parents, bb->index);
}
find_obviously_necessary_stmts (struct edge_list *el)
{
basic_block bb;
- block_stmt_iterator i;
+ gimple_stmt_iterator gsi;
edge e;
+ gimple phi, stmt;
+ int flags;
FOR_EACH_BB (bb)
{
- tree phi;
-
/* PHI nodes are never inherently necessary. */
- for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
- NECESSARY (phi) = 0;
+ for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+ {
+ phi = gsi_stmt (gsi);
+ gimple_set_plf (phi, STMT_NECESSARY, false);
+ }
/* Check all statements in the block. */
- for (i = bsi_start (bb); ! bsi_end_p (i); bsi_next (&i))
+ for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
{
- tree stmt = bsi_stmt (i);
- NECESSARY (stmt) = 0;
+ stmt = gsi_stmt (gsi);
+ gimple_set_plf (stmt, STMT_NECESSARY, false);
mark_stmt_if_obviously_necessary (stmt, el != NULL);
}
}
+ /* Pure and const functions are finite and thus have no infinite loops in
+ them. */
+ flags = flags_from_decl_or_type (current_function_decl);
+ if ((flags & (ECF_CONST|ECF_PURE)) && !(flags & ECF_LOOPING_CONST_OR_PURE))
+ return;
+
+ /* Prevent the empty possibly infinite loops from being removed. */
if (el)
{
- /* Prevent the loops from being removed. We must keep the infinite loops,
- and we currently do not have a means to recognize the finite ones. */
- FOR_EACH_BB (bb)
+ loop_iterator li;
+ struct loop *loop;
+ scev_initialize ();
+ if (mark_irreducible_loops ())
+ FOR_EACH_BB (bb)
+ {
+ edge_iterator ei;
+ FOR_EACH_EDGE (e, ei, bb->succs)
+ if ((e->flags & EDGE_DFS_BACK)
+ && (e->flags & EDGE_IRREDUCIBLE_LOOP))
+ {
+ if (dump_file)
+ fprintf (dump_file, "Marking back edge of irreducible loop %i->%i\n",
+ e->src->index, e->dest->index);
+ mark_control_dependent_edges_necessary (e->dest, el, false);
+ }
+ }
+
+ FOR_EACH_LOOP (li, loop, 0)
+ if (!finite_loop_p (loop))
+ {
+ if (dump_file)
+ fprintf (dump_file, "can not prove finiteness of loop %i\n", loop->num);
+ mark_control_dependent_edges_necessary (loop->latch, el, false);
+ }
+ scev_finalize ();
+ }
+}
+
+
+/* Return true if REF is based on an aliased base, otherwise false. */
+
+static bool
+ref_may_be_aliased (tree ref)
+{
+ gcc_assert (TREE_CODE (ref) != WITH_SIZE_EXPR);
+ while (handled_component_p (ref))
+ ref = TREE_OPERAND (ref, 0);
+ if (TREE_CODE (ref) == MEM_REF
+ && TREE_CODE (TREE_OPERAND (ref, 0)) == ADDR_EXPR)
+ ref = TREE_OPERAND (TREE_OPERAND (ref, 0), 0);
+ return !(DECL_P (ref)
+ && !may_be_aliased (ref));
+}
+
+static bitmap visited = NULL;
+static unsigned int longest_chain = 0;
+static unsigned int total_chain = 0;
+static unsigned int nr_walks = 0;
+static bool chain_ovfl = false;
+
+/* Worker for the walker that marks reaching definitions of REF,
+ which is based on a non-aliased decl, necessary. It returns
+ true whenever the defining statement of the current VDEF is
+ a kill for REF, as no dominating may-defs are necessary for REF
+ anymore. DATA points to the basic-block that contains the
+ stmt that refers to REF. */
+
+static bool
+mark_aliased_reaching_defs_necessary_1 (ao_ref *ref, tree vdef, void *data)
+{
+ gimple def_stmt = SSA_NAME_DEF_STMT (vdef);
+
+ /* All stmts we visit are necessary. */
+ mark_operand_necessary (vdef);
+
+ /* If the stmt lhs kills ref, then we can stop walking. */
+ if (gimple_has_lhs (def_stmt)
+ && TREE_CODE (gimple_get_lhs (def_stmt)) != SSA_NAME
+ /* The assignment is not necessarily carried out if it can throw
+ and we can catch it in the current function where we could inspect
+ the previous value.
+ ??? We only need to care about the RHS throwing. For aggregate
+ assignments or similar calls and non-call exceptions the LHS
+ might throw as well. */
+ && !stmt_can_throw_internal (def_stmt))
+ {
+ tree base, lhs = gimple_get_lhs (def_stmt);
+ HOST_WIDE_INT size, offset, max_size;
+ ao_ref_base (ref);
+ base = get_ref_base_and_extent (lhs, &offset, &size, &max_size);
+ /* We can get MEM[symbol: sZ, index: D.8862_1] here,
+ so base == refd->base does not always hold. */
+ if (base == ref->base)
{
- edge_iterator ei;
- FOR_EACH_EDGE (e, ei, bb->succs)
- if (e->flags & EDGE_DFS_BACK)
- mark_control_dependent_edges_necessary (e->dest, el);
+ /* For a must-alias check we need to be able to constrain
+ the accesses properly. */
+ if (size != -1 && size == max_size
+ && ref->max_size != -1)
+ {
+ if (offset <= ref->offset
+ && offset + size >= ref->offset + ref->max_size)
+ return true;
+ }
+ /* Or they need to be exactly the same. */
+ else if (ref->ref
+ /* Make sure there is no induction variable involved
+ in the references (gcc.c-torture/execute/pr42142.c).
+ The simplest way is to check if the kill dominates
+ the use. */
+ /* But when both are in the same block we cannot
+ easily tell whether we came from a backedge
+ unless we decide to compute stmt UIDs
+ (see PR58246). */
+ && (basic_block) data != gimple_bb (def_stmt)
+ && dominated_by_p (CDI_DOMINATORS, (basic_block) data,
+ gimple_bb (def_stmt))
+ && operand_equal_p (ref->ref, lhs, 0))
+ return true;
}
}
+
+ /* Otherwise keep walking. */
+ return false;
}
+static void
+mark_aliased_reaching_defs_necessary (gimple stmt, tree ref)
+{
+ unsigned int chain;
+ ao_ref refd;
+ gcc_assert (!chain_ovfl);
+ ao_ref_init (&refd, ref);
+ chain = walk_aliased_vdefs (&refd, gimple_vuse (stmt),
+ mark_aliased_reaching_defs_necessary_1,
+ gimple_bb (stmt), NULL);
+ if (chain > longest_chain)
+ longest_chain = chain;
+ total_chain += chain;
+ nr_walks++;
+}
+
+/* Worker for the walker that marks reaching definitions of REF, which
+ is not based on a non-aliased decl. For simplicity we need to end
+ up marking all may-defs necessary that are not based on a non-aliased
+ decl. The only job of this walker is to skip may-defs based on
+ a non-aliased decl. */
+
+static bool
+mark_all_reaching_defs_necessary_1 (ao_ref *ref ATTRIBUTE_UNUSED,
+ tree vdef, void *data ATTRIBUTE_UNUSED)
+{
+ gimple def_stmt = SSA_NAME_DEF_STMT (vdef);
+
+ /* We have to skip already visited (and thus necessary) statements
+ to make the chaining work after we dropped back to simple mode. */
+ if (chain_ovfl
+ && TEST_BIT (processed, SSA_NAME_VERSION (vdef)))
+ {
+ gcc_assert (gimple_nop_p (def_stmt)
+ || gimple_plf (def_stmt, STMT_NECESSARY));
+ return false;
+ }
+
+ /* We want to skip stores to non-aliased variables. */
+ if (!chain_ovfl
+ && gimple_assign_single_p (def_stmt))
+ {
+ tree lhs = gimple_assign_lhs (def_stmt);
+ if (!ref_may_be_aliased (lhs))
+ return false;
+ }
+
+ /* We want to skip statments that do not constitute stores but have
+ a virtual definition. */
+ if (is_gimple_call (def_stmt))
+ {
+ tree callee = gimple_call_fndecl (def_stmt);
+ if (callee != NULL_TREE
+ && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL)
+ switch (DECL_FUNCTION_CODE (callee))
+ {
+ case BUILT_IN_MALLOC:
+ case BUILT_IN_CALLOC:
+ case BUILT_IN_ALLOCA:
+ case BUILT_IN_ALLOCA_WITH_ALIGN:
+ case BUILT_IN_FREE:
+ return false;
+
+ default:;
+ }
+ }
+
+ mark_operand_necessary (vdef);
+
+ return false;
+}
+
+static void
+mark_all_reaching_defs_necessary (gimple stmt)
+{
+ walk_aliased_vdefs (NULL, gimple_vuse (stmt),
+ mark_all_reaching_defs_necessary_1, NULL, &visited);
+}
+
+/* Return true for PHI nodes with one or identical arguments
+ can be removed. */
+static bool
+degenerate_phi_p (gimple phi)
+{
+ unsigned int i;
+ tree op = gimple_phi_arg_def (phi, 0);
+ for (i = 1; i < gimple_phi_num_args (phi); i++)
+ if (gimple_phi_arg_def (phi, i) != op)
+ return false;
+ return true;
+}
/* Propagate necessity using the operands of necessary statements.
Process the uses on each statement in the worklist, and add all
feeding statements which contribute to the calculation of this
- value to the worklist.
+ value to the worklist.
In conservative mode, EL is NULL. */
static void
propagate_necessity (struct edge_list *el)
{
- tree stmt;
- bool aggressive = (el ? true : false);
+ gimple stmt;
+ bool aggressive = (el ? true : false);
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "\nProcessing worklist:\n");
- while (VEC_length (tree, worklist) > 0)
+ while (VEC_length (gimple, worklist) > 0)
{
/* Take STMT from worklist. */
- stmt = VEC_pop (tree, worklist);
+ stmt = VEC_pop (gimple, worklist);
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "processing: ");
- print_generic_stmt (dump_file, stmt, TDF_SLIM);
+ print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
fprintf (dump_file, "\n");
}
if (aggressive)
{
- /* Mark the last statements of the basic blocks that the block
- containing STMT is control dependent on, but only if we haven't
+ /* Mark the last statement of the basic blocks on which the block
+ containing STMT is control dependent, but only if we haven't
already done so. */
- basic_block bb = bb_for_stmt (stmt);
+ basic_block bb = gimple_bb (stmt);
if (bb != ENTRY_BLOCK_PTR
- && ! TEST_BIT (visited_control_parents, bb->index))
- {
- SET_BIT (visited_control_parents, bb->index);
- mark_control_dependent_edges_necessary (bb, el);
- }
+ && !TEST_BIT (visited_control_parents, bb->index))
+ mark_control_dependent_edges_necessary (bb, el, false);
}
- if (TREE_CODE (stmt) == PHI_NODE)
+ if (gimple_code (stmt) == GIMPLE_PHI
+ /* We do not process virtual PHI nodes nor do we track their
+ necessity. */
+ && is_gimple_reg (gimple_phi_result (stmt)))
{
/* PHI nodes are somewhat special in that each PHI alternative has
data and control dependencies. All the statements feeding the
we also consider the control dependent edges leading to the
predecessor block associated with each PHI alternative as
necessary. */
- int k;
+ size_t k;
- for (k = 0; k < PHI_NUM_ARGS (stmt); k++)
+ for (k = 0; k < gimple_phi_num_args (stmt); k++)
{
tree arg = PHI_ARG_DEF (stmt, k);
if (TREE_CODE (arg) == SSA_NAME)
mark_operand_necessary (arg);
}
- if (aggressive)
+ /* For PHI operands it matters from where the control flow arrives
+ to the BB. Consider the following example:
+
+ a=exp1;
+ b=exp2;
+ if (test)
+ ;
+ else
+ ;
+ c=PHI(a,b)
+
+ We need to mark control dependence of the empty basic blocks, since they
+ contains computation of PHI operands.
+
+ Doing so is too restrictive in the case the predecestor block is in
+ the loop. Consider:
+
+ if (b)
+ {
+ int i;
+ for (i = 0; i<1000; ++i)
+ ;
+ j = 0;
+ }
+ return j;
+
+ There is PHI for J in the BB containing return statement.
+ In this case the control dependence of predecestor block (that is
+ within the empty loop) also contains the block determining number
+ of iterations of the block that would prevent removing of empty
+ loop in this case.
+
+ This scenario can be avoided by splitting critical edges.
+ To save the critical edge splitting pass we identify how the control
+ dependence would look like if the edge was split.
+
+ Consider the modified CFG created from current CFG by splitting
+ edge B->C. In the postdominance tree of modified CFG, C' is
+ always child of C. There are two cases how chlids of C' can look
+ like:
+
+ 1) C' is leaf
+
+ In this case the only basic block C' is control dependent on is B.
+
+ 2) C' has single child that is B
+
+ In this case control dependence of C' is same as control
+ dependence of B in original CFG except for block B itself.
+ (since C' postdominate B in modified CFG)
+
+ Now how to decide what case happens? There are two basic options:
+
+ a) C postdominate B. Then C immediately postdominate B and
+ case 2 happens iff there is no other way from B to C except
+ the edge B->C.
+
+ There is other way from B to C iff there is succesor of B that
+ is not postdominated by B. Testing this condition is somewhat
+ expensive, because we need to iterate all succesors of B.
+ We are safe to assume that this does not happen: we will mark B
+ as needed when processing the other path from B to C that is
+ conrol dependent on B and marking control dependencies of B
+ itself is harmless because they will be processed anyway after
+ processing control statement in B.
+
+ b) C does not postdominate B. Always case 1 happens since there is
+ path from C to exit that does not go through B and thus also C'. */
+
+ if (aggressive && !degenerate_phi_p (stmt))
{
- for (k = 0; k < PHI_NUM_ARGS (stmt); k++)
+ for (k = 0; k < gimple_phi_num_args (stmt); k++)
{
- basic_block arg_bb = PHI_ARG_EDGE (stmt, k)->src;
- if (arg_bb != ENTRY_BLOCK_PTR
- && ! TEST_BIT (visited_control_parents, arg_bb->index))
+ basic_block arg_bb = gimple_phi_arg_edge (stmt, k)->src;
+
+ if (gimple_bb (stmt)
+ != get_immediate_dominator (CDI_POST_DOMINATORS, arg_bb))
{
- SET_BIT (visited_control_parents, arg_bb->index);
- mark_control_dependent_edges_necessary (arg_bb, el);
+ if (!TEST_BIT (last_stmt_necessary, arg_bb->index))
+ mark_last_stmt_necessary (arg_bb);
}
+ else if (arg_bb != ENTRY_BLOCK_PTR
+ && !TEST_BIT (visited_control_parents,
+ arg_bb->index))
+ mark_control_dependent_edges_necessary (arg_bb, el, true);
}
}
}
else
{
/* Propagate through the operands. Examine all the USE, VUSE and
- VDEF operands in this statement. Mark all the statements
- which feed this statement's uses as necessary. The
- operands of VDEF expressions are also needed as they
- represent potential definitions that may reach this
- statement (VDEF operands allow us to follow def-def
- links). */
+ VDEF operands in this statement. Mark all the statements
+ which feed this statement's uses as necessary. */
ssa_op_iter iter;
tree use;
- FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_ALL_USES)
+ /* If this is a call to free which is directly fed by an
+ allocation function do not mark that necessary through
+ processing the argument. */
+ if (gimple_call_builtin_p (stmt, BUILT_IN_FREE))
+ {
+ tree ptr = gimple_call_arg (stmt, 0);
+ gimple def_stmt;
+ tree def_callee;
+ /* If the pointer we free is defined by an allocation
+ function do not add the call to the worklist. */
+ if (TREE_CODE (ptr) == SSA_NAME
+ && is_gimple_call (def_stmt = SSA_NAME_DEF_STMT (ptr))
+ && (def_callee = gimple_call_fndecl (def_stmt))
+ && DECL_BUILT_IN_CLASS (def_callee) == BUILT_IN_NORMAL
+ && (DECL_FUNCTION_CODE (def_callee) == BUILT_IN_MALLOC
+ || DECL_FUNCTION_CODE (def_callee) == BUILT_IN_CALLOC))
+ continue;
+ }
+
+ FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
mark_operand_necessary (use);
+
+ use = gimple_vuse (stmt);
+ if (!use)
+ continue;
+
+ /* If we dropped to simple mode make all immediately
+ reachable definitions necessary. */
+ if (chain_ovfl)
+ {
+ mark_all_reaching_defs_necessary (stmt);
+ continue;
+ }
+
+ /* For statements that may load from memory (have a VUSE) we
+ have to mark all reaching (may-)definitions as necessary.
+ We partition this task into two cases:
+ 1) explicit loads based on decls that are not aliased
+ 2) implicit loads (like calls) and explicit loads not
+ based on decls that are not aliased (like indirect
+ references or loads from globals)
+ For 1) we mark all reaching may-defs as necessary, stopping
+ at dominating kills. For 2) we want to mark all dominating
+ references necessary, but non-aliased ones which we handle
+ in 1). By keeping a global visited bitmap for references
+ we walk for 2) we avoid quadratic behavior for those. */
+
+ if (is_gimple_call (stmt))
+ {
+ tree callee = gimple_call_fndecl (stmt);
+ unsigned i;
+
+ /* Calls to functions that are merely acting as barriers
+ or that only store to memory do not make any previous
+ stores necessary. */
+ if (callee != NULL_TREE
+ && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL
+ && (DECL_FUNCTION_CODE (callee) == BUILT_IN_MEMSET
+ || DECL_FUNCTION_CODE (callee) == BUILT_IN_MEMSET_CHK
+ || DECL_FUNCTION_CODE (callee) == BUILT_IN_MALLOC
+ || DECL_FUNCTION_CODE (callee) == BUILT_IN_CALLOC
+ || DECL_FUNCTION_CODE (callee) == BUILT_IN_FREE
+ || DECL_FUNCTION_CODE (callee) == BUILT_IN_VA_END
+ || DECL_FUNCTION_CODE (callee) == BUILT_IN_ALLOCA
+ || (DECL_FUNCTION_CODE (callee)
+ == BUILT_IN_ALLOCA_WITH_ALIGN)
+ || DECL_FUNCTION_CODE (callee) == BUILT_IN_STACK_SAVE
+ || DECL_FUNCTION_CODE (callee) == BUILT_IN_STACK_RESTORE
+ || DECL_FUNCTION_CODE (callee) == BUILT_IN_ASSUME_ALIGNED))
+ continue;
+
+ /* Calls implicitly load from memory, their arguments
+ in addition may explicitly perform memory loads. */
+ mark_all_reaching_defs_necessary (stmt);
+ for (i = 0; i < gimple_call_num_args (stmt); ++i)
+ {
+ tree arg = gimple_call_arg (stmt, i);
+ if (TREE_CODE (arg) == SSA_NAME
+ || is_gimple_min_invariant (arg))
+ continue;
+ if (TREE_CODE (arg) == WITH_SIZE_EXPR)
+ arg = TREE_OPERAND (arg, 0);
+ if (!ref_may_be_aliased (arg))
+ mark_aliased_reaching_defs_necessary (stmt, arg);
+ }
+ }
+ else if (gimple_assign_single_p (stmt))
+ {
+ tree rhs;
+ /* If this is a load mark things necessary. */
+ rhs = gimple_assign_rhs1 (stmt);
+ if (TREE_CODE (rhs) != SSA_NAME
+ && !is_gimple_min_invariant (rhs)
+ && TREE_CODE (rhs) != CONSTRUCTOR)
+ {
+ if (!ref_may_be_aliased (rhs))
+ mark_aliased_reaching_defs_necessary (stmt, rhs);
+ else
+ mark_all_reaching_defs_necessary (stmt);
+ }
+ }
+ else if (gimple_code (stmt) == GIMPLE_RETURN)
+ {
+ tree rhs = gimple_return_retval (stmt);
+ /* A return statement may perform a load. */
+ if (rhs
+ && TREE_CODE (rhs) != SSA_NAME
+ && !is_gimple_min_invariant (rhs)
+ && TREE_CODE (rhs) != CONSTRUCTOR)
+ {
+ if (!ref_may_be_aliased (rhs))
+ mark_aliased_reaching_defs_necessary (stmt, rhs);
+ else
+ mark_all_reaching_defs_necessary (stmt);
+ }
+ }
+ else if (gimple_code (stmt) == GIMPLE_ASM)
+ {
+ unsigned i;
+ mark_all_reaching_defs_necessary (stmt);
+ /* Inputs may perform loads. */
+ for (i = 0; i < gimple_asm_ninputs (stmt); ++i)
+ {
+ tree op = TREE_VALUE (gimple_asm_input_op (stmt, i));
+ if (TREE_CODE (op) != SSA_NAME
+ && !is_gimple_min_invariant (op)
+ && TREE_CODE (op) != CONSTRUCTOR
+ && !ref_may_be_aliased (op))
+ mark_aliased_reaching_defs_necessary (stmt, op);
+ }
+ }
+ else if (gimple_code (stmt) == GIMPLE_TRANSACTION)
+ {
+ /* The beginning of a transaction is a memory barrier. */
+ /* ??? If we were really cool, we'd only be a barrier
+ for the memories touched within the transaction. */
+ mark_all_reaching_defs_necessary (stmt);
+ }
+ else
+ gcc_unreachable ();
+
+ /* If we over-used our alias oracle budget drop to simple
+ mode. The cost metric allows quadratic behavior
+ (number of uses times number of may-defs queries) up to
+ a constant maximal number of queries and after that falls back to
+ super-linear complexity. */
+ if (/* Constant but quadratic for small functions. */
+ total_chain > 128 * 128
+ /* Linear in the number of may-defs. */
+ && total_chain > 32 * longest_chain
+ /* Linear in the number of uses. */
+ && total_chain > nr_walks * 32)
+ {
+ chain_ovfl = true;
+ if (visited)
+ bitmap_clear (visited);
+ }
}
}
}
+/* Replace all uses of NAME by underlying variable and mark it
+ for renaming. */
+
+void
+mark_virtual_operand_for_renaming (tree name)
+{
+ bool used = false;
+ imm_use_iterator iter;
+ use_operand_p use_p;
+ gimple stmt;
+ tree name_var;
+
+ name_var = SSA_NAME_VAR (name);
+ FOR_EACH_IMM_USE_STMT (stmt, iter, name)
+ {
+ FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
+ SET_USE (use_p, name_var);
+ update_stmt (stmt);
+ used = true;
+ }
+ if (used)
+ mark_sym_for_renaming (name_var);
+}
+
+/* Replace all uses of result of PHI by underlying variable and mark it
+ for renaming. */
+
+void
+mark_virtual_phi_result_for_renaming (gimple phi)
+{
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "Marking result for renaming : ");
+ print_gimple_stmt (dump_file, phi, 0, TDF_SLIM);
+ fprintf (dump_file, "\n");
+ }
+
+ mark_virtual_operand_for_renaming (gimple_phi_result (phi));
+}
+
/* Remove dead PHI nodes from block BB. */
static bool
remove_dead_phis (basic_block bb)
{
- tree prev, phi;
bool something_changed = false;
+ gimple_seq phis;
+ gimple phi;
+ gimple_stmt_iterator gsi;
+ phis = phi_nodes (bb);
- prev = NULL_TREE;
- phi = phi_nodes (bb);
- while (phi)
+ for (gsi = gsi_start (phis); !gsi_end_p (gsi);)
{
stats.total_phis++;
+ phi = gsi_stmt (gsi);
- if (! NECESSARY (phi))
+ /* We do not track necessity of virtual PHI nodes. Instead do
+ very simple dead PHI removal here. */
+ if (!is_gimple_reg (gimple_phi_result (phi)))
{
- tree next = PHI_CHAIN (phi);
+ /* Virtual PHI nodes with one or identical arguments
+ can be removed. */
+ if (degenerate_phi_p (phi))
+ {
+ tree vdef = gimple_phi_result (phi);
+ tree vuse = gimple_phi_arg_def (phi, 0);
+
+ use_operand_p use_p;
+ imm_use_iterator iter;
+ gimple use_stmt;
+ FOR_EACH_IMM_USE_STMT (use_stmt, iter, vdef)
+ FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
+ SET_USE (use_p, vuse);
+ if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef)
+ && TREE_CODE (vuse) == SSA_NAME)
+ SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse) = 1;
+ }
+ else
+ gimple_set_plf (phi, STMT_NECESSARY, true);
+ }
+ if (!gimple_plf (phi, STMT_NECESSARY))
+ {
something_changed = true;
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "Deleting : ");
- print_generic_stmt (dump_file, phi, TDF_SLIM);
+ print_gimple_stmt (dump_file, phi, 0, TDF_SLIM);
fprintf (dump_file, "\n");
}
- remove_phi_node (phi, prev, true);
+ remove_phi_node (&gsi, true);
stats.removed_phis++;
- phi = next;
- }
- else
- {
- prev = phi;
- phi = PHI_CHAIN (phi);
+ continue;
}
+
+ gsi_next (&gsi);
}
return something_changed;
}
+/* Forward edge E to respective POST_DOM_BB and update PHIs. */
+
+static edge
+forward_edge_to_pdom (edge e, basic_block post_dom_bb)
+{
+ gimple_stmt_iterator gsi;
+ edge e2 = NULL;
+ edge_iterator ei;
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, "Redirecting edge %i->%i to %i\n", e->src->index,
+ e->dest->index, post_dom_bb->index);
+
+ e2 = redirect_edge_and_branch (e, post_dom_bb);
+ cfg_altered = true;
+
+ /* If edge was already around, no updating is neccesary. */
+ if (e2 != e)
+ return e2;
+
+ if (!gimple_seq_empty_p (phi_nodes (post_dom_bb)))
+ {
+ /* We are sure that for every live PHI we are seeing control dependent BB.
+ This means that we can pick any edge to duplicate PHI args from. */
+ FOR_EACH_EDGE (e2, ei, post_dom_bb->preds)
+ if (e2 != e)
+ break;
+ for (gsi = gsi_start_phis (post_dom_bb); !gsi_end_p (gsi);)
+ {
+ gimple phi = gsi_stmt (gsi);
+ tree op;
+ source_location locus;
+
+ /* PHIs for virtuals have no control dependency relation on them.
+ We are lost here and must force renaming of the symbol. */
+ if (!is_gimple_reg (gimple_phi_result (phi)))
+ {
+ mark_virtual_phi_result_for_renaming (phi);
+ remove_phi_node (&gsi, true);
+ continue;
+ }
+
+ /* Dead PHI do not imply control dependency. */
+ if (!gimple_plf (phi, STMT_NECESSARY))
+ {
+ gsi_next (&gsi);
+ continue;
+ }
+
+ op = gimple_phi_arg_def (phi, e2->dest_idx);
+ locus = gimple_phi_arg_location (phi, e2->dest_idx);
+ add_phi_arg (phi, op, e, locus);
+ /* The resulting PHI if not dead can only be degenerate. */
+ gcc_assert (degenerate_phi_p (phi));
+ gsi_next (&gsi);
+ }
+ }
+ return e;
+}
/* Remove dead statement pointed to by iterator I. Receives the basic block BB
containing I so that we don't have to look it up. */
static void
-remove_dead_stmt (block_stmt_iterator *i, basic_block bb)
+remove_dead_stmt (gimple_stmt_iterator *i, basic_block bb)
{
- tree t = bsi_stmt (*i);
+ gimple stmt = gsi_stmt (*i);
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "Deleting : ");
- print_generic_stmt (dump_file, t, TDF_SLIM);
+ print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
fprintf (dump_file, "\n");
}
immediate post-dominator. The blocks we are circumventing will be
removed by cleanup_tree_cfg if this change in the flow graph makes them
unreachable. */
- if (is_ctrl_stmt (t))
+ if (is_ctrl_stmt (stmt))
{
basic_block post_dom_bb;
+ edge e, e2;
+ edge_iterator ei;
- /* The post dominance info has to be up-to-date. */
- gcc_assert (dom_info_state (CDI_POST_DOMINATORS) == DOM_OK);
- /* Get the immediate post dominator of bb. */
post_dom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, bb);
- /* There are three particularly problematical cases.
-
- 1. Blocks that do not have an immediate post dominator. This
- can happen with infinite loops.
+ e = find_edge (bb, post_dom_bb);
- 2. Blocks that are only post dominated by the exit block. These
- can also happen for infinite loops as we create fake edges
- in the dominator tree.
-
- 3. If the post dominator has PHI nodes we may be able to compute
- the right PHI args for them.
-
- In each of these cases we must remove the control statement
- as it may reference SSA_NAMEs which are going to be removed and
- we remove all but one outgoing edge from the block. */
- if (! post_dom_bb
- || post_dom_bb == EXIT_BLOCK_PTR
- || phi_nodes (post_dom_bb))
- ;
+ /* If edge is already there, try to use it. This avoids need to update
+ PHI nodes. Also watch for cases where post dominator does not exists
+ or is exit block. These can happen for infinite loops as we create
+ fake edges in the dominator tree. */
+ if (e)
+ ;
+ else if (! post_dom_bb || post_dom_bb == EXIT_BLOCK_PTR)
+ e = EDGE_SUCC (bb, 0);
else
- {
- /* Redirect the first edge out of BB to reach POST_DOM_BB. */
- redirect_edge_and_branch (EDGE_SUCC (bb, 0), post_dom_bb);
- PENDING_STMT (EDGE_SUCC (bb, 0)) = NULL;
-
- /* It is not sufficient to set cfg_altered below during edge
- removal, in case BB has two successors and one of them
- is POST_DOM_BB. */
- cfg_altered = true;
- }
- EDGE_SUCC (bb, 0)->probability = REG_BR_PROB_BASE;
- EDGE_SUCC (bb, 0)->count = bb->count;
+ e = forward_edge_to_pdom (EDGE_SUCC (bb, 0), post_dom_bb);
+ gcc_assert (e);
+ e->probability = REG_BR_PROB_BASE;
+ e->count = bb->count;
/* The edge is no longer associated with a conditional, so it does
not have TRUE/FALSE flags. */
- EDGE_SUCC (bb, 0)->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
+ e->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
/* The lone outgoing edge from BB will be a fallthru edge. */
- EDGE_SUCC (bb, 0)->flags |= EDGE_FALLTHRU;
+ e->flags |= EDGE_FALLTHRU;
+
+ /* Remove the remaining outgoing edges. */
+ for (ei = ei_start (bb->succs); (e2 = ei_safe_edge (ei)); )
+ if (e != e2)
+ {
+ cfg_altered = true;
+ remove_edge (e2);
+ }
+ else
+ ei_next (&ei);
+ }
- /* Remove the remaining the outgoing edges. */
- while (!single_succ_p (bb))
+ /* If this is a store into a variable that is being optimized away,
+ add a debug bind stmt if possible. */
+ if (MAY_HAVE_DEBUG_STMTS
+ && gimple_assign_single_p (stmt)
+ && is_gimple_val (gimple_assign_rhs1 (stmt)))
+ {
+ tree lhs = gimple_assign_lhs (stmt);
+ if ((TREE_CODE (lhs) == VAR_DECL || TREE_CODE (lhs) == PARM_DECL)
+ && !DECL_IGNORED_P (lhs)
+ && is_gimple_reg_type (TREE_TYPE (lhs))
+ && !is_global_var (lhs)
+ && !DECL_HAS_VALUE_EXPR_P (lhs))
{
- /* FIXME. When we remove the edge, we modify the CFG, which
- in turn modifies the dominator and post-dominator tree.
- Is it safe to postpone recomputing the dominator and
- post-dominator tree until the end of this pass given that
- the post-dominators are used above? */
- cfg_altered = true;
- remove_edge (EDGE_SUCC (bb, 1));
+ tree rhs = gimple_assign_rhs1 (stmt);
+ gimple note
+ = gimple_build_debug_bind (lhs, unshare_expr (rhs), stmt);
+ gsi_insert_after (i, note, GSI_SAME_STMT);
}
}
-
- bsi_remove (i, true);
- release_defs (t);
-}
+ unlink_stmt_vdef (stmt);
+ gsi_remove (i, true);
+ release_defs (stmt);
+}
/* Eliminate unnecessary statements. Any instruction not marked as necessary
contributes nothing to the program, and can be deleted. */
{
bool something_changed = false;
basic_block bb;
- block_stmt_iterator i;
+ gimple_stmt_iterator gsi, psi;
+ gimple stmt;
+ tree call;
+ VEC (basic_block, heap) *h;
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "\nEliminating unnecessary statements:\n");
clear_special_calls ();
- FOR_EACH_BB (bb)
- {
- /* Remove dead PHI nodes. */
- something_changed |= remove_dead_phis (bb);
- }
- FOR_EACH_BB (bb)
+ /* Walking basic blocks and statements in reverse order avoids
+ releasing SSA names before any other DEFs that refer to them are
+ released. This helps avoid loss of debug information, as we get
+ a chance to propagate all RHSs of removed SSAs into debug uses,
+ rather than only the latest ones. E.g., consider:
+
+ x_3 = y_1 + z_2;
+ a_5 = x_3 - b_4;
+ # DEBUG a => a_5
+
+ If we were to release x_3 before a_5, when we reached a_5 and
+ tried to substitute it into the debug stmt, we'd see x_3 there,
+ but x_3's DEF, type, etc would have already been disconnected.
+ By going backwards, the debug stmt first changes to:
+
+ # DEBUG a => x_3 - b_4
+
+ and then to:
+
+ # DEBUG a => y_1 + z_2 - b_4
+
+ as desired. */
+ gcc_assert (dom_info_available_p (CDI_DOMINATORS));
+ h = get_all_dominated_blocks (CDI_DOMINATORS, single_succ (ENTRY_BLOCK_PTR));
+
+ while (VEC_length (basic_block, h))
{
+ bb = VEC_pop (basic_block, h);
+
/* Remove dead statements. */
- for (i = bsi_start (bb); ! bsi_end_p (i) ; )
+ for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi = psi)
{
- tree t = bsi_stmt (i);
+ stmt = gsi_stmt (gsi);
+
+ psi = gsi;
+ gsi_prev (&psi);
stats.total++;
- /* If `i' is not necessary then remove it. */
- if (! NECESSARY (t))
+ /* We can mark a call to free as not necessary if the
+ defining statement of its argument is an allocation
+ function and that is not necessary itself. */
+ if (gimple_call_builtin_p (stmt, BUILT_IN_FREE))
{
- remove_dead_stmt (&i, bb);
- something_changed = true;
+ tree ptr = gimple_call_arg (stmt, 0);
+ tree callee2;
+ gimple def_stmt;
+ if (TREE_CODE (ptr) != SSA_NAME)
+ continue;
+ def_stmt = SSA_NAME_DEF_STMT (ptr);
+ if (!is_gimple_call (def_stmt)
+ || gimple_plf (def_stmt, STMT_NECESSARY))
+ continue;
+ callee2 = gimple_call_fndecl (def_stmt);
+ if (callee2 == NULL_TREE
+ || DECL_BUILT_IN_CLASS (callee2) != BUILT_IN_NORMAL
+ || (DECL_FUNCTION_CODE (callee2) != BUILT_IN_MALLOC
+ && DECL_FUNCTION_CODE (callee2) != BUILT_IN_CALLOC))
+ continue;
+ gimple_set_plf (stmt, STMT_NECESSARY, false);
}
- else
+
+ /* If GSI is not necessary then remove it. */
+ if (!gimple_plf (stmt, STMT_NECESSARY))
{
- tree call = get_call_expr_in (t);
- if (call)
+ if (!is_gimple_debug (stmt))
+ something_changed = true;
+ remove_dead_stmt (&gsi, bb);
+ }
+ else if (is_gimple_call (stmt))
+ {
+ tree name = gimple_call_lhs (stmt);
+
+ notice_special_calls (stmt);
+
+ /* When LHS of var = call (); is dead, simplify it into
+ call (); saving one operand. */
+ if (name
+ && TREE_CODE (name) == SSA_NAME
+ && !TEST_BIT (processed, SSA_NAME_VERSION (name))
+ /* Avoid doing so for allocation calls which we
+ did not mark as necessary, it will confuse the
+ special logic we apply to malloc/free pair removal. */
+ && (!(call = gimple_call_fndecl (stmt))
+ || DECL_BUILT_IN_CLASS (call) != BUILT_IN_NORMAL
+ || (DECL_FUNCTION_CODE (call) != BUILT_IN_MALLOC
+ && DECL_FUNCTION_CODE (call) != BUILT_IN_CALLOC
+ && DECL_FUNCTION_CODE (call) != BUILT_IN_ALLOCA
+ && (DECL_FUNCTION_CODE (call)
+ != BUILT_IN_ALLOCA_WITH_ALIGN))))
{
- tree name;
-
- /* When LHS of var = call (); is dead, simplify it into
- call (); saving one operand. */
- if (TREE_CODE (t) == GIMPLE_MODIFY_STMT
- && (TREE_CODE ((name = GIMPLE_STMT_OPERAND (t, 0)))
- == SSA_NAME)
- && !TEST_BIT (processed, SSA_NAME_VERSION (name)))
+ something_changed = true;
+ if (dump_file && (dump_flags & TDF_DETAILS))
{
- tree oldlhs = GIMPLE_STMT_OPERAND (t, 0);
- something_changed = true;
- if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, "Deleting LHS of call: ");
+ print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
+ fprintf (dump_file, "\n");
+ }
+
+ gimple_call_set_lhs (stmt, NULL_TREE);
+ maybe_clean_or_replace_eh_stmt (stmt, stmt);
+ update_stmt (stmt);
+ release_ssa_name (name);
+ }
+ }
+ }
+ }
+
+ VEC_free (basic_block, heap, h);
+
+ /* Since we don't track liveness of virtual PHI nodes, it is possible that we
+ rendered some PHI nodes unreachable while they are still in use.
+ Mark them for renaming. */
+ if (cfg_altered)
+ {
+ basic_block prev_bb;
+
+ find_unreachable_blocks ();
+
+ /* Delete all unreachable basic blocks in reverse dominator order. */
+ for (bb = EXIT_BLOCK_PTR->prev_bb; bb != ENTRY_BLOCK_PTR; bb = prev_bb)
+ {
+ prev_bb = bb->prev_bb;
+
+ if (!TEST_BIT (bb_contains_live_stmts, bb->index)
+ || !(bb->flags & BB_REACHABLE))
+ {
+ for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+ if (!is_gimple_reg (gimple_phi_result (gsi_stmt (gsi))))
+ {
+ bool found = false;
+ imm_use_iterator iter;
+
+ FOR_EACH_IMM_USE_STMT (stmt, iter, gimple_phi_result (gsi_stmt (gsi)))
+ {
+ if (!(gimple_bb (stmt)->flags & BB_REACHABLE))
+ continue;
+ if (gimple_code (stmt) == GIMPLE_PHI
+ || gimple_plf (stmt, STMT_NECESSARY))
+ {
+ found = true;
+ BREAK_FROM_IMM_USE_STMT (iter);
+ }
+ }
+ if (found)
+ mark_virtual_phi_result_for_renaming (gsi_stmt (gsi));
+ }
+
+ if (!(bb->flags & BB_REACHABLE))
+ {
+ /* Speed up the removal of blocks that don't
+ dominate others. Walking backwards, this should
+ be the common case. ??? Do we need to recompute
+ dominators because of cfg_altered? */
+ if (!MAY_HAVE_DEBUG_STMTS
+ || !first_dom_son (CDI_DOMINATORS, bb))
+ delete_basic_block (bb);
+ else
+ {
+ h = get_all_dominated_blocks (CDI_DOMINATORS, bb);
+
+ while (VEC_length (basic_block, h))
{
- fprintf (dump_file, "Deleting LHS of call: ");
- print_generic_stmt (dump_file, t, TDF_SLIM);
- fprintf (dump_file, "\n");
+ bb = VEC_pop (basic_block, h);
+ prev_bb = bb->prev_bb;
+ /* Rearrangements to the CFG may have failed
+ to update the dominators tree, so that
+ formerly-dominated blocks are now
+ otherwise reachable. */
+ if (!!(bb->flags & BB_REACHABLE))
+ continue;
+ delete_basic_block (bb);
}
- push_stmt_changes (bsi_stmt_ptr (i));
- TREE_BLOCK (call) = TREE_BLOCK (t);
- bsi_replace (&i, call, false);
- maybe_clean_or_replace_eh_stmt (t, call);
- mark_symbols_for_renaming (call);
- pop_stmt_changes (bsi_stmt_ptr (i));
- release_ssa_name (oldlhs);
+
+ VEC_free (basic_block, heap, h);
}
- notice_special_calls (call);
}
- bsi_next (&i);
}
}
}
+ FOR_EACH_BB (bb)
+ {
+ /* Remove dead PHI nodes. */
+ something_changed |= remove_dead_phis (bb);
+ }
return something_changed;
}
static void
print_stats (void)
{
- if (dump_file && (dump_flags & (TDF_STATS|TDF_DETAILS)))
- {
- float percg;
+ float percg;
- percg = ((float) stats.removed / (float) stats.total) * 100;
- fprintf (dump_file, "Removed %d of %d statements (%d%%)\n",
- stats.removed, stats.total, (int) percg);
+ percg = ((float) stats.removed / (float) stats.total) * 100;
+ fprintf (dump_file, "Removed %d of %d statements (%d%%)\n",
+ stats.removed, stats.total, (int) percg);
- if (stats.total_phis == 0)
- percg = 0;
- else
- percg = ((float) stats.removed_phis / (float) stats.total_phis) * 100;
+ if (stats.total_phis == 0)
+ percg = 0;
+ else
+ percg = ((float) stats.removed_phis / (float) stats.total_phis) * 100;
- fprintf (dump_file, "Removed %d of %d PHI nodes (%d%%)\n",
- stats.removed_phis, stats.total_phis, (int) percg);
- }
+ fprintf (dump_file, "Removed %d of %d PHI nodes (%d%%)\n",
+ stats.removed_phis, stats.total_phis, (int) percg);
}
-\f
+
/* Initialization for this pass. Set up the used data structures. */
static void
last_stmt_necessary = sbitmap_alloc (last_basic_block);
sbitmap_zero (last_stmt_necessary);
+ bb_contains_live_stmts = sbitmap_alloc (last_basic_block);
+ sbitmap_zero (bb_contains_live_stmts);
}
processed = sbitmap_alloc (num_ssa_names + 1);
sbitmap_zero (processed);
- worklist = VEC_alloc (tree, heap, 64);
+ worklist = VEC_alloc (gimple, heap, 64);
cfg_altered = false;
}
sbitmap_free (visited_control_parents);
sbitmap_free (last_stmt_necessary);
+ sbitmap_free (bb_contains_live_stmts);
+ bb_contains_live_stmts = NULL;
}
sbitmap_free (processed);
- VEC_free (tree, heap, worklist);
+ VEC_free (gimple, heap, worklist);
}
-\f
+
/* Main routine to eliminate dead code.
AGGRESSIVE controls the aggressiveness of the algorithm.
struct edge_list *el = NULL;
bool something_changed = 0;
+ calculate_dominance_info (CDI_DOMINATORS);
+
+ /* Preheaders are needed for SCEV to work.
+ Simple lateches and recorded exits improve chances that loop will
+ proved to be finite in testcases such as in loop-15.c and loop-24.c */
+ if (aggressive)
+ loop_optimizer_init (LOOPS_NORMAL
+ | LOOPS_HAVE_RECORDED_EXITS);
+
tree_dce_init (aggressive);
if (aggressive)
find_obviously_necessary_stmts (el);
+ if (aggressive)
+ loop_optimizer_finalize ();
+
+ longest_chain = 0;
+ total_chain = 0;
+ nr_walks = 0;
+ chain_ovfl = false;
+ visited = BITMAP_ALLOC (NULL);
propagate_necessity (el);
+ BITMAP_FREE (visited);
something_changed |= eliminate_unnecessary_stmts ();
something_changed |= cfg_altered;
if (cfg_altered)
free_dominance_info (CDI_DOMINATORS);
+ statistics_counter_event (cfun, "Statements deleted", stats.removed);
+ statistics_counter_event (cfun, "PHI nodes deleted", stats.removed_phis);
+
/* Debugging dumps. */
- if (dump_file)
+ if (dump_file && (dump_flags & (TDF_STATS|TDF_DETAILS)))
print_stats ();
tree_dce_done (aggressive);
free_edge_list (el);
if (something_changed)
- return (TODO_update_ssa | TODO_cleanup_cfg | TODO_ggc_collect
+ return (TODO_update_ssa | TODO_cleanup_cfg | TODO_ggc_collect
| TODO_remove_unused_locals);
else
return 0;
return flag_tree_dce != 0;
}
-struct tree_opt_pass pass_dce =
+struct gimple_opt_pass pass_dce =
{
+ {
+ GIMPLE_PASS,
"dce", /* name */
gate_dce, /* gate */
tree_ssa_dce, /* execute */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
- TODO_dump_func | TODO_verify_ssa, /* todo_flags_finish */
- 0 /* letter */
+ TODO_verify_ssa /* todo_flags_finish */
+ }
};
-struct tree_opt_pass pass_dce_loop =
+struct gimple_opt_pass pass_dce_loop =
{
+ {
+ GIMPLE_PASS,
"dceloop", /* name */
gate_dce, /* gate */
tree_ssa_dce_loop, /* execute */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
- TODO_dump_func | TODO_verify_ssa, /* todo_flags_finish */
- 0 /* letter */
+ TODO_verify_ssa /* todo_flags_finish */
+ }
};
-struct tree_opt_pass pass_cd_dce =
+struct gimple_opt_pass pass_cd_dce =
{
+ {
+ GIMPLE_PASS,
"cddce", /* name */
gate_dce, /* gate */
tree_ssa_cd_dce, /* execute */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
- TODO_dump_func | TODO_verify_ssa
- | TODO_verify_flow, /* todo_flags_finish */
- 0 /* letter */
+ TODO_verify_ssa
+ | TODO_verify_flow /* todo_flags_finish */
+ }
};
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