/* Dead store elimination
- Copyright (C) 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
+ Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010
+ Free Software Foundation, Inc.
This file is part of GCC.
#include "tm.h"
#include "ggc.h"
#include "tree.h"
-#include "rtl.h"
#include "tm_p.h"
#include "basic-block.h"
#include "timevar.h"
#include "diagnostic.h"
+#include "gimple-pretty-print.h"
#include "tree-flow.h"
#include "tree-pass.h"
#include "tree-dump.h"
#include "domwalk.h"
#include "flags.h"
-#include "hashtab.h"
-#include "sbitmap.h"
+#include "langhooks.h"
/* This file implements dead store elimination.
In our SSA + virtual operand world we use immediate uses of virtual
operands to detect dead stores. If a store's virtual definition
is used precisely once by a later store to the same location which
- post dominates the first store, then the first store is dead.
+ post dominates the first store, then the first store is dead.
The single use of the store's virtual definition ensures that
there are no intervening aliased loads and the requirement that
It may help to think of this as first moving the earlier store to
the point immediately before the later store. Again, the single
use of the virtual definition and the post-dominance relationship
- ensure that such movement would be safe. Clearly if there are
+ ensure that such movement would be safe. Clearly if there are
back to back stores, then the second is redundant.
Reviewing section 10.7.2 in Morgan's "Building an Optimizing Compiler"
relationship between dead store and redundant load elimination. In
fact, they are the same transformation applied to different views of
the CFG. */
-
-/* Given an aggregate, this records the parts of it which have been
- stored into. */
-struct aggregate_vardecl_d
-{
- /* The aggregate. */
- tree decl;
-
- /* Some aggregates are too big for us to handle or never get stored
- to as a whole. If this field is TRUE, we don't care about this
- aggregate. */
- bool ignore;
-
- /* Number of parts in the whole. */
- unsigned nparts;
-
- /* A bitmap of parts of the aggregate that have been set. If part N
- of an aggregate has been stored to, bit N should be on. */
- sbitmap parts_set;
-};
struct dse_global_data
{
that we want to record, set the bit corresponding to the statement's
unique ID in this bitmap. */
bitmap stores;
-
- /* A hash table containing the parts of an aggregate which have been
- stored to. */
- htab_t aggregate_vardecl;
};
/* We allocate a bitmap-per-block for stores which are encountered
- during the scan of that block. This allows us to restore the
+ during the scan of that block. This allows us to restore the
global bitmap of stores when we finish processing a block. */
struct dse_block_local_data
{
bitmap stores;
};
-/* Basic blocks of the potentially dead store and the following
- store, for memory_address_same. */
-struct address_walk_data
-{
- basic_block store1_bb, store2_bb;
-};
-
static bool gate_dse (void);
static unsigned int tree_ssa_dse (void);
static void dse_initialize_block_local_data (struct dom_walk_data *,
basic_block,
bool);
-static void dse_optimize_stmt (struct dom_walk_data *,
- basic_block,
- block_stmt_iterator);
-static void dse_record_phis (struct dom_walk_data *, basic_block);
-static void dse_finalize_block (struct dom_walk_data *, basic_block);
+static void dse_enter_block (struct dom_walk_data *, basic_block);
+static void dse_leave_block (struct dom_walk_data *, basic_block);
static void record_voperand_set (bitmap, bitmap *, unsigned int);
-static void dse_record_partial_aggregate_store (tree, struct dse_global_data *);
-
-static unsigned max_stmt_uid; /* Maximal uid of a statement. Uids to phi
- nodes are assigned using the versions of
- ssa names they define. */
/* Returns uid of statement STMT. */
static unsigned
-get_stmt_uid (tree stmt)
+get_stmt_uid (gimple stmt)
{
- if (TREE_CODE (stmt) == PHI_NODE)
- return SSA_NAME_VERSION (PHI_RESULT (stmt)) + max_stmt_uid;
+ if (gimple_code (stmt) == GIMPLE_PHI)
+ return SSA_NAME_VERSION (gimple_phi_result (stmt))
+ + gimple_stmt_max_uid (cfun);
- return stmt_ann (stmt)->uid;
+ return gimple_uid (stmt);
}
/* Set bit UID in bitmaps GLOBAL and *LOCAL, creating *LOCAL as needed. */
}
}
-/* Helper function for memory_address_same via walk_tree. Returns
- non-NULL if it finds an SSA_NAME which is part of the address,
- such that the definition of the SSA_NAME post-dominates the store
- we want to delete but not the store that we believe makes it
- redundant. This indicates that the address may change between
- the two stores. */
-
-static tree
-memory_ssa_name_same (tree *expr_p, int *walk_subtrees ATTRIBUTE_UNUSED,
- void *data)
-{
- struct address_walk_data *walk_data = (struct address_walk_data *) data;
- tree expr = *expr_p;
- tree def_stmt;
- basic_block def_bb;
-
- if (TREE_CODE (expr) != SSA_NAME)
- return NULL_TREE;
-
- /* If we've found a default definition, then there's no problem. Both
- stores will post-dominate it. And def_bb will be NULL. */
- if (SSA_NAME_IS_DEFAULT_DEF (expr))
- return NULL_TREE;
-
- def_stmt = SSA_NAME_DEF_STMT (expr);
- def_bb = bb_for_stmt (def_stmt);
-
- /* DEF_STMT must dominate both stores. So if it is in the same
- basic block as one, it does not post-dominate that store. */
- if (walk_data->store1_bb != def_bb
- && dominated_by_p (CDI_POST_DOMINATORS, walk_data->store1_bb, def_bb))
- {
- if (walk_data->store2_bb == def_bb
- || !dominated_by_p (CDI_POST_DOMINATORS, walk_data->store2_bb,
- def_bb))
- /* Return non-NULL to stop the walk. */
- return def_stmt;
- }
-
- return NULL_TREE;
-}
-
-/* Return TRUE if the destination memory address in STORE1 and STORE2
- might be modified after STORE1, before control reaches STORE2. */
-
-static bool
-memory_address_same (tree store1, tree store2)
-{
- struct address_walk_data walk_data;
-
- walk_data.store1_bb = bb_for_stmt (store1);
- walk_data.store2_bb = bb_for_stmt (store2);
-
- return (walk_tree (&GIMPLE_STMT_OPERAND (store1, 0), memory_ssa_name_same,
- &walk_data, NULL)
- == NULL);
-}
-
-/* Return the use stmt for the lhs of STMT following the virtual
- def-use chains. Returns the MODIFY_EXPR stmt which lhs is equal to
- the lhs of STMT or NULL_TREE if no such stmt can be found. */
-static tree
-get_use_of_stmt_lhs (tree stmt,
- use_operand_p * first_use_p,
- use_operand_p * use_p, tree * use_stmt)
-{
- tree usevar, lhs;
- def_operand_p def_p;
-
- if (TREE_CODE (stmt) != GIMPLE_MODIFY_STMT)
- return NULL_TREE;
-
- lhs = GIMPLE_STMT_OPERAND (stmt, 0);
-
- /* The stmt must have a single VDEF. */
- def_p = SINGLE_SSA_DEF_OPERAND (stmt, SSA_OP_VDEF);
- if (def_p == NULL_DEF_OPERAND_P)
- return NULL_TREE;
-
- if (!has_single_use (DEF_FROM_PTR (def_p)))
- return NULL_TREE;
- /* Get the immediate use of the def. */
- single_imm_use (DEF_FROM_PTR (def_p), use_p, use_stmt);
- gcc_assert (*use_p != NULL_USE_OPERAND_P);
- first_use_p = use_p;
- if (TREE_CODE (*use_stmt) != GIMPLE_MODIFY_STMT)
- return NULL_TREE;
-
- do
- {
- /* Look at the use stmt and see if it's LHS matches
- stmt's lhs SSA_NAME. */
- def_p = SINGLE_SSA_DEF_OPERAND (*use_stmt, SSA_OP_VDEF);
- if (def_p == NULL_DEF_OPERAND_P)
- return NULL_TREE;
-
- usevar = GIMPLE_STMT_OPERAND (*use_stmt, 0);
- if (operand_equal_p (usevar, lhs, 0))
- return *use_stmt;
-
- if (!has_single_use (DEF_FROM_PTR (def_p)))
- return NULL_TREE;
- single_imm_use (DEF_FROM_PTR (def_p), use_p, use_stmt);
- gcc_assert (*use_p != NULL_USE_OPERAND_P);
- if (TREE_CODE (*use_stmt) != GIMPLE_MODIFY_STMT)
- return NULL_TREE;
- }
- while (1);
-
- return NULL_TREE;
-}
-
/* A helper of dse_optimize_stmt.
- Given a GIMPLE_MODIFY_STMT in STMT, check that each VDEF has one
- use, and that one use is another VDEF clobbering the first one.
-
+ Given a GIMPLE_ASSIGN in STMT, find a candidate statement *USE_STMT that
+ may prove STMT to be dead.
Return TRUE if the above conditions are met, otherwise FALSE. */
static bool
-dse_possible_dead_store_p (tree stmt,
- use_operand_p *first_use_p,
- use_operand_p *use_p,
- tree *use_stmt,
- struct dse_global_data *dse_gd,
- struct dse_block_local_data *bd)
+dse_possible_dead_store_p (gimple stmt, gimple *use_stmt)
{
- ssa_op_iter op_iter;
- bool fail = false;
- def_operand_p var1;
- vuse_vec_p vv;
- tree defvar = NULL_TREE, temp;
- tree prev_defvar = NULL_TREE;
- stmt_ann_t ann = stmt_ann (stmt);
-
- /* We want to verify that each virtual definition in STMT has
- precisely one use and that all the virtual definitions are
- used by the same single statement. When complete, we
- want USE_STMT to refer to the one statement which uses
- all of the virtual definitions from STMT. */
- *use_stmt = NULL;
- FOR_EACH_SSA_VDEF_OPERAND (var1, vv, stmt, op_iter)
- {
- defvar = DEF_FROM_PTR (var1);
+ gimple temp;
+ unsigned cnt = 0;
- /* If this virtual def does not have precisely one use, then
- we will not be able to eliminate STMT. */
- if (!has_single_use (defvar))
- {
- fail = true;
- break;
- }
-
- /* Get the one and only immediate use of DEFVAR. */
- single_imm_use (defvar, use_p, &temp);
- gcc_assert (*use_p != NULL_USE_OPERAND_P);
- *first_use_p = *use_p;
-
- /* In the case of memory partitions, we may get:
+ *use_stmt = NULL;
- # MPT.764_162 = VDEF <MPT.764_161(D)>
- x = {};
- # MPT.764_167 = VDEF <MPT.764_162>
- y = {};
+ /* Find the first dominated statement that clobbers (part of) the
+ memory stmt stores to with no intermediate statement that may use
+ part of the memory stmt stores. That is, find a store that may
+ prove stmt to be a dead store. */
+ temp = stmt;
+ do
+ {
+ gimple use_stmt;
+ imm_use_iterator ui;
+ bool fail = false;
+ tree defvar;
+
+ /* Limit stmt walking to be linear in the number of possibly
+ dead stores. */
+ if (++cnt > 256)
+ return false;
- So we must make sure we're talking about the same LHS.
- */
- if (TREE_CODE (temp) == GIMPLE_MODIFY_STMT)
+ if (gimple_code (temp) == GIMPLE_PHI)
+ defvar = PHI_RESULT (temp);
+ else
+ defvar = gimple_vdef (temp);
+ temp = NULL;
+ FOR_EACH_IMM_USE_STMT (use_stmt, ui, defvar)
{
- tree base1 = get_base_address (GIMPLE_STMT_OPERAND (stmt, 0));
- tree base2 = get_base_address (GIMPLE_STMT_OPERAND (temp, 0));
-
- while (base1 && INDIRECT_REF_P (base1))
- base1 = TREE_OPERAND (base1, 0);
- while (base2 && INDIRECT_REF_P (base2))
- base2 = TREE_OPERAND (base2, 0);
+ cnt++;
- if (base1 != base2)
+ /* If we ever reach our DSE candidate stmt again fail. We
+ cannot handle dead stores in loops. */
+ if (use_stmt == stmt)
{
fail = true;
- break;
+ BREAK_FROM_IMM_USE_STMT (ui);
}
- }
-
- /* If the immediate use of DEF_VAR is not the same as the
- previously find immediate uses, then we will not be able
- to eliminate STMT. */
- if (*use_stmt == NULL)
- {
- *use_stmt = temp;
- prev_defvar = defvar;
- }
- else if (temp != *use_stmt)
- {
- /* The immediate use and the previously found immediate use
- must be the same, except... if they're uses of different
- parts of the whole. */
- if (TREE_CODE (defvar) == SSA_NAME
- && TREE_CODE (SSA_NAME_VAR (defvar)) == STRUCT_FIELD_TAG
- && TREE_CODE (prev_defvar) == SSA_NAME
- && TREE_CODE (SSA_NAME_VAR (prev_defvar)) == STRUCT_FIELD_TAG
- && (SFT_PARENT_VAR (SSA_NAME_VAR (defvar))
- == SFT_PARENT_VAR (SSA_NAME_VAR (prev_defvar))))
- ;
- else
+ /* In simple cases we can look through PHI nodes, but we
+ have to be careful with loops and with memory references
+ containing operands that are also operands of PHI nodes.
+ See gcc.c-torture/execute/20051110-*.c. */
+ else if (gimple_code (use_stmt) == GIMPLE_PHI)
+ {
+ if (temp
+ /* Make sure we are not in a loop latch block. */
+ || gimple_bb (stmt) == gimple_bb (use_stmt)
+ || dominated_by_p (CDI_DOMINATORS,
+ gimple_bb (stmt), gimple_bb (use_stmt))
+ /* We can look through PHIs to regions post-dominating
+ the DSE candidate stmt. */
+ || !dominated_by_p (CDI_POST_DOMINATORS,
+ gimple_bb (stmt), gimple_bb (use_stmt)))
+ {
+ fail = true;
+ BREAK_FROM_IMM_USE_STMT (ui);
+ }
+ temp = use_stmt;
+ }
+ /* If the statement is a use the store is not dead. */
+ else if (ref_maybe_used_by_stmt_p (use_stmt,
+ gimple_assign_lhs (stmt)))
{
fail = true;
- break;
+ BREAK_FROM_IMM_USE_STMT (ui);
+ }
+ /* If this is a store, remember it or bail out if we have
+ multiple ones (the will be in different CFG parts then). */
+ else if (gimple_vdef (use_stmt))
+ {
+ if (temp)
+ {
+ fail = true;
+ BREAK_FROM_IMM_USE_STMT (ui);
+ }
+ temp = use_stmt;
}
}
- }
-
- if (fail)
- {
- record_voperand_set (dse_gd->stores, &bd->stores, ann->uid);
- dse_record_partial_aggregate_store (stmt, dse_gd);
- return false;
- }
-
- /* Skip through any PHI nodes we have already seen if the PHI
- represents the only use of this store.
-
- Note this does not handle the case where the store has
- multiple VDEFs which all reach a set of PHI nodes in the same block. */
- while (*use_p != NULL_USE_OPERAND_P
- && TREE_CODE (*use_stmt) == PHI_NODE
- && bitmap_bit_p (dse_gd->stores, get_stmt_uid (*use_stmt)))
- {
- /* A PHI node can both define and use the same SSA_NAME if
- the PHI is at the top of a loop and the PHI_RESULT is
- a loop invariant and copies have not been fully propagated.
- The safe thing to do is exit assuming no optimization is
- possible. */
- if (SSA_NAME_DEF_STMT (PHI_RESULT (*use_stmt)) == *use_stmt)
+ if (fail)
return false;
- /* Skip past this PHI and loop again in case we had a PHI
- chain. */
- single_imm_use (PHI_RESULT (*use_stmt), use_p, use_stmt);
- }
-
- return true;
-}
-
-
-/* Given a DECL, return its AGGREGATE_VARDECL_D entry. If no entry is
- found and INSERT is TRUE, add a new entry. */
-
-static struct aggregate_vardecl_d *
-get_aggregate_vardecl (tree decl, struct dse_global_data *dse_gd, bool insert)
-{
- struct aggregate_vardecl_d av, *av_p;
- void **slot;
-
- av.decl = decl;
- slot = htab_find_slot (dse_gd->aggregate_vardecl, &av, insert ? INSERT : NO_INSERT);
-
-
- /* Not found, and we don't want to insert. */
- if (slot == NULL)
- return NULL;
-
- /* Create new entry. */
- if (*slot == NULL)
- {
- av_p = XNEW (struct aggregate_vardecl_d);
- av_p->decl = decl;
-
- /* Record how many parts the whole has. */
- if (TREE_CODE (TREE_TYPE (decl)) == COMPLEX_TYPE)
- av_p->nparts = 2;
- else if (TREE_CODE (TREE_TYPE (decl)) == RECORD_TYPE)
+ /* If we didn't find any definition this means the store is dead
+ if it isn't a store to global reachable memory. In this case
+ just pretend the stmt makes itself dead. Otherwise fail. */
+ if (!temp)
{
- tree fields;
+ if (is_hidden_global_store (stmt))
+ return false;
- /* Count the number of fields. */
- fields = TYPE_FIELDS (TREE_TYPE (decl));
- av_p->nparts = 0;
- while (fields)
- {
- av_p->nparts++;
- fields = TREE_CHAIN (fields);
- }
+ temp = stmt;
+ break;
}
- else
- abort ();
-
- av_p->ignore = true;
- av_p->parts_set = sbitmap_alloc (HOST_BITS_PER_LONG);
- sbitmap_zero (av_p->parts_set);
- *slot = av_p;
}
- else
- av_p = (struct aggregate_vardecl_d *) *slot;
-
- return av_p;
-}
-
-
-/* If STMT is a partial store into an aggregate, record which part got set. */
+ /* We deliberately stop on clobbering statements and not only on
+ killing ones to make walking cheaper. Otherwise we can just
+ continue walking until both stores have equal reference trees. */
+ while (!stmt_may_clobber_ref_p (temp, gimple_assign_lhs (stmt)));
-static void
-dse_record_partial_aggregate_store (tree stmt, struct dse_global_data *dse_gd)
-{
- tree lhs, decl;
- enum tree_code code;
- struct aggregate_vardecl_d *av_p;
- int part;
-
- gcc_assert (TREE_CODE (stmt) == GIMPLE_MODIFY_STMT);
-
- lhs = GIMPLE_STMT_OPERAND (stmt, 0);
- code = TREE_CODE (lhs);
- if (code != IMAGPART_EXPR
- && code != REALPART_EXPR
- && code != COMPONENT_REF)
- return;
- decl = TREE_OPERAND (lhs, 0);
- /* Early bail on things like nested COMPONENT_REFs. */
- if (TREE_CODE (decl) != VAR_DECL)
- return;
- /* Early bail on unions. */
- if (code == COMPONENT_REF
- && TREE_CODE (TREE_TYPE (TREE_OPERAND (lhs, 0))) != RECORD_TYPE)
- return;
-
- av_p = get_aggregate_vardecl (decl, dse_gd, /*insert=*/false);
- /* Run away, this isn't an aggregate we care about. */
- if (!av_p || av_p->ignore)
- return;
-
- switch (code)
- {
- case IMAGPART_EXPR:
- part = 0;
- break;
- case REALPART_EXPR:
- part = 1;
- break;
- case COMPONENT_REF:
- {
- tree orig_field, fields;
- tree record_type = TREE_TYPE (TREE_OPERAND (lhs, 0));
-
- /* Get FIELD_DECL. */
- orig_field = TREE_OPERAND (lhs, 1);
-
- /* FIXME: Eeech, do this more efficiently. Perhaps
- calculate bit/byte offsets. */
- part = -1;
- fields = TYPE_FIELDS (record_type);
- while (fields)
- {
- ++part;
- if (fields == orig_field)
- break;
- fields = TREE_CHAIN (fields);
- }
- gcc_assert (part >= 0);
- }
- break;
- default:
- return;
- }
-
- /* Record which part was set. */
- SET_BIT (av_p->parts_set, part);
-}
-
-
-/* Return TRUE if all parts in an AGGREGATE_VARDECL have been set. */
-
-static inline bool
-dse_whole_aggregate_clobbered_p (struct aggregate_vardecl_d *av_p)
-{
- unsigned int i;
- sbitmap_iterator sbi;
- int nbits_set = 0;
-
- /* Count the number of partial stores (bits set). */
- EXECUTE_IF_SET_IN_SBITMAP (av_p->parts_set, 0, i, sbi)
- nbits_set++;
- return ((unsigned) nbits_set == av_p->nparts);
-}
-
-
-/* Return TRUE if STMT is a store into a whole aggregate whose parts we
- have already seen and recorded. */
-
-static bool
-dse_partial_kill_p (tree stmt, struct dse_global_data *dse_gd)
-{
- tree decl;
- struct aggregate_vardecl_d *av_p;
-
- /* Make sure this is a store into the whole. */
- if (TREE_CODE (stmt) == GIMPLE_MODIFY_STMT)
- {
- enum tree_code code;
-
- decl = GIMPLE_STMT_OPERAND (stmt, 0);
- code = TREE_CODE (TREE_TYPE (decl));
-
- if (code != COMPLEX_TYPE && code != RECORD_TYPE)
- return false;
-
- if (TREE_CODE (decl) != VAR_DECL)
- return false;
- }
- else
+ if (!is_gimple_assign (temp))
return false;
- av_p = get_aggregate_vardecl (decl, dse_gd, /*insert=*/false);
- gcc_assert (av_p != NULL);
+ *use_stmt = temp;
- return dse_whole_aggregate_clobbered_p (av_p);
+ return true;
}
post dominates the first store, then the first store is dead. */
static void
-dse_optimize_stmt (struct dom_walk_data *walk_data,
- basic_block bb ATTRIBUTE_UNUSED,
- block_stmt_iterator bsi)
+dse_optimize_stmt (struct dse_global_data *dse_gd,
+ struct dse_block_local_data *bd,
+ gimple_stmt_iterator gsi)
{
- struct dse_block_local_data *bd
- = (struct dse_block_local_data *)
- VEC_last (void_p, walk_data->block_data_stack);
- struct dse_global_data *dse_gd
- = (struct dse_global_data *) walk_data->global_data;
- tree stmt = bsi_stmt (bsi);
- stmt_ann_t ann = stmt_ann (stmt);
+ gimple stmt = gsi_stmt (gsi);
/* If this statement has no virtual defs, then there is nothing
to do. */
- if (ZERO_SSA_OPERANDS (stmt, SSA_OP_VDEF))
+ if (!gimple_vdef (stmt))
return;
- /* We know we have virtual definitions. If this is a GIMPLE_MODIFY_STMT
+ /* We know we have virtual definitions. If this is a GIMPLE_ASSIGN
that's not also a function call, then record it into our table. */
- if (get_call_expr_in (stmt))
+ if (is_gimple_call (stmt) && gimple_call_fndecl (stmt))
return;
- if (ann->has_volatile_ops)
+ if (gimple_has_volatile_ops (stmt))
return;
- if (TREE_CODE (stmt) == GIMPLE_MODIFY_STMT)
+ if (is_gimple_assign (stmt))
{
- use_operand_p first_use_p = NULL_USE_OPERAND_P;
- use_operand_p use_p = NULL;
- tree use_stmt;
+ gimple use_stmt;
- if (!dse_possible_dead_store_p (stmt, &first_use_p, &use_p, &use_stmt,
- dse_gd, bd))
- return;
+ record_voperand_set (dse_gd->stores, &bd->stores, gimple_uid (stmt));
- /* If this is a partial store into an aggregate, record it. */
- dse_record_partial_aggregate_store (stmt, dse_gd);
-
- if (use_p != NULL_USE_OPERAND_P
- && bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt))
- && (!operand_equal_p (GIMPLE_STMT_OPERAND (stmt, 0),
- GIMPLE_STMT_OPERAND (use_stmt, 0), 0)
- && !dse_partial_kill_p (stmt, dse_gd))
- && memory_address_same (stmt, use_stmt))
- {
- /* If we have precisely one immediate use at this point, but
- the stores are not to the same memory location then walk the
- virtual def-use chain to get the stmt which stores to that same
- memory location. */
- if (get_use_of_stmt_lhs (stmt, &first_use_p, &use_p, &use_stmt) ==
- NULL_TREE)
- {
- record_voperand_set (dse_gd->stores, &bd->stores, ann->uid);
- return;
- }
- }
+ if (!dse_possible_dead_store_p (stmt, &use_stmt))
+ return;
/* If we have precisely one immediate use at this point and the
stores are to the same memory location or there is a chain of
virtual uses from stmt and the stmt which stores to that same
memory location, then we may have found redundant store. */
- if (use_p != NULL_USE_OPERAND_P
- && bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt))
- && (operand_equal_p (GIMPLE_STMT_OPERAND (stmt, 0),
- GIMPLE_STMT_OPERAND (use_stmt, 0), 0)
- || dse_partial_kill_p (stmt, dse_gd))
- && memory_address_same (stmt, use_stmt))
+ if (bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt))
+ && operand_equal_p (gimple_assign_lhs (stmt),
+ gimple_assign_lhs (use_stmt), 0))
{
- ssa_op_iter op_iter;
- def_operand_p var1;
- vuse_vec_p vv;
- tree stmt_lhs;
+ /* If use_stmt is or might be a nop assignment, e.g. for
+ struct { ... } S a, b, *p; ...
+ b = a; b = b;
+ or
+ b = a; b = *p; where p might be &b,
+ or
+ *p = a; *p = b; where p might be &b,
+ or
+ *p = *u; *p = *v; where p might be v, then USE_STMT
+ acts as a use as well as definition, so store in STMT
+ is not dead. */
+ if (stmt != use_stmt
+ && !is_gimple_reg (gimple_assign_rhs1 (use_stmt))
+ && !is_gimple_min_invariant (gimple_assign_rhs1 (use_stmt))
+ /* ??? Should {} be invariant? */
+ && gimple_assign_rhs_code (use_stmt) != CONSTRUCTOR
+ && refs_may_alias_p (gimple_assign_lhs (use_stmt),
+ gimple_assign_rhs1 (use_stmt)))
+ return;
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, " Deleted dead store '");
- print_generic_expr (dump_file, bsi_stmt (bsi), dump_flags);
+ print_gimple_stmt (dump_file, gsi_stmt (gsi), dump_flags, 0);
fprintf (dump_file, "'\n");
}
/* Then we need to fix the operand of the consuming stmt. */
- stmt_lhs = USE_FROM_PTR (first_use_p);
- FOR_EACH_SSA_VDEF_OPERAND (var1, vv, stmt, op_iter)
- {
- tree usevar, temp;
-
- single_imm_use (DEF_FROM_PTR (var1), &use_p, &temp);
- gcc_assert (VUSE_VECT_NUM_ELEM (*vv) == 1);
- usevar = VUSE_ELEMENT_VAR (*vv, 0);
- SET_USE (use_p, usevar);
-
- /* Make sure we propagate the ABNORMAL bit setting. */
- if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (stmt_lhs))
- SSA_NAME_OCCURS_IN_ABNORMAL_PHI (usevar) = 1;
- }
+ unlink_stmt_vdef (stmt);
/* Remove the dead store. */
- bsi_remove (&bsi, true);
+ gsi_remove (&gsi, true);
/* And release any SSA_NAMEs set in this statement back to the
SSA_NAME manager. */
release_defs (stmt);
}
-
- record_voperand_set (dse_gd->stores, &bd->stores, ann->uid);
}
}
/* Record that we have seen the PHIs at the start of BB which correspond
to virtual operands. */
static void
-dse_record_phis (struct dom_walk_data *walk_data, basic_block bb)
+dse_record_phi (struct dse_global_data *dse_gd,
+ struct dse_block_local_data *bd,
+ gimple phi)
+{
+ if (!is_gimple_reg (gimple_phi_result (phi)))
+ record_voperand_set (dse_gd->stores, &bd->stores, get_stmt_uid (phi));
+}
+
+static void
+dse_enter_block (struct dom_walk_data *walk_data, basic_block bb)
{
struct dse_block_local_data *bd
= (struct dse_block_local_data *)
VEC_last (void_p, walk_data->block_data_stack);
struct dse_global_data *dse_gd
= (struct dse_global_data *) walk_data->global_data;
- tree phi;
+ gimple_stmt_iterator gsi;
- for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
- if (!is_gimple_reg (PHI_RESULT (phi)))
- record_voperand_set (dse_gd->stores,
- &bd->stores,
- get_stmt_uid (phi));
+ for (gsi = gsi_last (bb_seq (bb)); !gsi_end_p (gsi); gsi_prev (&gsi))
+ dse_optimize_stmt (dse_gd, bd, gsi);
+ for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+ dse_record_phi (dse_gd, bd, gsi_stmt (gsi));
}
static void
-dse_finalize_block (struct dom_walk_data *walk_data,
- basic_block bb ATTRIBUTE_UNUSED)
+dse_leave_block (struct dom_walk_data *walk_data,
+ basic_block bb ATTRIBUTE_UNUSED)
{
struct dse_block_local_data *bd
= (struct dse_block_local_data *)
}
}
-
-/* Hashing and equality functions for AGGREGATE_VARDECL. */
-
-static hashval_t
-aggregate_vardecl_hash (const void *p)
-{
- return htab_hash_pointer
- ((const void *)((const struct aggregate_vardecl_d *)p)->decl);
-}
-
-static int
-aggregate_vardecl_eq (const void *p1, const void *p2)
-{
- return ((const struct aggregate_vardecl_d *)p1)->decl
- == ((const struct aggregate_vardecl_d *)p2)->decl;
-}
-
-
-/* Free memory allocated by one entry in AGGREGATE_VARDECL. */
-
-static void
-aggregate_vardecl_free (void *p)
-{
- struct aggregate_vardecl_d *entry = (struct aggregate_vardecl_d *) p;
- sbitmap_free (entry->parts_set);
- free (entry);
-}
-
-
-/* Return true if STMT is a store into an entire aggregate. */
-
-static bool
-aggregate_whole_store_p (tree stmt)
-{
- if (TREE_CODE (stmt) == GIMPLE_MODIFY_STMT)
- {
- tree lhs = GIMPLE_STMT_OPERAND (stmt, 0);
- enum tree_code code = TREE_CODE (TREE_TYPE (lhs));
-
- if (code == COMPLEX_TYPE || code == RECORD_TYPE)
- return true;
- }
- return false;
-}
-
-
/* Main entry point. */
static unsigned int
{
struct dom_walk_data walk_data;
struct dse_global_data dse_gd;
- basic_block bb;
-
- dse_gd.aggregate_vardecl =
- htab_create (37, aggregate_vardecl_hash,
- aggregate_vardecl_eq, aggregate_vardecl_free);
- max_stmt_uid = 0;
- FOR_EACH_BB (bb)
- {
- block_stmt_iterator bsi;
-
- for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
- {
- tree stmt = bsi_stmt (bsi);
-
- /* Record aggregates which have been stored into as a whole. */
- if (aggregate_whole_store_p (stmt))
- {
- tree lhs = GIMPLE_STMT_OPERAND (stmt, 0);
- if (TREE_CODE (lhs) == VAR_DECL)
- {
- struct aggregate_vardecl_d *av_p;
-
- av_p = get_aggregate_vardecl (lhs, &dse_gd, /*insert=*/true);
- av_p->ignore = false;
-
- /* Ignore aggregates with too many parts. */
- if (av_p->nparts > HOST_BITS_PER_LONG)
- av_p->ignore = true;
- }
- }
-
- /* Create a UID for each statement in the function.
- Ordering of the UIDs is not important for this pass. */
- stmt_ann (stmt)->uid = max_stmt_uid++;
- }
- }
+ renumber_gimple_stmt_uids ();
/* We might consider making this a property of each pass so that it
can be [re]computed on an as-needed basis. Particularly since
this pass could be seen as an extension of DCE which needs post
dominators. */
calculate_dominance_info (CDI_POST_DOMINATORS);
+ calculate_dominance_info (CDI_DOMINATORS);
/* Dead store elimination is fundamentally a walk of the post-dominator
tree and a backwards walk of statements within each block. */
- walk_data.walk_stmts_backward = true;
walk_data.dom_direction = CDI_POST_DOMINATORS;
walk_data.initialize_block_local_data = dse_initialize_block_local_data;
- walk_data.before_dom_children_before_stmts = NULL;
- walk_data.before_dom_children_walk_stmts = dse_optimize_stmt;
- walk_data.before_dom_children_after_stmts = dse_record_phis;
- walk_data.after_dom_children_before_stmts = NULL;
- walk_data.after_dom_children_walk_stmts = NULL;
- walk_data.after_dom_children_after_stmts = dse_finalize_block;
- walk_data.interesting_blocks = NULL;
+ walk_data.before_dom_children = dse_enter_block;
+ walk_data.after_dom_children = dse_leave_block;
walk_data.block_local_data_size = sizeof (struct dse_block_local_data);
/* This is the main hash table for the dead store elimination pass. */
dse_gd.stores = BITMAP_ALLOC (NULL);
-
walk_data.global_data = &dse_gd;
/* Initialize the dominator walker. */
/* Finalize the dominator walker. */
fini_walk_dominator_tree (&walk_data);
- /* Release unneeded data. */
+ /* Release the main bitmap. */
BITMAP_FREE (dse_gd.stores);
- htab_delete (dse_gd.aggregate_vardecl);
/* For now, just wipe the post-dominator information. */
free_dominance_info (CDI_POST_DOMINATORS);
return flag_tree_dse != 0;
}
-struct tree_opt_pass pass_dse = {
+struct gimple_opt_pass pass_dse =
+{
+ {
+ GIMPLE_PASS,
"dse", /* name */
gate_dse, /* gate */
tree_ssa_dse, /* execute */
NULL, /* next */
0, /* static_pass_number */
TV_TREE_DSE, /* tv_id */
- PROP_cfg
- | PROP_ssa
- | PROP_alias, /* properties_required */
+ PROP_cfg | PROP_ssa, /* properties_required */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
TODO_dump_func
| TODO_ggc_collect
- | TODO_verify_ssa, /* todo_flags_finish */
- 0 /* letter */
+ | TODO_verify_ssa /* todo_flags_finish */
+ }
};
-/* A very simple dead store pass eliminating write only local variables.
- The pass does not require alias information and thus can be run before
- inlining to quickly eliminate artifacts of some common C++ constructs. */
-
-static unsigned int
-execute_simple_dse (void)
-{
- block_stmt_iterator bsi;
- basic_block bb;
- bitmap variables_loaded = BITMAP_ALLOC (NULL);
- unsigned int todo = 0;
-
- /* Collect into VARIABLES LOADED all variables that are read in function
- body. */
- FOR_EACH_BB (bb)
- for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
- if (LOADED_SYMS (bsi_stmt (bsi)))
- bitmap_ior_into (variables_loaded,
- LOADED_SYMS (bsi_stmt (bsi)));
-
- /* Look for statements writting into the write only variables.
- And try to remove them. */
-
- FOR_EACH_BB (bb)
- for (bsi = bsi_start (bb); !bsi_end_p (bsi);)
- {
- tree stmt = bsi_stmt (bsi), op;
- bool removed = false;
- ssa_op_iter iter;
-
- if (STORED_SYMS (stmt) && TREE_CODE (stmt) == GIMPLE_MODIFY_STMT
- && TREE_CODE (stmt) != RETURN_EXPR
- && !bitmap_intersect_p (STORED_SYMS (stmt), variables_loaded))
- {
- unsigned int i;
- bitmap_iterator bi;
- bool dead = true;
-
-
-
- /* See if STMT only stores to write-only variables and
- verify that there are no volatile operands. tree-ssa-operands
- sets has_volatile_ops flag for all statements involving
- reads and writes when aliases are not built to prevent passes
- from removing them as dead. The flag thus has no use for us
- and we need to look into all operands. */
-
- EXECUTE_IF_SET_IN_BITMAP (STORED_SYMS (stmt), 0, i, bi)
- {
- tree var = referenced_var_lookup (i);
- if (TREE_ADDRESSABLE (var)
- || is_global_var (var)
- || TREE_THIS_VOLATILE (var))
- dead = false;
- }
-
- if (dead && LOADED_SYMS (stmt))
- EXECUTE_IF_SET_IN_BITMAP (LOADED_SYMS (stmt), 0, i, bi)
- if (TREE_THIS_VOLATILE (referenced_var_lookup (i)))
- dead = false;
-
- if (dead)
- FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_ALL_OPERANDS)
- if (TREE_THIS_VOLATILE (op))
- dead = false;
-
- /* Look for possible occurence var = indirect_ref (...) where
- indirect_ref itself is volatile. */
-
- if (dead && TREE_THIS_VOLATILE (GIMPLE_STMT_OPERAND (stmt, 1)))
- dead = false;
-
- if (dead)
- {
- tree call = get_call_expr_in (stmt);
-
- /* When LHS of var = call (); is dead, simplify it into
- call (); saving one operand. */
- if (TREE_CODE (stmt) == GIMPLE_MODIFY_STMT
- && call
- && TREE_SIDE_EFFECTS (call))
- {
- if (dump_file && (dump_flags & TDF_DETAILS))
- {
- fprintf (dump_file, "Deleted LHS of call: ");
- print_generic_stmt (dump_file, stmt, TDF_SLIM);
- fprintf (dump_file, "\n");
- }
- push_stmt_changes (bsi_stmt_ptr (bsi));
- TREE_BLOCK (call) = TREE_BLOCK (stmt);
- bsi_replace (&bsi, call, false);
- maybe_clean_or_replace_eh_stmt (stmt, call);
- mark_symbols_for_renaming (call);
- pop_stmt_changes (bsi_stmt_ptr (bsi));
- }
- else
- {
- if (dump_file && (dump_flags & TDF_DETAILS))
- {
- fprintf (dump_file, " Deleted dead store '");
- print_generic_expr (dump_file, stmt, dump_flags);
- fprintf (dump_file, "'\n");
- }
- removed = true;
- bsi_remove (&bsi, true);
- todo |= TODO_cleanup_cfg;
- }
- todo |= TODO_remove_unused_locals | TODO_ggc_collect;
- }
- }
- if (!removed)
- bsi_next (&bsi);
- }
- BITMAP_FREE (variables_loaded);
- return todo;
-}
-
-struct tree_opt_pass pass_simple_dse =
-{
- "sdse", /* name */
- NULL, /* gate */
- execute_simple_dse, /* execute */
- NULL, /* sub */
- NULL, /* next */
- 0, /* static_pass_number */
- 0, /* tv_id */
- PROP_ssa, /* properties_required */
- 0, /* properties_provided */
- 0, /* properties_destroyed */
- 0, /* todo_flags_start */
- TODO_dump_func, /* todo_flags_finish */
- 0 /* letter */
-};
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