/* Dead store elimination
- Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009
+ 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"
the CFG. */
-struct dse_global_data
-{
- /* This is the global bitmap for store statements.
-
- Each statement has a unique ID. When we encounter a store statement
- that we want to record, set the bit corresponding to the statement's
- unique ID in this bitmap. */
- bitmap stores;
-};
-
-/* We allocate a bitmap-per-block for stores which are encountered
- 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;
-};
+/* Bitmap of blocks that have had EH statements cleaned. We should
+ remove their dead edges eventually. */
+static bitmap need_eh_cleanup;
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_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);
-
-/* Returns uid of statement STMT. */
-
-static unsigned
-get_stmt_uid (gimple stmt)
-{
- if (gimple_code (stmt) == GIMPLE_PHI)
- return SSA_NAME_VERSION (gimple_phi_result (stmt))
- + gimple_stmt_max_uid (cfun);
-
- return gimple_uid (stmt);
-}
-
-/* Set bit UID in bitmaps GLOBAL and *LOCAL, creating *LOCAL as needed. */
-static void
-record_voperand_set (bitmap global, bitmap *local, unsigned int uid)
-{
- /* Lazily allocate the bitmap. Note that we do not get a notification
- when the block local data structures die, so we allocate the local
- bitmap backed by the GC system. */
- if (*local == NULL)
- *local = BITMAP_GGC_ALLOC ();
-
- /* Set the bit in the local and global bitmaps. */
- bitmap_set_bit (*local, uid);
- bitmap_set_bit (global, uid);
-}
-
-/* Initialize block local data structures. */
-
-static void
-dse_initialize_block_local_data (struct dom_walk_data *walk_data,
- basic_block bb ATTRIBUTE_UNUSED,
- bool recycled)
-{
- struct dse_block_local_data *bd
- = (struct dse_block_local_data *)
- VEC_last (void_p, walk_data->block_data_stack);
-
- /* If we are given a recycled block local data structure, ensure any
- bitmap associated with the block is cleared. */
- if (recycled)
- {
- if (bd->stores)
- bitmap_clear (bd->stores);
- }
-}
/* A helper of dse_optimize_stmt.
Given a GIMPLE_ASSIGN in STMT, find a candidate statement *USE_STMT that
temp = stmt;
do
{
- gimple prev, use_stmt;
+ gimple use_stmt;
imm_use_iterator ui;
bool fail = false;
tree defvar;
defvar = PHI_RESULT (temp);
else
defvar = gimple_vdef (temp);
- prev = temp;
temp = NULL;
FOR_EACH_IMM_USE_STMT (use_stmt, ui, defvar)
{
cnt++;
+ /* If we ever reach our DSE candidate stmt again fail. We
+ cannot handle dead stores in loops. */
+ if (use_stmt == stmt)
+ {
+ fail = true;
+ BREAK_FROM_IMM_USE_STMT (ui);
+ }
/* 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. */
- if (gimple_code (use_stmt) == GIMPLE_PHI)
+ else if (gimple_code (use_stmt) == GIMPLE_PHI)
{
if (temp
- /* We can look through PHIs to post-dominated regions
- without worrying if the use not also dominates prev
- (in which case it would be a loop PHI with the use
- in a latch block). */
- || gimple_bb (prev) == gimple_bb (use_stmt)
- || !dominated_by_p (CDI_POST_DOMINATORS,
- gimple_bb (prev), gimple_bb (use_stmt))
+ /* Make sure we are not in a loop latch block. */
+ || gimple_bb (stmt) == gimple_bb (use_stmt)
|| dominated_by_p (CDI_DOMINATORS,
- gimple_bb (prev), gimple_bb (use_stmt)))
+ 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);
continue walking until both stores have equal reference trees. */
while (!stmt_may_clobber_ref_p (temp, gimple_assign_lhs (stmt)));
- if (!is_gimple_assign (temp))
- return false;
-
*use_stmt = temp;
return true;
post dominates the first store, then the first store is dead. */
static void
-dse_optimize_stmt (struct dse_global_data *dse_gd,
- struct dse_block_local_data *bd,
- gimple_stmt_iterator gsi)
+dse_optimize_stmt (gimple_stmt_iterator gsi)
{
gimple stmt = gsi_stmt (gsi);
{
gimple use_stmt;
- record_voperand_set (dse_gd->stores, &bd->stores, gimple_uid (stmt));
-
if (!dse_possible_dead_store_p (stmt, &use_stmt))
return;
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 (bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt))
- && operand_equal_p (gimple_assign_lhs (stmt),
- gimple_assign_lhs (use_stmt), 0))
+ if ((gimple_has_lhs (use_stmt)
+ && (operand_equal_p (gimple_assign_lhs (stmt),
+ gimple_get_lhs (use_stmt), 0)))
+ || stmt_kills_ref_p (use_stmt, gimple_assign_lhs (stmt)))
{
/* If use_stmt is or might be a nop assignment, e.g. for
struct { ... } S a, b, *p; ...
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)))
+ && ref_maybe_used_by_stmt_p (use_stmt, gimple_assign_lhs (stmt)))
return;
if (dump_file && (dump_flags & TDF_DETAILS))
/* Then we need to fix the operand of the consuming stmt. */
unlink_stmt_vdef (stmt);
+ bitmap_set_bit (need_eh_cleanup, gimple_bb (stmt)->index);
+
/* Remove the dead store. */
gsi_remove (&gsi, true);
}
}
-/* Record that we have seen the PHIs at the start of BB which correspond
- to virtual operands. */
-static void
-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)
+dse_enter_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
+ 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;
gimple_stmt_iterator gsi;
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_leave_block (struct dom_walk_data *walk_data,
- basic_block bb ATTRIBUTE_UNUSED)
-{
- 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;
- bitmap stores = dse_gd->stores;
- unsigned int i;
- bitmap_iterator bi;
-
- /* Unwind the stores noted in this basic block. */
- if (bd->stores)
- EXECUTE_IF_SET_IN_BITMAP (bd->stores, 0, i, bi)
- {
- bitmap_clear_bit (stores, i);
- }
+ dse_optimize_stmt (gsi);
}
/* Main entry point. */
tree_ssa_dse (void)
{
struct dom_walk_data walk_data;
- struct dse_global_data dse_gd;
+
+ need_eh_cleanup = BITMAP_ALLOC (NULL);
renumber_gimple_stmt_uids ();
/* Dead store elimination is fundamentally a walk of the post-dominator
tree and a backwards walk of statements within each block. */
walk_data.dom_direction = CDI_POST_DOMINATORS;
- walk_data.initialize_block_local_data = dse_initialize_block_local_data;
+ walk_data.initialize_block_local_data = 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);
+ walk_data.after_dom_children = NULL;
- /* This is the main hash table for the dead store elimination pass. */
- dse_gd.stores = BITMAP_ALLOC (NULL);
- walk_data.global_data = &dse_gd;
+ walk_data.block_local_data_size = 0;
+ walk_data.global_data = NULL;
/* Initialize the dominator walker. */
init_walk_dominator_tree (&walk_data);
/* Finalize the dominator walker. */
fini_walk_dominator_tree (&walk_data);
- /* Release the main bitmap. */
- BITMAP_FREE (dse_gd.stores);
+ /* Removal of stores may make some EH edges dead. Purge such edges from
+ the CFG as needed. */
+ if (!bitmap_empty_p (need_eh_cleanup))
+ {
+ gimple_purge_all_dead_eh_edges (need_eh_cleanup);
+ cleanup_tree_cfg ();
+ }
+ BITMAP_FREE (need_eh_cleanup);
+
/* For now, just wipe the post-dominator information. */
free_dominance_info (CDI_POST_DOMINATORS);
return 0;
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