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Improve maybe_remove_writeonly_store to do a simple DCE for defining statement 

Instead of putting a full blow DCE after execute_fixup_cfg, it makes sense
to try to remove the defining statement for the store that is being removed.
Using simple_dce_from_worklist makes this easier, just mark the ssa_name on
the rhs side of the store (if it was one) in a bitmap and then call
simple_dce_from_worklist at the end.

gcc.dg/pr36902.c needed to be changed such that the static array was no
longer a static array but a global array.  This is because this new dce
will remove the load as it is dead. I also filed PR 102864 for the warning
on dead loads.

gcc/ChangeLog:

	* tree-cfg.c (maybe_remove_writeonly_store): Add dce_ssa_names argument.
	Mark the ssa-name of the rhs as one to be removed.
	(execute_fixup_cfg): Update call to maybe_remove_writeonly_store.
	Call simple_dce_from_worklist at the end to a simple dce.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr36902.c: Move buf to be a non-static variable.
This commit is contained in:
Andrew Pinski 2021-10-16 04:14:57 +00:00
parent 36ec4a3c92
commit 113860301f
2 changed files with 17 additions and 6 deletions
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5
gcc/testsuite/gcc.dg/pr36902.c
View File

@ -24,10 +24,9 @@ struct {
unsigned char pcr_select[4];
} sel;
unsigned char buf[64];
int bar(void)
{
static unsigned char buf[64];
sel.size_of_select = 3;
foo(buf, sel.pcr_select, sel.size_of_select);
@ -52,8 +51,6 @@ foo2(unsigned char * to, const unsigned char * from, int n)
int baz(void)
{
static unsigned char buf[64];
sel.size_of_select = 5;
foo2(buf, sel.pcr_select, sel.size_of_select);

18
gcc/tree-cfg.c
View File

@ -54,6 +54,7 @@ along with GCC; see the file COPYING3. If not see
#include "value-prof.h"
#include "tree-inline.h"
#include "tree-ssa-live.h"
#include "tree-ssa-dce.h"
#include "omp-general.h"
#include "omp-expand.h"
#include "tree-cfgcleanup.h"
@ -9669,7 +9670,8 @@ make_pass_warn_unused_result (gcc::context *ctxt)
/* Maybe Remove stores to variables we marked write-only.
Return true if a store was removed. */
static bool
maybe_remove_writeonly_store (gimple_stmt_iterator &gsi, gimple *stmt)
maybe_remove_writeonly_store (gimple_stmt_iterator &gsi, gimple *stmt,
bitmap dce_ssa_names)
{
/* Keep access when store has side effect, i.e. in case when source
is volatile. */
@ -9692,6 +9694,15 @@ maybe_remove_writeonly_store (gimple_stmt_iterator &gsi, gimple *stmt)
print_gimple_stmt (dump_file, stmt, 0,
TDF_VOPS|TDF_MEMSYMS);
}
/* Mark ssa name defining to be checked for simple dce. */
if (gimple_assign_single_p (stmt))
{
tree rhs = gimple_assign_rhs1 (stmt);
if (TREE_CODE (rhs) == SSA_NAME
&& !SSA_NAME_IS_DEFAULT_DEF (rhs))
bitmap_set_bit (dce_ssa_names, SSA_NAME_VERSION (rhs));
}
unlink_stmt_vdef (stmt);
gsi_remove (&gsi, true);
release_defs (stmt);
@ -9714,6 +9725,7 @@ execute_fixup_cfg (void)
profile_count num = node->count;
profile_count den = ENTRY_BLOCK_PTR_FOR_FN (cfun)->count;
bool scale = num.initialized_p () && !(num == den);
auto_bitmap dce_ssa_names;
if (scale)
{
@ -9754,7 +9766,7 @@ execute_fixup_cfg (void)
}
/* Remove stores to variables we marked write-only. */
if (maybe_remove_writeonly_store (gsi, stmt))
if (maybe_remove_writeonly_store (gsi, stmt, dce_ssa_names))
{
todo |= TODO_update_ssa | TODO_cleanup_cfg;
continue;
@ -9820,6 +9832,8 @@ execute_fixup_cfg (void)
&& (todo & TODO_cleanup_cfg))
loops_state_set (LOOPS_NEED_FIXUP);
simple_dce_from_worklist (dce_ssa_names);
return todo;
}