DSE performs a backwards walk over stmts removing stores but it
leaves removing resulting dead SSA defs to later passes. This
eats into its own alias walking budget if the removed stores kept
loads live. The following patch adds removal of trivially dead
SSA defs which helps in this situation and reduces the amount of
garbage followup passes need to deal with.
Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
2021-04-28 Richard Biener <rguent...@suse.de>
PR tree-optimization/99912
* tree-ssa-dse.c (dse_dom_walker::m_need_cfg_cleanup): New.
(dse_dom_walker::todo): Likewise.
(dse_dom_walker::dse_optimize_stmt): Move VDEF check to the
caller.
(dse_dom_walker::before_dom_children): Remove trivially
dead SSA defs and schedule CFG cleanup if we removed all
PHIs in a block.
(pass_dse::execute): Get TODO as computed by the DOM walker
and return it. Wipe dominator info earlier.
* gcc.dg/pr95580.c: Disable DSE.
* gcc.dg/Wrestrict-8.c: Place a use after each memcpy.
* c-c++-common/ubsan/overflow-negate-3.c: Make asms volatile
to prevent them from being removed.
* c-c++-common/ubsan/overflow-sub-4.c: Likewise.
---
.../c-c++-common/ubsan/overflow-negate-3.c | 6 +-
.../c-c++-common/ubsan/overflow-sub-4.c | 6 +-
gcc/testsuite/gcc.dg/Wrestrict-8.c | 4 +-
gcc/testsuite/gcc.dg/pr95580.c | 2 +-
gcc/tree-ssa-dse.c | 71 +++++++++++++++----
5 files changed, 69 insertions(+), 20 deletions(-)
diff --git a/gcc/testsuite/c-c++-common/ubsan/overflow-negate-3.c
b/gcc/testsuite/c-c++-common/ubsan/overflow-negate-3.c
index 85acce8e729..6b612fa3fb7 100644
--- a/gcc/testsuite/c-c++-common/ubsan/overflow-negate-3.c
+++ b/gcc/testsuite/c-c++-common/ubsan/overflow-negate-3.c
@@ -8,11 +8,11 @@ main ()
{
int x = INT_MIN;
int y;
- asm ("" : "+g" (x));
+ __asm__ volatile ("" : "+g" (x));
y = -(-x);
- asm ("" : "+g" (y));
+ __asm__ volatile ("" : "+g" (y));
y = -(-INT_MIN);
- asm ("" : "+g" (y));
+ __asm__ volatile ("" : "+g" (y));
}
/* { dg-output "negation of -2147483648 cannot be represented in type
'int'\[^\n\r]*; cast to an unsigned type to negate this value to
itself\[^\n\r]*(\n|\r\n|\r)" } */
diff --git a/gcc/testsuite/c-c++-common/ubsan/overflow-sub-4.c
b/gcc/testsuite/c-c++-common/ubsan/overflow-sub-4.c
index d3fb9baeec9..14ed5fb93cd 100644
--- a/gcc/testsuite/c-c++-common/ubsan/overflow-sub-4.c
+++ b/gcc/testsuite/c-c++-common/ubsan/overflow-sub-4.c
@@ -9,10 +9,10 @@ main ()
int x = INT_MIN;
int y = 0;
int z;
- asm ("" : "+g" (y));
- asm ("" : "+g" (x));
+ __asm__ volatile ("" : "+g" (y));
+ __asm__ volatile ("" : "+g" (x));
z = y - (-x);
- asm ("" : "+g" (z));
+ __asm__ volatile ("" : "+g" (z));
}
/* { dg-output "negation of -2147483648 cannot be represented in type
'int'\[^\n\r]*; cast to an unsigned type to negate this value to
itself\[^\n\r]*(\n|\r\n|\r)" } */
diff --git a/gcc/testsuite/gcc.dg/Wrestrict-8.c
b/gcc/testsuite/gcc.dg/Wrestrict-8.c
index 24946b08c3b..62e8bbc3027 100644
--- a/gcc/testsuite/gcc.dg/Wrestrict-8.c
+++ b/gcc/testsuite/gcc.dg/Wrestrict-8.c
@@ -7,7 +7,9 @@ typedef __SIZE_TYPE__ size_t;
extern void* memcpy (void* restrict, const void* restrict, size_t);
-#define T(d, s, n) memcpy (d, s, n)
+void foo (void *);
+
+#define T(d, s, n) do { memcpy (d, s, n); foo (d); } while (0)
struct S1 { char c; } a8_1[8];
diff --git a/gcc/testsuite/gcc.dg/pr95580.c b/gcc/testsuite/gcc.dg/pr95580.c
index 330a3137f1e..77d8150baa8 100644
--- a/gcc/testsuite/gcc.dg/pr95580.c
+++ b/gcc/testsuite/gcc.dg/pr95580.c
@@ -1,6 +1,6 @@
/* PR c/95580 */
/* { dg-do compile } */
-/* { dg-options "-O1 -W -fno-tree-dce" } */
+/* { dg-options "-O1 -W -fno-tree-dce -fno-tree-dse" } */
void bar (void);
diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c
index 4967a5a9927..aecf6ab8c46 100644
--- a/gcc/tree-ssa-dse.c
+++ b/gcc/tree-ssa-dse.c
@@ -963,16 +963,25 @@ public:
dse_dom_walker (cdi_direction direction)
: dom_walker (direction),
m_live_bytes (param_dse_max_object_size),
- m_byte_tracking_enabled (false) {}
+ m_byte_tracking_enabled (false),
+ m_need_cfg_cleanup (false) {}
virtual edge before_dom_children (basic_block);
+ unsigned todo () const;
private:
auto_sbitmap m_live_bytes;
bool m_byte_tracking_enabled;
+ bool m_need_cfg_cleanup;
void dse_optimize_stmt (gimple_stmt_iterator *);
};
+unsigned
+dse_dom_walker::todo () const
+{
+ return m_need_cfg_cleanup ? TODO_cleanup_cfg : 0;
+}
+
/* Delete a dead call at GSI, which is mem* call of some kind. */
static void
delete_dead_or_redundant_call (gimple_stmt_iterator *gsi, const char *type)
@@ -1049,11 +1058,6 @@ dse_dom_walker::dse_optimize_stmt (gimple_stmt_iterator
*gsi)
{
gimple *stmt = gsi_stmt (*gsi);
- /* If this statement has no virtual defs, then there is nothing
- to do. */
- if (!gimple_vdef (stmt))
- return;
-
/* Don't return early on *this_2(D) ={v} {CLOBBER}. */
if (gimple_has_volatile_ops (stmt)
&& (!gimple_clobber_p (stmt)
@@ -1180,12 +1184,53 @@ dse_dom_walker::before_dom_children (basic_block bb)
for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi);)
{
- dse_optimize_stmt (&gsi);
+ gimple *stmt = gsi_stmt (gsi);
+
+ if (gimple_vdef (stmt))
+ dse_optimize_stmt (&gsi);
+ else if (def_operand_p def_p = single_ssa_def_operand (stmt, SSA_OP_DEF))
+ {
+ /* When we remove dead stores make sure to also delete trivially
+ dead SSA defs. */
+ if (has_zero_uses (DEF_FROM_PTR (def_p))
+ && !gimple_has_side_effects (stmt))
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, " Deleted trivially dead stmt: ");
+ print_gimple_stmt (dump_file, stmt, 0, dump_flags);
+ fprintf (dump_file, "\n");
+ }
+ if (gsi_remove (&gsi, true) && need_eh_cleanup)
+ bitmap_set_bit (need_eh_cleanup, bb->index);
+ release_defs (stmt);
+ }
+ }
if (gsi_end_p (gsi))
gsi = gsi_last_bb (bb);
else
gsi_prev (&gsi);
}
+ bool removed_phi = false;
+ for (gphi_iterator si = gsi_start_phis (bb); !gsi_end_p (si);)
+ {
+ gphi *phi = si.phi ();
+ if (has_zero_uses (gimple_phi_result (phi)))
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, " Deleted trivially dead PHI: ");
+ print_gimple_stmt (dump_file, phi, 0, dump_flags);
+ fprintf (dump_file, "\n");
+ }
+ remove_phi_node (&si, true);
+ removed_phi = true;
+ }
+ else
+ gsi_next (&si);
+ }
+ if (removed_phi && gimple_seq_empty_p (phi_nodes (bb)))
+ m_need_cfg_cleanup = true;
return NULL;
}
@@ -1234,21 +1279,23 @@ pass_dse::execute (function *fun)
/* Dead store elimination is fundamentally a walk of the post-dominator
tree and a backwards walk of statements within each block. */
- dse_dom_walker (CDI_POST_DOMINATORS).walk (fun->cfg->x_exit_block_ptr);
+ dse_dom_walker walker (CDI_POST_DOMINATORS);
+ walker.walk (fun->cfg->x_exit_block_ptr);
+ free_dominance_info (CDI_POST_DOMINATORS);
+
+ unsigned todo = walker.todo ();
/* 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 ();
+ todo |= TODO_cleanup_cfg;
}
BITMAP_FREE (need_eh_cleanup);
- /* For now, just wipe the post-dominator information. */
- free_dominance_info (CDI_POST_DOMINATORS);
- return 0;
+ return todo;
}
} // anon namespace
--
2.26.2
