https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85757
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Ontop of recent patches:
diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c
index 32a25b9eb1e..1b672ad204a 100644
--- a/gcc/tree-ssa-dse.c
+++ b/gcc/tree-ssa-dse.c
@@ -577,6 +577,7 @@ dse_classify_store (ao_ref *ref, gimple *stmt,
else
defvar = gimple_vdef (temp);
auto_vec<gimple *, 10> defs;
+ gimple *phi_def = NULL;
FOR_EACH_IMM_USE_STMT (use_stmt, ui, defvar)
{
/* Limit stmt walking. */
@@ -600,7 +601,10 @@ dse_classify_store (ao_ref *ref, gimple *stmt,
processing. */
if (!bitmap_bit_p (visited,
SSA_NAME_VERSION (PHI_RESULT (use_stmt))))
- defs.safe_push (use_stmt);
+ {
+ defs.safe_push (use_stmt);
+ phi_def = use_stmt;
+ }
}
/* If the statement is a use the store is not dead. */
else if (ref_maybe_used_by_stmt_p (use_stmt, ref))
@@ -660,12 +671,25 @@ dse_classify_store (ao_ref *ref, gimple *stmt,
/* Process defs and remove paths starting with a kill from further
processing. */
for (unsigned i = 0; i < defs.length (); ++i)
- if (stmt_kills_ref_p (defs[i], ref))
- {
- if (by_clobber_p && !gimple_clobber_p (defs[i]))
- *by_clobber_p = false;
+ {
+ gimple *def = defs[i];
+ gimple *use_stmt;
+ use_operand_p use_p;
+ if (stmt_kills_ref_p (def, ref))
+ {
+ if (by_clobber_p && !gimple_clobber_p (def))
+ *by_clobber_p = false;
+ defs.unordered_remove (i);
+ }
+ /* In addition to kills we can remove defs whose only use
+ is another def in defs. That can only ever be PHIs of which
+ we track a single for simplicity reasons (we fail for multiple
+ PHIs anyways). */
+ else if (gimple_code (def) != GIMPLE_PHI
+ && single_imm_use (gimple_vdef (def), &use_p, &use_stmt)
+ && use_stmt == phi_def)
defs.unordered_remove (i);
- }
+ }
/* If all defs kill the ref we are done. */
if (defs.is_empty ())
