https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111231
--- Comment #30 from Richard Biener <rguenth at gcc dot gnu.org> ---
I have tested the following since that might confuse the redundant store
removal sanity checks. It bootstraps fine on x86-64-unknown-linux-gnu but
causes
FAIL: gcc.dg/tree-ssa/ssa-dse-36.c scan-tree-dump-times dse1 "Deleted redundant
call" 3
FAIL: gcc.dg/tree-ssa/ssa-dse-36.c scan-tree-dump-times dse1 "Deleted redundant
store" 3
in particular foo1 and foo2 are no longer optimized. Specifically foo1:
- x = {};
+ MEM <char[10]> [(struct X *)&x] = {};
+ memset (&x.mem1, 0, 10);
the lack of the 'memset' removal looks fishy since memset uses alias set
zero while the earlier store uses the alias set of struct X (but contains
alias set zero because of the char[] members). For foo2:
x = {};
+ x.mem1[5] = 0;
the issue is less clear since 'x' is also involved in the store to
x.mem1[5] (but that store also uses alias-set zero). This shows the
situation is a bit odd wrt the behavior of a whole-aggregate store vs.
a component-wise store. But again in both cases a later conflict check
with say *(int *)p, while conflicting with the memset and x.mem1[5] stores,
would not conflict with the x = {} store.
So this fallout is to be expected and desired.
diff --git a/gcc/alias.cc b/gcc/alias.cc
index 808e2095d9b..bacae30db18 100644
--- a/gcc/alias.cc
+++ b/gcc/alias.cc
@@ -427,9 +427,7 @@ alias_set_subset_of (alias_set_type set1, alias_set_type
set2)
/* Check if set1 is a subset of set2. */
ase2 = get_alias_set_entry (set2);
- if (ase2 != 0
- && (ase2->has_zero_child
- || (ase2->children && ase2->children->get (set1))))
+ if (ase2 != 0 && ase2->children && ase2->children->get (set1))
return true;
/* As a special case we consider alias set of "void *" to be both subset
