https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107389
Bug ID: 107389
Summary: Alignment not inferred from type at -O0
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: rth at gcc dot gnu.org
Target Milestone: ---
Consider
typedef __uint128_t aligned_type __attribute__((aligned(16)));
_Static_assert(__alignof(aligned_type) == 16);
__uint128_t foo(aligned_type *p) { return __atomic_load_n(p, 0); }
For s390x, atomic_loadti should expand this to LPQ.
For my purposes, it must also do this at -O0, not just with
optimization. But the alignment seen by gen_atomic_loadti
is only 8, so it FAILs the expansion and falls back to libatomic.
The following appears to solve the problem:
--- a/gcc/builtins.cc
+++ b/gcc/builtins.cc
@@ -468,8 +468,11 @@ get_pointer_alignment_1
}
else
{
+ /* Assume alignment from the type. */
+ tree ptr_type = TREE_TYPE (exp);
+ tree obj_type = TREE_TYPE (ptr_type);
+ *alignp = TYPE_ALIGN (obj_type);
*bitposp = 0;
- *alignp = BITS_PER_UNIT;
return false;
}
}
but I have an inkling that would have undesired effects
for other usages. If so, perhaps a special case could be
made for the usage in get_builtin_sync_mem.
