567d5f3d62
On gcc.c-torture/execute/pr103376.c in the following code we trigger UB
in the compiler. n->range is 8 because it is 64-bit load and rsize is 0
because it is a bswap sequence with load and known to be 0:
/* Find real size of result (highest non-zero byte). */
if (n->base_addr)
for (tmpn = n->n, rsize = 0; tmpn; tmpn >>= BITS_PER_MARKER, rsize++);
else
rsize = n->range;
The shifts then shift uint64_t by 64 bits. For this case mask is 0
and we want both *cmpxchg and *cmpnop as 0, the operation can be done as
both nop and bswap and callers will prefer nop.
2021-11-27 Jakub Jelinek <jakub@redhat.com>
PR tree-optimization/103435
* gimple-ssa-store-merging.c (find_bswap_or_nop_finalize): Avoid UB if
n->range - rsize == 8, just clear both *cmpnop and *cmpxchg in that
case.
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