From 567d5f3d62fba2a23a9e975f7e7c7b61bb67cf24 Mon Sep 17 00:00:00 2001
From: Jakub Jelinek <jakub@redhat.com>
Date: Sat, 27 Nov 2021 13:00:55 +0100
Subject: [PATCH] bswap: Fix UB in find_bswap_or_nop_finalize [PR103435]
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.
---
gcc/gimple-ssa-store-merging.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/gcc/gimple-ssa-store-merging.c b/gcc/gimple-ssa-store-merging.c
index e7c90ba8b59c..a00370e2a374 100644
--- a/gcc/gimple-ssa-store-merging.c
+++ b/gcc/gimple-ssa-store-merging.c
@@ -871,12 +871,18 @@ find_bswap_or_nop_finalize (struct symbolic_number *n, uint64_t *cmpxchg,
{
mask = ((uint64_t) 1 << (rsize * BITS_PER_MARKER)) - 1;
*cmpxchg &= mask;
- *cmpnop >>= (n->range - rsize) * BITS_PER_MARKER;
+ if (n->range - rsize == sizeof (int64_t))
+ *cmpnop = 0;
+ else
+ *cmpnop >>= (n->range - rsize) * BITS_PER_MARKER;
}
else
{
mask = ((uint64_t) 1 << (rsize * BITS_PER_MARKER)) - 1;
- *cmpxchg >>= (n->range - rsize) * BITS_PER_MARKER;
+ if (n->range - rsize == sizeof (int64_t))
+ *cmpxchg = 0;
+ else
+ *cmpxchg >>= (n->range - rsize) * BITS_PER_MARKER;
*cmpnop &= mask;
}
n->range = rsize;
--
GitLab