From: Jakub Jelinek <jakub@redhat.com>
Date: Sat, 27 Nov 2021 12:00:55 +0000 (+0100)
Subject: bswap: Fix UB in find_bswap_or_nop_finalize [PR103435]
X-Git-Tag: releases/gcc-10.4.0~212
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9a0152509234c514dcdb34468155459dfd7afacf;p=thirdparty%2Fgcc.git

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.

(cherry picked from commit 567d5f3d62fba2a23a9e975f7e7c7b61bb67cf24)
---

diff --git a/gcc/gimple-ssa-store-merging.c b/gcc/gimple-ssa-store-merging.c
index 1678e439e8fe..0623e6ec80b5 100644
--- a/gcc/gimple-ssa-store-merging.c
+++ b/gcc/gimple-ssa-store-merging.c
@@ -822,12 +822,18 @@ 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;