[PATCH] Fix UB in store-merging or bswap opt (PR tree-optimization/87826)

[Richard Biener]

On November 1, 2018 10:14:13 AM GMT+01:00, Jakub Jelinek <jakub@redhat.com> wrote:
>Hi!
>
>When compiling code with UB shifts/rotates where the shift count is out
>of
>range constant, the store-merging and bswap opts will invoke UB in the
>compiler too.
>The following patch prevents that.
>
>Bootstrapped/regtested on x86_64-linux and i686-linux, ok for
>trunk/8.x?

OK. 

Richard. 

>2018-11-01  Jakub Jelinek  <jakub@redhat.com>
>
>	PR tree-optimization/87826
>	* gimple-ssa-store-merging.c (do_shift_rotate): Punt if count is
>	negative or larger or equal to type's precision.
>
>	* gcc.dg/pr87826.c: New test.
>
>--- gcc/gimple-ssa-store-merging.c.jj	2018-10-23 10:13:25.199876583
>+0200
>+++ gcc/gimple-ssa-store-merging.c	2018-10-31 11:07:50.961296026 +0100
>@@ -262,7 +262,9 @@ do_shift_rotate (enum tree_code code,
>   int i, size = TYPE_PRECISION (n->type) / BITS_PER_UNIT;
>   unsigned head_marker;
> 
>-  if (count % BITS_PER_UNIT != 0)
>+  if (count < 0
>+      || count >= TYPE_PRECISION (n->type)
>+      || count % BITS_PER_UNIT != 0)
>     return false;
>   count = (count / BITS_PER_UNIT) * BITS_PER_MARKER;
> 
>--- gcc/testsuite/gcc.dg/pr87826.c.jj	2018-10-31 11:08:56.907209723
>+0100
>+++ gcc/testsuite/gcc.dg/pr87826.c	2018-10-31 11:25:48.078579206 +0100
>@@ -0,0 +1,13 @@
>+/* PR tree-optimization/87826 */
>+/* { dg-do compile } */
>+/* { dg-options "-O3 -w" } */
>+
>+int c;
>+
>+void
>+foo (int *b)
>+{
>+  int e;
>+  for (e = 0; e < 16; ++e)
>+    b[e] = c >> e * 8;
>+}
>
>	Jakub