On November 1, 2018 10:14:13 AM GMT+01:00, Jakub Jelinek <ja...@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 <ja...@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
