diff mbox series

cse: avoid signed overflow in compute_const_anchors [PR 104843]

Message ID a2561b832ad3ffc1a5c3a50762f916aa60068815.camel@mengyan1223.wang
State New
Headers
Series cse: avoid signed overflow in compute_const_anchors [PR 104843] |

Commit Message

Xi Ruoyao March 9, 2022, 11:19 a.m. UTC 
  Bootstrapped and tested on mips64el-linux-gnuabi64, and MIPS is the only
port with a non-zero targetm.const_anchor.  Ok for trunk?

-- >8 --

With a non-zero const_anchor, the behavior of this function relied on
signed overflow.

gcc/

	PR rtl-optimization/104843
	* cse.cc (compute_const_anchors): Cast to unsigned HOST_WIDE_INT
	to perform overflow arithmetics safely.
---
 gcc/cse.cc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Richard Biener March 9, 2022, 2:55 p.m. UTC | #1 
On Wed, Mar 9, 2022 at 12:20 PM Xi Ruoyao via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Bootstrapped and tested on mips64el-linux-gnuabi64, and MIPS is the only
> port with a non-zero targetm.const_anchor.  Ok for trunk?
>
> -- >8 --
>
> With a non-zero const_anchor, the behavior of this function relied on
> signed overflow.
>
> gcc/
>
>         PR rtl-optimization/104843
>         * cse.cc (compute_const_anchors): Cast to unsigned HOST_WIDE_INT
>         to perform overflow arithmetics safely.
> ---
>  gcc/cse.cc | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/gcc/cse.cc b/gcc/cse.cc
> index a18b599d324..7c39a009449 100644
> --- a/gcc/cse.cc
> +++ b/gcc/cse.cc
> @@ -1169,10 +1169,10 @@ compute_const_anchors (rtx cst,
>                        HOST_WIDE_INT *lower_base, HOST_WIDE_INT *lower_offs,
>                        HOST_WIDE_INT *upper_base, HOST_WIDE_INT *upper_offs)
>  {
> -  HOST_WIDE_INT n = INTVAL (cst);
> +  unsigned HOST_WIDE_INT n = INTVAL (cst);

UINTVAL (cst)?

>
>    *lower_base = n & ~(targetm.const_anchor - 1);

isn't it better to make targetm.const_anchor unsigned?
The & and ~ are not subject to overflow rules.

> -  if (*lower_base == n)
> +  if (*lower_base == INTVAL (cst))

duplicating this here is definitely ugly.

>      return false;
>
>    *upper_base =
> --
> 2.35.1
>
>
diff mbox series

Patch

diff --git a/gcc/cse.cc b/gcc/cse.cc
index a18b599d324..7c39a009449 100644
--- a/gcc/cse.cc
+++ b/gcc/cse.cc
@@ -1169,10 +1169,10 @@  compute_const_anchors (rtx cst,
 		       HOST_WIDE_INT *lower_base, HOST_WIDE_INT *lower_offs,
 		       HOST_WIDE_INT *upper_base, HOST_WIDE_INT *upper_offs)
 {
-  HOST_WIDE_INT n = INTVAL (cst);
+  unsigned HOST_WIDE_INT n = INTVAL (cst);
 
   *lower_base = n & ~(targetm.const_anchor - 1);
-  if (*lower_base == n)
+  if (*lower_base == INTVAL (cst))
     return false;
 
   *upper_base =