On Wed, 2022-03-09 at 15:55 +0100, Richard Biener wrote:
> isn't it better to make targetm.const_anchor unsigned?
> The & and ~ are not subject to overflow rules.
It's not enough: if n is the minimum value of HOST_WIDE_INT and
const_anchor = 0x8000 (the value for MIPS), we'll have a signed 0x7fff
in *upper_base. Then the next line, "*upper_offs = n - *upper_base;"
will be a signed overflow again.
How about the following?
-- >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): Use unsigned HOST_WIDE_INT for
n to perform overflow arithmetics safely.
---
gcc/cse.cc | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/gcc/cse.cc b/gcc/cse.cc
index a18b599d324..052fa0c3490 100644
--- a/gcc/cse.cc
+++ b/gcc/cse.cc
@@ -1169,12 +1169,12 @@ 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);
-
- *lower_base = n & ~(targetm.const_anchor - 1);
- if (*lower_base == n)
+ unsigned HOST_WIDE_INT n = UINTVAL (cst);
+ unsigned HOST_WIDE_INT lb = n & ~(targetm.const_anchor - 1);
+ if (lb == n)
return false;
+ *lower_base = lb;
*upper_base =
(n + (targetm.const_anchor - 1)) & ~(targetm.const_anchor - 1);
*upper_offs = n - *upper_base;
--
2.35.1
>
