https://gcc.gnu.org/g:9d63110c4334335a920424c301691dae9ecf398f
commit r16-3351-g9d63110c4334335a920424c301691dae9ecf398f
Author: Kishan Parmar <kis...@linux.ibm.com>
Date: Sat Aug 23 00:28:09 2025 +0530
rs6000: Add shift count guards to avoid undefined behavior [PR118890]
This patch adds missing guards on shift amounts to prevent UB when the
shift count equals or exceeds HOST_BITS_PER_WIDE_INT.
In the patch (r16-2666-g647bd0a02789f1), shift counts were only checked
for nonzero but not for being within valid bounds. This patch tightens
those conditions by enforcing that shift counts are greater than zero
and less than HOST_BITS_PER_WIDE_INT.
2025-08-23 Kishan Parmar <kis...@linux.ibm.com>
gcc/
PR target/118890
* config/rs6000/rs6000.cc (can_be_rotated_to_negative_lis): Add
bounds
checks for shift counts to prevent undefined behavior.
(rs6000_emit_set_long_const): Likewise.
Diff:
---
gcc/config/rs6000/rs6000.cc | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index 764b4992fb56..8dd23f8619cd 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -10322,7 +10322,7 @@ can_be_rotated_to_negative_lis (HOST_WIDE_INT c, int
*rot)
rotated over the highest bit. */
unsigned HOST_WIDE_INT uc = c;
int pos_one = clz_hwi ((HOST_WIDE_INT) (uc << 16) >> 16);
- if (pos_one != 0)
+ if (pos_one > 0 && pos_one < HOST_BITS_PER_WIDE_INT)
{
middle_zeros = ctz_hwi (c >> (HOST_BITS_PER_WIDE_INT - pos_one));
int middle_ones = clz_hwi (~(uc << pos_one));
@@ -10585,7 +10585,7 @@ rs6000_emit_set_long_const (rtx dest, HOST_WIDE_INT c,
int *num_insns)
{
/* li/lis; rldicX */
unsigned HOST_WIDE_INT imm = (c | ~mask);
- if (shift != 0)
+ if (shift > 0 && shift < HOST_BITS_PER_WIDE_INT)
imm = (imm >> shift) | (imm << (HOST_BITS_PER_WIDE_INT - shift));
count_or_emit_insn (temp, GEN_INT (imm));
