From: Kishan Parmar <kishan@linux.ibm.com>
Date: Fri, 22 Aug 2025 18:58:09 +0000 (+0530)
Subject: rs6000: Add shift count guards to avoid undefined behavior [PR118890]
X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=refs%2Fheads%2Ftrunk;p=thirdparty%2Fgcc.git

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  <kishan@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 --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index 764b4992fb5..8dd23f8619c 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));