In combine_simplify_rtx, CLOBBER can be returned, which is propagated to
make_compound_operation.
When make_compound_operation_int then calls simplify_subreg, it triggers a
gcc_assert, because the mode is neither inner, nor void. This results in
an ICE.
We fix this by checking if we got CLOBBER before calling simplify_subreg
from make_compound_operation and bail out; we return NULL_RTX.
Testcase from the bug report by Zhendong Su.
Bootstrapped and tested on x86_64-linux-gnu.
PR rtl-optimization/125209
2026-05-08 Boudewijn van der Heide <[email protected]>
gcc/
* combine.cc (make_compound_operation_int): Return NULL_RTX if we got
CLOBBER.
gcc/testsuite/
* gcc.dg/pr125209.c: New test.
Signed-off-by: Boudewijn van der Heide <[email protected]>
---
gcc/combine.cc | 6 ++++++
gcc/testsuite/gcc.dg/pr125209.c | 13 +++++++++++++
2 files changed, 19 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/pr125209.c
diff --git a/gcc/combine.cc b/gcc/combine.cc
index d401ca100..f98c36cf0 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -8390,6 +8390,12 @@ make_compound_operation_int (scalar_int_mode mode, rtx
*x_ptr,
tem = make_compound_operation (inner, subreg_code);
+ /* TEM's code might be CLOBBER if combine_simplify_rtx
+ could not transform a subexpression, e.g. a volatile MEM.
+ simplify_subreg cannot be called with clobber, so bail out. */
+ if (GET_CODE (tem) == CLOBBER)
+ return NULL_RTX;
+
simplified
= simplify_subreg (mode, tem, GET_MODE (inner), SUBREG_BYTE (x));
if (simplified)
diff --git a/gcc/testsuite/gcc.dg/pr125209.c b/gcc/testsuite/gcc.dg/pr125209.c
new file mode 100644
index 000000000..8fb81cc82
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr125209.c
@@ -0,0 +1,13 @@
+/* PR rtl-optimization/125209 */
+/* { dg-do compile } */
+/* { dg-options "-O1 -fno-tree-sink" } */
+
+int a, b;
+volatile unsigned c;
+extern void d(unsigned short);
+int e(long f) { return a ? f : 0; }
+int main() {
+ int g = e(c ^ !b);
+ d(g);
+ return 0;
+}
--
2.53.0
