[gcc r16-9384] [PATCH] combine: Check against CLOBBER in make_compound_operation_int [PR125209]

https://gcc.gnu.org/g:8b146837cefcee5955687879a60fb6aa8accc11d

commit r16-9384-g8b146837cefcee5955687879a60fb6aa8accc11d
Author: Boudewijn van der Heide <[email protected]>
Date:   Sun May 10 21:46:48 2026 -0600

    [PATCH] combine: Check against CLOBBER in make_compound_operation_int [PR125209]
    
    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
    
    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]>
    (cherry picked from commit a33f80c6ed06037bd1d31680ae3152e362931f51)

Diff:
---
 gcc/combine.cc                  |  6 ++++++
 gcc/testsuite/gcc.dg/pr125209.c | 13 +++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/gcc/combine.cc b/gcc/combine.cc
index e0dab3d88280..081b13fa4e43 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -8437,6 +8437,12 @@ 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 000000000000..8fb81cc820e9
--- /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;
+}