File gcc15-pr124250.patch of Package gcc15

From e0c46cdf3d12dd0d41d14f56dde890181497bed3 Mon Sep 17 00:00:00 2001
From: Xi Ruoyao <xry111@xry111.site>
Date: Thu, 26 Feb 2026 11:55:22 +0800
Subject: middle-end: extend the narrower shift amount before broadcasting it
 [PR 124250]

The comment above expand_vector_broadcast() states a precondition that
the mode of op must be the element mode of vmode.  But when
expand_binop() called expand_vector_broadcast() to broadcast the shift
amount, it only truncated the shift amount if it's too wide, but no
action is performed if the shift amount is too narrow.

Note that the assertion in expand_vector_broadcast is deliberately
skipped in the backport, in order not to wake up latent "harmless" bugs.

	PR middle-end/124250
	PR target/123807

gcc/
	* optabs.cc (expand_binop): Extend the shift amount if it's
	narrower than the element of the shifted vector.

gcc/testsuite/

	* gcc.c-torture/compile/pr124250.c: New test.

(cherry picked from commit 1139fdadc85a0b602a2833e6b7f2cfe2a8a90cdb)
---
 gcc/optabs.cc                                  | 32 +++++++++++++++++---------
 gcc/testsuite/gcc.c-torture/compile/pr124250.c |  8 +++++++
 2 files changed, 29 insertions(+), 11 deletions(-)
 create mode 100644 gcc/testsuite/gcc.c-torture/compile/pr124250.c

diff --git a/gcc/optabs.cc b/gcc/optabs.cc
index 0a14b1eef8a5..45c692747fd3 100644
--- a/gcc/optabs.cc
+++ b/gcc/optabs.cc
@@ -422,9 +422,9 @@ force_expand_binop (machine_mode mode, optab binoptab,
   return true;
 }
 
-/* Create a new vector value in VMODE with all elements set to OP.  The
-   mode of OP must be the element mode of VMODE.  If OP is a constant,
-   then the return value will be a constant.  */
+/* Create a new vector value in VMODE with all elements set to OP.  If OP
+   is not a constant, the mode of it must be the element mode of VMODE.
+   If OP is a constant, then the return value will be a constant.  */
 
 rtx
 expand_vector_broadcast (machine_mode vmode, rtx op)
@@ -1623,15 +1623,25 @@ expand_binop (machine_mode mode, optab binoptab, rtx op0, rtx op1,
       if (otheroptab
 	  && (icode = optab_handler (otheroptab, mode)) != CODE_FOR_nothing)
 	{
-	  /* The scalar may have been extended to be too wide.  Truncate
-	     it back to the proper size to fit in the broadcast vector.  */
+	  /* The scalar may be wider or narrower than the vector element.
+	     Truncate or extend it to the proper size to fit in the
+	     broadcast vector.  */
 	  scalar_mode inner_mode = GET_MODE_INNER (mode);
-	  if (!CONST_INT_P (op1)
-	      && (GET_MODE_BITSIZE (as_a <scalar_int_mode> (GET_MODE (op1)))
-		  > GET_MODE_BITSIZE (inner_mode)))
-	    op1 = force_reg (inner_mode,
-			     simplify_gen_unary (TRUNCATE, inner_mode, op1,
-						 GET_MODE (op1)));
+	  if (!CONST_INT_P (op1))
+	    {
+	      auto mode1 = as_a <scalar_int_mode> (GET_MODE (op1));
+	      int size1 = GET_MODE_BITSIZE (mode1);
+	      int inner_size = GET_MODE_BITSIZE (inner_mode);
+
+	      if (size1 != inner_size)
+		{
+		  auto unary = size1 > inner_size ? TRUNCATE : ZERO_EXTEND;
+		  op1 = force_reg (inner_mode,
+				   simplify_gen_unary (unary, inner_mode,
+						       op1, mode1));
+		}
+	    }
+
 	  rtx vop1 = expand_vector_broadcast (mode, op1);
 	  if (vop1)
 	    {
diff --git a/gcc/testsuite/gcc.c-torture/compile/pr124250.c b/gcc/testsuite/gcc.c-torture/compile/pr124250.c
new file mode 100644
index 000000000000..1435091dc0b8
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr124250.c
@@ -0,0 +1,8 @@
+typedef long long v2i64 __attribute__ ((vector_size (16), aligned (16)));
+v2i64 a, b;
+
+void
+test (int l)
+{
+  a = b >> (-l);
+}
-- 
cgit