From edb45d8ae4b3f4cad257e509db2e01e84bf0aa84 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov@redhat.com>
Date: Tue, 9 Dec 2025 12:18:21 +0100
Subject: [PATCH] [SDAG] Allow implicit trunc in BUILD_VECTOR legalization

BUILD_VECTOR may have operands larger than the result element type,
in which case it is specified to truncate. As such, allow implicit
truncation.
---
 llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index 1630dd783e82..fc3e9ff0d623 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -2051,7 +2051,8 @@ SDValue SelectionDAGLegalize::ExpandBUILD_VECTOR(SDNode *Node) {
           // we don't want a v16i8 to become a v16i32 for example.
           const ConstantInt *CI = V->getConstantIntValue();
           CV.push_back(ConstantInt::get(EltVT.getTypeForEVT(*DAG.getContext()),
-                                        CI->getZExtValue()));
+                                        CI->getZExtValue(), /*IsSigned=*/false,
+                                        /*ImplicitTrunc=*/true));
         }
       } else {
         assert(Node->getOperand(i).isUndef());