[SelectionDAG] Fix mismatched truncate when combine BUILD_VECTOR with EXTRACT_SUBVECTOR

[junparser]

Summary

Just use correct type for truncation. Fixes PR59625

[RKSimon]

LGTM

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

if (ExtractSize % EltSize == 0) {
            (NumElems == 1 ||
             TLI.isOperationLegal(ISD::BUILD_VECTOR, ExtractVT))) &&
           (!LegalTypes || TLI.isTypeLegal(ExtractVT))) {
         unsigned IdxVal = (ExtIdx * NVT.getScalarSizeInBits()) / EltSize;
 
         if (NumElems == 1) {
           SDValue Src = V->getOperand(IdxVal);
           if (EltVT != Src.getValueType())
-            Src = DAG.getNode(ISD::TRUNCATE, SDLoc(N), InVT, Src);
+            Src = DAG.getNode(ISD::TRUNCATE, SDLoc(N), EltVT, Src);
           return DAG.getBitcast(NVT, Src);
         }
 
         // Extract the pieces from the original build_vector.
         SDValue BuildVec = DAG.getBuildVector(ExtractVT, SDLoc(N),
                                               V->ops().slice(IdxVal, NumElems));
         return DAG.getBitcast(NVT, BuildVec);
       }

llvm/test/CodeGen/WebAssembly/pr59625.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 2
+; RUN: llc < %s -mtriple=wasm32-- -mattr=+simd128 | FileCheck --check-prefix=CHECK %s
+; RUN: llc < %s -mtriple=wasm64-- -mattr=+simd128 | FileCheck --check-prefix=CHECK %s
+
+define <1 x i16> @f(<1 x i16> %0) {
+; CHECK-LABEL: f:
+; CHECK:         .functype f (v128) -> (v128)
+; CHECK-NEXT:  # %bb.0: # %BB
+; CHECK-NEXT:    v128.const 0, 0, 0, 0, 0, 0, 0, 0
+; CHECK-NEXT:    # fallthrough-return
+BB:
+  %B2 = srem <1 x i16> %0, %0
+  br label %BB1
+
+BB1:                                             ; preds = %BB
+  %B = urem <1 x i16> %B2, <i16 3>
+  ret <1 x i16> %B
+}