DAG: Fix extract of load combine with mismatched vector element type

Fix the case where the vector element type of the loaded extractelement
input does not match the result type of the extract.

This fixes a regression reported after
c55a765

Author: arsenm

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -23188,7 +23188,7 @@ SDValue DAGCombiner::visitEXTRACT_VECTOR_ELT(SDNode *N) {
     auto *VecLoad = dyn_cast<LoadSDNode>(VecOp);
     if (VecLoad && VecLoad->isSimple()) {
       if (SDValue Scalarized = TLI.scalarizeExtractedVectorLoad(
-              ExtVT, SDLoc(N), VecVT, Index, VecLoad, DAG)) {
+              ScalarVT, SDLoc(N), VecVT, Index, VecLoad, DAG)) {
         ++OpsNarrowed;
         return Scalarized;
       }

llvm/test/CodeGen/ARM/pr122670-regression.ll

@@ -0,0 +1,20 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -mtriple=armv7-unknown-linux-gnueabihf < %s | FileCheck %s
+
+; Check for assertion when extractelement of load optimization
+; involves a result element type different from the input vector
+; element type.
+
+define i8 @baz(ptr %ptr, i32 %arg) {
+; CHECK-LABEL: baz:
+; CHECK:       @ %bb.0: @ %bb
+; CHECK-NEXT:    add r1, r1, r1
+; CHECK-NEXT:    and r1, r1, #3
+; CHECK-NEXT:    ldr r0, [r0, r1, lsl #2]
+; CHECK-NEXT:    bx lr
+bb:
+  %load = load <2 x i64>, ptr %ptr, align 8
+  %extractelement = extractelement <2 x i64> %load, i32 %arg
+  %trunc = trunc i64 %extractelement to i8
+  ret i8 %trunc
+}