[AArch64][GlobalISel] Add selection support for <8 x s16> G_INSERT_VECTOR_ELT with GPR scalar.

Fixes the neon intrinsics test in the test suite.

Author: aemerson

llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp

@@ -3799,7 +3799,10 @@ static std::pair<unsigned, unsigned>
 getInsertVecEltOpInfo(const RegisterBank &RB, unsigned EltSize) {
   unsigned Opc, SubregIdx;
   if (RB.getID() == AArch64::GPRRegBankID) {
-    if (EltSize == 32) {
+    if (EltSize == 16) {
+      Opc = AArch64::INSvi16gpr;
+      SubregIdx = AArch64::ssub;
+    } else if (EltSize == 32) {
       Opc = AArch64::INSvi32gpr;
       SubregIdx = AArch64::ssub;
     } else if (EltSize == 64) {

llvm/test/CodeGen/AArch64/GlobalISel/select-insert-vector-elt.mir

@@ -1,6 +1,32 @@
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
 # RUN: llc -verify-machineinstrs -mtriple aarch64-unknown-unknown -run-pass=instruction-select %s -o - | FileCheck %s
 ---
+name:            v8s16_gpr
+alignment:       4
+legalized:       true
+regBankSelected: true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $q1, $w0
+
+    ; CHECK-LABEL: name: v8s16_gpr
+    ; CHECK: liveins: $q1, $w0
+    ; CHECK: [[COPY:%[0-9]+]]:gpr32 = COPY $w0
+    ; CHECK: [[COPY1:%[0-9]+]]:fpr128 = COPY $q1
+    ; CHECK: [[INSvi16gpr:%[0-9]+]]:fpr128 = INSvi16gpr [[COPY1]], 1, [[COPY]]
+    ; CHECK: $q0 = COPY [[INSvi16gpr]]
+    ; CHECK: RET_ReallyLR implicit $q0
+    %0:gpr(s32) = COPY $w0
+    %trunc:gpr(s16) = G_TRUNC %0
+    %1:fpr(<8 x s16>) = COPY $q1
+    %3:gpr(s32) = G_CONSTANT i32 1
+    %2:fpr(<8 x s16>) = G_INSERT_VECTOR_ELT %1, %trunc:gpr(s16), %3:gpr(s32)
+    $q0 = COPY %2(<8 x s16>)
+    RET_ReallyLR implicit $q0
+
+...
+---
 name:            v8s16_fpr
 alignment:       4
 legalized:       true