[GlobalISel] support lowering of G_SHUFFLEVECTOR with pointer args

Author: stanleygambarin

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

@@ -8446,10 +8446,10 @@ LegalizerHelper::lowerShuffleVector(MachineInstr &MI) {
     }
   }
 
-  if (DstTy.isScalar())
-    MIRBuilder.buildCopy(DstReg, BuildVec[0]);
-  else
+  if (DstTy.isVector())
     MIRBuilder.buildBuildVector(DstReg, BuildVec);
+  else
+    MIRBuilder.buildCopy(DstReg, BuildVec[0]);
   MI.eraseFromParent();
   return Legalized;
 }

llvm/test/CodeGen/AMDGPU/shufflevector-pointer-crash.mir

@@ -0,0 +1,21 @@
+# RUN: llc -march=amdgcn -run-pass=legalizer -verify-machineinstrs %s -o - 
+
+--- |
+  define i32 @test(i64 %arg) {
+    ret i32 0
+  }
+...
+name:            test
+tracksRegLiveness: true
+body: |
+  bb.0:
+    %9:_(p0) = G_CONSTANT i64 0
+    %10:_(<2 x p0>) = G_BUILD_VECTOR %9:_(p0), %9:_(p0)
+    %8:_(<2 x p0>) = G_LOAD %9:_(p0) :: (load (<2 x p0>) from `ptr null`, align 64)
+    %11:_(p0) = G_SHUFFLE_VECTOR %8:_(<2 x p0>), %10:_, shufflemask(0)
+    %12:_(s32), %13:_(s32) = G_UNMERGE_VALUES %11:_(p0)
+    $vgpr0 = COPY %12:_(s32)
+    $vgpr1 = COPY %13:_(s32)
+    SI_RETURN implicit $vgpr0, implicit $vgpr1
+...
+