[DirectX] Limit GEP transformations to Arrays

fixes #145408

Before we see the GEP we already have transformed Allocas that
get passed the `isArrayOfVectors`.
The problem with our `visitGetElementPtrInst` is that it was
doing transformations for all allocas when it should be limiting it
to the array cases. Technically we would have liked to make
sure it was an array of vectors cases but by the time we see
the GEP the type has been changed by replace all uses.
There should not be a problem with looking at all Arrays
since DXILDataScalarization does not change any indicies.

Author: farzonl

llvm/lib/Target/DirectX/DXILDataScalarization.cpp

@@ -308,9 +308,8 @@ bool DataScalarizerVisitor::visitGetElementPtrInst(GetElementPtrInst &GEPI) {
     NeedsTransform = true;
   } else if (AllocaInst *Alloca = dyn_cast<AllocaInst>(PtrOperand)) {
     Type *AllocatedType = Alloca->getAllocatedType();
-    // OrigGEPType might just be a pointer lets make sure
-    // to add the allocated type so we have a size
-    if (AllocatedType != OrigGEPType) {
+    // Only transform if the allocated type is an array
+    if (AllocatedType != OrigGEPType && isa<ArrayType>(AllocatedType)) {
       NewGEPType = AllocatedType;
       NeedsTransform = true;
     }

llvm/test/CodeGen/DirectX/issue-145408-gep-struct-fix.ll

@@ -0,0 +1,17 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -dxil-data-scalarization -mtriple=dxil-pc-shadermodel6.3-library %s | FileCheck %s
+
+%struct.RawStruct8D = type { [8 x i32] }
+
+define void @test_no_transform_of_struct()  {
+; CHECK-LABEL: define void @test_no_transform_of_struct() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[OUTPUTSIZESLOCAL_I:%.*]] = alloca [[STRUCT_RAWSTRUCT8D:%.*]], align 4
+; CHECK-NEXT:    [[ARRAYINIT_ELEMENT13_I76:%.*]] = getelementptr inbounds nuw [1 x %struct.RawStruct8D], ptr [[OUTPUTSIZESLOCAL_I]], i32 0, i32 0
+; CHECK-NEXT:    ret void
+;
+entry:
+  %outputSizesLocal.i = alloca %struct.RawStruct8D, align 4
+  %arrayinit.element13.i76 = getelementptr inbounds nuw [1 x %struct.RawStruct8D], ptr %outputSizesLocal.i, i32 0, i32 0
+  ret void
+}