[DirectX] Limit GEP transformations to Arrays (#145758)

fixes #145408

Before we see the GEP we already have transformed Allocas that get
passed the `isArrayOfVectors`.
The bug is because we are trying to transform a gep for struct of arrays
when we should only be transforming arrays.

The problem with our `visitGetElementPtrInst` is that it was doing
transformations for all allocas when it should be limiting it to the
alloca of 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
+}