[DirectX] Do not flatten GEP chains for unsupported types (llvm#150484)

Fixes llvm#150463 by not processing GEPs for unsupported types such as
structs in the DXILFlattenArrays pass.

Author: Icohedron

llvm/lib/Target/DirectX/DXILFlattenArrays.cpp

@@ -263,8 +263,13 @@ bool DXILFlattenArraysVisitor::visitGetElementPtrInst(GetElementPtrInst &GEP) {
   // merge the byte offsets. Otherwise, this GEP is itself the root of a GEP
   // chain and we need to deterine the root array type
   if (auto *PtrOpGEP = dyn_cast<GEPOperator>(PtrOperand)) {
-    assert(GEPChainInfoMap.contains(PtrOpGEP) &&
-           "Expected parent GEP to be visited before this GEP");
+
+    // If the parent GEP was not processed, then we do not want to process its
+    // descendants. This can happen if the GEP chain is for an unsupported type
+    // such as a struct -- we do not flatten structs nor GEP chains for structs
+    if (!GEPChainInfoMap.contains(PtrOpGEP))
+      return false;
+
     GEPInfo &PGEPInfo = GEPChainInfoMap[PtrOpGEP];
     Info.RootFlattenedArrayType = PGEPInfo.RootFlattenedArrayType;
     Info.RootPointerOperand = PGEPInfo.RootPointerOperand;

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

@@ -8,10 +8,12 @@ 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:    [[ARRAYINIT_ELEMENT13_I76_I1:%.*]] = getelementptr inbounds nuw [8 x i32], ptr [[ARRAYINIT_ELEMENT13_I76]], i32 0, i32 1
 ; 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
+  %arrayinit.element13.i76.i1 = getelementptr inbounds nuw [8 x i32], ptr %arrayinit.element13.i76, i32 0, i32 1
   ret void
 }