[HLSL] Enable InitList code to handle zero sized structs (#160355)

Enable InitList code to handle zero sized structs; this includes structs
with no fields and those with only unnamed bitfields.
Closes #157920

Author: spall

clang/lib/Sema/SemaHLSL.cpp

@@ -4283,6 +4283,9 @@ bool SemaHLSL::transformInitList(const InitializedEntity &Entity,
   }
   size_t ExpectedSize = ILT.DestTypes.size();
   size_t ActualSize = ILT.ArgExprs.size();
+  if (ExpectedSize == 0 && ActualSize == 0)
+    return true;
+
   // For incomplete arrays it is completely arbitrary to choose whether we think
   // the user intended fewer or more elements. This implementation assumes that
   // the user intended more, and errors that there are too few initializers to

clang/test/CodeGenHLSL/BasicFeatures/InitLists.hlsl

@@ -50,6 +50,22 @@ struct Unnamed {
   int : 8;
 };
 
+struct Empty {
+};
+
+struct UnnamedOnly {
+  int : 8;
+};
+
+struct EmptyDerived : Empty {};
+
+struct UnnamedDerived : UnnamedOnly {};
+
+// CHECK-DAG: [[ConstE:@.*]] = private unnamed_addr constant %struct.Empty undef, align 1
+// CHECK-DAG: [[ConstUO:@.*]] = private unnamed_addr constant %struct.UnnamedOnly undef, align 1
+// CHECK-DAG: [[ConstED:@.*]] = private unnamed_addr constant %struct.EmptyDerived undef, align 1
+// CHECK-DAG: [[ConstUD:@.*]] = private unnamed_addr constant %struct.UnnamedDerived undef, align 1
+
 // Case 1: Extraneous braces get ignored in literal instantiation.
 // CHECK-LABEL: define hidden void @_Z5case1v(
 // CHECK-SAME: ptr dead_on_unwind noalias writable sret([[STRUCT_TWOFLOATS:%.*]]) align 1 [[AGG_RESULT:%.*]]) #[[ATTR0:[0-9]+]] {
@@ -985,3 +1001,57 @@ void case18() {
 void case19(Unnamed U) {
   TwoInts TI = {U, 1};
 }
+
+// InitList with Empty Struct on LHS
+// CHECK-LABEL: case20
+// CHECK: [[E:%.*]] = alloca %struct.Empty, align 1
+// CHECK-NEXT: call void @llvm.memcpy.p0.p0.i32(ptr align 1 [[E]], ptr align 1 [[ConstE]], i32 1, i1 false)
+void case20() {
+  Empty E = {};
+}
+
+// InitList with Empty Struct on RHS
+// CHECK-LABEL: case21
+// CHECK: [[TI:%.*]] = alloca %struct.TwoInts, align 1
+// CHECK-NEXT: call void @llvm.memcpy.p0.p0.i32(ptr align 1 %TI, ptr align 1 {{.*}}, i32 8, i1 false)
+void case21(Empty E) {
+  TwoInts TI = {E, 1, 2};
+}
+
+// InitList with Struct with only unnamed bitfield on LHS
+// CHECK-LABEL: case22
+// CHECK: [[UO:%.*]] = alloca %struct.UnnamedOnly, align 1
+// CHECK-NEXT: call void @llvm.memcpy.p0.p0.i32(ptr align 1 [[UO]], ptr align 1 [[ConstUO]], i32 1, i1 false)
+void case22() {
+ UnnamedOnly UO = {}; 
+}
+
+// InitList with Struct with only unnamed bitfield on RHS
+// CHECK-LABEL: case23
+// CHECK: [[TI:%.*]] = alloca %struct.TwoInts, align 1
+// CHECK-NEXT: call void @llvm.memcpy.p0.p0.i32(ptr align 1 [[TI]], ptr align 1 {{.*}}, i32 8, i1 false)
+void case23(UnnamedOnly UO) {
+  TwoInts TI = {UO, 1, 2};
+}
+
+// InitList with Derived empty struct on LHS
+// InitList with Derived unnamed bitfield on LHS
+// CHECK-LABEL: case24
+// CHECK: [[ED:%.*]] = alloca %struct.EmptyDerived, align 1
+// CHECK-NEXT: [[UD:%.*]] = alloca %struct.UnnamedDerived, align 1
+// CHECK-NEXT: call void @llvm.memcpy.p0.p0.i32(ptr align 1 %ED, ptr align 1 [[ConstED]], i32 1, i1 false)
+// CHECK-NEXT: call void @llvm.memcpy.p0.p0.i32(ptr align 1 %UD, ptr align 1 [[ConstUD]], i32 1, i1 false)
+void case24() {
+ EmptyDerived ED = {};
+ UnnamedDerived UD = {};
+}
+
+// CHECK-LABEL: case25
+// CHECK: [[TI1:%.*]] = alloca %struct.TwoInts, align 1
+// CHECK-NEXT: [[TI2:%.*]] = alloca %struct.TwoInts, align 1
+// CHECK-NEXT: call void @llvm.memcpy.p0.p0.i32(ptr align 1 %TI1, ptr align 1 {{.*}}, i32 8, i1 false)
+// CHECK-NEXT: call void @llvm.memcpy.p0.p0.i32(ptr align 1 %TI2, ptr align 1 {{.*}}, i32 8, i1 false)
+void case25(EmptyDerived ED, UnnamedDerived UD) {
+ TwoInts TI1 = {ED, 1, 2};
+ TwoInts TI2 = {UD, 1, 2};
+}