[HLSL] Allow arrays to be returned by value in HLSL (#127896)

Enable Arrays to be returned in HLSL, and a test for this.
Closes #126568

Author: spall

clang/include/clang/Basic/LangOptions.h

@@ -816,6 +816,8 @@ class LangOptions : public LangOptionsBase {
            VisibilityForcedKinds::ForceHidden;
   }
 
+  bool allowArrayReturnTypes() const { return HLSL; }
+
   /// Remap path prefix according to -fmacro-prefix-path option.
   void remapPathPrefix(SmallVectorImpl<char> &Path) const;
 

clang/lib/Sema/SemaExpr.cpp

@@ -20679,7 +20679,8 @@ ExprResult RebuildUnknownAnyExpr::VisitCallExpr(CallExpr *E) {
   const FunctionType *FnType = CalleeType->castAs<FunctionType>();
 
   // Verify that this is a legal result type of a function.
-  if (DestType->isArrayType() || DestType->isFunctionType()) {
+  if ((DestType->isArrayType() && !S.getLangOpts().allowArrayReturnTypes()) ||
+      DestType->isFunctionType()) {
     unsigned diagID = diag::err_func_returning_array_function;
     if (Kind == FK_BlockPointer)
       diagID = diag::err_block_returning_array_function;

clang/lib/Sema/SemaType.cpp

@@ -2530,7 +2530,8 @@ QualType Sema::BuildMatrixType(QualType ElementTy, Expr *NumRows, Expr *NumCols,
 }
 
 bool Sema::CheckFunctionReturnType(QualType T, SourceLocation Loc) {
-  if (T->isArrayType() || T->isFunctionType()) {
+  if ((T->isArrayType() && !getLangOpts().allowArrayReturnTypes()) ||
+      T->isFunctionType()) {
     Diag(Loc, diag::err_func_returning_array_function)
       << T->isFunctionType() << T;
     return true;
@@ -4934,7 +4935,9 @@ static TypeSourceInfo *GetFullTypeForDeclarator(TypeProcessingState &state,
 
       // C99 6.7.5.3p1: The return type may not be a function or array type.
       // For conversion functions, we'll diagnose this particular error later.
-      if (!D.isInvalidType() && (T->isArrayType() || T->isFunctionType()) &&
+      if (!D.isInvalidType() &&
+          ((T->isArrayType() && !S.getLangOpts().allowArrayReturnTypes()) ||
+           T->isFunctionType()) &&
           (D.getName().getKind() !=
            UnqualifiedIdKind::IK_ConversionFunctionId)) {
         unsigned diagID = diag::err_func_returning_array_function;

clang/test/CodeGenHLSL/BasicFeatures/ArrayReturn.hlsl

@@ -0,0 +1,33 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.0-library -disable-llvm-passes -emit-llvm -finclude-default-header -o - %s | FileCheck %s
+
+typedef int Foo[2];
+
+// CHECK-LABEL: define void {{.*}}boop{{.*}}(ptr dead_on_unwind noalias writable sret([2 x i32]) align 4 %agg.result)
+// CHECK: [[G:%.*]] = alloca [2 x i32], align 4
+// CHECK-NEXT: call void @llvm.memcpy.p0.p0.i32(ptr align 4 [[G]], ptr align 4 {{.*}}, i32 8, i1 false)
+// CHECK-NEXT: [[AIB:%.*]] = getelementptr inbounds [2 x i32], ptr %agg.result, i32 0, i32 0
+// CHECK-NEXT: br label %arrayinit.body
+// CHECK: arrayinit.body:
+// CHECK-NEXT: [[AII:%.*]] = phi i32 [ 0, %entry ], [ %arrayinit.next, %arrayinit.body ]
+// CHECK-NEXT: [[X:%.*]] = getelementptr inbounds i32, ptr [[AIB]], i32 [[AII]]
+// CHECK-NEXT: [[AI:%.*]] = getelementptr inbounds nuw [2 x i32], ptr [[G]], i32 0, i32 [[AII]]
+// CHECK-NEXT: [[Y:%.*]] = load i32, ptr [[AI]], align 4
+// CHECK-NEXT: store i32 [[Y]], ptr [[X]], align 4
+// CHECK-NEXT: [[AIN:%.*]] = add nuw i32 [[AII]], 1
+// CHECK-NEXT: [[AID:%.*]] = icmp eq i32 [[AIN]], 2
+// CHECK-NEXT: br i1 [[AID]], label %arrayinit.end, label %arrayinit.body
+// CHECK: arrayinit.end:           
+// CHECK-NEXT: ret void
+export Foo boop() {
+  Foo G = {1,2};
+  return G;
+}
+
+// CHECK-LABEL: define void {{.*}}foo{{.*}}(ptr dead_on_unwind noalias writable sret([2 x i32]) align 4 %agg.result)
+// CHECK: store i32 1, ptr %agg.result, align 4
+// CHECK-NEXT: [[E:%.*]] = getelementptr inbounds i32, ptr %agg.result, i32 1
+// CHECK-NEXT: store i32 2, ptr [[E]], align 4
+// CHECK-NEXT: ret void
+export int foo()[2] {
+  return {1,2};
+}