[clang] [HLSL] Update type for `out` arguments only for dependent params types (PR #163832)

[Helena Kotas via cfe-commits]

https://github.com/hekota created https://github.com/llvm/llvm-project/pull/163832

When a template function with `out` arguments is instantiated, only the arguments with dependent types need to have their `out` type updated to a restricted reference. Non-dependent argument types have already been converted and the template instantiation should not change that.

Fixes #163648

>From 607518b418053e4ef29c7b1a9b9a9bded4c48fb2 Mon Sep 17 00:00:00 2001
From: Helena Kotas <hekotas at microsoft.com>
Date: Thu, 16 Oct 2025 10:46:12 -0700
Subject: [PATCH] [HLSL] Update type for `out` arguments on template
 instantiation only for dependent params types

Non-dependent argument types have already been converted to a reference and the template instantiation should not change that.

Fixes #163648
---
 .../lib/Sema/SemaTemplateInstantiateDecl.cpp  | 18 +++++---
 .../SemaHLSL/Language/TemplateOutArg.hlsl     | 42 +++++++++++++++++++
 2 files changed, 55 insertions(+), 5 deletions(-)

diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 468bc1d677ac2..f515704aca5b3 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -765,10 +765,18 @@ static bool isRelevantAttr(Sema &S, const Decl *D, const Attr *A) {
 
 static void instantiateDependentHLSLParamModifierAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
-    const HLSLParamModifierAttr *Attr, Decl *New) {
-  ParmVarDecl *P = cast<ParmVarDecl>(New);
-  P->addAttr(Attr->clone(S.getASTContext()));
-  P->setType(S.HLSL().getInoutParameterType(P->getType()));
+    const HLSLParamModifierAttr *Attr, const Decl *Old, Decl *New) {
+  ParmVarDecl *NewParm = cast<ParmVarDecl>(New);
+  NewParm->addAttr(Attr->clone(S.getASTContext()));
+
+  const Type *OldParmTy = cast<ParmVarDecl>(Old)->getType().getTypePtr();
+  if (OldParmTy->isDependentType())
+    NewParm->setType(S.HLSL().getInoutParameterType(NewParm->getType()));
+
+  assert(!Attr->isAnyOut() || (NewParm->getType().isRestrictQualified() &&
+                               NewParm->getType()->isReferenceType()) &&
+                                  "out or inout parameter type must be a "
+                                  "reference and restrict qualified");
 }
 
 void Sema::InstantiateAttrsForDecl(
@@ -923,7 +931,7 @@ void Sema::InstantiateAttrs(const MultiLevelTemplateArgumentList &TemplateArgs,
 
     if (const auto *ParamAttr = dyn_cast<HLSLParamModifierAttr>(TmplAttr)) {
       instantiateDependentHLSLParamModifierAttr(*this, TemplateArgs, ParamAttr,
-                                                New);
+                                                Tmpl, New);
       continue;
     }
 
diff --git a/clang/test/SemaHLSL/Language/TemplateOutArg.hlsl b/clang/test/SemaHLSL/Language/TemplateOutArg.hlsl
index 2d6252cbb4d2b..543869ef058db 100644
--- a/clang/test/SemaHLSL/Language/TemplateOutArg.hlsl
+++ b/clang/test/SemaHLSL/Language/TemplateOutArg.hlsl
@@ -195,6 +195,44 @@ T buzz(int X, T Y) {
   return X + Y;
 }
 
+// Case 4: Verify that the parameter modifier attributes are instantiated 
+// for both templated and non-templated arguments, and that the non-templated
+// out argument type is not modified by the template instantiation.
+
+// CHECK-LABEL: FunctionTemplateDecl {{.*}} fizz_two
+
+// Check the pattern decl.
+// CHECK: FunctionDecl {{.*}} fizz_two 'void (inout T, out int)'
+// CHECK-NEXT: ParmVarDecl {{.*}} referenced V 'T'
+// CHECK-NEXT: HLSLParamModifierAttr {{.*}} inout
+// CHECK-NEXT: ParmVarDecl {{.*}} referenced I 'int &__restrict'
+// CHECK-NEXT: HLSLParamModifierAttr {{.*}} out
+
+// Check the 3 instantiations (int, float, & double).
+
+// CHECK-LABEL: FunctionDecl {{.*}} used fizz_two 'void (inout int, out int)' implicit_instantiation
+// CHECK: ParmVarDecl {{.*}} used V 'int &__restrict'
+// CHECK-NEXT: HLSLParamModifierAttr {{.*}} inout
+// CHECK: ParmVarDecl {{.*}} used I 'int &__restrict'
+// CHECK-NEXT: HLSLParamModifierAttr {{.*}} out
+
+// CHECK-LABEL: FunctionDecl {{.*}} used fizz_two 'void (inout float, out int)' implicit_instantiation
+// CHECK: ParmVarDecl {{.*}} used V 'float &__restrict'
+// CHECK-NEXT: HLSLParamModifierAttr {{.*}} inout
+// CHECK: ParmVarDecl {{.*}} used I 'int &__restrict'
+// CHECK-NEXT: HLSLParamModifierAttr {{.*}} out
+
+// CHECK-LABEL: FunctionDecl {{.*}} used fizz_two 'void (inout double, out int)' implicit_instantiation
+// CHECK: ParmVarDecl {{.*}} used V 'double &__restrict'
+// CHECK-NEXT: HLSLParamModifierAttr {{.*}} inout
+// CHECK: ParmVarDecl {{.*}} used I 'int &__restrict'
+// CHECK-NEXT: HLSLParamModifierAttr {{.*}} out
+template <typename T>
+void fizz_two(inout T V, out int I) {
+  V += 2;
+  I = V;
+}
+
 export void caller() {
   int X = 2;
   float Y = 3.3;
@@ -211,4 +249,8 @@ export void caller() {
   X = buzz(X, X);
   Y = buzz(X, Y);
   Z = buzz(X, Z);
+
+  fizz_two(X, X);
+  fizz_two(Y, X);
+  fizz_two(Z, X);
 }