[clang] [Clang] [Sema] Handle `__restrict`-qualified member functions properly (PR #83187)

[via cfe-commits]

https://github.com/Sirraide created https://github.com/llvm/llvm-project/pull/83187

When resolving the type of `this` inside a member function, we were attaching all qualifiers present on the member function to the class type and then making it a pointer; however, `__restrict`, unlike `const` and `volatile`, needs to be attached to the pointer type rather than the pointee type.

This fixes #82941.

>From e9df22166fd5768e11273446cb9e52953e55cd5d Mon Sep 17 00:00:00 2001
From: Sirraide <aeternalmail at gmail.com>
Date: Tue, 27 Feb 2024 22:07:23 +0100
Subject: [PATCH 1/3] [Clang] [Sema] Handle __restrict-qualified member
 functions properly

---
 clang/lib/AST/DeclCXX.cpp            | 15 ++++++--
 clang/lib/Sema/SemaExprCXX.cpp       |  2 +-
 clang/test/SemaCXX/restrict-this.cpp | 51 ++++++++++++++++++++++++++++
 3 files changed, 65 insertions(+), 3 deletions(-)
 create mode 100644 clang/test/SemaCXX/restrict-this.cpp

diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
index 117e802dae2d9d..b4f2327d9c560a 100644
--- a/clang/lib/AST/DeclCXX.cpp
+++ b/clang/lib/AST/DeclCXX.cpp
@@ -2543,8 +2543,19 @@ QualType CXXMethodDecl::getThisType(const FunctionProtoType *FPT,
                                     const CXXRecordDecl *Decl) {
   ASTContext &C = Decl->getASTContext();
   QualType ObjectTy = ::getThisObjectType(C, FPT, Decl);
-  return C.getLangOpts().HLSL ? C.getLValueReferenceType(ObjectTy)
-                              : C.getPointerType(ObjectTy);
+
+  // Unlike 'const' and 'volatile', a '__restrict' qualifier must be
+  // attached to the pointer type, not the pointee.
+  bool Restrict = FPT->getMethodQuals().hasRestrict();
+  if (Restrict)
+    ObjectTy.removeLocalRestrict();
+
+  ObjectTy = C.getLangOpts().HLSL ? C.getLValueReferenceType(ObjectTy)
+                                  : C.getPointerType(ObjectTy);
+
+  if (Restrict)
+    ObjectTy.addRestrict();
+  return ObjectTy;
 }
 
 QualType CXXMethodDecl::getThisType() const {
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index 59758d3bd6d1a3..c4750ce78fa9c1 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -1220,7 +1220,7 @@ static QualType adjustCVQualifiersForCXXThisWithinLambda(
                     : nullptr;
     }
   }
-  return ASTCtx.getPointerType(ClassType);
+  return ThisTy;
 }
 
 QualType Sema::getCurrentThisType() {
diff --git a/clang/test/SemaCXX/restrict-this.cpp b/clang/test/SemaCXX/restrict-this.cpp
new file mode 100644
index 00000000000000..79c6081f904275
--- /dev/null
+++ b/clang/test/SemaCXX/restrict-this.cpp
@@ -0,0 +1,51 @@
+// RUN: %clang_cc1 -verify -fsyntax-only %s
+// expected-no-diagnostics
+
+struct C {
+  void f() __restrict {
+    static_assert(__is_same(decltype(this), C *__restrict));
+    (void) [this]() {
+      static_assert(__is_same(decltype(this), C *__restrict));
+      (void) [this]() { static_assert(__is_same(decltype(this), C *__restrict)); };
+
+      // By-value capture means 'this' is now a different object; do not
+      // make it __restrict.
+      (void) [*this]() { static_assert(__is_same(decltype(this), const C *)); };
+      (void) [*this]() mutable { static_assert(__is_same(decltype(this), C *)); };
+    };
+  }
+};
+
+template <typename T> struct TC {
+  void f() __restrict {
+    static_assert(__is_same(decltype(this), TC<int> *__restrict));
+    (void) [this]() {
+      static_assert(__is_same(decltype(this), TC<int> *__restrict));
+      (void) [this]() { static_assert(__is_same(decltype(this), TC<int> *__restrict)); };
+
+      // By-value capture means 'this' is now a different object; do not
+      // make it __restrict.
+      (void) [*this]() { static_assert(__is_same(decltype(this), const TC<int> *)); };
+      (void) [*this]() mutable { static_assert(__is_same(decltype(this), TC<int> *)); };
+    };
+  }
+};
+
+void f() {
+  TC<int>{}.f();
+}
+
+namespace gh82941 {
+void f(int& x) {
+    (void)x;
+}
+
+class C {
+    int x;
+    void g() __restrict;
+};
+
+void C::g() __restrict {
+    f(this->x);
+}
+}
\ No newline at end of file

>From c3031a9699582391e25e1bccd58fad59fbec379b Mon Sep 17 00:00:00 2001
From: Sirraide <aeternalmail at gmail.com>
Date: Tue, 27 Feb 2024 22:13:09 +0100
Subject: [PATCH 2/3] [Clang] Update release notes

---
 clang/docs/ReleaseNotes.rst | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 7e16b9f0c67dbd..d420f572a84487 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -290,6 +290,9 @@ Bug Fixes to C++ Support
   lookup searches the bases of an incomplete class.
 - Fix a crash when an unresolved overload set is encountered on the RHS of a ``.*`` operator.
   (`#53815 <https://github.com/llvm/llvm-project/issues/53815>`_)
+- In ``__restrict``-qualified member functions, attach ``__restrict`` to the pointer type of
+  ``this`` rather than the pointee type.
+  Fixes (`#82941 <https://github.com/llvm/llvm-project/issues/82941>`_).
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

>From 073be09acf2b20bc20b15615c81b5ae89e490786 Mon Sep 17 00:00:00 2001
From: Sirraide <aeternalmail at gmail.com>
Date: Tue, 27 Feb 2024 22:16:43 +0100
Subject: [PATCH 3/3] [NFC] Add newline at end of file

---
 clang/test/SemaCXX/restrict-this.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/test/SemaCXX/restrict-this.cpp b/clang/test/SemaCXX/restrict-this.cpp
index 79c6081f904275..8cd89f0f36a76c 100644
--- a/clang/test/SemaCXX/restrict-this.cpp
+++ b/clang/test/SemaCXX/restrict-this.cpp
@@ -48,4 +48,4 @@ class C {
 void C::g() __restrict {
     f(this->x);
 }
-}
\ No newline at end of file
+}