[clang] `__noop` not marked as constexpr #102064 (PR #105983)

[via cfe-commits]

https://github.com/ofAlpaca updated https://github.com/llvm/llvm-project/pull/105983

>From 7f13ff52821a6c2ba58236fe363fb9a3a378c33b Mon Sep 17 00:00:00 2001
From: ofAlpaca <frank70199 at gmail.com>
Date: Sun, 25 Aug 2024 17:02:11 +0800
Subject: [PATCH 1/4] Fix for GH102064

---
 clang/include/clang/Basic/Builtins.td | 2 +-
 clang/lib/AST/ExprConstant.cpp        | 4 ++++
 clang/test/SemaCXX/GH102064.cpp       | 3 +++
 3 files changed, 8 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/SemaCXX/GH102064.cpp

diff --git a/clang/include/clang/Basic/Builtins.td b/clang/include/clang/Basic/Builtins.td
index f5b15cf90d1f83..b42f7ea1d9de68 100644
--- a/clang/include/clang/Basic/Builtins.td
+++ b/clang/include/clang/Basic/Builtins.td
@@ -2516,7 +2516,7 @@ def IsoVolatileStore : MSLangBuiltin, Int8_16_32_64Template {
 
 def Noop : MSLangBuiltin {
   let Spellings = ["__noop"];
-  let Attributes = [NoThrow];
+  let Attributes = [NoThrow, Constexpr];
   let Prototype = "int(...)";
 }
 
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 5af712dd7257b1..d505346bccd9b3 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -12586,6 +12586,10 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
     return false;
   }
 
+  case Builtin::BI__noop:
+  // __noop always evaluates successfully
+    return true;
+
   case Builtin::BI__builtin_is_constant_evaluated: {
     const auto *Callee = Info.CurrentCall->getCallee();
     if (Info.InConstantContext && !Info.CheckingPotentialConstantExpression &&
diff --git a/clang/test/SemaCXX/GH102064.cpp b/clang/test/SemaCXX/GH102064.cpp
new file mode 100644
index 00000000000000..52213b66e9eccc
--- /dev/null
+++ b/clang/test/SemaCXX/GH102064.cpp
@@ -0,0 +1,3 @@
+// RUN: %clang_cc1 -std=c++20 -fms-extensions %s
+// expected-no-diagnostics
+constexpr int x = []{ __noop; return 0; }();
\ No newline at end of file

>From 676b1b352d7e3279c6e3681466605e88b81dfdde Mon Sep 17 00:00:00 2001
From: ofAlpaca <frank70199 at gmail.com>
Date: Sun, 25 Aug 2024 20:03:19 +0800
Subject: [PATCH 2/4] Add release note

---
 clang/docs/ReleaseNotes.rst | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 971df672b6ca1e..e60407061ccd3b 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -861,6 +861,8 @@ Bug Fixes to Compiler Builtins
 - Clang now allows pointee types of atomic builtin arguments to be complete template types
   that was not instantiated elsewhere.
 
+- Fix ``__noop`` not marked as constexpr. (#GH102064)
+
 Bug Fixes to Attribute Support
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

>From 9730d9c50033c44766b370ccc92de6575c1eca29 Mon Sep 17 00:00:00 2001
From: ofAlpaca <frank70199 at gmail.com>
Date: Sun, 25 Aug 2024 20:13:48 +0800
Subject: [PATCH 3/4] Update testcase for end of file newline

---
 clang/test/SemaCXX/GH102064.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/test/SemaCXX/GH102064.cpp b/clang/test/SemaCXX/GH102064.cpp
index 52213b66e9eccc..0ed930439e3d75 100644
--- a/clang/test/SemaCXX/GH102064.cpp
+++ b/clang/test/SemaCXX/GH102064.cpp
@@ -1,3 +1,3 @@
 // RUN: %clang_cc1 -std=c++20 -fms-extensions %s
 // expected-no-diagnostics
-constexpr int x = []{ __noop; return 0; }();
\ No newline at end of file
+constexpr int x = []{ __noop; return 0; }();

>From 1a9a0740a1360443bf5f2ba42f7d263fdf06fdc7 Mon Sep 17 00:00:00 2001
From: ofAlpaca <frank70199 at gmail.com>
Date: Wed, 28 Aug 2024 00:48:44 +0800
Subject: [PATCH 4/4] Update ReleaseNotes.rst and testcase

---
 clang/docs/ReleaseNotes.rst     | 2 +-
 clang/test/SemaCXX/GH102064.cpp | 3 ---
 clang/test/SemaCXX/builtins.cpp | 7 +++++++
 3 files changed, 8 insertions(+), 4 deletions(-)
 delete mode 100644 clang/test/SemaCXX/GH102064.cpp

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index e60407061ccd3b..e458c1ba1550f8 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -861,7 +861,7 @@ Bug Fixes to Compiler Builtins
 - Clang now allows pointee types of atomic builtin arguments to be complete template types
   that was not instantiated elsewhere.
 
-- Fix ``__noop`` not marked as constexpr. (#GH102064)
+- ``__noop`` can now be used in a constant expression. (#GH102064)
 
 Bug Fixes to Attribute Support
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/test/SemaCXX/GH102064.cpp b/clang/test/SemaCXX/GH102064.cpp
deleted file mode 100644
index 0ed930439e3d75..00000000000000
--- a/clang/test/SemaCXX/GH102064.cpp
+++ /dev/null
@@ -1,3 +0,0 @@
-// RUN: %clang_cc1 -std=c++20 -fms-extensions %s
-// expected-no-diagnostics
-constexpr int x = []{ __noop; return 0; }();
diff --git a/clang/test/SemaCXX/builtins.cpp b/clang/test/SemaCXX/builtins.cpp
index 080b4476c7eec1..da4023fd467065 100644
--- a/clang/test/SemaCXX/builtins.cpp
+++ b/clang/test/SemaCXX/builtins.cpp
@@ -1,5 +1,7 @@
 // RUN: %clang_cc1 %s -fsyntax-only -verify -std=c++11 -fcxx-exceptions
 // RUN: %clang_cc1 %s -fsyntax-only -verify -std=c++1z -fcxx-exceptions
+// RUN: %clang_cc1 %s -fsyntax-only -verify -std=c++20 -fms-extensions -DNOOP
+#ifndef NOOP
 typedef const struct __CFString * CFStringRef;
 #define CFSTR __builtin___CFStringMakeConstantString
 
@@ -175,3 +177,8 @@ template void test_builtin_complex(int, double); // expected-note {{instantiatio
 static void __builtin_cpu_init(); // expected-error {{static declaration of '__builtin_cpu_init' follows non-static declaration}} \
                                      expected-note {{'__builtin_cpu_init' is a builtin with type 'void () noexcept'}}
 #endif
+#endif // end of NOOP
+
+#if NOOP
+constexpr int x = []{ __noop; return 0; }(); // expected-no-diagnostics
+#endif