[clang] [Clang] Permit both `gnu` and `clang` prefixes on attributes (PR #125796)

[Joseph Huber via cfe-commits]

https://github.com/jhuber6 created https://github.com/llvm/llvm-project/pull/125796

Summary:
Some attributes have gnu extensions that share names with clang
attributes. If these imply the same thing, we can specially declare this
to be an alternate but equivalent spelling.

Discussions welcome on whether or not we want to bind ourselves to GNU
behavior, since theoretically it's possible for GNU to silently change
the semantics away from our implementation, but I'm not an expert.

Fixes: https://github.com/llvm/llvm-project/issues/125760


>From c3b70b93e40474ca66b7ddae28e4c69d888833d1 Mon Sep 17 00:00:00 2001
From: Joseph Huber <huberjn at outlook.com>
Date: Tue, 4 Feb 2025 20:03:33 -0600
Subject: [PATCH] [Clang] Permit both `gnu` and `clang` prefixes on attributes

Summary:
Some attributes have gnu extensions that share names with clang
attributes. If these imply the same thing, we can specially declare this
to be an alternate but equivalent spelling.

Discussions welcome on whether or not we want to bind ourselves to GNU
behavior, since theoretically it's possible for GNU to silently change
the semantics away from our implementation, but I'm not an expert.

Fixes: https://github.com/llvm/llvm-project/issues/125760
---
 clang/include/clang/Basic/Attr.td         | 10 +++++++++-
 clang/test/SemaCXX/attr-no-sanitize.cpp   |  4 ++--
 clang/utils/TableGen/ClangAttrEmitter.cpp |  8 ++++++++
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index 2a3a29bd2ee1cf..bf746c2da51299 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -380,6 +380,14 @@ class Clang<string name, bit allowInC = 1, int version = 1>
   bit AllowInC = allowInC;
 }
 
+// The Clang spelling implies GNU<name>, CXX11<"clang", name>, and optionally,
+// C23<"clang", name>. This spelling should be used for any Clang-specific
+// attributes.
+class ClangGCC<string name, bit allowInC = 1, int version = 1>
+    : Spelling<name, "ClangGCC", version> {
+  bit AllowInC = allowInC;
+}
+
 // HLSL Annotation spellings
 class HLSLAnnotation<string name> : Spelling<name, "HLSLAnnotation">;
 
@@ -3677,7 +3685,7 @@ def X86ForceAlignArgPointer : InheritableAttr, TargetSpecificAttr<TargetAnyX86>
 }
 
 def NoSanitize : InheritableAttr {
-  let Spellings = [Clang<"no_sanitize">];
+  let Spellings = [ClangGCC<"no_sanitize">];
   let Args = [VariadicStringArgument<"Sanitizers">];
   let Subjects = SubjectList<[Function, ObjCMethod, GlobalVar], ErrorDiag>;
   let Documentation = [NoSanitizeDocs];
diff --git a/clang/test/SemaCXX/attr-no-sanitize.cpp b/clang/test/SemaCXX/attr-no-sanitize.cpp
index 8951f616ce0f05..cd60e71963ac30 100644
--- a/clang/test/SemaCXX/attr-no-sanitize.cpp
+++ b/clang/test/SemaCXX/attr-no-sanitize.cpp
@@ -21,8 +21,8 @@ int f3() __attribute__((no_sanitize("address")));
 
 // DUMP-LABEL: FunctionDecl {{.*}} f4
 // DUMP: NoSanitizeAttr {{.*}} hwaddress
-// PRINT: {{\[\[}}clang::no_sanitize("hwaddress")]] int f4()
-[[clang::no_sanitize("hwaddress")]] int f4();
+// PRINT: {{\[\[}}gnu::no_sanitize("hwaddress")]] int f4()
+[[gnu::no_sanitize("hwaddress")]] int f4();
 
 // DUMP-LABEL: FunctionDecl {{.*}} f5
 // DUMP: NoSanitizeAttr {{.*}} address thread hwaddress
diff --git a/clang/utils/TableGen/ClangAttrEmitter.cpp b/clang/utils/TableGen/ClangAttrEmitter.cpp
index de12c7062666a4..af7478b7986f92 100644
--- a/clang/utils/TableGen/ClangAttrEmitter.cpp
+++ b/clang/utils/TableGen/ClangAttrEmitter.cpp
@@ -108,6 +108,14 @@ GetFlattenedSpellings(const Record &Attr) {
       Ret.emplace_back("CXX11", Name, "clang", false, *Spelling);
       if (Spelling->getValueAsBit("AllowInC"))
         Ret.emplace_back("C23", Name, "clang", false, *Spelling);
+    } else if (Variety == "ClangGCC") {
+      Ret.emplace_back("GNU", Name, "", false, *Spelling);
+      Ret.emplace_back("CXX11", Name, "clang", false, *Spelling);
+      Ret.emplace_back("CXX11", Name, "gnu", false, *Spelling);
+      if (Spelling->getValueAsBit("AllowInC")) {
+        Ret.emplace_back("C23", Name, "clang", false, *Spelling);
+        Ret.emplace_back("C23", Name, "gnu", false, *Spelling);
+      }
     } else {
       Ret.push_back(FlattenedSpelling(*Spelling));
     }