[Clang] Permit both gnu and clang prefixes on some attributes

[jhuber6]

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. This patch enables this for
no_sanitize and provides the infrastructure for more to be added if
needed.

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: #125760

[llvmbot]

@llvm/pr-subscribers-clang

Author: Joseph Huber (jhuber6)

Changes

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: #125760

---

Full diff: https://github.com/llvm/llvm-project/pull/125796.diff

3 Files Affected:

• (modified) clang/include/clang/Basic/Attr.td (+9-1)
• (modified) clang/test/SemaCXX/attr-no-sanitize.cpp (+2-2)
• (modified) clang/utils/TableGen/ClangAttrEmitter.cpp (+8)

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));
     }

[AaronBallman]

LGTM, but please be sure to add a release note to clang/docs/ReleaseNotes.rst so users know about the changes as well. Also, before landing, please change the summary -- this isn't allowing both clang and gnu on all attributes, just on no_sanitize (I was pretty confused at first!).

[nickdesaulniers]

Nice! Could have probably used this for NoStackProtector, too.

NoSanitizeSpecific was almost a candidate, but the attribute has different spellings between compiler namespaces. Same for AcquireCapability.