[clang][FMV] Allow declaration of function versions in namespaces.

[labrinea]

Fixes the following bug:

namespace Name {
int __attribute((target_version("default"))) foo() { return 0; }
}

namespace Name {
int __attribute((target_version("sve"))) foo() { return 1; }
}

int bar() { return Name::foo(); }

error: redefinition of 'foo'
int __attribute((target_version("sve"))) foo() { return 1; }

note: previous definition is here
int __attribute((target_version("default"))) foo() { return 0; }

While fixing this I also found that in the absence of default version
declaration, the one we implicitly create has incorrect mangling if
we are in a namespace:

namespace OtherName {
int __attribute((target_version("sve"))) foo() { return 2; }
}

int baz() { return OtherName::foo(); }

In this example instead of creating a declaration for the symbol
@_ZN9OtherName3fooEv.default we are creating one for the symbol
@_Z3foov.default (the namespace mangling prefix is omitted).
This has now been fixed.

[llvmbot]

@llvm/pr-subscribers-clang-codegen

@llvm/pr-subscribers-clang

Author: Alexandros Lamprineas (labrinea)

Changes

Fixes a bug:

../llvm-project/clang/test/Sema/fmv-namespace.cpp:8:18: warning: attribute declaration must precede definition [-Wignored-attributes]

8 | int __attribute((target_version("sve"))) foo() { return 1; }
  |                  ^

../llvm-project/clang/test/Sema/fmv-namespace.cpp:4:46: note:
previous definition is here
4 | int __attribute((target_version("default"))) foo() { return 0; }
| ^
../llvm-project/clang/test/Sema/fmv-namespace.cpp:8:42: error:
redefinition of 'foo'
8 | int __attribute((target_version("sve"))) foo() { return 1; }
| ^
../llvm-project/clang/test/Sema/fmv-namespace.cpp:4:46: note:
previous definition is here
4 | int __attribute((target_version("default"))) foo() { return 0; }
| ^
1 warning and 1 error generated.

---

Full diff: https://github.com/llvm/llvm-project/pull/93044.diff

3 Files Affected:

• (modified) clang/lib/Sema/SemaDecl.cpp (+4-2)
• (added) clang/test/CodeGenCXX/fmv-namespace.cpp (+56)
• (added) clang/test/Sema/fmv-namespace.cpp (+12)

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index b5c3a27ab06e9..297a2feb66cbc 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -11868,8 +11868,10 @@ static bool CheckMultiVersionFunction(Sema &S, FunctionDecl *NewFD,
     return false;
 
   if (!OldDecl || !OldDecl->getAsFunction() ||
-      OldDecl->getDeclContext()->getRedeclContext() !=
-          NewFD->getDeclContext()->getRedeclContext()) {
+      (OldDecl->getDeclContext()->getRedeclContext() !=
+       NewFD->getDeclContext()->getRedeclContext() &&
+       OldDecl->getDeclContext()->getEnclosingNamespaceContext() !=
+       NewFD->getDeclContext()->getEnclosingNamespaceContext())) {
     // If there's no previous declaration, AND this isn't attempting to cause
     // multiversioning, this isn't an error condition.
     if (MVKind == MultiVersionKind::None)
diff --git a/clang/test/CodeGenCXX/fmv-namespace.cpp b/clang/test/CodeGenCXX/fmv-namespace.cpp
new file mode 100644
index 0000000000000..4d56e3be3e264
--- /dev/null
+++ b/clang/test/CodeGenCXX/fmv-namespace.cpp
@@ -0,0 +1,56 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --check-globals all --include-generated-funcs --version 5
+// RUN: %clang_cc1 -triple aarch64-linux-gnu -emit-llvm %s -o - | FileCheck %s
+
+namespace Name {
+int __attribute((target_version("default"))) foo() { return 0; }
+}
+
+namespace Name {
+int __attribute((target_version("sve"))) foo() { return 1; }
+}
+
+int bar() { return Name::foo(); }
+//.
+// CHECK: @__aarch64_cpu_features = external dso_local global { i64 }
+// CHECK: @_ZN4Name3fooEv.ifunc = weak_odr alias i32 (), ptr @_ZN4Name3fooEv
+// CHECK: @_ZN4Name3fooEv = weak_odr ifunc i32 (), ptr @_ZN4Name3fooEv.resolver
+//.
+// CHECK-LABEL: define dso_local noundef i32 @_ZN4Name3fooEv.default(
+// CHECK-SAME: ) #[[ATTR0:[0-9]+]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    ret i32 0
+//
+//
+// CHECK-LABEL: define dso_local noundef i32 @_ZN4Name3fooEv._Msve(
+// CHECK-SAME: ) #[[ATTR1:[0-9]+]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    ret i32 1
+//
+//
+// CHECK-LABEL: define dso_local noundef i32 @_Z3barv(
+// CHECK-SAME: ) #[[ATTR0]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    [[CALL:%.*]] = call noundef i32 @_ZN4Name3fooEv()
+// CHECK-NEXT:    ret i32 [[CALL]]
+//
+//
+// CHECK-LABEL: define weak_odr ptr @_ZN4Name3fooEv.resolver() comdat {
+// CHECK-NEXT:  [[RESOLVER_ENTRY:.*:]]
+// CHECK-NEXT:    call void @__init_cpu_features_resolver()
+// CHECK-NEXT:    [[TMP0:%.*]] = load i64, ptr @__aarch64_cpu_features, align 8
+// CHECK-NEXT:    [[TMP1:%.*]] = and i64 [[TMP0]], 1073741824
+// CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i64 [[TMP1]], 1073741824
+// CHECK-NEXT:    [[TMP3:%.*]] = and i1 true, [[TMP2]]
+// CHECK-NEXT:    br i1 [[TMP3]], label %[[RESOLVER_RETURN:.*]], label %[[RESOLVER_ELSE:.*]]
+// CHECK:       [[RESOLVER_RETURN]]:
+// CHECK-NEXT:    ret ptr @_ZN4Name3fooEv._Msve
+// CHECK:       [[RESOLVER_ELSE]]:
+// CHECK-NEXT:    ret ptr @_ZN4Name3fooEv.default
+//
+//.
+// CHECK: attributes #[[ATTR0]] = { mustprogress noinline nounwind optnone "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
+// CHECK: attributes #[[ATTR1]] = { mustprogress noinline nounwind optnone "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-features"="+fp-armv8,+fullfp16,+neon,+sve" }
+//.
+// CHECK: [[META0:![0-9]+]] = !{i32 1, !"wchar_size", i32 4}
+// CHECK: [[META1:![0-9]+]] = !{!"{{.*}}clang version {{.*}}"}
+//.
diff --git a/clang/test/Sema/fmv-namespace.cpp b/clang/test/Sema/fmv-namespace.cpp
new file mode 100644
index 0000000000000..1c12fd66cf243
--- /dev/null
+++ b/clang/test/Sema/fmv-namespace.cpp
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -triple aarch64-linux-gnu  -fsyntax-only -verify %s
+// expected-no-diagnostics
+
+namespace Name {
+int __attribute((target_version("default"))) foo() { return 0; }
+}
+
+namespace Name {
+int __attribute((target_version("sve"))) foo() { return 1; }
+}
+
+int bar() { return Name::foo(); }

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[labrinea]

I found another bug for implicitly declared default versions not having the namespace mangling. Fixed now, please take another look.