[clang] Produce a "multiversion" annotation in textual AST output.

[tahonermann]

Summary

This change adds a "multiversion" annotation to textual AST output.
For example:

FunctionDecl 0xb6628b0 <t.c:1:1, col:13> col:5 multiversion foo 'int (void)'

[aaron.ballman]

Is there a need for this functionality? The text node dumper already dumps attributes associated with the function: https://godbolt.org/z/EbW8E74TT

If the change is necessary, it needs some test coverage (I'd recommend adding the test to the clang/test/AST directory).

[erichkeane]

In D121961#3391988, @aaron.ballman wrote:

Is there a need for this functionality? The text node dumper already dumps attributes associated with the function: https://godbolt.org/z/EbW8E74TT

If the change is necessary, it needs some test coverage (I'd recommend adding the test to the clang/test/AST directory).

I would have found this helpful while working with MV functions in the past, particularly 'target' ones. So there is perhaps some value and minimal harm to this. That said, we definitely need a test.

[tahonermann]

Is there a need for this functionality?

Not a strong need, but I found it helpful in two scenarios:

1. A forward declaration of a multiversion function is not required to include a multiversion function attribute; later declarations might trigger multiversioning.
2. The target attribute does not necessarily declare a multiversion function.

Some examples:

void f();
__attribute__((target("default"))) void f(); // Causes multiversioning for the prior declaration.

__attribute__((target("mmx"))) void g(); // Not a multiversion function declaration.

__attribute__((target("mmx"))) void h();
__attribute__((target("sse"))) void h(); // Causes multiversioning for the prior declaration.

I'll add a test; thank you for the hint for where to add it.

[tahonermann]

Added a test.

[tahonermann]

Rebase.

[tahonermann]

Rebase to acquire fixes from parent commits.

[aaron.ballman]

LGTM (I was surprised to see the Windows CI pass with that sed invocation!)

[tahonermann]

I was surprised to see the Windows CI pass with that sed invocation!

Ha! I didn't even think about that. I had copied the RUN lines from another test and only adjusted what was necessary. The bots must have Cygwin, MSYS[2], GnuWin32, or similar installed.

clang/lib/AST/TextNodeDumper.cpp

void TextNodeDumper::Visit(const Decl *D) {
 
   if (D->isInvalidDecl())
     OS << " invalid";
   if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
     if (FD->isConstexprSpecified())
       OS << " constexpr";
     if (FD->isConsteval())
       OS << " consteval";
+    if (FD->isMultiVersion())
+      OS << " multiversion";
   }
 
   if (!isa<FunctionDecl>(*D)) {
     const auto *MD = dyn_cast<ObjCMethodDecl>(D);
     if (!MD || !MD->isThisDeclarationADefinition()) {
       const auto *DC = dyn_cast<DeclContext>(D);
       if (DC && DC->hasExternalLexicalStorage()) {
         ColorScope Color(OS, ShowColors, UndeserializedColor);

clang/test/AST/ast-dump-funcs-multiversion.c

+// Test without serialization:
+// RUN: %clang_cc1 -triple x86_64-pc-linux -ast-dump -ast-dump-filter Test %s \
+// RUN: | FileCheck --strict-whitespace %s
+//
+// Test with serialization:
+// RUN: %clang_cc1 -triple x86_64-pc-linux -emit-pch -o %t %s
+// RUN: %clang_cc1 -x c -triple x86_64-pc-linux -include-pch %t \
+// RUN:            -ast-dump-all -ast-dump-filter Test /dev/null \
+// RUN: | sed -e "s/ <undeserialized declarations>//" -e "s/ imported//" \
+// RUN: | FileCheck --strict-whitespace %s
+
+void TestUnattributedMVF(void);
+// CHECK:      FunctionDecl 0x{{[^ ]*}} <{{.*}}> col:{{[0-9]*}} multiversion TestUnattributedMVF
+__attribute__((target("default"))) void TestUnattributedMVF(void);
+// CHECK:      FunctionDecl 0x{{[^ ]*}} prev 0x{{[^ ]*}} <{{.*}}> col:{{[0-9]*}} multiversion TestUnattributedMVF
+
+__attribute__((target("mmx"))) void TestNonMVF(void);
+// CHECK:      FunctionDecl 0x{{[^ ]*}} <{{.*}}> col:{{[0-9]*}} TestNonMVF
+
+__attribute__((target("mmx"))) void TestRetroMVF(void);
+// CHECK:      FunctionDecl 0x{{[^ ]*}} <{{.*}}> col:{{[0-9]*}} multiversion TestRetroMVF
+__attribute__((target("sse"))) void TestRetroMVF(void);
+// CHECK:      FunctionDecl 0x{{[^ ]*}} <{{.*}}> col:{{[0-9]*}} multiversion TestRetroMVF