[AST] Mangle LambdaContextDecl for top level decl

[zequanwu]

Summary

Bug filed here: https://bugs.llvm.org/show_bug.cgi?id=45213

To resolve it, we let the checks for mangling LambdaContextDecl to be analogous to ItaniumMangle strategy: https://github.com/llvm/llvm-project/blob/master/clang/lib/AST/ItaniumMangle.cpp#L1829

[rnk]

clang/lib/AST/MicrosoftMangle.cpp

949–952

Will this fix work if the inline variable is in a namespace, or inline function?

This code seems like maybe it should live in getEffectiveDeclContext. Are you sure the fix won't be there?

[zequanwu]

clang/lib/AST/MicrosoftMangle.cpp

949–952

Because whenever we got a LambdaExpr and it is inside VarDecl, we want to add @[varaible] after @<lambda_1>. So, the demangled result will have [variable]::<lambda_1>.

I think we should remove the check for record and translation unit.

[zequanwu]

clang/lib/AST/MicrosoftMangle.cpp

949–952

Otherwise, the fix won't work if inline variable is inside namespace.

[zequanwu]

Remove check for context of LambdaContextDecl.
Update test cases.

[zequanwu]

Update test cases.

[rnk]

After looking at the code more, I'm more convinced that your fix is in the right place.

clang/lib/AST/MicrosoftMangle.cpp

955

I think this code is supposed to be analogous to the ItaniumMangle.cpp code here:
https://github.com/llvm/llvm-project/blob/master/clang/lib/AST/ItaniumMangle.cpp#L1829

Can you add in && !isa<ParmVarDecl>(LambdaContextDecl) to this condition? I believe it will prevent changing the mangling in some of the test cases you have.

clang/test/CodeGenCXX/mangle-ms-cxx11.cpp

329 ↗

(On Diff #265046)

I see, this incorporate the field name x here, explaining the FieldDecl check.

340 ↗

(On Diff #265046)

I think these should not change, because they are parameters, and in this particular area we are attempting to follow the Itanium mangling strategy. Even if clang is not ABI compatible with MSVC for this feature, I would prefer it if we didn't break ABI compatibility with old versions of clang when possible.

[zequanwu]

Check LambdaContextDecl is not ParamVarDecl.

[zequanwu]

Don't mangle ParmVarDecl.

[hans]

lgtm

[zequanwu]

rebase

clang/lib/AST/MicrosoftMangle.cpp

case DeclarationName::Identifier: {
             LambdaId = LambdaManglingNumber;
           else
             LambdaId = Context.getLambdaId(Record);
 
           Name += llvm::utostr(LambdaId);
           Name += ">";
 
           mangleSourceName(Name);
 
-          // If the context of a closure type is an initializer for a class
-          // member (static or nonstatic), it is encoded in a qualified name.
+          // If the context is a variable or a class member and not a parameter,
+          // it is encoded in a qualified name.
           if (LambdaManglingNumber && LambdaContextDecl) {
             if ((isa<VarDecl>(LambdaContextDecl) ||
                  isa<FieldDecl>(LambdaContextDecl)) &&
-                LambdaContextDecl->getDeclContext()->isRecord()) {
+                !isa<ParmVarDecl>(LambdaContextDecl)) {
               mangleUnqualifiedName(cast<NamedDecl>(LambdaContextDecl));
             }
           }
           break;
         }
       }
 
       llvm::SmallString<64> Name;

clang/test/CodeGenCXX/mangle-ms-cxx17.cpp

 
 static union {
 int a;
 double b;
 };
 
 // CHECK-DAG: "?$S4@@3US@@B"
 const auto [x2, y2] = f();
+
+// CHECK-DAG: "?i1@@3V<lambda_1>@0@B"
+inline const auto i1 = [](auto x) { return 0; };
+// CHECK-DAG: "?i2@@3V<lambda_1>@0@B"
+inline const auto i2 = [](auto x) { return 1; };
+// CHECK-DAG: "??$?RH@<lambda_1>@i1@@QBE?A?<auto>@@H@Z"
+// CHECK-DAG: "??$?RH@<lambda_1>@i2@@QBE?A?<auto>@@H@Z"
+int g() {return i1(1) + i2(1); }