[clang][CodeGen] Fix global variables initialized with an inheriting constructor.

[efriedma]

Summary

For inheriting constructors which have to be emitted inline, we use CodeGenFunction::EmitInlinedInheritingCXXConstructorCall to emit the required code. This code uses EmitParmDecl to emit the "this" argument of the call. EmitParmDecl then helpfully calls llvm::Value::setName to name the parameter... which renames the global variable to "this".

To fix the issue, skip the setName call on globals.

The renaming still has slightly weird results in other cases (it renames all local variables initialized with an inlined inheriting constructor to "this"), but the result isn't actually wrong in those cases, so I'm just going to leave it for now.

Fixes https://github.com/llvm/llvm-project/issues/63618

[rsmith]

Wow, what an amazing bug :)

clang/lib/CodeGen/CGDecl.cpp

2459

Is it feasible to only set the name if the value doesn't already have a name, or do we give values bad names often enough that it's better to overwrite an existing name here?

[efriedma]

clang/lib/CodeGen/CGDecl.cpp

2459

Outside the EmitInlinedInheritingCXXConstructorCall case, the arguments are generally either llvm::Argument, or llvm::Instruction generated by calling convention code. It might make sense to just make the calling convention code name the values itself (it already names some of the values it generates).

But I'll stick with the conservative fix here, and leave that for a followup.

clang/lib/CodeGen/CGDecl.cpp

 /// for the specified parameter and set up LocalDeclMap.
 void CodeGenFunction::EmitParmDecl(const VarDecl &D, ParamValue Arg,
                                    unsigned ArgNo) {
   bool NoDebugInfo = false;
   // FIXME: Why isn't ImplicitParamDecl a ParmVarDecl?
   assert((isa<ParmVarDecl>(D) || isa<ImplicitParamDecl>(D)) &&
          "Invalid argument to EmitParmDecl");
 
+  // Set the name of the parameter's initial value to make IR easier to
+  // read. Don't modify the names of globals.
+  if (!isa<llvm::GlobalValue>(Arg.getAnyValue()))
     Arg.getAnyValue()->setName(D.getName());
 
   QualType Ty = D.getType();
 
   // Use better IR generation for certain implicit parameters.
   if (auto IPD = dyn_cast<ImplicitParamDecl>(&D)) {
     // The only implicit argument a block has is its literal.
     // This may be passed as an inalloca'ed value on Windows x86.
     if (BlockInfo) {

clang/test/CodeGenCXX/inheriting-constructor.cpp

 // RUN: %clang_cc1 -no-enable-noundef-analysis -std=c++11 -triple i386-linux -emit-llvm -o - %s | FileCheck %s --check-prefix=ITANIUM
 // RUN: %clang_cc1 -no-enable-noundef-analysis -std=c++11 -triple x86_64-darwin -emit-llvm -o - %s | FileCheck %s --check-prefix=ITANIUM
 // RUN: %clang_cc1 -no-enable-noundef-analysis -std=c++11 -triple arm64-ehabi -emit-llvm -o - %s | FileCheck %s --check-prefix=ITANIUM
 // RUN: %clang_cc1 -no-enable-noundef-analysis -std=c++11 -triple i386-windows -emit-llvm -o - %s | FileCheck %s --check-prefix=MSABI --check-prefix=WIN32
 // RUN: %clang_cc1 -no-enable-noundef-analysis -std=c++11 -triple x86_64-windows -emit-llvm -o - %s | FileCheck %s --check-prefix=MSABI --check-prefix=WIN64
 
+// PR63618: make sure we generate definitions for all the globals defined in the test
+// MSABI: @"?b@@3UB@@A" = {{.*}} zeroinitializer
+// MSABI: @"?d@@3UD@@A" = {{.*}} zeroinitializer
+// MSABI: @"?b@noninline_nonvirt@@3UB@1@A" = {{.*}} zeroinitializer
+// MSABI: @"?c@noninline_nonvirt@@3UC@1@A" = {{.*}} zeroinitializer
+// MSABI: @"?b@noninline_virt@@3UB@1@A" = {{.*}} zeroinitializer
+// MSABI: @"?c@noninline_virt@@3UC@1@A" = {{.*}} zeroinitializer
+// MSABI: @"?b@inalloca_nonvirt@@3UB@1@A" = {{.*}} zeroinitializer
+// MSABI: @"?c@inalloca_nonvirt@@3UC@1@A" = {{.*}} zeroinitializer
+// MSABI: @"?b@inalloca_virt@@3UB@1@A" = {{.*}} zeroinitializer
+// MSABI: @"?c@inalloca_virt@@3UC@1@A" = {{.*}} zeroinitializer
+// MSABI: @"?b@inline_nonvirt@@3UB@1@A" = {{.*}} zeroinitializer
+// MSABI: @"?c@inline_nonvirt@@3UC@1@A" = {{.*}} zeroinitializer
+// MSABI: @"?b@inline_virt@@3UB@1@A" = {{.*}} zeroinitializer
+// MSABI: @"?c@inline_virt@@3UC@1@A" = {{.*}} zeroinitializer
+
+// MSABI-NOT: @this
+
 // PR12219
 struct A { A(int); virtual ~A(); };
 struct B : A { using A::A; ~B(); };
 B::~B() {}
 
 B b(123);
 
 struct C { template<typename T> C(T); };