[Clang][CodeGen] Another follow-up for `vtable`, `typeinfo` et al. are globals

[AlexVlx]

Summary

Turns out that in https://reviews.llvm.org/rG8acdcf4016876d122733991561be706b64026e73 I missed another use case (dynamic_cast relies on typeinfo, which its signature assumed to be in the generic address space), sadly. This patch corrects the oversight and adds an associated test.

P.S.: the current and @bjope 's inquiry on https://reviews.llvm.org/D153092 makes me wonder if we want to consider a more centralised approach to all of the polymorphism related bits, so that future changes can be localised to one / a few spots, and then propagate around. I admit I've not thought deeply about it though and it would probably be non-trivial.

[AlexVlx]

Rebase.

[AlexVlx]

Gentle ping.

[yaxunl]

__dynamic_cast is part of standard C++ library. If we ever implement it for GPU, chances are we will use libc++abi with the same signature as other targets, i.e., the 2nd and 3rd arguments are generic pointers.

I feel it is safer to do an address space cast when calling the function instead of changing its signature.

[AlexVlx]

In D155870#4535425, @yaxunl wrote:

__dynamic_cast is part of standard C++ library. If we ever implement it for GPU, chances are we will use libc++abi with the same signature as other targets, i.e., the 2nd and 3rd arguments are generic pointers.

I feel it is safer to do an address space cast when calling the function instead of changing its signature.

That's a fair point, and one I admit to not having considered (I'm not sure this would harm linking in practice though, since __dynamic_cast is extern "C" and thus unmangled; it might lead to broken IR depending on how we codegen the body). The concern I have with doing the cast at the callsite is that there might be many callsites, and it's going to make things a bit noisier than they need to be (IMHO). Also, this is an internal implementation detail of the standard library, and not the interface that users are expected to touch; I wonder if given the target specific nature of these bits it wouldn't be natural for our future implementation to carry the AS in the signature?

[yaxunl]

LGTM. Thanks.

[AlexVlx]

Ping @rjmccall or @efriedma for a non AMD perspective, if possible.

[AlexVlx]

Ping?

[AlexVlx]

Rebase.

clang/lib/CodeGen/ItaniumCXXABI.cpp

void ItaniumCXXABI::emitThrow(CodeGenFunction &CGF, const CXXThrowExpr *E) {
   if (!Dtor) Dtor = llvm::Constant::getNullValue(CGM.Int8PtrTy);
 
   llvm::Value *args[] = { ExceptionPtr, TypeInfo, Dtor };
   CGF.EmitNoreturnRuntimeCallOrInvoke(getThrowFn(CGM), args);
 }
 
 static llvm::FunctionCallee getItaniumDynamicCastFn(CodeGenFunction &CGF) {
   // void *__dynamic_cast(const void *sub,
-  //                      const abi::__class_type_info *src,
-  //                      const abi::__class_type_info *dst,
+  //                      global_as const abi::__class_type_info *src,
+  //                      global_as const abi::__class_type_info *dst,
   //                      std::ptrdiff_t src2dst_offset);
 
   llvm::Type *Int8PtrTy = CGF.Int8PtrTy;
+  llvm::Type *GlobInt8PtrTy = CGF.GlobalsInt8PtrTy;
   llvm::Type *PtrDiffTy =
     CGF.ConvertType(CGF.getContext().getPointerDiffType());
 
-  llvm::Type *Args[4] = { Int8PtrTy, Int8PtrTy, Int8PtrTy, PtrDiffTy };
+  llvm::Type *Args[4] = { Int8PtrTy, GlobInt8PtrTy, GlobInt8PtrTy, PtrDiffTy };
 
   llvm::FunctionType *FTy = llvm::FunctionType::get(Int8PtrTy, Args, false);
 
   // Mark the function as nounwind readonly.
   llvm::AttrBuilder FuncAttrs(CGF.getLLVMContext());
   FuncAttrs.addAttribute(llvm::Attribute::NoUnwind);
   FuncAttrs.addMemoryAttr(llvm::MemoryEffects::readOnly());
   llvm::AttributeList Attrs = llvm::AttributeList::get(

clang/test/CodeGenCXX/dynamic-cast-address-space.cpp

+// RUN: %clang_cc1 -I%S %s -triple amdgcn-amd-amdhsa -emit-llvm -fcxx-exceptions -fexceptions -o - | FileCheck %s
+struct A { virtual void f(); };
+struct B : A { };
+
+// CHECK: {{define.*@_Z1fP1A}}
+// CHECK-SAME:  personality ptr @__gxx_personality_v0
+B fail;
+const B& f(A *a) {
+  try {
+    // CHECK: call ptr @__dynamic_cast
+    // CHECK: br i1
+    // CHECK: invoke void @__cxa_bad_cast() [[NR:#[0-9]+]]
+    dynamic_cast<const B&>(*a);
+  } catch (...) {
+    // CHECK:      landingpad { ptr, i32 }
+    // CHECK-NEXT:   catch ptr null
+  }
+  return fail;
+}
+
+// CHECK: declare ptr @__dynamic_cast(ptr, ptr addrspace(1), ptr addrspace(1), i64) [[NUW_RO:#[0-9]+]]
+
+// CHECK: attributes [[NUW_RO]] = { nounwind memory(read) }
+// CHECK: attributes [[NR]] = { noreturn }