[c++20] For P0732R2 / P1907R1: Basic code generation and name

mangling support for non-type template parameters of class type and
template parameter objects.

The Itanium side of this follows the approach I proposed in
https://github.com/itanium-cxx-abi/cxx-abi/issues/47 on 2020-09-06.

The MSVC side of this was determined empirically by observing MSVC's
output.

Differential Revision: https://reviews.llvm.org/D89998

1 files changed, 23 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 92b2b5c..f50aaf3 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -2636,8 +2636,29 @@ ConstantAddress CodeGenModule::GetAddrOfMSGuidDecl(const MSGuidDecl *GD) {
 
 ConstantAddress CodeGenModule::GetAddrOfTemplateParamObject(
     const TemplateParamObjectDecl *TPO) {
-  ErrorUnsupported(TPO, "template parameter object");
-  return ConstantAddress::invalid();
+  StringRef Name = getMangledName(TPO);
+  CharUnits Alignment = getNaturalTypeAlignment(TPO->getType());
+
+  if (llvm::GlobalVariable *GV = getModule().getNamedGlobal(Name))
+    return ConstantAddress(GV, Alignment);
+
+  ConstantEmitter Emitter(*this);
+  llvm::Constant *Init = Emitter.emitForInitializer(
+        TPO->getValue(), TPO->getType().getAddressSpace(), TPO->getType());
+
+  if (!Init) {
+    ErrorUnsupported(TPO, "template parameter object");
+    return ConstantAddress::invalid();
+  }
+
+  auto *GV = new llvm::GlobalVariable(
+      getModule(), Init->getType(),
+      /*isConstant=*/true, llvm::GlobalValue::LinkOnceODRLinkage, Init, Name);
+  if (supportsCOMDAT())
+    GV->setComdat(TheModule.getOrInsertComdat(GV->getName()));
+  Emitter.finalize(GV);
+
+  return ConstantAddress(GV, Alignment);
 }
 
 ConstantAddress CodeGenModule::GetWeakRefReference(const ValueDecl *VD) {