[CUDA][HIP] Support accessing static device variable in host code for -fgpu-rdc

For -fgpu-rdc mode, static device vars in different TU's may have the same name.
To support accessing file-scope static device variables in host code, we need to give them
a distinct name and external linkage. This can be done by postfixing each static device variable with
a distinct CUID (Compilation Unit ID) hash.

Since the static device variables have different name across compilation units, now we let
them have external linkage so that they can be looked up by the runtime.

Reviewed by: Artem Belevich, and Jon Chesterfield

Differential Revision: https://reviews.llvm.org/D85223

1 files changed, 20 insertions, 3 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 7e45ae3acb3e..9dcdc8da4d92 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1184,6 +1184,11 @@ static std::string getMangledNameImpl(const CodeGenModule &CGM, GlobalDecl GD,
       }
     }
 
+  // Make unique name for device side static file-scope variable for HIP.
+  if (CGM.getContext().shouldExternalizeStaticVar(ND) &&
+      CGM.getLangOpts().GPURelocatableDeviceCode &&
+      CGM.getLangOpts().CUDAIsDevice && !CGM.getLangOpts().CUID.empty())
+    CGM.printPostfixForExternalizedStaticVar(Out);
   return std::string(Out.str());
 }
 
@@ -1241,9 +1246,16 @@ StringRef CodeGenModule::getMangledName(GlobalDecl GD) {
     }
   }
 
-  auto FoundName = MangledDeclNames.find(CanonicalGD);
-  if (FoundName != MangledDeclNames.end())
-    return FoundName->second;
+  // In CUDA/HIP device compilation with -fgpu-rdc, the mangled name of a
+  // static device variable depends on whether the variable is referenced by
+  // a host or device host function. Therefore the mangled name cannot be
+  // cached.
+  if (!LangOpts.CUDAIsDevice ||
+      !getContext().mayExternalizeStaticVar(GD.getDecl())) {
+    auto FoundName = MangledDeclNames.find(CanonicalGD);
+    if (FoundName != MangledDeclNames.end())
+      return FoundName->second;
+  }
 
   // Keep the first result in the case of a mangling collision.
   const auto *ND = cast<NamedDecl>(GD.getDecl());
@@ -6249,3 +6261,8 @@ bool CodeGenModule::stopAutoInit() {
   }
   return false;
 }
+
+void CodeGenModule::printPostfixForExternalizedStaticVar(
+    llvm::raw_ostream &OS) const {
+  OS << ".static." << getContext().getCUIDHash();
+}