[Cuda] Use fallback method to mangle externalized decls if no CUID given

CUDA requires that static variables be visible to the host when
offloading. However, The standard semantics of a stiatc variable dictate
that it should not be visible outside of the current file. In order to
access it from the host we need to perform "externalization" on the
static variable on the device. This requires generating a semi-unique
name that can be affixed to the variable as to not cause linker errors.

This is currently done using the CUID functionality, an MD5 hash value
set up by the clang driver. This allows us to achieve is mostly unique
ID that is unique even between multiple compilations of the same file.
However, this is not always availible. Instead, this patch uses the
unique ID from the file to generate a unique symbol name. This will
create a unique name that is consistent between the host and device side
compilations without requiring the CUID to be entered by the driver. The
one downside to this is that we are no longer stable under multiple
compilations of the same file. However, this is a very niche use-case
and is not supported by Nvidia's CUDA compiler so it likely to be good
enough.

Reviewed By: tra

Differential Revision: https://reviews.llvm.org/D125904

1 files changed, 32 insertions, 5 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 703cf4edf5f5..a035e5ddd9e6 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1416,8 +1416,9 @@ static std::string getMangledNameImpl(CodeGenModule &CGM, GlobalDecl GD,
   // Make unique name for device side static file-scope variable for HIP.
   if (CGM.getContext().shouldExternalize(ND) &&
       CGM.getLangOpts().GPURelocatableDeviceCode &&
-      CGM.getLangOpts().CUDAIsDevice && !CGM.getLangOpts().CUID.empty())
+      CGM.getLangOpts().CUDAIsDevice)
     CGM.printPostfixForExternalizedDecl(Out, ND);
+
   return std::string(Out.str());
 }
 
@@ -6825,12 +6826,38 @@ bool CodeGenModule::stopAutoInit() {
 
 void CodeGenModule::printPostfixForExternalizedDecl(llvm::raw_ostream &OS,
                                                     const Decl *D) const {
-  StringRef Tag;
   // ptxas does not allow '.' in symbol names. On the other hand, HIP prefers
   // postfix beginning with '.' since the symbol name can be demangled.
   if (LangOpts.HIP)
-    Tag = (isa<VarDecl>(D) ? ".static." : ".intern.");
+    OS << (isa<VarDecl>(D) ? ".static." : ".intern.");
   else
-    Tag = (isa<VarDecl>(D) ? "__static__" : "__intern__");
-  OS << Tag << getContext().getCUIDHash();
+    OS << (isa<VarDecl>(D) ? "__static__" : "__intern__");
+
+  // If the CUID is not specified we try to generate a unique postfix.
+  if (getLangOpts().CUID.empty()) {
+    SourceManager &SM = getContext().getSourceManager();
+    PresumedLoc PLoc = SM.getPresumedLoc(D->getLocation());
+    assert(PLoc.isValid() && "Source location is expected to be valid.");
+
+    // Get the hash of the user defined macros.
+    llvm::MD5 Hash;
+    llvm::MD5::MD5Result Result;
+    for (const auto &Arg : PreprocessorOpts.Macros)
+      Hash.update(Arg.first);
+    Hash.final(Result);
+
+    // Get the UniqueID for the file containing the decl.
+    llvm::sys::fs::UniqueID ID;
+    if (auto EC = llvm::sys::fs::getUniqueID(PLoc.getFilename(), ID)) {
+      PLoc = SM.getPresumedLoc(D->getLocation(), /*UseLineDirectives=*/false);
+      assert(PLoc.isValid() && "Source location is expected to be valid.");
+      if (auto EC = llvm::sys::fs::getUniqueID(PLoc.getFilename(), ID))
+        SM.getDiagnostics().Report(diag::err_cannot_open_file)
+            << PLoc.getFilename() << EC.message();
+    }
+    OS << llvm::format("%x", ID.getFile()) << llvm::format("%x", ID.getDevice())
+       << "_" << llvm::utohexstr(Result.low(), /*LowerCase=*/true, /*Width=*/8);
+  } else {
+    OS << getContext().getCUIDHash();
+  }
 }