Check for nullptr argument.

[tra]

Summary

GetOrCreateLLVMGlobal() accepts nullptr D, but in some cases we end up dereferencing it without checking if it's non-null.

Fixes PR15492.

[jlebar]

Can we have a test?

[tra]

I've never seen it triggered. Fix is based on the comment above the function that D==nullptr is acceptable and the fact that we are checking D in other places in this function.

Two cases where nullptr D is passed explicitly has something to do with -fblocks, but that does not seem to be used neither with CUDA nor with 'IsForDefinition' which was brought in to deal with a strange case of redefining C++ symbols in C. This is probably why it's not triggered.

[dblaikie]

If you have a check that doesn't have a test/is never triggered - simple
thing to do is just make it an assert & run some testing of your own
(selfhost, etc) then if there's insufficient evidence that it's needed,
ship it and wait until it fails on a buildbot, etc. Then reduce the test
case and check that in.

• Dave

[jlebar]

OK, if the function explicitly says it accepts null values and if we check elsewhere in the function, I'm personally OK adding the checks.

lib/CodeGen/CodeGenModule.cpp

if (Entry) {
     // If there are two attempts to define the same mangled name, issue an
     // error.
     if (IsForDefinition && !Entry->isDeclaration()) {
       GlobalDecl OtherGD;
       const VarDecl *OtherD;
 
       // Check that D is not yet in DiagnosedConflictingDefinitions is required
       // to make sure that we issue an error only once.
-      if (lookupRepresentativeDecl(MangledName, OtherGD) &&
+      if (D && lookupRepresentativeDecl(MangledName, OtherGD) &&
           (D->getCanonicalDecl() != OtherGD.getCanonicalDecl().getDecl()) &&
           (OtherD = dyn_cast<VarDecl>(OtherGD.getDecl())) &&
           OtherD->hasInit() &&
           DiagnosedConflictingDefinitions.insert(D).second) {
         getDiags().Report(D->getLocation(),
                           diag::err_duplicate_mangled_name);
         getDiags().Report(OtherGD.getDecl()->getLocation(),
                           diag::note_previous_definition);

 
 CharUnits CodeGenModule::GetTargetTypeStoreSize(llvm::Type *Ty) const {
   return Context.toCharUnitsFromBits(
       getDataLayout().getTypeStoreSizeInBits(Ty));
 }
 
 unsigned CodeGenModule::GetGlobalVarAddressSpace(const VarDecl *D,
                                                  unsigned AddrSpace) {
-  if (LangOpts.CUDA && LangOpts.CUDAIsDevice) {
+  if (D && LangOpts.CUDA && LangOpts.CUDAIsDevice) {
     if (D->hasAttr<CUDAConstantAttr>())
       AddrSpace = getContext().getTargetAddressSpace(LangAS::cuda_constant);
     else if (D->hasAttr<CUDASharedAttr>())
       AddrSpace = getContext().getTargetAddressSpace(LangAS::cuda_shared);
     else
       AddrSpace = getContext().getTargetAddressSpace(LangAS::cuda_device);
   }