[Openmp-commits] [PATCH] D129694: [OPENMP] Make declare target static global externally visible

[Sunil Shrestha via Phabricator via Openmp-commits]

ssquare08 marked an inline comment as not done.
ssquare08 added inline comments.


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Comment at: clang/lib/CodeGen/TargetInfo.cpp:9439
     const Decl *D, llvm::GlobalValue *GV, CodeGen::CodeGenModule &M) const {
+  // Make sure any variable with OpenMP declare target is visible to runtime
+  // except for those with hidden visibility
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ssquare08 wrote:
> jhuber6 wrote:
> > ssquare08 wrote:
> > > jhuber6 wrote:
> > > > jhuber6 wrote:
> > > > > ssquare08 wrote:
> > > > > > jhuber6 wrote:
> > > > > > > Just spitballing, is it possible to do this when we make the global instead?
> > > > > > This is something I was wondering as well.  In CodeGenModule::GetOrCreateLLVMGlobal, when it creates a new global variable, it always uses the llvm::GlobalValue::ExternalLinkage. Seems like this changes somewhere later to internal for static globals. Do you know where that would be?
> > > > > I'm not exactly sure, I remember deleting some code in D117806 that did something like that, albeit incorrectly. But I'm not sure if you'd have the necessary information to check whether or not there are updates attached to it. We don't want to externalize things if we don't need to, otherwise we'd get a lot of our device runtime variables with external visibility that now can't be optimized out.
> > > > Were you able to find a place for this when we generate the variable? You should be able to do something similar to the patch above if it's a declare target static to force it to have external visibility, but as mentioned before I would prefer we only do this if necessary which might take some extra analysis.
> > > If you are asking about the GV, it is created in 'CodeGenModule::GetOrCreateLLVMGlobal' with external linkage always.
> > > ```
> > >   auto *GV = new llvm::GlobalVariable(
> > >       getModule(), Ty, false, llvm::GlobalValue::ExternalLinkage, nullptr,
> > >       MangledName, nullptr, llvm::GlobalVariable::NotThreadLocal,
> > >       getContext().getTargetAddressSpace(DAddrSpace));
> > > ```
> > > The linkage, however, changes in 'CodeGenModule::EmitGlobalVarDefinition' based on the information VarDecl
> > > 
> > > ```
> > >   llvm::GlobalValue::LinkageTypes Linkage =
> > >       getLLVMLinkageVarDefinition(D, GV->isConstant());
> > > ```
> > > 
> > > Maybe you are suggesting changing the linkage information in 'VarDecl' itself?
> > Yes, the patch I linked previously did something like that where it set the `LinkageValue` based on some information. Although I'm not sure if it would be excessively difficult to try to prune definitions that don't need to be externalized. I haven't looked too deep into this, but I believe CUDA does this inside of `adjustGVALinkageForAttributes`, there we also check some variable called `CUDADeviceVarODRUsedByHost` that I'm assuming tracks if we need to bother externalizing this.
> The exter
Thanks for the information, I'll take a look


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https://reviews.llvm.org/D129694