[llvm] [ThinLTO] Don't convert functions to declarations if `force-import-all` is enabled (PR #134541)

[Steven Wu via llvm-commits]

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@@ -1701,13 +1701,16 @@ void llvm::thinLTOFinalizeInModule(Module &TheModule,
     if (NewLinkage == GV.getLinkage())
       return;
 
+    bool ForceImportFunction = isa<Function>(GV) && ForceImportAll;
+
     // Check for a non-prevailing def that has interposable linkage
     // (e.g. non-odr weak or linkonce). In that case we can't simply
     // convert to available_externally, since it would lose the
     // interposable property and possibly get inlined. Simply drop
     // the definition in that case.
     if (GlobalValue::isAvailableExternallyLinkage(NewLinkage) &&
-        GlobalValue::isInterposableLinkage(GV.getLinkage())) {
+        GlobalValue::isInterposableLinkage(GV.getLinkage()) &&
+        !ForceImportFunction) {
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cachemeifyoucan wrote:

I am not familiar with AMDGPU backend setup and how device function is modeled in LLVM IR. How does available_externally linkage behave in AMDGPU Codegen? Does it still get dropped if not used, and do you need to prevent it from dropped (or you just need them in IR for some reason)?

If the goal is to have all definitions, maybe we should avoid function importer getting to `available_externally` linkage from the first place and keep weak function as weak. I am not sure if you need to also prevent them from turning into available externally in other linkage type.

https://github.com/llvm/llvm-project/pull/134541