[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:

Isn't the comment above explained why such function should not be inlined? Converting to available externally linkage is changing the behavior of the interposable linkage, and only a declaration (undef) can preserve the behavior.

I don't think a `-mllvm` option (even it is debugging option) should violate the linkage behavior for the IR language.

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