[clang] [Clang] Access tls_guard via llvm.threadlocal.address (PR #96633)

[John McCall via cfe-commits]

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@@ -1059,9 +1059,15 @@ CodeGenFunction::GenerateCXXGlobalInitFunc(llvm::Function *Fn,
     if (Guard.isValid()) {
       // If we have a guard variable, check whether we've already performed
       // these initializations. This happens for TLS initialization functions.
-      llvm::Value *GuardVal = Builder.CreateLoad(Guard);
-      llvm::Value *Uninit = Builder.CreateIsNull(GuardVal,
-                                                 "guard.uninitialized");
+      Address GuardAddr = Guard;
+      if (auto *GV = dyn_cast<llvm::GlobalValue>(Guard.getPointer()))
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rjmccall wrote:

We need to do this unconditionally, and we should be able to do because `Guard` is a constant address.  But if there's some code pattern where that's not true, we need to fix that code pattern rather than silently just not using this intrinsic.

https://github.com/llvm/llvm-project/pull/96633