[clang] [Clang] Add fake use emission to Clang with -fextend-lifetimes (PR #110102)

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<!--LLVM CODE FORMAT COMMENT: {clang-format}-->


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``````````bash
git-clang-format --diff 22829f757dc76b23071d9438ae9c6ddc3e966db0 e04a16c6d51539421dd134f7524641e843f5d555 --extensions cpp,c,h -- clang/test/CodeGen/extend-liveness1.c clang/test/CodeGen/extend-liveness2.cpp clang/test/CodeGen/fake-use-determinism.c clang/test/CodeGen/fake-use-lambda.cpp clang/test/CodeGen/fake-use-landingpad.c clang/test/CodeGen/fake-use-noreturn.cpp clang/test/CodeGen/fake-use-return-line.c clang/test/CodeGen/fake-use-sanitizer.cpp clang/test/CodeGen/fake-use-scalar.c clang/test/CodeGen/fake-use-small-aggs.c clang/test/CodeGen/fake-use-while.c clang/test/CodeGen/fake-use.cpp clang/test/CodeGen/no-fake-use-O0.cpp clang/lib/CodeGen/CGCall.cpp clang/lib/CodeGen/CGCleanup.cpp clang/lib/CodeGen/CGCleanup.h clang/lib/CodeGen/CGDecl.cpp clang/lib/CodeGen/CodeGenFunction.cpp clang/lib/CodeGen/CodeGenFunction.h clang/lib/CodeGen/CodeGenModule.h clang/lib/CodeGen/EHScopeStack.h
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View the diff from clang-format here.
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``````````diff
diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 13c556a4e2..26441b4135 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -3566,26 +3566,27 @@ static llvm::StoreInst *findDominatingStoreToReturnValue(CodeGenFunction &CGF) {
     llvm::BasicBlock *IP = CGF.Builder.GetInsertBlock();
     if (IP->empty()) return nullptr;
 
-   // Look at directly preceding instruction, skipping bitcasts, lifetime
-   // markers, and fake uses and their operands.
-   const llvm::Instruction *LoadIntoFakeUse = nullptr;
-   for (llvm::Instruction &I : make_range(IP->rbegin(), IP->rend())) {
-     // Ignore instructions that are just loads for fake uses; the load should
-     // immediately precede the fake use, so we only need to remember the
-     // operand for the last fake use seen.
-     if (LoadIntoFakeUse == &I)
-       continue;
-     if (isa<llvm::BitCastInst>(&I))
-       continue;
-     if (auto *II = dyn_cast<llvm::IntrinsicInst>(&I)) {
-       if (II->getIntrinsicID() == llvm::Intrinsic::lifetime_end)
-         continue;
-
-       if (II->getIntrinsicID() == llvm::Intrinsic::fake_use) {
-         LoadIntoFakeUse = dyn_cast<llvm::Instruction>(II->getArgOperand(0));
-         continue;
-       }
-     }      return GetStoreIfValid(&I);
+    // Look at directly preceding instruction, skipping bitcasts, lifetime
+    // markers, and fake uses and their operands.
+    const llvm::Instruction *LoadIntoFakeUse = nullptr;
+    for (llvm::Instruction &I : make_range(IP->rbegin(), IP->rend())) {
+      // Ignore instructions that are just loads for fake uses; the load should
+      // immediately precede the fake use, so we only need to remember the
+      // operand for the last fake use seen.
+      if (LoadIntoFakeUse == &I)
+        continue;
+      if (isa<llvm::BitCastInst>(&I))
+        continue;
+      if (auto *II = dyn_cast<llvm::IntrinsicInst>(&I)) {
+        if (II->getIntrinsicID() == llvm::Intrinsic::lifetime_end)
+          continue;
+
+        if (II->getIntrinsicID() == llvm::Intrinsic::fake_use) {
+          LoadIntoFakeUse = dyn_cast<llvm::Instruction>(II->getArgOperand(0));
+          continue;
+        }
+      }
+      return GetStoreIfValid(&I);
     }
     return nullptr;
   }

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https://github.com/llvm/llvm-project/pull/110102