[CGCall] Make findDominatingStoreToReturnValue() more robust

This was skipping specific lifetime + bitcast patterns, but with
opaque pointers the bitcast will not be present, and we did not
perform this fold.

Instead skip over lifetime.end and bitcasts generally, without
trying to correlate them.

1 files changed, 12 insertions, 21 deletions

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index e2ffd57..c4d342e 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -3242,28 +3242,19 @@ static llvm::StoreInst *findDominatingStoreToReturnValue(CodeGenFunction &CGF) {
   if (!CGF.ReturnValue.getPointer()->hasOneUse()) {
     llvm::BasicBlock *IP = CGF.Builder.GetInsertBlock();
     if (IP->empty()) return nullptr;
-    llvm::Instruction *I = &IP->back();
-
-    // Skip lifetime markers
-    for (llvm::BasicBlock::reverse_iterator II = IP->rbegin(),
-                                            IE = IP->rend();
-         II != IE; ++II) {
-      if (llvm::IntrinsicInst *Intrinsic =
-              dyn_cast<llvm::IntrinsicInst>(&*II)) {
-        if (Intrinsic->getIntrinsicID() == llvm::Intrinsic::lifetime_end) {
-          const llvm::Value *CastAddr = Intrinsic->getArgOperand(1);
-          ++II;
-          if (II == IE)
-            break;
-          if (isa<llvm::BitCastInst>(&*II) && (CastAddr == &*II))
-            continue;
-        }
-      }
-      I = &*II;
-      break;
-    }
 
-    return GetStoreIfValid(I);
+    // Look at directly preceding instruction, skipping bitcasts and lifetime
+    // markers.
+    for (llvm::Instruction &I : make_range(IP->rbegin(), IP->rend())) {
+      if (isa<llvm::BitCastInst>(&I))
+        continue;
+      if (auto *II = dyn_cast<llvm::IntrinsicInst>(&I))
+        if (II->getIntrinsicID() == llvm::Intrinsic::lifetime_end)
+          continue;
+
+      return GetStoreIfValid(&I);
+    }
+    return nullptr;
   }
 
   llvm::StoreInst *store =