Revert "Revert r234581, it might have caused a few miscompiles in Chromium."

This reverts commit r234700.  It turns out that the lifetime markers
were not the cause of Chromium failing but a bug which was uncovered by
optimizations exposed by the markers.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@235553 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 26 insertions, 2 deletions

diff --git a/lib/CodeGen/CGCall.cpp b/lib/CodeGen/CGCall.cpp
index c031bd7940..d82c58fb7e 100644
--- a/lib/CodeGen/CGCall.cpp
+++ b/lib/CodeGen/CGCall.cpp
@@ -30,6 +30,7 @@
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/InlineAsm.h"
 #include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include <sstream>
 using namespace clang;
@@ -2216,7 +2217,29 @@ static llvm::StoreInst *findDominatingStoreToReturnValue(CodeGenFunction &CGF) {
   if (!CGF.ReturnValue->hasOneUse()) {
     llvm::BasicBlock *IP = CGF.Builder.GetInsertBlock();
     if (IP->empty()) return nullptr;
-    llvm::StoreInst *store = dyn_cast<llvm::StoreInst>(&IP->back());
+    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 (isa<llvm::BitCastInst>(&*II)) {
+            if (CastAddr == &*II) {
+              continue;
+            }
+          }
+        }
+      }
+      I = &*II;
+      break;
+    }
+
+    llvm::StoreInst *store = dyn_cast<llvm::StoreInst>(I);
     if (!store) return nullptr;
     if (store->getPointerOperand() != CGF.ReturnValue) return nullptr;
     assert(!store->isAtomic() && !store->isVolatile()); // see below
@@ -2314,7 +2337,8 @@ void CodeGenFunction::EmitFunctionEpilog(const CGFunctionInfo &FI,
 
       // If there is a dominating store to ReturnValue, we can elide
       // the load, zap the store, and usually zap the alloca.
-      if (llvm::StoreInst *SI = findDominatingStoreToReturnValue(*this)) {
+      if (llvm::StoreInst *SI =
+              findDominatingStoreToReturnValue(*this)) {
         // Reuse the debug location from the store unless there is
         // cleanup code to be emitted between the store and return
         // instruction.