[ObjCARC] Do not move a release between a call and a

retainAutoreleasedReturnValue that retains the returned value.

This commit fixes a bug in ARC optimizer where it moves a release
between a call and a retainAutoreleasedReturnValue, causing the returned
object to be released before the retainAutoreleasedReturnValue can
retain it.

This commit accomplishes that by doing a lookahead and checking whether
the call prevents the release from moving upwards. In the long term, we
should treat the region between the retainAutoreleasedReturnValue and
the call as a critical section and disallow moving anything there
(possibly using operand bundles).

rdar://problem/20449878

llvm-svn: 301724

2 files changed, 33 insertions, 16 deletions

diff --git a/llvm/lib/Transforms/ObjCARC/ObjCARC.h b/llvm/lib/Transforms/ObjCARC/ObjCARC.h
index f02b75f0b45..cd9b3d96a14 100644
--- a/llvm/lib/Transforms/ObjCARC/ObjCARC.h
+++ b/llvm/lib/Transforms/ObjCARC/ObjCARC.h
@@ -69,6 +69,19 @@ static inline void EraseInstruction(Instruction *CI) {
     RecursivelyDeleteTriviallyDeadInstructions(OldArg);
 }
 
+/// If Inst is a ReturnRV and its operand is a call or invoke, return the
+/// operand. Otherwise return null.
+static inline const Instruction *getreturnRVOperand(const Instruction &Inst,
+                                                    ARCInstKind Class) {
+  if (Class != ARCInstKind::RetainRV)
+    return nullptr;
+
+  const auto *Opnd = Inst.getOperand(0)->stripPointerCasts();
+  if (const auto *C = dyn_cast<CallInst>(Opnd))
+    return C;
+  return dyn_cast<InvokeInst>(Opnd);
+}
+
 } // end namespace objcarc
 } // end namespace llvm
 
diff --git a/llvm/lib/Transforms/ObjCARC/PtrState.cpp b/llvm/lib/Transforms/ObjCARC/PtrState.cpp
index c1bbc4e96b1..d13e941044f 100644
--- a/llvm/lib/Transforms/ObjCARC/PtrState.cpp
+++ b/llvm/lib/Transforms/ObjCARC/PtrState.cpp
@@ -244,6 +244,18 @@ void BottomUpPtrState::HandlePotentialUse(BasicBlock *BB, Instruction *Inst,
                                           const Value *Ptr,
                                           ProvenanceAnalysis &PA,
                                           ARCInstKind Class) {
+  auto SetSeqAndInsertReverseInsertPt = [&](Sequence NewSeq){
+    assert(!HasReverseInsertPts());
+    SetSeq(NewSeq);
+    // If this is an invoke instruction, we're scanning it as part of
+    // one of its successor blocks, since we can't insert code after it
+    // in its own block, and we don't want to split critical edges.
+    if (isa<InvokeInst>(Inst))
+      InsertReverseInsertPt(&*BB->getFirstInsertionPt());
+    else
+      InsertReverseInsertPt(&*++Inst->getIterator());
+  };
+
   // Check for possible direct uses.
   switch (GetSeq()) {
   case S_Release:
@@ -251,26 +263,18 @@ void BottomUpPtrState::HandlePotentialUse(BasicBlock *BB, Instruction *Inst,
     if (CanUse(Inst, Ptr, PA, Class)) {
       DEBUG(dbgs() << "            CanUse: Seq: " << GetSeq() << "; " << *Ptr
                    << "\n");
-      assert(!HasReverseInsertPts());
-      // If this is an invoke instruction, we're scanning it as part of
-      // one of its successor blocks, since we can't insert code after it
-      // in its own block, and we don't want to split critical edges.
-      if (isa<InvokeInst>(Inst))
-        InsertReverseInsertPt(&*BB->getFirstInsertionPt());
-      else
-        InsertReverseInsertPt(&*++Inst->getIterator());
-      SetSeq(S_Use);
+      SetSeqAndInsertReverseInsertPt(S_Use);
     } else if (Seq == S_Release && IsUser(Class)) {
       DEBUG(dbgs() << "            PreciseReleaseUse: Seq: " << GetSeq() << "; "
                    << *Ptr << "\n");
       // Non-movable releases depend on any possible objc pointer use.
-      SetSeq(S_Stop);
-      assert(!HasReverseInsertPts());
-      // As above; handle invoke specially.
-      if (isa<InvokeInst>(Inst))
-        InsertReverseInsertPt(&*BB->getFirstInsertionPt());
-      else
-        InsertReverseInsertPt(&*++Inst->getIterator());
+      SetSeqAndInsertReverseInsertPt(S_Stop);
+    } else if (const auto *Call = getreturnRVOperand(*Inst, Class)) {
+      if (CanUse(Call, Ptr, PA, GetBasicARCInstKind(Call))) {
+        DEBUG(dbgs() << "            ReleaseUse: Seq: " << GetSeq() << "; "
+                     << *Ptr << "\n");
+        SetSeqAndInsertReverseInsertPt(S_Stop);
+      }
     }
     break;
   case S_Stop: