Make provenance checking conservative in cases when
pointers-to-strong-pointers may be in play. These can lead to retains and
releases happening in unstructured ways, foiling the optimizer. This fixes
rdar://12150909.
llvm-svn: 163180
diff --git a/llvm/lib/Transforms/Scalar/ObjCARC.cpp b/llvm/lib/Transforms/Scalar/ObjCARC.cpp
index e7947d0..dce8e8b 100644
--- a/llvm/lib/Transforms/Scalar/ObjCARC.cpp
+++ b/llvm/lib/Transforms/Scalar/ObjCARC.cpp
@@ -1236,16 +1236,19 @@
// An ObjC-Identified object can't alias a load if it is never locally stored.
if (AIsIdentified) {
+ // Check for an obvious escape.
+ if (isa<LoadInst>(B))
+ return isStoredObjCPointer(A);
if (BIsIdentified) {
- // If both pointers have provenance, they can be directly compared.
- if (A != B)
- return false;
- } else {
- if (isa<LoadInst>(B))
- return isStoredObjCPointer(A);
+ // Check for an obvious escape.
+ if (isa<LoadInst>(A))
+ return isStoredObjCPointer(B);
+ // Both pointers are identified and escapes aren't an evident problem.
+ return false;
}
- } else {
- if (BIsIdentified && isa<LoadInst>(A))
+ } else if (BIsIdentified) {
+ // Check for an obvious escape.
+ if (isa<LoadInst>(A))
return isStoredObjCPointer(B);
}
@@ -1381,9 +1384,6 @@
/// PtrState - This class summarizes several per-pointer runtime properties
/// which are propogated through the flow graph.
class PtrState {
- /// NestCount - The known minimum level of retain+release nesting.
- unsigned NestCount;
-
/// KnownPositiveRefCount - True if the reference count is known to
/// be incremented.
bool KnownPositiveRefCount;
@@ -1401,7 +1401,7 @@
/// TODO: Encapsulate this better.
RRInfo RRI;
- PtrState() : NestCount(0), KnownPositiveRefCount(false), Partial(false),
+ PtrState() : KnownPositiveRefCount(false), Partial(false),
Seq(S_None) {}
void SetKnownPositiveRefCount() {
@@ -1416,18 +1416,6 @@
return KnownPositiveRefCount;
}
- void IncrementNestCount() {
- if (NestCount != UINT_MAX) ++NestCount;
- }
-
- void DecrementNestCount() {
- if (NestCount != 0) --NestCount;
- }
-
- bool IsKnownNested() const {
- return NestCount > 0;
- }
-
void SetSeq(Sequence NewSeq) {
Seq = NewSeq;
}
@@ -1454,7 +1442,6 @@
PtrState::Merge(const PtrState &Other, bool TopDown) {
Seq = MergeSeqs(Seq, Other.Seq, TopDown);
KnownPositiveRefCount = KnownPositiveRefCount && Other.KnownPositiveRefCount;
- NestCount = std::min(NestCount, Other.NestCount);
// We can't merge a plain objc_retain with an objc_retainBlock.
if (RRI.IsRetainBlock != Other.RRI.IsRetainBlock)
@@ -1868,6 +1855,26 @@
return AutoreleaseCallee;
}
+/// IsPotentialUse - Test whether the given value is possible a
+/// reference-counted pointer, including tests which utilize AliasAnalysis.
+static bool IsPotentialUse(const Value *Op, AliasAnalysis &AA) {
+ // First make the rudimentary check.
+ if (!IsPotentialUse(Op))
+ return false;
+
+ // Objects in constant memory are not reference-counted.
+ if (AA.pointsToConstantMemory(Op))
+ return false;
+
+ // Pointers in constant memory are not pointing to reference-counted objects.
+ if (const LoadInst *LI = dyn_cast<LoadInst>(Op))
+ if (AA.pointsToConstantMemory(LI->getPointerOperand()))
+ return false;
+
+ // Otherwise assume the worst.
+ return true;
+}
+
/// CanAlterRefCount - Test whether the given instruction can result in a
/// reference count modification (positive or negative) for the pointer's
/// object.
@@ -1894,7 +1901,7 @@
for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
I != E; ++I) {
const Value *Op = *I;
- if (IsPotentialUse(Op) && PA.related(Ptr, Op))
+ if (IsPotentialUse(Op, *PA.getAA()) && PA.related(Ptr, Op))
return true;
}
return false;
@@ -1919,14 +1926,14 @@
// Comparing a pointer with null, or any other constant, isn't really a use,
// because we don't care what the pointer points to, or about the values
// of any other dynamic reference-counted pointers.
- if (!IsPotentialUse(ICI->getOperand(1)))
+ if (!IsPotentialUse(ICI->getOperand(1), *PA.getAA()))
return false;
} else if (ImmutableCallSite CS = static_cast<const Value *>(Inst)) {
// For calls, just check the arguments (and not the callee operand).
for (ImmutableCallSite::arg_iterator OI = CS.arg_begin(),
OE = CS.arg_end(); OI != OE; ++OI) {
const Value *Op = *OI;
- if (IsPotentialUse(Op) && PA.related(Ptr, Op))
+ if (IsPotentialUse(Op, *PA.getAA()) && PA.related(Ptr, Op))
return true;
}
return false;
@@ -1936,14 +1943,14 @@
const Value *Op = GetUnderlyingObjCPtr(SI->getPointerOperand());
// If we can't tell what the underlying object was, assume there is a
// dependence.
- return IsPotentialUse(Op) && PA.related(Op, Ptr);
+ return IsPotentialUse(Op, *PA.getAA()) && PA.related(Op, Ptr);
}
// Check each operand for a match.
for (User::const_op_iterator OI = Inst->op_begin(), OE = Inst->op_end();
OI != OE; ++OI) {
const Value *Op = *OI;
- if (IsPotentialUse(Op) && PA.related(Ptr, Op))
+ if (IsPotentialUse(Op, *PA.getAA()) && PA.related(Ptr, Op))
return true;
}
return false;
@@ -2612,11 +2619,11 @@
MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
S.ResetSequenceProgress(ReleaseMetadata ? S_MovableRelease : S_Release);
S.RRI.ReleaseMetadata = ReleaseMetadata;
- S.RRI.KnownSafe = S.IsKnownNested() || S.IsKnownIncremented();
+ S.RRI.KnownSafe = S.IsKnownIncremented();
S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall();
S.RRI.Calls.insert(Inst);
- S.IncrementNestCount();
+ S.SetKnownPositiveRefCount();
break;
}
case IC_RetainBlock:
@@ -2631,7 +2638,6 @@
PtrState &S = MyStates.getPtrBottomUpState(Arg);
S.SetKnownPositiveRefCount();
- S.DecrementNestCount();
switch (S.GetSeq()) {
case S_Stop:
@@ -2823,12 +2829,11 @@
S.ResetSequenceProgress(S_Retain);
S.RRI.IsRetainBlock = Class == IC_RetainBlock;
- // Don't check S.IsKnownIncremented() here because it's not sufficient.
- S.RRI.KnownSafe = S.IsKnownNested();
+ S.RRI.KnownSafe = S.IsKnownIncremented();
S.RRI.Calls.insert(Inst);
}
- S.IncrementNestCount();
+ S.SetKnownPositiveRefCount();
// A retain can be a potential use; procede to the generic checking
// code below.
@@ -2838,7 +2843,7 @@
Arg = GetObjCArg(Inst);
PtrState &S = MyStates.getPtrTopDownState(Arg);
- S.DecrementNestCount();
+ S.ClearRefCount();
switch (S.GetSeq()) {
case S_Retain: