[objc-arc] Track if we encountered an additive overflow while computing {TopDown,BottomUp}PathCounts and do nothing if it occurred.
I fixed the aforementioned problems that came up on some of the linux boxes.
Major thanks to Nick Lewycky for his help debugging!
rdar://14590914
llvm-svn: 188122
diff --git a/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp b/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
index 6d4ff65..0385de5 100644
--- a/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
+++ b/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
@@ -674,7 +674,9 @@
SmallVector<BasicBlock *, 2> Succs;
public:
- BBState() : TopDownPathCount(0), BottomUpPathCount(0) {}
+ static const unsigned OverflowOccurredValue;
+
+ BBState() : TopDownPathCount(0), BottomUpPathCount(0) { }
typedef MapTy::iterator ptr_iterator;
typedef MapTy::const_iterator ptr_const_iterator;
@@ -745,13 +747,15 @@
/// Returns true if overflow occured. Returns false if overflow did not
/// occur.
bool GetAllPathCountWithOverflow(unsigned &PathCount) const {
- assert(TopDownPathCount != 0);
- assert(BottomUpPathCount != 0);
+ if (TopDownPathCount == OverflowOccurredValue ||
+ BottomUpPathCount == OverflowOccurredValue)
+ return true;
unsigned long long Product =
(unsigned long long)TopDownPathCount*BottomUpPathCount;
- PathCount = Product;
- // Overflow occured if any of the upper bits of Product are set.
- return Product >> 32;
+ // Overflow occured if any of the upper bits of Product are set or if all
+ // the lower bits of Product are all set.
+ return (Product >> 32) ||
+ ((PathCount = Product) == OverflowOccurredValue);
}
// Specialized CFG utilities.
@@ -766,6 +770,8 @@
bool isExit() const { return Succs.empty(); }
};
+
+ const unsigned BBState::OverflowOccurredValue = 0xffffffff;
}
void BBState::InitFromPred(const BBState &Other) {
@@ -781,13 +787,25 @@
/// The top-down traversal uses this to merge information about predecessors to
/// form the initial state for a new block.
void BBState::MergePred(const BBState &Other) {
+ if (TopDownPathCount == OverflowOccurredValue)
+ return;
+
// Other.TopDownPathCount can be 0, in which case it is either dead or a
// loop backedge. Loop backedges are special.
TopDownPathCount += Other.TopDownPathCount;
+ // In order to be consistent, we clear the top down pointers when by adding
+ // TopDownPathCount becomes OverflowOccurredValue even though "true" overflow
+ // has not occured.
+ if (TopDownPathCount == OverflowOccurredValue) {
+ clearTopDownPointers();
+ return;
+ }
+
// Check for overflow. If we have overflow, fall back to conservative
// behavior.
if (TopDownPathCount < Other.TopDownPathCount) {
+ TopDownPathCount = OverflowOccurredValue;
clearTopDownPointers();
return;
}
@@ -813,13 +831,25 @@
/// The bottom-up traversal uses this to merge information about successors to
/// form the initial state for a new block.
void BBState::MergeSucc(const BBState &Other) {
+ if (BottomUpPathCount == OverflowOccurredValue)
+ return;
+
// Other.BottomUpPathCount can be 0, in which case it is either dead or a
// loop backedge. Loop backedges are special.
BottomUpPathCount += Other.BottomUpPathCount;
+ // In order to be consistent, we clear the top down pointers when by adding
+ // BottomUpPathCount becomes OverflowOccurredValue even though "true" overflow
+ // has not occured.
+ if (BottomUpPathCount == OverflowOccurredValue) {
+ clearBottomUpPointers();
+ return;
+ }
+
// Check for overflow. If we have overflow, fall back to conservative
// behavior.
if (BottomUpPathCount < Other.BottomUpPathCount) {
+ BottomUpPathCount = OverflowOccurredValue;
clearBottomUpPointers();
return;
}
@@ -2526,9 +2556,12 @@
// If we overflow when we compute the path count, don't remove/move
// anything.
const BBState &NRRBBState = BBStates[NewRetainRelease->getParent()];
- unsigned PathCount;
+ unsigned PathCount = BBState::OverflowOccurredValue;
if (NRRBBState.GetAllPathCountWithOverflow(PathCount))
return false;
+ assert(PathCount != BBState::OverflowOccurredValue &&
+ "PathCount at this point can not be "
+ "OverflowOccurredValue.");
OldDelta -= PathCount;
// Merge the ReleaseMetadata and IsTailCallRelease values.
@@ -2558,8 +2591,12 @@
// If we overflow when we compute the path count, don't
// remove/move anything.
const BBState &RIPBBState = BBStates[RIP->getParent()];
+ PathCount = BBState::OverflowOccurredValue;
if (RIPBBState.GetAllPathCountWithOverflow(PathCount))
return false;
+ assert(PathCount != BBState::OverflowOccurredValue &&
+ "PathCount at this point can not be "
+ "OverflowOccurredValue.");
NewDelta -= PathCount;
}
}
@@ -2595,9 +2632,12 @@
// If we overflow when we compute the path count, don't remove/move
// anything.
const BBState &NRRBBState = BBStates[NewReleaseRetain->getParent()];
- unsigned PathCount;
+ unsigned PathCount = BBState::OverflowOccurredValue;
if (NRRBBState.GetAllPathCountWithOverflow(PathCount))
return false;
+ assert(PathCount != BBState::OverflowOccurredValue &&
+ "PathCount at this point can not be "
+ "OverflowOccurredValue.");
OldDelta += PathCount;
OldCount += PathCount;
@@ -2612,8 +2652,13 @@
// If we overflow when we compute the path count, don't
// remove/move anything.
const BBState &RIPBBState = BBStates[RIP->getParent()];
+
+ PathCount = BBState::OverflowOccurredValue;
if (RIPBBState.GetAllPathCountWithOverflow(PathCount))
return false;
+ assert(PathCount != BBState::OverflowOccurredValue &&
+ "PathCount at this point can not be "
+ "OverflowOccurredValue.");
NewDelta += PathCount;
NewCount += PathCount;
}