// For each opcode, keep a list of potential CSE instructions.
DenseMap<unsigned, std::vector<const MachineInstr*> > CSEMap;
+ enum {
+ SpeculateFalse = 0,
+ SpeculateTrue = 1,
+ SpeculateUnknown = 2
+ };
+
// If a MBB does not dominate loop exiting blocks then it may not safe
// to hoist loads from this block.
- bool CurrentMBBDominatesLoopExitingBlocks;
- bool NeedToCheckMBBDominance;
+ // Tri-state: 0 - false, 1 - true, 2 - unknown
+ unsigned SpeculationState;
public:
static char ID; // Pass identification, replacement for typeid
MRI = &MF.getRegInfo();
InstrItins = TM->getInstrItineraryData();
AllocatableSet = TRI->getAllocatableSet(MF);
- // Stay conservative.
- CurrentMBBDominatesLoopExitingBlocks = false;
- NeedToCheckMBBDominance = true;
if (PreRegAlloc) {
// Estimate register pressure during pre-regalloc pass.
++PhysRegDefs[*AS];
}
- NeedToCheckMBBDominance = true;
+ SpeculationState = SpeculateUnknown;
for (MachineBasicBlock::iterator
MII = BB->begin(), E = BB->end(); MII != E; ++MII) {
MachineInstr *MI = &*MII;
// IsGuaranteedToExecute - Check if this mbb is guaranteed to execute.
// If not then a load from this mbb may not be safe to hoist.
bool MachineLICM::IsGuaranteedToExecute(MachineBasicBlock *BB) {
- // Do not check if we already have checked it once.
- if (NeedToCheckMBBDominance == false)
- return CurrentMBBDominatesLoopExitingBlocks;
-
- NeedToCheckMBBDominance = false;
-
+ if (SpeculationState != SpeculateUnknown)
+ return SpeculationState == SpeculateFalse;
+
if (BB != CurLoop->getHeader()) {
// Check loop exiting blocks.
SmallVector<MachineBasicBlock*, 8> CurrentLoopExitingBlocks;
CurLoop->getExitingBlocks(CurrentLoopExitingBlocks);
for (unsigned i = 0, e = CurrentLoopExitingBlocks.size(); i != e; ++i)
if (!DT->dominates(BB, CurrentLoopExitingBlocks[i])) {
- CurrentMBBDominatesLoopExitingBlocks = false;
- return CurrentMBBDominatesLoopExitingBlocks;
+ SpeculationState = SpeculateTrue;
+ return false;
}
}
- CurrentMBBDominatesLoopExitingBlocks = true;
- return CurrentMBBDominatesLoopExitingBlocks;
+ SpeculationState = SpeculateFalse;
+ return true;
}
/// HoistRegion - Walk the specified region of the CFG (defined by all blocks
// Remember livein register pressure.
BackTrace.push_back(RegPressure);
- NeedToCheckMBBDominance = true;
+ SpeculationState = SpeculateUnknown;
for (MachineBasicBlock::iterator
MII = BB->begin(), E = BB->end(); MII != E; ) {
MachineBasicBlock::iterator NextMII = MII; ++NextMII;
// High register pressure situation, only hoist if the instruction is going to
// be remat'ed.
- if (!TII->isTriviallyReMaterializable(&MI, AA) &&
- !MI.isInvariantLoad(AA))
+ // Also, do not "speculate" in high register pressure situation. If an
+ // instruction is not guaranteed to be executed in the loop, it's best to be
+ // conservative.
+ if (SpeculationState == SpeculateTrue ||
+ (!TII->isTriviallyReMaterializable(&MI, AA) &&
+ !MI.isInvariantLoad(AA)))
return false;
}