char MachineBranchProbabilityInfo::ID = 0;
-uint32_t MachineBranchProbabilityInfo::
-getSumForBlock(MachineBasicBlock *MBB) const {
- uint32_t Sum = 0;
+void MachineBranchProbabilityInfo::anchor() { }
+uint32_t MachineBranchProbabilityInfo::
+getSumForBlock(MachineBasicBlock *MBB, uint32_t &Scale) const {
+ // First we compute the sum with 64-bits of precision, ensuring that cannot
+ // overflow by bounding the number of weights considered. Hopefully no one
+ // actually needs 2^32 successors.
+ assert(MBB->succ_size() < UINT32_MAX);
+ uint64_t Sum = 0;
+ Scale = 1;
for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
E = MBB->succ_end(); I != E; ++I) {
- MachineBasicBlock *Succ = *I;
- uint32_t Weight = getEdgeWeight(MBB, Succ);
- uint32_t PrevSum = Sum;
-
+ uint32_t Weight = getEdgeWeight(MBB, *I);
Sum += Weight;
- assert(Sum > PrevSum); (void) PrevSum;
}
+ // If the computed sum fits in 32-bits, we're done.
+ if (Sum <= UINT32_MAX)
+ return Sum;
+
+ // Otherwise, compute the scale necessary to cause the weights to fit, and
+ // re-sum with that scale applied.
+ assert((Sum / UINT32_MAX) < UINT32_MAX);
+ Scale = (Sum / UINT32_MAX) + 1;
+ Sum = 0;
+ for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
+ E = MBB->succ_end(); I != E; ++I) {
+ uint32_t Weight = getEdgeWeight(MBB, *I);
+ Sum += Weight / Scale;
+ }
+ assert(Sum <= UINT32_MAX);
return Sum;
}
MachineBasicBlock *
MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const {
- uint32_t Sum = 0;
uint32_t MaxWeight = 0;
MachineBasicBlock *MaxSucc = 0;
-
for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
E = MBB->succ_end(); I != E; ++I) {
- MachineBasicBlock *Succ = *I;
- uint32_t Weight = getEdgeWeight(MBB, Succ);
- uint32_t PrevSum = Sum;
-
- Sum += Weight;
- assert(Sum > PrevSum); (void) PrevSum;
-
+ uint32_t Weight = getEdgeWeight(MBB, *I);
if (Weight > MaxWeight) {
MaxWeight = Weight;
- MaxSucc = Succ;
+ MaxSucc = *I;
}
}
- if (BranchProbability(MaxWeight, Sum) >= BranchProbability(4, 5))
+ if (getEdgeProbability(MBB, MaxSucc) >= BranchProbability(4, 5))
return MaxSucc;
return 0;
BranchProbability
MachineBranchProbabilityInfo::getEdgeProbability(MachineBasicBlock *Src,
MachineBasicBlock *Dst) const {
- uint32_t N = getEdgeWeight(Src, Dst);
- uint32_t D = getSumForBlock(Src);
+ uint32_t Scale = 1;
+ uint32_t D = getSumForBlock(Src, Scale);
+ uint32_t N = getEdgeWeight(Src, Dst) / Scale;
return BranchProbability(N, D);
}