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[ARM] Use BranchProbability::scale() to scale an integer with a probability in ARMBaseInstrInfo.cpp,

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Previously in isProfitableToIfCvt() in ARMBaseInstrInfo.cpp, the multiplication between an integer and a branch probability is done manually in an unsafe way that may lead to overflow. This patch corrects those cases by using BranchProbability's member function scale() to avoid overflow (which stores the intermediate result in int64).

Differential Revision: http://reviews.llvm.org/D12295



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@246106 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Cong Hou 2015-08-26 23:17:52 +00:00
parent 6dc18d8d3a
commit b99373e1a6
1 changed files with 3 additions and 9 deletions
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12
lib/Target/ARM/ARMBaseInstrInfo.cpp
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@ -1670,8 +1670,7 @@ isProfitableToIfCvt(MachineBasicBlock &MBB,
}
// Attempt to estimate the relative costs of predication versus branching.
unsigned UnpredCost = Probability.getNumerator() * NumCycles;
UnpredCost /= Probability.getDenominator();
unsigned UnpredCost = Probability.scale(NumCycles);
UnpredCost += 1; // The branch itself
UnpredCost += Subtarget.getMispredictionPenalty() / 10;
@ -1688,13 +1687,8 @@ isProfitableToIfCvt(MachineBasicBlock &TMBB,
return false;
// Attempt to estimate the relative costs of predication versus branching.
unsigned TUnpredCost = Probability.getNumerator() * TCycles;
TUnpredCost /= Probability.getDenominator();
uint32_t Comp = Probability.getDenominator() - Probability.getNumerator();
unsigned FUnpredCost = Comp * FCycles;
FUnpredCost /= Probability.getDenominator();
unsigned TUnpredCost = Probability.scale(TCycles);
unsigned FUnpredCost = Probability.getCompl().scale(FCycles);
unsigned UnpredCost = TUnpredCost + FUnpredCost;
UnpredCost += 1; // The branch itself
UnpredCost += Subtarget.getMispredictionPenalty() / 10;