[llvm] r246106 - [ARM] Use BranchProbability::scale() to scale an integer with a probability in ARMBaseInstrInfo.cpp,

[Cong Hou via llvm-commits]

Author: conghou
Date: Wed Aug 26 18:17:52 2015
New Revision: 246106

URL: http://llvm.org/viewvc/llvm-project?rev=246106&view=rev
Log:
[ARM] Use BranchProbability::scale() to scale an integer with a probability in ARMBaseInstrInfo.cpp,

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


Modified:
    llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp

Modified: llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp?rev=246106&r1=246105&r2=246106&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp Wed Aug 26 18:17:52 2015
@@ -1670,8 +1670,7 @@ isProfitableToIfCvt(MachineBasicBlock &M
   }
 
   // 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 &T
     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;