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

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

diff --git a/lib/Target/ARM/ARMBaseInstrInfo.cpp b/lib/Target/ARM/ARMBaseInstrInfo.cpp
index 2f97b2ef4d2edf7d17457b580c693e58dc171092..47a6338f4c3141c7bc09ff974e8b6e5a77046481 100644 (file)
--- a/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -1670,8 +1670,7 @@ isProfitableToIfCvt(MachineBasicBlock &MBB,
   }
 
   // Attempt to estimate the relative costs of predication versus branching.
   }
 
   // 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;
 
   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.
     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;
   unsigned UnpredCost = TUnpredCost + FUnpredCost;
   UnpredCost += 1; // The branch itself
   UnpredCost += Subtarget.getMispredictionPenalty() / 10;