Scaling up values in ARMBaseInstrInfo::isProfitableToIfCvt() before they are scaled...

[oota-llvm.git] / lib / Target / ARM / ARMBaseInstrInfo.cpp

diff --git a/lib/Target/ARM/ARMBaseInstrInfo.cpp b/lib/Target/ARM/ARMBaseInstrInfo.cpp
index 79ab692c76a44ca35a4fbb2b26ea43a1b5f23df8..abb1fdad080f43b933e71160d68c4248112d08e2 100644 (file)
--- a/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -1670,11 +1670,14 @@ isProfitableToIfCvt(MachineBasicBlock &MBB,
   }
 
   // Attempt to estimate the relative costs of predication versus branching.
-  unsigned UnpredCost = Probability.scale(NumCycles);
-  UnpredCost += 1; // The branch itself
-  UnpredCost += Subtarget.getMispredictionPenalty() / 10;
-
-  return (NumCycles + ExtraPredCycles) <= UnpredCost;
+  // Here we scale up each component of UnpredCost to avoid precision issue when
+  // scaling NumCycles by Probability.
+  const unsigned ScalingUpFactor = 1024;
+  unsigned UnpredCost = Probability.scale(NumCycles * ScalingUpFactor);
+  UnpredCost += ScalingUpFactor; // The branch itself
+  UnpredCost += Subtarget.getMispredictionPenalty() * ScalingUpFactor / 10;
+
+  return (NumCycles + ExtraPredCycles) * ScalingUpFactor <= UnpredCost;
 }
 
 bool ARMBaseInstrInfo::
@@ -1687,13 +1690,17 @@ isProfitableToIfCvt(MachineBasicBlock &TMBB,
     return false;
 
   // Attempt to estimate the relative costs of predication versus branching.
-  unsigned TUnpredCost = Probability.scale(TCycles);
-  unsigned FUnpredCost = Probability.getCompl().scale(FCycles);
+  // Here we scale up each component of UnpredCost to avoid precision issue when
+  // scaling TCycles/FCycles by Probability.
+  const unsigned ScalingUpFactor = 1024;
+  unsigned TUnpredCost = Probability.scale(TCycles * ScalingUpFactor);
+  unsigned FUnpredCost =
+      Probability.getCompl().scale(FCycles * ScalingUpFactor);
   unsigned UnpredCost = TUnpredCost + FUnpredCost;
-  UnpredCost += 1; // The branch itself
-  UnpredCost += Subtarget.getMispredictionPenalty() / 10;
+  UnpredCost += 1 * ScalingUpFactor; // The branch itself
+  UnpredCost += Subtarget.getMispredictionPenalty() * ScalingUpFactor / 10;
 
-  return (TCycles + FCycles + TExtra + FExtra) <= UnpredCost;
+  return (TCycles + FCycles + TExtra + FExtra) * ScalingUpFactor <= UnpredCost;
 }
 
 bool