Add a subtarget hook for reporting the misprediction penalty. Use this to provide more precise

cost modeling for if-conversion.  Now if only we had a way to estimate the misprediction probability.

Adjsut CodeGen/ARM/ifcvt10.ll.  The pipeline on Cortex-A8 is long enough that it is still profitable
to predicate an ldm, but the shorter pipeline on Cortex-A9 makes it unprofitable.

llvm-svn: 114995

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
index f92317c322c..c38b89534bf 100644
--- a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -1203,7 +1203,8 @@ bool ARMBaseInstrInfo::isProfitableToIfCvt(MachineBasicBlock &MBB,
   
   // Attempt to estimate the relative costs of predication versus branching.
   float UnpredCost = Probability * NumInstrs;
-  UnpredCost += 2.0; // FIXME: Should model a misprediction cost.
+  UnpredCost += 1.0; // The branch itself
+  UnpredCost += 0.1 * Subtarget.getMispredictionPenalty();
   
   float PredCost = NumInstrs;
   
@@ -1220,7 +1221,8 @@ isProfitableToIfCvt(MachineBasicBlock &TMBB, unsigned NumT,
   
   // Attempt to estimate the relative costs of predication versus branching.
   float UnpredCost = Probability * NumT + (1.0 - Probability) * NumF;
-  UnpredCost += 2.0; // FIXME: Should model a misprediction cost.
+  UnpredCost += 1.0; // The branch itself
+  UnpredCost += 0.1 * Subtarget.getMispredictionPenalty();
   
   float PredCost = NumT + NumF;