Add a new target hook "predictableSelectIsExpensive".

This will be used to determine whether it's profitable to turn a select into a
branch when the branch is likely to be predicted.

Currently enabled for everything but Atom on X86 and Cortex-A9 devices on ARM.

I'm not entirely happy with the name of this flag, suggestions welcome ;)

llvm-svn: 156233

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/include/llvm/Target/TargetLowering.h b/llvm/include/llvm/Target/TargetLowering.h
index 78ccb12d90f..29abc191dda 100644
--- a/llvm/include/llvm/Target/TargetLowering.h
+++ b/llvm/include/llvm/Target/TargetLowering.h
@@ -150,6 +150,12 @@ public:
   /// that should be avoided.
   bool isJumpExpensive() const { return JumpIsExpensive; }
 
+  /// isPredictableSelectExpensive - Return true if selects are only cheaper
+  /// than branches if the branch is unlikely to be predicted right.
+  bool isPredictableSelectExpensive() const {
+    return predictableSelectIsExpensive;
+  }
+
   /// getSetCCResultType - Return the ValueType of the result of SETCC
   /// operations.  Also used to obtain the target's preferred type for
   /// the condition operand of SELECT and BRCOND nodes.  In the case of
@@ -2028,6 +2034,10 @@ protected:
   /// optimization.
   bool benefitFromCodePlacementOpt;
 
+  /// predictableSelectIsExpensive - Tells the code generator that select is
+  /// more expensive than a branch if the branch is usually predicted right.
+  bool predictableSelectIsExpensive;
+
 private:
   /// isLegalRC - Return true if the value types that can be represented by the
   /// specified register class are all legal.