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 ;)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@156233 91177308-0d34-0410-b5e6-96231b3b80d8

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.