Add a helper method that will be used to support EXTRACT_SUBREG for selecting trunc's in fast-isel.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@55439 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/FastISel.h

@@ -193,6 +193,11 @@ protected:
                           const TargetRegisterClass *RC,
                           uint64_t Imm);
 
+  /// FastEmitInst_extractsubreg - Emit a MachineInstr for an extract_subreg
+  /// from a specified index of a superregister.
+  unsigned FastEmitInst_extractsubreg(const TargetRegisterClass *RC,
+                                      unsigned Op0, uint32_t Idx);
+
 private:
   unsigned getRegForValue(Value *V,
                           DenseMap<const Value*, unsigned> &ValueMap);