R600: Add a SubtargetFeatture for disabling the ifcvt pass.

This is useful when writing test cases for the AMDIL structurizer.

llvm-svn: 195029
diff --git a/llvm/lib/Target/R600/AMDGPUSubtarget.h b/llvm/lib/Target/R600/AMDGPUSubtarget.h
index c08cd6a..4288d27 100644
--- a/llvm/lib/Target/R600/AMDGPUSubtarget.h
+++ b/llvm/lib/Target/R600/AMDGPUSubtarget.h
@@ -50,6 +50,7 @@
   bool FP64;
   bool CaymanISA;
   bool EnableIRStructurizer;
+  bool EnableIfCvt;
 
   InstrItineraryData InstrItins;
 
@@ -66,6 +67,7 @@
   bool hasHWFP64() const;
   bool hasCaymanISA() const;
   bool IsIRStructurizerEnabled() const;
+  bool isIfCvtEnabled() const;
 
   virtual bool enableMachineScheduler() const {
     return getGeneration() <= NORTHERN_ISLANDS;