AMDGPU: Combine fp16/fp64 subtarget features

The same control register controls both, and are set to
the same defaults. Keep the old names around as aliases.

llvm-svn: 292837
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.h b/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.h
index 26c4c34..c8414f9 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.h
+++ b/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.h
@@ -81,9 +81,8 @@
   bool HalfRate64Ops;
 
   // Dynamially set bits that enable features.
-  bool FP16Denormals;
   bool FP32Denormals;
-  bool FP64Denormals;
+  bool FP64FP16Denormals;
   bool FPExceptions;
   bool FlatForGlobal;
   bool UnalignedScratchAccess;
@@ -282,7 +281,7 @@
   unsigned getOccupancyWithLocalMemSize(uint32_t Bytes) const;
 
   bool hasFP16Denormals() const {
-    return FP16Denormals;
+    return FP64FP16Denormals;
   }
 
   bool hasFP32Denormals() const {
@@ -290,7 +289,7 @@
   }
 
   bool hasFP64Denormals() const {
-    return FP64Denormals;
+    return FP64FP16Denormals;
   }
 
   bool hasFPExceptions() const {