AMDGPU: Refactor Subtarget classes

Summary:
This is a follow-up to r335942.
- Merge SISubtarget into AMDGPUSubtarget and rename to GCNSubtarget
- Rename AMDGPUCommonSubtarget to AMDGPUSubtarget
- Merge R600Subtarget::Generation and GCNSubtarget::Generation into
  AMDGPUSubtarget::Generation.

Reviewers: arsenm, jvesely

Subscribers: kzhuravl, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye, javed.absar, llvm-commits

Differential Revision: https://reviews.llvm.org/D49037

llvm-svn: 336851
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.h b/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.h
index 50b219d..0fe1449 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.h
+++ b/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.h
@@ -100,7 +100,7 @@
 class GCNTargetMachine final : public AMDGPUTargetMachine {
 private:
   AMDGPUIntrinsicInfo IntrinsicInfo;
-  mutable StringMap<std::unique_ptr<SISubtarget>> SubtargetMap;
+  mutable StringMap<std::unique_ptr<GCNSubtarget>> SubtargetMap;
 
 public:
   GCNTargetMachine(const Target &T, const Triple &TT, StringRef CPU,
@@ -110,7 +110,7 @@
 
   TargetPassConfig *createPassConfig(PassManagerBase &PM) override;
 
-  const SISubtarget *getSubtargetImpl(const Function &) const override;
+  const GCNSubtarget *getSubtargetImpl(const Function &) const override;
 
   TargetTransformInfo getTargetTransformInfo(const Function &F) override;