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/AMDGPUInstructionSelector.cpp b/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
index 1801015..73b7241 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
@@ -37,11 +37,13 @@
 using namespace llvm;
 
 #define GET_GLOBALISEL_IMPL
+#define AMDGPUSubtarget GCNSubtarget
 #include "AMDGPUGenGlobalISel.inc"
 #undef GET_GLOBALISEL_IMPL
+#undef AMDGPUSubtarget
 
 AMDGPUInstructionSelector::AMDGPUInstructionSelector(
-    const SISubtarget &STI, const AMDGPURegisterBankInfo &RBI,
+    const GCNSubtarget &STI, const AMDGPURegisterBankInfo &RBI,
     const AMDGPUTargetMachine &TM)
     : InstructionSelector(), TII(*STI.getInstrInfo()),
       TRI(*STI.getRegisterInfo()), RBI(RBI), TM(TM),
@@ -447,7 +449,7 @@
 
   MachineBasicBlock *BB = I.getParent();
   MachineFunction *MF = BB->getParent();
-  const SISubtarget &Subtarget = MF->getSubtarget<SISubtarget>();
+  const GCNSubtarget &Subtarget = MF->getSubtarget<GCNSubtarget>();
   MachineRegisterInfo &MRI = MF->getRegInfo();
   unsigned DstReg = I.getOperand(0).getReg();
   const DebugLoc &DL = I.getDebugLoc();