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/GCNRegPressure.cpp b/llvm/lib/Target/AMDGPU/GCNRegPressure.cpp
index 53b552a..3d8cacc 100644
--- a/llvm/lib/Target/AMDGPU/GCNRegPressure.cpp
+++ b/llvm/lib/Target/AMDGPU/GCNRegPressure.cpp
@@ -132,7 +132,7 @@
   }
 }
 
-bool GCNRegPressure::less(const SISubtarget &ST,
+bool GCNRegPressure::less(const GCNSubtarget &ST,
                           const GCNRegPressure& O,
                           unsigned MaxOccupancy) const {
   const auto SGPROcc = std::min(MaxOccupancy,
@@ -178,7 +178,7 @@
 
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 LLVM_DUMP_METHOD
-void GCNRegPressure::print(raw_ostream &OS, const SISubtarget *ST) const {
+void GCNRegPressure::print(raw_ostream &OS, const GCNSubtarget *ST) const {
   OS << "VGPRs: " << getVGPRNum();
   if (ST) OS << "(O" << ST->getOccupancyWithNumVGPRs(getVGPRNum()) << ')';
   OS << ", SGPRs: " << getSGPRNum();