RegAllocFast: Cleanup; NFC

- Use range based for
- Variable names should start with upper case
- Add `const`
- Change class name to match filename
- Fix doxygen comments
- Use MCPhysReg instead of unsigned
- Use references instead of pointers where things cannot be nullptr
- Misc coding style improvements

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@312846 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/InitializePasses.h

@@ -304,7 +304,7 @@ void initializeProfileSummaryInfoWrapperPassPass(PassRegistry&);
 void initializePromoteLegacyPassPass(PassRegistry&);
 void initializePruneEHPass(PassRegistry&);
 void initializeRABasicPass(PassRegistry&);
-void initializeRAFastPass(PassRegistry&);
+void initializeRegAllocFastPass(PassRegistry&);
 void initializeRAGreedyPass(PassRegistry&);
 void initializeReassociateLegacyPassPass(PassRegistry&);
 void initializeRegBankSelectPass(PassRegistry&);

lib/CodeGen/CodeGen.cpp

@@ -78,7 +78,7 @@ void llvm::initializeCodeGen(PassRegistry &Registry) {
   initializePreISelIntrinsicLoweringLegacyPassPass(Registry);
   initializeProcessImplicitDefsPass(Registry);
   initializeRABasicPass(Registry);
-  initializeRAFastPass(Registry);
+  initializeRegAllocFastPass(Registry);
   initializeRAGreedyPass(Registry);
   initializeRegisterCoalescerPass(Registry);
   initializeRenameIndependentSubregsPass(Registry);