Add VirtRegMap::rewrite() and use it in the new register allocators.

The rewriter works almost identically to -rewriter=trivial, except it also
eliminates any identity copies.

This makes the new register allocators independent of VirtRegRewriter.cpp which
will be going away at the same time as RegAllocLinearScan.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@125967 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/RegAllocBasic.cpp

@@ -18,7 +18,6 @@
 #include "RenderMachineFunction.h"
 #include "Spiller.h"
 #include "VirtRegMap.h"
-#include "VirtRegRewriter.h"
 #include "llvm/ADT/OwningPtr.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/AliasAnalysis.h"
@@ -510,8 +509,7 @@ bool RABasic::runOnMachineFunction(MachineFunction &mf) {
 #endif // !NDEBUG
 
   // Run rewriter
-  std::auto_ptr<VirtRegRewriter> rewriter(createVirtRegRewriter());
-  rewriter->runOnMachineFunction(*MF, *VRM, LIS);
+  VRM->rewrite(LIS->getSlotIndexes());
 
   // The pass output is in VirtRegMap. Release all the transient data.
   releaseMemory();