Store CodeGenRegisters as pointers so they won't be reallocated.

Reuse the CodeGenRegBank DenseMap in a few places that would build their
own or use linear search.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@133333 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/FastISelEmitter.cpp b/utils/TableGen/FastISelEmitter.cpp
index 6c2a767..ef912df 100644
--- a/utils/TableGen/FastISelEmitter.cpp
+++ b/utils/TableGen/FastISelEmitter.cpp
@@ -406,15 +406,7 @@
   PhysReg += static_cast<StringInit*>(OpLeafRec->getValue( \
              "Namespace")->getValue())->getValue();
   PhysReg += "::";
-
-  std::vector<CodeGenRegister> Regs = Target.getRegisters();
-  for (unsigned i = 0; i < Regs.size(); ++i) {
-    if (Regs[i].TheDef == OpLeafRec) {
-      PhysReg += Regs[i].getName();
-      break;
-    }
-  }
-
+  PhysReg += Target.getRegBank().getReg(OpLeafRec)->getName();
   return PhysReg;
 }