[RegisterConfiguration] Streamline access to arch defaults, simplify Registers.

src/crankshaft/mips64/lithium-codegen-mips64.cc

Index: src/crankshaft/mips64/lithium-codegen-mips64.cc
diff --git a/src/crankshaft/mips64/lithium-codegen-mips64.cc b/src/crankshaft/mips64/lithium-codegen-mips64.cc
index 75cce299d66ee665b69ab1185d40fb6010a7c7cf..41ed95ed615da98fb4ef696dc89967103c7aa6a2 100644
--- a/src/crankshaft/mips64/lithium-codegen-mips64.cc
+++ b/src/crankshaft/mips64/lithium-codegen-mips64.cc
@@ -3737,7 +3737,9 @@ void LCodeGen::PrepareForTailCall(const ParameterCount& actual,
 #endif
   if (FLAG_code_comments) {
     if (actual.is_reg()) {
-      Comment(";;; PrepareForTailCall, actual: %s {", actual.reg().ToString());
+      Comment(";;; PrepareForTailCall, actual: %s {",
+              RegisterConfiguration::Crankshaft()->GetGeneralRegisterName(
+                  actual.reg().code()));
     } else {
       Comment(";;; PrepareForTailCall, actual: %d {", actual.immediate());
     }