Revert of Remove register index/code indirection

src/x64/assembler-x64.cc

Index: src/x64/assembler-x64.cc
diff --git a/src/x64/assembler-x64.cc b/src/x64/assembler-x64.cc
index 059b576beaa42d52765c8b383762199a0a14e392..cb93ab878b9517a1348d32df1914fa9cff856f65 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -113,6 +113,20 @@
       CpuFeatures::IsSupported(BMI2), CpuFeatures::IsSupported(LZCNT),
       CpuFeatures::IsSupported(POPCNT), CpuFeatures::IsSupported(ATOM));
 }
+
+
+// -----------------------------------------------------------------------------
+// Register constants.
+
+const int
+    Register::kRegisterCodeByAllocationIndex[kMaxNumAllocatableRegisters] = {
+  // rax, rbx, rdx, rcx, rsi, rdi, r8, r9, r11, r12, r14, r15
+  0, 3, 2, 1, 6, 7, 8, 9, 11, 12, 14, 15
+};
+
+const int Register::kAllocationIndexByRegisterCode[kNumRegisters] = {
+  0, 3, 2, 1, -1, -1, 4, 5, 6, 7, -1, 8, 9, -1, 10, 11
+};
 
 
 // -----------------------------------------------------------------------------