X87: Re-reland: Remove register index/code indirection.

src/x87/code-stubs-x87.h

Index: src/x87/code-stubs-x87.h
diff --git a/src/x87/code-stubs-x87.h b/src/x87/code-stubs-x87.h
index 41c77f5df784d6fd0aee342ed5864a5e84097d2a..a6a2a1305735b33b78ae9da1c95a22ba8dddfe2c 100644
--- a/src/x87/code-stubs-x87.h
+++ b/src/x87/code-stubs-x87.h
@@ -309,13 +309,15 @@ class RecordWriteStub: public PlatformCodeStub {
     Register GetRegThatIsNotEcxOr(Register r1,
                                   Register r2,
                                   Register r3) {
-      for (int i = 0; i < Register::NumAllocatableRegisters(); i++) {
-        Register candidate = Register::FromAllocationIndex(i);
-        if (candidate.is(ecx)) continue;
-        if (candidate.is(r1)) continue;
-        if (candidate.is(r2)) continue;
-        if (candidate.is(r3)) continue;
-        return candidate;
+      for (int i = 0; i < Register::kNumRegisters; i++) {
+        Register candidate = Register::from_code(i);
+        if (candidate.IsAllocatable()) {
+          if (candidate.is(ecx)) continue;
+          if (candidate.is(r1)) continue;
+          if (candidate.is(r2)) continue;
+          if (candidate.is(r3)) continue;
+          return candidate;
+        }
       }
       UNREACHABLE();
       return no_reg;