Rename some x64 macros to be more precise about their semantics.

src/x64/code-stubs-x64.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3783 matching lines @@
   __ j(zero, &runtime);
   Condition is_string = masm->IsObjectStringType(rax, rbx, rbx);
   __ j(NegateCondition(is_string), &runtime);
 
   // rax: string
   // rbx: instance type
   // Calculate length of sub string using the smi values.
   Label result_longer_than_two;
   __ movq(rcx, Operand(rsp, kToOffset));
   __ movq(rdx, Operand(rsp, kFromOffset));
-  __ JumpIfNotBothPositiveSmi(rcx, rdx, &runtime);
+  __ JumpUnlessBothNonNegativeSmi(rcx, rdx, &runtime);
 
   __ SmiSub(rcx, rcx, rdx);  // Overflow doesn't happen.
   __ cmpq(FieldOperand(rax, String::kLengthOffset), rcx);
   Label return_rax;
   __ j(equal, &return_rax);
   // Special handling of sub-strings of length 1 and 2. One character strings
   // are handled in the runtime system (looked up in the single character
   // cache). Two character strings are looked for in the symbol cache.
   __ SmiToInteger32(rcx, rcx);
   __ cmpl(rcx, Immediate(2));
@@ skipping 230 matching lines @@
   // tagged as a small integer.
   __ bind(&runtime);
   __ TailCallRuntime(Runtime::kStringCompare, 2, 1);
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64