X64: Optimize access to external references.

src/x64/regexp-macro-assembler-x64.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
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@@ skipping 45 matching lines @@
  *         RegExp registers.
  * - rsp : points to tip of C stack.
  * - rcx : points to tip of backtrack stack. The backtrack stack contains
  *         only 32-bit values. Most are offsets from some base (e.g., character
  *         positions from end of string or code location from Code* pointer).
  * - r8  : code object pointer. Used to convert between absolute and
  *         code-object-relative addresses.
  *
  * The registers rax, rbx, r9 and r11 are free to use for computations.
  * If changed to use r12+, they should be saved as callee-save registers.
+ * The macro assembler special registers r12 and r13 (kSmiConstantRegister,
+ * kRootRegister) are not initialized during RegExp code.

[William Hesse, 2011/03/22 14:05:08]

"are not initialized" is confusing.  Do you mean "free for general purpose use
during RegExp code"?

[Lasse Reichstein, 2011/03/22 14:12:21]

Except that they are not free either (since we don't save them and they are
callee-save).
Rewording.

  *
  * Each call to a C++ method should retain these registers.
  *
  * The stack will have the following content, in some order, indexable from the
  * frame pointer (see, e.g., kStackHighEnd):
  *    - Isolate* isolate     (Address of the current isolate)
  *    - direct_call          (if 1, direct call from JavaScript code, if 0 call
  *                            through the runtime system)
  *    - stack_area_base      (High end of the memory area to use as
  *                            backtracking stack)
@@ skipping 28 matching lines @@
  *              byte* stack_area_base,
  *              bool direct_call)
  */
 
 #define __ ACCESS_MASM(masm_)
 
 RegExpMacroAssemblerX64::RegExpMacroAssemblerX64(
     Mode mode,
     int registers_to_save)
     : masm_(new MacroAssembler(NULL, kRegExpCodeSize)),
+      no_root_array_scope_(masm_),
       code_relative_fixup_positions_(4),
       mode_(mode),
       num_registers_(registers_to_save),
       num_saved_registers_(registers_to_save),
       entry_label_(),
       start_label_(),
       success_label_(),
       backtrack_label_(),
       exit_label_() {
   ASSERT_EQ(0, registers_to_save % 2);
@@ skipping 1253 matching lines @@
   }
 }
 
 #undef __
 
 #endif  // V8_INTERPRETED_REGEXP
 
 }}  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64