Refine CopyBytes macro instruction in IA32/X64

src/ia32/macro-assembler-ia32.cc

 // Copyright 2012 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 1992 matching lines @@
 // Source and destination are incremented by length.
 // Many variants of movsb, loop unrolling, word moves, and indexed operands
 // have been tried here already, and this is fastest.
 // A simpler loop is faster on small copies, but 30% slower on large ones.
 // The cld() instruction must have been emitted, to set the direction flag(),
 // before calling this function.
 void MacroAssembler::CopyBytes(Register source,
                                Register destination,
                                Register length,
                                Register scratch) {
-  Label loop, done, short_string, short_loop;
-  // Experimentation shows that the short string loop is faster if length < 10.
-  cmp(length, Immediate(10));
-  j(less_equal, &short_string);
-
+  Label short_loop, len4, len8, len12, done, short_string;
   ASSERT(source.is(esi));
   ASSERT(destination.is(edi));
   ASSERT(length.is(ecx));
+  cmp(length, Immediate(4));
+  j(below, &short_string, Label::kNear);
 
   // Because source is 4-byte aligned in our uses of this function,
   // we keep source aligned for the rep_movs call by copying the odd bytes
   // at the end of the ranges.
   mov(scratch, Operand(source, length, times_1, -4));
   mov(Operand(destination, length, times_1, -4), scratch);
+
+  cmp(length, Immediate(8));
+  j(below_equal, &len4, Label::kNear);
+  cmp(length, Immediate(12));
+  j(below_equal, &len8, Label::kNear);
+  cmp(length, Immediate(16));
+  j(below_equal, &len12, Label::kNear);
+
   mov(scratch, ecx);
   shr(ecx, 2);
   rep_movs();
   and_(scratch, Immediate(0x3));
   add(destination, scratch);
-  jmp(&done);
+  jmp(&done, Label::kNear);
+
+  bind(&len12);
+  mov(scratch, Operand(source, 8));
+  mov(Operand(destination, 8), scratch);
+  bind(&len8);
+  mov(scratch, Operand(source, 4));
+  mov(Operand(destination, 4), scratch);
+  bind(&len4);
+  mov(scratch, Operand(source, 0));
+  mov(Operand(destination, 0), scratch);
+  add(destination, length);
+  jmp(&done, Label::kNear);
 
   bind(&short_string);
   test(length, length);
-  j(zero, &done);
+  j(zero, &done, Label::kNear);
 
   bind(&short_loop);
   mov_b(scratch, Operand(source, 0));
   mov_b(Operand(destination, 0), scratch);
   inc(source);
   inc(destination);
   dec(length);
   j(not_zero, &short_loop);
 
   bind(&done);
@@ skipping 1550 matching lines @@
   cmp(scratch1, Immediate(DICTIONARY_ELEMENTS));
   j(equal, found);
   mov(current, FieldOperand(current, Map::kPrototypeOffset));
   cmp(current, Immediate(factory->null_value()));
   j(not_equal, &loop_again);
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32