[heap] Black is encoded with 11, grey with 10.

src/x64/macro-assembler-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/base/bits.h"
 #include "src/base/division-by-constant.h"
 #include "src/bootstrapper.h"
 #include "src/codegen.h"
@@ skipping 5262 matching lines @@
   if (mask < (1 << kBitsPerByte)) {
     testb(Operand(scratch, MemoryChunk::kFlagsOffset),
           Immediate(static_cast<uint8_t>(mask)));
   } else {
     testl(Operand(scratch, MemoryChunk::kFlagsOffset), Immediate(mask));
   }
   j(cc, condition_met, condition_met_distance);
 }
 
 
-void MacroAssembler::JumpIfBlack(Register object,
-                                 Register bitmap_scratch,
-                                 Register mask_scratch,
-                                 Label* on_black,
-                                 Label::Distance on_black_distance) {
-  DCHECK(!AreAliased(object, bitmap_scratch, mask_scratch, rcx));
-  GetMarkBits(object, bitmap_scratch, mask_scratch);
-
-  DCHECK(strcmp(Marking::kBlackBitPattern, "10") == 0);
-  // The mask_scratch register contains a 1 at the position of the first bit
-  // and a 0 at all other positions, including the position of the second bit.
-  movp(rcx, mask_scratch);
-  // Make rcx into a mask that covers both marking bits using the operation
-  // rcx = mask | (mask << 1).
-  leap(rcx, Operand(mask_scratch, mask_scratch, times_2, 0));
-  // Note that we are using a 4-byte aligned 8-byte load.

[ulan, 2016/01/05 14:45:23]

// This change here should be sufficient to convert the function to HasColor.
if (first_bit == 0 && second_bit == 0) {
  movp(mask_scratch, Immediate(0));
} else if (first_bit == 1 && second_bit == 1) {
  movp(mask_scratch, rcx);
} else {
  DCHECK(first_bit == 1 && second_bit == 0);
}

[Hannes Payer (out of office), 2016/01/07 20:17:33]

Not sure what you mean here? Should I bring back the old code and patch it
accordingly? The current HasColor implementation is in sync with the other
platforms.

[Hannes Payer (out of office), 2016/01/11 12:24:32]

After discussing offline, I kept x64 special and simplified it.

-  andp(rcx, Operand(bitmap_scratch, MemoryChunk::kHeaderSize));
-  cmpp(mask_scratch, rcx);
-  j(equal, on_black, on_black_distance);
+void MacroAssembler::JumpIfBlack(Register object, Register scratch0,
+                                 Register scratch1, Label* on_black,
+                                 Label::Distance on_black_near) {

[ulan, 2016/01/05 14:45:23]

let's keep the old name for on_black_distance.

[Hannes Payer (out of office), 2016/01/07 20:17:33]

Done.

+  HasColor(object, scratch0, scratch1, on_black, on_black_near, 1,
+           1);  // kBlackBitPattern.
+  DCHECK(strcmp(Marking::kBlackBitPattern, "11") == 0);
 }
 
 
+void MacroAssembler::HasColor(Register object, Register bitmap_scratch,
+                              Register mask_scratch, Label* has_color,
+                              Label::Distance has_color_distance, int first_bit,
+                              int second_bit) {
+  DCHECK(!AreAliased(object, bitmap_scratch, mask_scratch, rcx));
+
+  GetMarkBits(object, bitmap_scratch, mask_scratch);
+
+  Label other_color, word_boundary;
+  testp(Operand(bitmap_scratch, MemoryChunk::kHeaderSize), mask_scratch);
+  j(first_bit == 1 ? zero : not_zero, &other_color, Label::kNear);
+  shlp(mask_scratch, Immediate(1));
+  j(zero, &word_boundary, Label::kNear);
+  testp(Operand(bitmap_scratch, MemoryChunk::kHeaderSize), mask_scratch);
+  j(second_bit == 1 ? not_zero : zero, has_color, has_color_distance);
+  jmp(&other_color, Label::kNear);
+
+  bind(&word_boundary);
+  testb(Operand(bitmap_scratch, MemoryChunk::kHeaderSize + kPointerSize),
+        Immediate(1));
+
+  j(second_bit == 1 ? not_zero : zero, has_color, has_color_distance);
+  bind(&other_color);
+}
+
+
 void MacroAssembler::GetMarkBits(Register addr_reg,
                                  Register bitmap_reg,
                                  Register mask_reg) {
   DCHECK(!AreAliased(addr_reg, bitmap_reg, mask_reg, rcx));
   movp(bitmap_reg, addr_reg);
   // Sign extended 32 bit immediate.
   andp(bitmap_reg, Immediate(~Page::kPageAlignmentMask));
   movp(rcx, addr_reg);
   int shift =
       Bitmap::kBitsPerCellLog2 + kPointerSizeLog2 - Bitmap::kBytesPerCellLog2;
   shrl(rcx, Immediate(shift));
   andp(rcx,
        Immediate((Page::kPageAlignmentMask >> shift) &
                  ~(Bitmap::kBytesPerCell - 1)));
 
   addp(bitmap_reg, rcx);
   movp(rcx, addr_reg);
   shrl(rcx, Immediate(kPointerSizeLog2));
   andp(rcx, Immediate((1 << Bitmap::kBitsPerCellLog2) - 1));
-  movl(mask_reg, Immediate(1));
+  movl(mask_reg, Immediate(3));
   shlp_cl(mask_reg);
 }
 
 
 void MacroAssembler::JumpIfWhite(Register value, Register bitmap_scratch,
                                  Register mask_scratch, Label* value_is_white,
                                  Label::Distance distance) {
   DCHECK(!AreAliased(value, bitmap_scratch, mask_scratch, rcx));
   GetMarkBits(value, bitmap_scratch, mask_scratch);
 
   // If the value is black or grey we don't need to do anything.
   DCHECK(strcmp(Marking::kWhiteBitPattern, "00") == 0);
-  DCHECK(strcmp(Marking::kBlackBitPattern, "10") == 0);
-  DCHECK(strcmp(Marking::kGreyBitPattern, "11") == 0);
+  DCHECK(strcmp(Marking::kBlackBitPattern, "11") == 0);
+  DCHECK(strcmp(Marking::kGreyBitPattern, "10") == 0);
   DCHECK(strcmp(Marking::kImpossibleBitPattern, "01") == 0);
 
   // Since both black and grey have a 1 in the first position and white does
   // not have a 1 there we only need to check one bit.
   testp(Operand(bitmap_scratch, MemoryChunk::kHeaderSize), mask_scratch);
   j(zero, value_is_white, distance);
 }
 
 
 void MacroAssembler::CheckEnumCache(Register null_value, Label* call_runtime) {
@@ skipping 111 matching lines @@
   movl(rax, dividend);
   shrl(rax, Immediate(31));
   addl(rdx, rax);
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64