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

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index e302a419ea47513c4474aad05991f411cd89f62f..694832a18df2cd0b253293cbfd370e0a827beb3d 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -5280,25 +5280,38 @@ void MacroAssembler::CheckPageFlag(
 }
 
 
-void MacroAssembler::JumpIfBlack(Register object,
-                                 Register bitmap_scratch,
-                                 Register mask_scratch,
-                                 Label* on_black,
-                                 Label::Distance 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);
 
-  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);
+  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);
 }
 
 
@@ -5321,7 +5334,7 @@ void MacroAssembler::GetMarkBits(Register addr_reg,
   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);
 }
 
@@ -5334,8 +5347,8 @@ void MacroAssembler::JumpIfWhite(Register value, Register bitmap_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