Provide a tagged allocation top pointer.

src/mips64/macro-assembler-mips64.cc

Index: src/mips64/macro-assembler-mips64.cc
diff --git a/src/mips64/macro-assembler-mips64.cc b/src/mips64/macro-assembler-mips64.cc
index f409c0fb49a564d862437213a8fd3ad62cf92947..f8dfa1b0e819175fe91933806314e376e9cd39b9 100644
--- a/src/mips64/macro-assembler-mips64.cc
+++ b/src/mips64/macro-assembler-mips64.cc
@@ -4318,11 +4318,11 @@ void MacroAssembler::Allocate(int object_size,
   }
 
   // We can ignore DOUBLE_ALIGNMENT flags here because doubles and pointers have
-  // the same alignment on ARM64.
+  // the same alignment on MIPS64.
   STATIC_ASSERT(kPointerAlignment == kDoubleAlignment);
 
   if (emit_debug_code()) {
-    And(at, result, Operand(kDoubleAlignmentMask));
+    And(at, result, Operand(kDoubleAlignmentMaskTagged));
     Check(eq, kAllocationIsNotDoubleAligned, at, Operand(zero_reg));
   }
 
@@ -4335,9 +4335,6 @@ void MacroAssembler::Allocate(int object_size,
     // The top pointer is not updated for allocation folding dominators.
     sd(result_end, MemOperand(top_address));
   }
-
-  // Tag object.
-  Daddu(result, result, Operand(kHeapObjectTag));
 }
 
 
@@ -4391,11 +4388,11 @@ void MacroAssembler::Allocate(Register object_size, Register result,
   }
 
   // We can ignore DOUBLE_ALIGNMENT flags here because doubles and pointers have
-  // the same alignment on ARM64.
+  // the same alignment on MIPS64.
   STATIC_ASSERT(kPointerAlignment == kDoubleAlignment);
 
   if (emit_debug_code()) {
-    And(at, result, Operand(kDoubleAlignmentMask));
+    And(at, result, Operand(kDoubleAlignmentMaskTagged));
     Check(eq, kAllocationIsNotDoubleAligned, at, Operand(zero_reg));
   }
 
@@ -4412,7 +4409,7 @@ void MacroAssembler::Allocate(Register object_size, Register result,
 
   // Update allocation top. result temporarily holds the new top.
   if (emit_debug_code()) {
-    And(at, result_end, Operand(kObjectAlignmentMask));
+    And(at, result_end, Operand(kObjectAlignmentMask - 1));
     Check(eq, kUnalignedAllocationInNewSpace, at, Operand(zero_reg));
   }
 
@@ -4420,9 +4417,6 @@ void MacroAssembler::Allocate(Register object_size, Register result,
     // The top pointer is not updated for allocation folding dominators.
     sd(result_end, MemOperand(top_address));
   }
-
-  // Tag object if.
-  Daddu(result, result, Operand(kHeapObjectTag));
 }
 
 void MacroAssembler::FastAllocate(int object_size, Register result,
@@ -4450,15 +4444,13 @@ void MacroAssembler::FastAllocate(int object_size, Register result,
   STATIC_ASSERT(kPointerAlignment == kDoubleAlignment);
 
   if (emit_debug_code()) {
-    And(at, result, Operand(kDoubleAlignmentMask));
+    And(at, result, Operand(kDoubleAlignmentMaskTagged));
     Check(eq, kAllocationIsNotDoubleAligned, at, Operand(zero_reg));
   }
 
   // Calculate new top and write it back.
   Daddu(result_end, result, Operand(object_size));
   sd(result_end, MemOperand(top_address));
-
-  Daddu(result, result, Operand(kHeapObjectTag));
 }
 
 void MacroAssembler::FastAllocate(Register object_size, Register result,
@@ -4481,7 +4473,7 @@ void MacroAssembler::FastAllocate(Register object_size, Register result,
   STATIC_ASSERT(kPointerAlignment == kDoubleAlignment);
 
   if (emit_debug_code()) {
-    And(at, result, Operand(kDoubleAlignmentMask));
+    And(at, result, Operand(kDoubleAlignmentMaskTagged));
     Check(eq, kAllocationIsNotDoubleAligned, at, Operand(zero_reg));
   }
 
@@ -4494,11 +4486,9 @@ void MacroAssembler::FastAllocate(Register object_size, Register result,
 
   // Update allocation top. result temporarily holds the new top.
   if (emit_debug_code()) {
-    And(at, result_end, Operand(kObjectAlignmentMask));
+    And(at, result_end, Operand(kObjectAlignmentMask - 1));
     Check(eq, kUnalignedAllocationInNewSpace, at, Operand(zero_reg));
   }
-
-  Daddu(result, result, Operand(kHeapObjectTag));
 }
 
 void MacroAssembler::AllocateTwoByteString(Register result,