Improve write barriers in optimized code.

src/arm/macro-assembler-arm.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.
 
 #include <limits.h>  // For LONG_MIN, LONG_MAX.
 
 #include "v8.h"
 
 #if V8_TARGET_ARCH_ARM
 
@@ skipping 435 matching lines @@
 
 
 void MacroAssembler::RecordWriteField(
     Register object,
     int offset,
     Register value,
     Register dst,
     LinkRegisterStatus lr_status,
     SaveFPRegsMode save_fp,
     RememberedSetAction remembered_set_action,
-    SmiCheck smi_check) {
+    SmiCheck smi_check,
+    bool value_is_in_new_space) {
   // First, check if a write barrier is even needed. The tests below
   // catch stores of Smis.
   Label done;
 
   // Skip barrier if writing a smi.
   if (smi_check == INLINE_SMI_CHECK) {
     JumpIfSmi(value, &done);
   }
 
   // Although the object register is tagged, the offset is relative to the start
   // of the object, so so offset must be a multiple of kPointerSize.
   ASSERT(IsAligned(offset, kPointerSize));
 
   add(dst, object, Operand(offset - kHeapObjectTag));
   if (emit_debug_code()) {
     Label ok;
     tst(dst, Operand((1 << kPointerSizeLog2) - 1));
     b(eq, &ok);
     stop("Unaligned cell in write barrier");
     bind(&ok);
   }
 
   RecordWrite(object,
               dst,
               value,
               lr_status,
               save_fp,
               remembered_set_action,
-              OMIT_SMI_CHECK);
+              OMIT_SMI_CHECK,
+              value_is_in_new_space);
 
   bind(&done);
 
   // Clobber clobbered input registers when running with the debug-code flag
   // turned on to provoke errors.
   if (emit_debug_code()) {
     mov(value, Operand(BitCast<int32_t>(kZapValue + 4)));
     mov(dst, Operand(BitCast<int32_t>(kZapValue + 8)));
   }
 }
 
 
+// Will clobber 4 registers: object, map, dst, ip.  The
+// register 'object' contains a heap object pointer.
+void MacroAssembler::RecordWriteForMap(Register object,
+                                       Register map,
+                                       Register dst,
+                                       LinkRegisterStatus lr_status,
+                                       SaveFPRegsMode fp_mode) {
+  Label done;
+
+  if (emit_debug_code()) {
+    ldr(dst, FieldMemOperand(map, HeapObject::kMapOffset));
+    cmp(dst, Operand(isolate()->factory()->meta_map()));
+    Check(eq, kWrongAddressOrValuePassedToRecordWrite);
+  }
+
+  // Count number of write barriers in generated code.
+  isolate()->counters()->write_barriers_static()->Increment();
+  // TODO(mstarzinger): Dynamic counter missing.

[Hannes Payer (out of office), 2014/06/03 05:51:48]

why TODO?

[Benedikt Meurer, 2014/06/03 07:48:02]

I just copied the TODO.

+
+  if (emit_debug_code()) {
+    ldr(ip, FieldMemOperand(object, HeapObject::kMapOffset));
+    cmp(ip, map);
+    Check(eq, kWrongAddressOrValuePassedToRecordWrite);
+  }
+
+  // A single check of the map's pages interesting flag suffices, since it is
+  // only set during incremental collection, and then it's also guaranteed that
+  // the from object's page's interesting flag is also set.  This optimization
+  // relies on the fact that maps can never be in new space.
+  CheckPageFlag(map,
+                map,  // Used as scratch.
+                MemoryChunk::kPointersToHereAreInterestingMask,
+                eq,
+                &done);
+
+  add(dst, object, Operand(HeapObject::kMapOffset - kHeapObjectTag));
+  if (emit_debug_code()) {
+    Label ok;
+    tst(dst, Operand((1 << kPointerSizeLog2) - 1));
+    b(eq, &ok);
+    stop("Unaligned cell in write barrier");
+    bind(&ok);
+  }
+
+  // Record the actual write.
+  if (lr_status == kLRHasNotBeenSaved) {
+    push(lr);
+  }
+  RecordWriteStub stub(isolate(), object, map, dst, OMIT_REMEMBERED_SET,
+                       fp_mode);
+  CallStub(&stub);
+  if (lr_status == kLRHasNotBeenSaved) {
+    pop(lr);
+  }
+
+  bind(&done);
+
+  // Clobber clobbered registers when running with the debug-code flag
+  // turned on to provoke errors.
+  if (emit_debug_code()) {
+    mov(dst, Operand(BitCast<int32_t>(kZapValue + 12)));
+    mov(map, Operand(BitCast<int32_t>(kZapValue + 16)));
+  }
+}
+
+
 // Will clobber 4 registers: object, address, scratch, ip.  The
 // register 'object' contains a heap object pointer.  The heap object
 // tag is shifted away.
 void MacroAssembler::RecordWrite(Register object,
                                  Register address,
                                  Register value,
                                  LinkRegisterStatus lr_status,
                                  SaveFPRegsMode fp_mode,
                                  RememberedSetAction remembered_set_action,
-                                 SmiCheck smi_check) {
+                                 SmiCheck smi_check,
+                                 bool value_is_in_new_space) {
   ASSERT(!object.is(value));
   if (emit_debug_code()) {
     ldr(ip, MemOperand(address));
     cmp(ip, value);
     Check(eq, kWrongAddressOrValuePassedToRecordWrite);
   }
 
   // Count number of write barriers in generated code.
   isolate()->counters()->write_barriers_static()->Increment();
   // TODO(mstarzinger): Dynamic counter missing.
 
   // First, check if a write barrier is even needed. The tests below
   // catch stores of smis and stores into the young generation.
   Label done;
 
   if (smi_check == INLINE_SMI_CHECK) {
     JumpIfSmi(value, &done);
   }
 
-  CheckPageFlag(value,
-                value,  // Used as scratch.
-                MemoryChunk::kPointersToHereAreInterestingMask,
-                eq,
-                &done);
+  if (!value_is_in_new_space) {
+    CheckPageFlag(value,
+                  value,  // Used as scratch.
+                  MemoryChunk::kPointersToHereAreInterestingMask,
+                  eq,
+                  &done);
+  }
   CheckPageFlag(object,
                 value,  // Used as scratch.
                 MemoryChunk::kPointersFromHereAreInterestingMask,
                 eq,
                 &done);
 
   // Record the actual write.
   if (lr_status == kLRHasNotBeenSaved) {
     push(lr);
   }
@@ skipping 3498 matching lines @@
     sub(result, result, Operand(dividend));
   }
   if (ms.shift() > 0) mov(result, Operand(result, ASR, ms.shift()));
   add(result, result, Operand(dividend, LSR, 31));
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM