Provide a tagged allocation top pointer.

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.
 
 #if V8_TARGET_ARCH_ARM
 
 #include "src/base/bits.h"
 #include "src/base/division-by-constant.h"
@@ skipping 2019 matching lines @@
       Check(eq, kUnexpectedAllocationTop);
     }
     // Load allocation limit. Result already contains allocation top.
     ldr(alloc_limit, MemOperand(top_address, limit - top));
   }
 
   if ((flags & DOUBLE_ALIGNMENT) != 0) {
     // Align the next allocation. Storing the filler map without checking top is
     // safe in new-space because the limit of the heap is aligned there.
     STATIC_ASSERT(kPointerAlignment * 2 == kDoubleAlignment);
-    and_(result_end, result, Operand(kDoubleAlignmentMask), SetCC);
+    and_(result_end, result, Operand(kDoubleAlignmentMaskTagged), SetCC);
     Label aligned;
     b(eq, &aligned);
     if ((flags & PRETENURE) != 0) {
       cmp(result, Operand(alloc_limit));
       b(hs, gc_required);
     }
     mov(result_end, Operand(isolate()->factory()->one_pointer_filler_map()));
-    str(result_end, MemOperand(result, kDoubleSize / 2, PostIndex));
+    str(result_end, MemOperand(result, -kHeapObjectTag));
+    add(result, result, Operand(kDoubleSize / 2));
     bind(&aligned);
   }
 
   // Calculate new top and bail out if new space is exhausted. Use result
   // to calculate the new top. We must preserve the ip register at this
   // point, so we cannot just use add().
   DCHECK(object_size > 0);
   Register source = result;
   Condition cond = al;
   int shift = 0;
@@ skipping 12 matching lines @@
     }
   }
 
   cmp(result_end, Operand(alloc_limit));
   b(hi, gc_required);
 
   if ((flags & ALLOCATION_FOLDING_DOMINATOR) == 0) {
     // The top pointer is not updated for allocation folding dominators.
     str(result_end, MemOperand(top_address));
   }
-
-  // Tag object.
-  add(result, result, Operand(kHeapObjectTag));
 }
 
 
 void MacroAssembler::Allocate(Register object_size, Register result,
                               Register result_end, Register scratch,
                               Label* gc_required, AllocationFlags flags) {
   DCHECK((flags & ALLOCATION_FOLDED) == 0);
   if (!FLAG_inline_new) {
     if (emit_debug_code()) {
       // Trash the registers to simulate an allocation failure.
@@ skipping 42 matching lines @@
       Check(eq, kUnexpectedAllocationTop);
     }
     // Load allocation limit. Result already contains allocation top.
     ldr(alloc_limit, MemOperand(top_address, limit - top));
   }
 
   if ((flags & DOUBLE_ALIGNMENT) != 0) {
     // Align the next allocation. Storing the filler map without checking top is
     // safe in new-space because the limit of the heap is aligned there.
     DCHECK(kPointerAlignment * 2 == kDoubleAlignment);
-    and_(result_end, result, Operand(kDoubleAlignmentMask), SetCC);
+    and_(result_end, result, Operand(kDoubleAlignmentMaskTagged), SetCC);
     Label aligned;
     b(eq, &aligned);
     if ((flags & PRETENURE) != 0) {
       cmp(result, Operand(alloc_limit));
       b(hs, gc_required);
     }
     mov(result_end, Operand(isolate()->factory()->one_pointer_filler_map()));
-    str(result_end, MemOperand(result, kDoubleSize / 2, PostIndex));
+    str(result_end, MemOperand(result, -kHeapObjectTag));
+    add(result, result, Operand(kDoubleSize / 2));
     bind(&aligned);
   }
 
   // Calculate new top and bail out if new space is exhausted. Use result
   // to calculate the new top. Object size may be in words so a shift is
   // required to get the number of bytes.
   if ((flags & SIZE_IN_WORDS) != 0) {
     add(result_end, result, Operand(object_size, LSL, kPointerSizeLog2), SetCC);
   } else {
     add(result_end, result, Operand(object_size), SetCC);
   }
 
   cmp(result_end, Operand(alloc_limit));
   b(hi, gc_required);
 
   // Update allocation top. result temporarily holds the new top.
   if (emit_debug_code()) {
     tst(result_end, Operand(kObjectAlignmentMask));
-    Check(eq, kUnalignedAllocationInNewSpace);
+    Check(ne, kUnalignedAllocationInNewSpace);
   }
   if ((flags & ALLOCATION_FOLDING_DOMINATOR) == 0) {
     // The top pointer is not updated for allocation folding dominators.
     str(result_end, MemOperand(top_address));
   }
-
-  // Tag object.
-  add(result, result, Operand(kHeapObjectTag));
 }
 
 void MacroAssembler::FastAllocate(Register object_size, Register result,
                                   Register result_end, Register scratch,
                                   AllocationFlags flags) {
   // |object_size| and |result_end| may overlap if the DOUBLE_ALIGNMENT flag
   // is not specified. Other registers must not overlap.
   DCHECK(!AreAliased(object_size, result, scratch, ip));
   DCHECK(!AreAliased(result_end, result, scratch, ip));
   DCHECK((flags & DOUBLE_ALIGNMENT) == 0 || !object_size.is(result_end));
 
   ExternalReference allocation_top =
       AllocationUtils::GetAllocationTopReference(isolate(), flags);
 
   Register top_address = scratch;
   mov(top_address, Operand(allocation_top));
   ldr(result, MemOperand(top_address));
 
   if ((flags & DOUBLE_ALIGNMENT) != 0) {
     // Align the next allocation. Storing the filler map without checking top is
     // safe in new-space because the limit of the heap is aligned there.
     DCHECK(kPointerAlignment * 2 == kDoubleAlignment);
-    and_(result_end, result, Operand(kDoubleAlignmentMask), SetCC);
+    and_(result_end, result, Operand(kDoubleAlignmentMaskTagged), SetCC);
     Label aligned;
     b(eq, &aligned);
     mov(result_end, Operand(isolate()->factory()->one_pointer_filler_map()));
-    str(result_end, MemOperand(result, kDoubleSize / 2, PostIndex));
+    str(result_end, MemOperand(result, -kHeapObjectTag));
+    add(result, result, Operand(kDoubleSize / 2));
     bind(&aligned);
   }
 
   // Calculate new top using result. Object size may be in words so a shift is
   // required to get the number of bytes.
   if ((flags & SIZE_IN_WORDS) != 0) {
     add(result_end, result, Operand(object_size, LSL, kPointerSizeLog2), SetCC);
   } else {
     add(result_end, result, Operand(object_size), SetCC);
   }
 
   // Update allocation top. result temporarily holds the new top.
   if (emit_debug_code()) {
     tst(result_end, Operand(kObjectAlignmentMask));
-    Check(eq, kUnalignedAllocationInNewSpace);
+    Check(ne, kUnalignedAllocationInNewSpace);
   }
   // The top pointer is not updated for allocation folding dominators.
   str(result_end, MemOperand(top_address));
-
-  add(result, result, Operand(kHeapObjectTag));
 }
 
 void MacroAssembler::FastAllocate(int object_size, Register result,
                                   Register scratch1, Register scratch2,
                                   AllocationFlags flags) {
   DCHECK(object_size <= Page::kMaxRegularHeapObjectSize);
   DCHECK(!AreAliased(result, scratch1, scratch2, ip));
 
   // Make object size into bytes.
   if ((flags & SIZE_IN_WORDS) != 0) {
     object_size *= kPointerSize;
   }
   DCHECK_EQ(0, object_size & kObjectAlignmentMask);
 
   ExternalReference allocation_top =
       AllocationUtils::GetAllocationTopReference(isolate(), flags);
 
   // Set up allocation top address register.
   Register top_address = scratch1;
   Register result_end = scratch2;
   mov(top_address, Operand(allocation_top));
   ldr(result, MemOperand(top_address));
 
   if ((flags & DOUBLE_ALIGNMENT) != 0) {
     // Align the next allocation. Storing the filler map without checking top is
     // safe in new-space because the limit of the heap is aligned there.
     STATIC_ASSERT(kPointerAlignment * 2 == kDoubleAlignment);
-    and_(result_end, result, Operand(kDoubleAlignmentMask), SetCC);
+    and_(result_end, result, Operand(kDoubleAlignmentMaskTagged), SetCC);
     Label aligned;
     b(eq, &aligned);
     mov(result_end, Operand(isolate()->factory()->one_pointer_filler_map()));
-    str(result_end, MemOperand(result, kDoubleSize / 2, PostIndex));
+    str(result_end, MemOperand(result, -kHeapObjectTag));
+    add(result, result, Operand(kDoubleSize / 2));
     bind(&aligned);
   }
 
   // Calculate new top using result. Object size may be in words so a shift is
   // required to get the number of bytes. We must preserve the ip register at
   // this point, so we cannot just use add().
   DCHECK(object_size > 0);
   Register source = result;
   Condition cond = al;
   int shift = 0;
   while (object_size != 0) {
     if (((object_size >> shift) & 0x03) == 0) {
       shift += 2;
     } else {
       int bits = object_size & (0xff << shift);
       object_size -= bits;
       shift += 8;
       Operand bits_operand(bits);
       DCHECK(bits_operand.instructions_required(this) == 1);
       add(result_end, source, bits_operand, LeaveCC, cond);
       source = result_end;
       cond = cc;
     }
   }
 
   // The top pointer is not updated for allocation folding dominators.
   str(result_end, MemOperand(top_address));
-
-  add(result, result, Operand(kHeapObjectTag));
 }
 
 void MacroAssembler::AllocateTwoByteString(Register result,
                                            Register length,
                                            Register scratch1,
                                            Register scratch2,
                                            Register scratch3,
                                            Label* gc_required) {
   // Calculate the number of bytes needed for the characters in the string while
   // observing object alignment.
@@ skipping 1742 matching lines @@
     }
   }
   if (mag.shift > 0) mov(result, Operand(result, ASR, mag.shift));
   add(result, result, Operand(dividend, LSR, 31));
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM