Fix object initialization when slack tracking for it's map is still enabled.

src/arm64/macro-assembler-arm64.cc

Index: src/arm64/macro-assembler-arm64.cc
diff --git a/src/arm64/macro-assembler-arm64.cc b/src/arm64/macro-assembler-arm64.cc
index 5b941a2a5a53648433605d6deb502bd7539e0622..e21903d087b3a4bcb851cdb17291405a52527372 100644
--- a/src/arm64/macro-assembler-arm64.cc
+++ b/src/arm64/macro-assembler-arm64.cc
@@ -2354,38 +2354,35 @@ void MacroAssembler::CopyBytes(Register dst,
 }
 
 
-void MacroAssembler::FillFields(Register dst,
-                                Register field_count,
-                                Register filler) {
-  DCHECK(!dst.Is(csp));
+void MacroAssembler::InitializeFieldsWithFiller(Register current_address,
+                                                Register end_address,
+                                                Register filler) {
+  DCHECK(!current_address.Is(csp));
   UseScratchRegisterScope temps(this);
-  Register field_ptr = temps.AcquireX();
-  Register counter = temps.AcquireX();
+  Register distance_in_words = temps.AcquireX();
   Label done;
 
-  // Decrement count. If the result < zero, count was zero, and there's nothing
-  // to do. If count was one, flags are set to fail the gt condition at the end
-  // of the pairs loop.
-  Subs(counter, field_count, 1);
-  B(lt, &done);
+  // Calculate the distance. If it's <= zero then there's nothing to do.
+  Subs(distance_in_words, end_address, current_address);
+  B(le, &done);
 
   // There's at least one field to fill, so do this unconditionally.
-  Str(filler, MemOperand(dst, kPointerSize, PostIndex));
+  Str(filler, MemOperand(current_address));
 
-  // If the bottom bit of counter is set, there are an even number of fields to
-  // fill, so pull the start pointer back by one field, allowing the pairs loop
-  // to overwrite the field that was stored above.
-  And(field_ptr, counter, 1);
-  Sub(field_ptr, dst, Operand(field_ptr, LSL, kPointerSizeLog2));
+  // If the distance_in_words consists of odd number of words we advance
+  // start_address by one word, otherwise the pairs loop will ovwerite the
+  // field that was stored above.
+  And(distance_in_words, distance_in_words, kPointerSize);
+  Add(current_address, current_address, distance_in_words);
 
   // Store filler to memory in pairs.
-  Label entry, loop;
+  Label loop, entry;
   B(&entry);
   Bind(&loop);
-  Stp(filler, filler, MemOperand(field_ptr, 2 * kPointerSize, PostIndex));
-  Subs(counter, counter, 2);
+  Stp(filler, filler, MemOperand(current_address, 2 * kPointerSize, PostIndex));
   Bind(&entry);
-  B(gt, &loop);
+  Cmp(current_address, end_address);
+  B(lo, &loop);
 
   Bind(&done);
 }
@@ -3120,30 +3117,27 @@ void MacroAssembler::Allocate(int object_size,
 }
 
 
-void MacroAssembler::Allocate(Register object_size,
-                              Register result,
-                              Register scratch1,
-                              Register scratch2,
-                              Label* gc_required,
-                              AllocationFlags flags) {
+void MacroAssembler::Allocate(Register object_size, Register result,
+                              Register result_end, Register scratch,
+                              Label* gc_required, AllocationFlags flags) {
   if (!FLAG_inline_new) {
     if (emit_debug_code()) {
       // Trash the registers to simulate an allocation failure.
       // We apply salt to the original zap value to easily spot the values.
       Mov(result, (kDebugZapValue & ~0xffL) | 0x11L);
-      Mov(scratch1, (kDebugZapValue & ~0xffL) | 0x21L);
-      Mov(scratch2, (kDebugZapValue & ~0xffL) | 0x21L);
+      Mov(scratch, (kDebugZapValue & ~0xffL) | 0x21L);
+      Mov(result_end, (kDebugZapValue & ~0xffL) | 0x21L);
     }
     B(gc_required);
     return;
   }
 
   UseScratchRegisterScope temps(this);
-  Register scratch3 = temps.AcquireX();
+  Register scratch2 = temps.AcquireX();
 
-  DCHECK(!AreAliased(object_size, result, scratch1, scratch2, scratch3));
-  DCHECK(object_size.Is64Bits() && result.Is64Bits() &&
-         scratch1.Is64Bits() && scratch2.Is64Bits());
+  DCHECK(!AreAliased(object_size, result, scratch, scratch2, result_end));
+  DCHECK(object_size.Is64Bits() && result.Is64Bits() && scratch.Is64Bits() &&
+         result_end.Is64Bits());
 
   // Check relative positions of allocation top and limit addresses.
   // The values must be adjacent in memory to allow the use of LDP.
@@ -3156,7 +3150,7 @@ void MacroAssembler::Allocate(Register object_size,
   DCHECK((limit - top) == kPointerSize);
 
   // Set up allocation top address and object size registers.
-  Register top_address = scratch1;
+  Register top_address = scratch;
   Register allocation_limit = scratch2;
   Mov(top_address, heap_allocation_top);
 
@@ -3166,8 +3160,8 @@ void MacroAssembler::Allocate(Register object_size,
   } else {
     if (emit_debug_code()) {
       // Assert that result actually contains top on entry.
-      Ldr(scratch3, MemOperand(top_address));
-      Cmp(result, scratch3);
+      Ldr(result_end, MemOperand(top_address));
+      Cmp(result, result_end);
       Check(eq, kUnexpectedAllocationTop);
     }
     // Load the allocation limit. 'result' already contains the allocation top.
@@ -3180,19 +3174,19 @@ void MacroAssembler::Allocate(Register object_size,
 
   // Calculate new top and bail out if new space is exhausted
   if ((flags & SIZE_IN_WORDS) != 0) {
-    Adds(scratch3, result, Operand(object_size, LSL, kPointerSizeLog2));
+    Adds(result_end, result, Operand(object_size, LSL, kPointerSizeLog2));
   } else {
-    Adds(scratch3, result, object_size);
+    Adds(result_end, result, object_size);
   }
 
   if (emit_debug_code()) {
-    Tst(scratch3, kObjectAlignmentMask);
+    Tst(result_end, kObjectAlignmentMask);
     Check(eq, kUnalignedAllocationInNewSpace);
   }
 
-  Ccmp(scratch3, allocation_limit, CFlag, cc);
+  Ccmp(result_end, allocation_limit, CFlag, cc);
   B(hi, gc_required);
-  Str(scratch3, MemOperand(top_address));
+  Str(result_end, MemOperand(top_address));
 
   // Tag the object if requested.
   if ((flags & TAG_OBJECT) != 0) {