Reland "Merge old data and pointer space."

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 65b65a36222637a7fba42ec9db03062f2c7f9434..b5155619886ac7433eab9555310fbe9f60b14256 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -4127,7 +4127,6 @@ void MacroAssembler::MakeSureDoubleAlignedHelper(Register result,
     // 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(kPointerSize * 2 == kDoubleSize);
-    DCHECK((flags & PRETENURE_OLD_POINTER_SPACE) == 0);
     DCHECK(kPointerAlignment * 2 == kDoubleAlignment);
     // Make sure scratch is not clobbered by this function as it might be
     // used in UpdateAllocationTopHelper later.
@@ -4135,7 +4134,7 @@ void MacroAssembler::MakeSureDoubleAlignedHelper(Register result,
     Label aligned;
     testl(result, Immediate(kDoubleAlignmentMask));
     j(zero, &aligned, Label::kNear);
-    if ((flags & PRETENURE_OLD_DATA_SPACE) != 0) {
+    if ((flags & PRETENURE) != 0) {
       ExternalReference allocation_limit =
           AllocationUtils::GetAllocationLimitReference(isolate(), flags);
       cmpp(result, ExternalOperand(allocation_limit));