X87: [crankshaft] Fragmentation-free allocation folding.

src/x87/macro-assembler-x87.h

Index: src/x87/macro-assembler-x87.h
diff --git a/src/x87/macro-assembler-x87.h b/src/x87/macro-assembler-x87.h
index 5d76d25a8a8ce80daf26fed78e6381d3b07f3f97..42b7eb15a02f330806937042c633abaae020eab5 100644
--- a/src/x87/macro-assembler-x87.h
+++ b/src/x87/macro-assembler-x87.h
@@ -629,6 +629,9 @@ class MacroAssembler: public Assembler {
   void Allocate(Register object_size, Register result, Register result_end,
                 Register scratch, Label* gc_required, AllocationFlags flags);
 
+  // FastAllocate is right now only used for folded allocations. It just
+  // increments the top pointer without checking against limit. This can only
+  // be done if it was proved earlier that the allocation will succeed.
   void FastAllocate(int object_size, Register result, Register result_end,
                     AllocationFlags flags);
   void FastAllocate(Register object_size, Register result, Register result_end,