The correctness of the logic depends on the fixed instruction size of the store instructions
emitted by the loop in MacroAssembler::fill_words and MacroAssembler::zero_memory assembler
routines. These store instructions won't be compressed into 16-bit format due to negative
offset immediate. But it will be safer to make it explict by declaring an incompressible scope
when emitting these store instructions. This also renames IncompressibleRegion to IncompressibleScope.