[Vm-dev] Interpreter>>isContextHeader: optimization

[Igor Stasenko]

Here the method:

isContextHeader: aHeader
	self inline: true.
	^ ((aHeader >> 12) bitAnd: 16r1F) = 13			"MethodContext"
		or: [((aHeader >> 12) bitAnd: 16r1F) = 14		"BlockContext"
		or: [((aHeader >> 12) bitAnd: 16r1F) = 4]]	"PseudoContext"

i think it wouldn't hurt to rewrite it as:

isContextHeader: aHeader
	self inline: true.
 | hdr |
  hdr := aHeader bitAnd: (16r1F << 12).
	^ hdr = (13 << 12)			"MethodContext"
		or: [ hdr = (14 << 12)		"BlockContext"
		or: [ hdr = (4 << 12)]]	 "PseudoContext"

which will allow GCC to optimize it more easily.
I'm not sure if it can optimize it in its current state.
This may impact a small speedup of copy operations and any other
operations which need to determine a number of pointer fields in
object (users of #lastPointerOf:)

-- 
Best regards,
Igor Stasenko AKA sig.