Re: Some more patches for GCC on NetBSD/VAX coming soon...

[Paul Koning <paulkoning%comcast.net@localhost>]

> On Apr 1, 2016, at 8:32 AM, Rhialto <rhialto%falu.nl@localhost> wrote:
> 
> On Thu 31 Mar 2016 at 21:24:04 -0700, Jake Hamby wrote:
>> On VAX, you might be able to do the same thing if there's a
>> particularly long instruction that's an effective nop and is faster to
>> execute than the number of bytes it is.
> 
> Is there any mechanism in gcc to jump into the middle of an instruction
> which is (effectively) a nop when executed from the start, but which can
> be mostly any (shorter) instruction when entered somewhere in the
> middle?
> 
> It's a common technique on 8-bitters such as the 6502, to avoid extra
> branches:

Also on the PDP11, where a classic way to exit with success or fail status from a function goes like this:

good:	tst (pc)+
bad:	sec
	rts pc

I haven't seen GCC do stuff like that, but it may be that it could be made to via peephole optimizers.

	paul