On Fri, Aug 17, 2018 at 08:45:02PM +0100, Ramsay Jones wrote:
>
>
> On 16/08/18 23:12, Luc Van Oostenryck wrote:
> > Doing a LSR(X, N) will drop the N right bits.
> > So any simplification that can be made when using an AND clearing
> > the right N bits can also be used on LSR (as if its first operand
> > would first be implicitly be ANDed with such a mask).
> >
> > So, in order to not duplicate complex simplifications involving
> > ANDs & ORs masks, merge these both function in a single one,
> > using the mask corresponding to the operation.
> >
> > Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
> > ---
> > simplify.c | 56 ++++++++++++++++++++++--------------------------------
> > 1 file changed, 23 insertions(+), 33 deletions(-)
> >
> > diff --git a/simplify.c b/simplify.c
> > index ef98b205a..ce48b3a91 100644
> > --- a/simplify.c
> > +++ b/simplify.c
> > @@ -546,6 +546,24 @@ undef:
> > return NULL;
> > }
> >
> > +static int simplify_mask_or_and(struct instruction *insn, unsigned long long mask,
> > + pseudo_t src, pseudo_t other)
> > +{
> > + unsigned long long omask, nmask;
> > + pseudo_t src2 = src->def->src2;
> > +
> > + if (!constant(src2))
> > + return 0;
> > + omask = src2->value;
> > + nmask = omask & mask;
> > + if (nmask != 0)
> > + return 0;
> > + // replace OP(((A & M') | B), C)
>
> Huh?, should that be OP(((A & M') | B), C) & M ?
> and ...
> > + // by OP(B, C)
>
> OP(B, C) & M ?
>
> confused.
Yes, sorry.
All this merits much better documentation.
OP(x, C) that I'm using here stand (or will stand) for either:
* AND(x, M) and then mask = M
* LSR(x, S) and then mask = (-1 << S)
* SHL(x, S) and then mask = (-1 >> S)
* TRUNC(x) and then mask = $mask(newbitsize) = (1 << newbitsize) - 1
because the very same simplifications apply to all of them.
-- Luc
