On Sat, May 25, 2024 at 11:42 AM Jeff Law <j...@ventanamicro.com> wrote:
>
> This is a revamp of what started as a target specific patch.
>
> Basically xalan (corrected, I originally thought it was perlbench) has a
> bitset implementation with a bit of an oddity. Specifically setBit will
> clear the bit before it is set:
>
> > if (bitToSet < 32)
> > {
> > fBits1 &= ~mask;
> > fBits1 |= mask;
> > }
> > else
> > {
> > fBits2 &= ~mask;
> > fBits2 |= mask;
> > }
>
> We can clean this up pretty easily in RTL with a small bit of code in
> simplify-rtx. While xalan doesn't have other cases, we can synthesize
> tests pretty easily and handle them as well.
>
>
> It turns out we don't actually have to recognize this stuff at the bit
> level, just standard logical identities are sufficient. For example
>
> (X | Y) & ~Y -> X & ~Y
>
>
>
> Andrew P. might poke at this at the gimple level. The type changes
> kindof get in the way in gimple but he's much better at match.pd than I
> am, so if he wants to chase it from the gimple side, I'll fully support
> that.
So we already have this pattern (without the type change) in gimple:
/* (~x | y) & x -> x & y */
/* (~x & y) | x -> x | y */
(simplify
(bitop:c (rbitop:c @2 @1) @0)
(with { bool wascmp; }
(if (bitwise_inverted_equal_p (@0, @2, wascmp)
&& (!wascmp || element_precision (type) == 1))
(bitop @0 @1))))
The problem is bitwise_inverted_equal_p does not see that:
c.0_4 = (signed char) _1;
_5 = ~c.0_4;
_16 = (charD.11) _5;
and
c_11 = (charD.11) _1;
are bitwise inversions of each other.
I filed https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115449 to keep
track of this.
Thanks,
Andrew Pinski
>
> Bootstrapped and regression tested on x86. Also run through my tester
> on its embedded targets.
>
> Pushing to the trunk.
>
> jeff
>
