Re: [PATCH] RISC-V: bitmanip: use bexti for "(a & (1 << BIT_NO)) ? 0 : -1"

[Philipp Tomsich <philipp.tomsich@vrull.eu>]

Committed to master. Thanks!
Philipp.

On Thu, 17 Nov 2022 at 15:43, Jeff Law <jeffreyalaw@gmail.com> wrote:
>
>
> On 11/8/22 12:55, Philipp Tomsich wrote:
> > Consider creating a polarity-reversed mask from a set-bit (i.e., if
> > the bit is set, produce all-ones; otherwise: all-zeros).  Using Zbb,
> > this can be expressed as bexti, followed by an addi of minus-one.  To
> > enable the combiner to discover this opportunity, we need to split the
> > canonical expression for "(a & (1 << BIT_NO)) ? 0 : -1" into a form
> > combinable into bexti.
> >
> > Consider the function:
> >      long f(long a)
> >      {
> >        return (a & (1 << BIT_NO)) ? 0 : -1;
> >      }
> > This produces the following sequence prior to this change:
> >       andi    a0,a0,16
> >       seqz    a0,a0
> >       neg     a0,a0
> >       ret
> > Following this change, it results in:
> >       bexti   a0,a0,4
> >       addi    a0,a0,-1
> >       ret
> >
> > gcc/ChangeLog:
> >
> >       * config/riscv/bitmanip.md: Add a splitter to generate
> >            polarity-reversed masks from a set bit using bexti + addi.
> >
> > gcc/testsuite/ChangeLog:
> >
> >       * gcc.target/riscv/zbs-bexti.c: New test.
>
> OK
>
>
> Jeff
>
>