On Sat, 2025-11-01 at 10:34 -0600, Jeff Law wrote:
> This is Shreya's work except for the SH testcase which I added after
> realizing her work would also fix the testcases for that port. I
> bootstrapped and regression tested this on sh4-linux-gnu, x86_64 &
> risc-v. It also was tested across all the embedded targets in my tester
> without regressions.
>
> --
>
>
> We are extracting two single-bit bitfields from a structure and
> determining whether they both have the value 0 or if at least one bit is
> set. This has been generating poor code:
>
> > lw a5,0(a0)
> > bexti a0,a5,1
> > bexti a5,a5,2
> > or a0,a0,a5
> > ret
>
> We address this as a simplification problem and optimize this using an
> andi of the original value and a mask with just the desired bits set,
> followed by a snez. This results in a 1 if any of those bits are set or
> 0 if none.
>
> For cases where we want to extract three or more single-bit bitfields,
> we build on the previous case. We take the result of the 2-bitfield
> case, extract the mask, update it to include the new single-bit
> bitfield, and again perform an andi + snez.
>
> In our new testfile, we scan to ensure we do not see a bexti or an or
> instruction, and that we have the correct assembly for both two and
> three single-bit bitfield cases: lw + andi + snez + ret.
>
Thanks for looking after the SH cases!
Best regards,
Oleg Endo
