Re: RISC-V: Eliminate redundant zero extension of minu/maxu operands

[Jeff Law <jeffreyalaw@gmail.com>]

On 4/28/23 06:29, Jivan Hakobyan via Gcc-patches wrote:
> RV64 the following code:
> 
>    unsigned Min(unsigned a, unsigned b) {
>        return a < b ? a : b;
>    }
> 
> Compiles to:
>    Min:
>         zext.w  a1,a1
>         zext.w  a0,a0
>         minu    a0,a1,a0
>         sext.w  a0,a0
>         ret
> 
> This patch removes unnecessary zero extensions of minu/maxu operands.
> 
> gcc/ChangeLog:
> 
>       * config/riscv/bitmanip.md: Added expanders for minu/maxu instructions
> 
> gcc/testsuite/ChangeLog:
> 
>     * gcc.target/riscv/zbb-min-max-02.c: Updated scanning check.
>     * gcc.target/riscv/zbb-min-max-03.c: New tests.
Thanks.  We had almost the exact same patch internally, the differences 
were just in naming rather than anything functional.  I went ahead and 
installed your variant and I'll drop Raphael's from my queue.

I realize this may make some planned work WRT eliminating unnecessary 
extensions in gimple somewhat harder.  If that work progresses to the 
point where this patch is a problem, then we'll re-evaluate.  But it's 
crazy to hold this up -- it's a measurable win on x264 in particular.

Thanks again,
jeff