Re: [PATCH] Minor improvement to genpreds.cc

[Richard Biener <richard.guenther@gmail.com>]

On Sun, May 22, 2022 at 11:03 AM Roger Sayle <roger@nextmovesoftware.com> wrote:
>
>
> This simple patch implements Richard Biener's suggestion in comment #6
> of PR tree-optimization/52171 (from February 2013) that the insn-preds
> code generated by genpreds can avoid using strncmp when matching constant
> strings of length one.
>
> The effect of this patch is best explained by the diff of insn-preds.cc:
> <       if (!strncmp (str + 1, "g", 1))
> ---
> >       if (str[1] == 'g')
> 3104c3104
> <       if (!strncmp (str + 1, "m", 1))
> ---
> >       if (str[1] == 'm')
> 3106c3106
> <       if (!strncmp (str + 1, "c", 1))
> ---
> >       if (str[1] == 'c')
> ...
>
> The equivalent optimization is performed by GCC (but perhaps not by the
> host compiler), but generating simpler/smaller code may encourage further
> optimizations (such as use of a switch statement).
>
> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> and make -k check with no new failures.  Ok for mainline?

OK.

Richard.

>
> 2022-05-22  Roger Sayle  <roger@nextmovesoftware.com>
>
> gcc/ChangeLog
>         * genpreds.cc (write_lookup_constraint_1): Avoid generating a call
>         to strncmp for strings of length one.
>
> Roger
> --
>