Re: [PATCH 7/7] riscv: Add support for str(n)cmp inline expansion

[Kito Cheng <kito.cheng@gmail.com>]

> > I would like to have a unified option interface,
> > maybe -m[no-]inline-str[n]cmp and -minline-str[n]cmp-limit.
>
> For the basic option (-m[no-]inline-str[n]cmp), I would punt to
> -fno-builtin-str[n]cmp.

-fno-bulitin-* will also suppress middle-end optimization for those builtins.

see:
https://github.com/gcc-mirror/gcc/blob/master/gcc/tree-ssa-strlen.cc#L5372

and
https://github.com/gcc-mirror/gcc/blob/master/gcc/tree-loop-distribution.cc
for -fno-bulitin-memcpy/memset/memmove

> The limit-one sounds more like a --param?

Use -param=inline-*-limit= sound good idea, aarch64 and x86 have few
options like that.

>
> > And add some option like this:
> > -minline-str[n]cmp=[bitmanip|vector|auto] in future,
>
> If we want to follow the lead of others, then x86 has a -mstringop-strategy=alg

Using same option name as x86 is SGTM.

> > since I assume we'll have different versions of those things.
> >
> > >
> > > gcc/ChangeLog:
> > >
> > >         * config/riscv/riscv-protos.h (riscv_expand_strn_compare): New
> > >           prototype.
> > >         * config/riscv/riscv-string.cc (GEN_EMIT_HELPER3): New helper
> > >           macros.
> > >         (GEN_EMIT_HELPER2): New helper macros.
> > >         (expand_strncmp_zbb_sequence): New function.
> > >         (riscv_emit_str_compare_zbb): New function.
> > >         (riscv_expand_strn_compare): New function.
> > >         * config/riscv/riscv.md (cmpstrnsi): Invoke expansion functions
> > >           for strn_compare.
> > >         (cmpstrsi): Invoke expansion functions for strn_compare.
> > >         * config/riscv/riscv.opt: Add new parameter
> > >           '-mstring-compare-inline-limit'.
> >
> > We need to document this option.