Re: [Qemu-devel] [PATCH 3/5] target-arm: convert shl and shr helpers to TCG

[Aurelien Jarno <aurelien@aurel32.net>]

On Mon, Sep 17, 2012 at 08:36:31AM -0700, Richard Henderson wrote:
> On 09/16/2012 04:08 PM, Aurelien Jarno wrote:
> > +    tcg_gen_setcondi_i32(TCG_COND_GE, tmp2, tmp1, 32); \
> > +    tcg_gen_andi_i32(tmp1, tmp1, 0x1f);                \
> > +    tcg_gen_##name##_i32(dest, t0, tmp1);              \
> > +    tcg_temp_free_i32(tmp1);                           \
> > +    tcg_gen_subi_i32(tmp2, tmp2, 1);                   \
> > +    tcg_gen_and_i32(dest, dest, tmp2);                 \
> 
> Ought I revive my movcond patch?
> 
> Surely you can agree it's much more natural to write this
> as a conditional move of zero than playing masking games.
> 

I agree it's more natural, that said in that case it doesn't spare that
many instructions, and I am still not sure we want to introduce such a
TCG op. What is important is to avoid helpers and branches which are 
really killing the performances.

If you insist, maybe we can just add a movcond op that uses setcond, so
it makes the code more readable?

We introduced setcond a lot of time ago, and there are still plenty of
places where it's not used. We can get higher performances already by
fixing that.

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net