[Mesa-dev] [PATCH 18/59] i965: fix brw_saturate_immediate() for doubles

[Pohjolainen, Topi]

On Mon, May 02, 2016 at 09:42:14AM +0200, Iago Toral wrote:
> On Mon, 2016-05-02 at 10:34 +0300, Pohjolainen, Topi wrote:
> > On Mon, May 02, 2016 at 09:22:49AM +0200, Iago Toral wrote:
> > > On Mon, 2016-05-02 at 10:08 +0300, Pohjolainen, Topi wrote:
> > > > On Mon, May 02, 2016 at 10:02:50AM +0300, Pohjolainen, Topi wrote:
> > > > > On Fri, Apr 29, 2016 at 01:29:15PM +0200, Samuel Iglesias Gons?lvez wrote:
> > > > > > From: Iago Toral Quiroga <itoral at igalia.com>
> > > > > > 
> > > > > > ---
> > > > > >  src/mesa/drivers/dri/i965/brw_shader.cpp | 28 ++++++++++++++++++++++------
> > > > > >  1 file changed, 22 insertions(+), 6 deletions(-)
> > > > > > 
> > > > > > diff --git a/src/mesa/drivers/dri/i965/brw_shader.cpp b/src/mesa/drivers/dri/i965/brw_shader.cpp
> > > > > > index d40937b..a063b88 100644
> > > > > > --- a/src/mesa/drivers/dri/i965/brw_shader.cpp
> > > > > > +++ b/src/mesa/drivers/dri/i965/brw_shader.cpp
> > > > > > @@ -476,7 +476,14 @@ brw_saturate_immediate(enum brw_reg_type type, struct brw_reg *reg)
> > > > > >        unsigned ud;
> > > > > >        int d;
> > > > > >        float f;
> > > > > > -   } imm = { reg->ud }, sat_imm = { 0 };
> > > > > > +      double df;
> > > > > > +   } imm, sat_imm = { 0 };
> > > > > > +
> > > > > > +   unsigned size = type_sz(type);
> > > > > 
> > > > > Could be 'const'.
> > > > > 
> > > > > > +   if (size < 8)
> > > > 
> > > > Thinking a little further, is there a reason we don't write directly:
> > > > 
> > > >         if (type == BRW_REGISTER_TYPE_DF)
> > > >            imm.df = reg->df;
> > > >         else
> > > >            imm.ud = reg->ud;
> > > 
> > > Because in the future we might want to support 64-bit integers too
> > > (BRW_REGISTER_TYPE_Q I think?) and then we would need to change this
> > > code again. The original implementation would do the right thing in that
> > > case without changes.
> > 
> > I was thinking about this as this idiom works elsewhere just fine. But here
> > wouldn't 64-bit integers have size >= 8 and therefore use:
> > 
> >                imm.df = reg->df;
> > 
> > Or is this the intention as it copies 64-bits regardless of the type?
> 
> Exactly, that's what we want to do here. Basically, we want to either do
> a 32-bit or 64-bit data copy, the type is otherwise irrelevant and doing
> it this way makes it so that we don't have to patch the code again in
> the future if we support 64-bit integers. Also, it is consistent with
> the way in which we were already handling 32-bit types where we used ud
> for all of them.

Ok. I would personally appreciate a comment clarifying this but as the
current logic doesn't have one either, I'll leave it to you to add some text
if you feel the same way.