[Mesa-dev] [PATCH] Gallium/tgsi: Correct signdness of return value of bit operations

[Gert Wollny]

Am Donnerstag, den 09.08.2018, 17:10 +0200 schrieb Roland Scheidegger:
> This is incorrect for umsb.
Hmm, according to the TGSI doc all of those operations including UMSB
are supposed to return -1 if no bits are set [1], for me that implies
that their return type should be signed. 

[1] http://gallium.readthedocs.io/en/latest/tgsi.html#opcode-UMSB

> If you really want to move so the dst type is signed, you need to add
> it to infer_src_type so the src args are unsigned.
I see the control flow now, so I guess I actually should add these
three cases to infer_dst_type, and also add the proper src type for
umsb.

> FWIW I'd like to think that all 3 of these always operate on unsigned
> data (even if they might return signed data), imho they are a lot
> more easier to understand that way (I mean the signed msb you have to
> look up what the hell it actually does, bit operations on unsigned
> data are just easier to understand). But of course it doesn't really
> make a difference, so I can live with the other 2 if the src type
> indicates signed.
GLSL bitCount and findLSB are both operating on both types, and I
assume that these are actually translated to these two TGSI
instructions, so the src type should not be set, 

thanks for the pointers,
Gert 

> 
> Roland
> 
> 
> Am 09.08.2018 um 10:43 schrieb Gert Wollny:
> > The GLSL functions  findLSB, findMSB, and countBits always return
> > a signed integer type. Let the according TGSI operations reflect
> > this.
> > 
> > Signed-off-by: Gert Wollny <gert.wollny at collabora.com>
> > ---
> >  src/gallium/auxiliary/tgsi/tgsi_info.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/src/gallium/auxiliary/tgsi/tgsi_info.c
> > b/src/gallium/auxiliary/tgsi/tgsi_info.c
> > index bbe1a21e43..a8c2bbe663 100644
> > --- a/src/gallium/auxiliary/tgsi/tgsi_info.c
> > +++ b/src/gallium/auxiliary/tgsi/tgsi_info.c
> > @@ -150,9 +150,6 @@ tgsi_opcode_infer_type(enum tgsi_opcode opcode)
> >     case TGSI_OPCODE_UBFE:
> >     case TGSI_OPCODE_BFI:
> >     case TGSI_OPCODE_BREV:
> > -   case TGSI_OPCODE_POPC:
> > -   case TGSI_OPCODE_LSB:
> > -   case TGSI_OPCODE_UMSB:
> >     case TGSI_OPCODE_IMG2HND:
> >     case TGSI_OPCODE_SAMP2HND:
> >        return TGSI_TYPE_UNSIGNED;
> > @@ -188,6 +185,9 @@ tgsi_opcode_infer_type(enum tgsi_opcode opcode)
> >     case TGSI_OPCODE_U64SGE:
> >     case TGSI_OPCODE_I64SLT:
> >     case TGSI_OPCODE_I64SGE:
> > +   case TGSI_OPCODE_LSB:
> > +   case TGSI_OPCODE_POPC:
> > +   case TGSI_OPCODE_UMSB:
> >        return TGSI_TYPE_SIGNED;
> >     case TGSI_OPCODE_DADD:
> >     case TGSI_OPCODE_DABS:
> > 
> 
>