[Mesa-dev] [PATCH 01/13] nir: allow 64 bit shifts

[Jason Ekstrand]

On Wed, Feb 28, 2018 at 1:35 PM, Rob Clark <robdclark at gmail.com> wrote:

> On Wed, Feb 28, 2018 at 4:18 PM, Karol Herbst <kherbst at redhat.com> wrote:
> > On Wed, Feb 28, 2018 at 9:46 PM, Jason Ekstrand <jason at jlekstrand.net>
> wrote:
> >> I do not think this patch does what you think it does.  The old opcode
> >> allowed you to shift any bit size integer by a 32-bit integer.  The new
> >> version allows you to shift N bits by N bits.  In particular, you can't
> >> shift a 16-bit by a 32-bit value.
> >>
> >> I'm not sure what the best thing is to do here.  Really, the size of
> src1
> >> doesn't really matter as 8-bit is enough to do any shifting needed for a
> >> 64-bit src0.  You can always compose with a u2u32 to get any src1 bit
> size
> >> you want.  We picked 32 because it's been the GL default for a long
> time.
> >>
> >
> > Well the thing is we ended up with a shift in spirv having two 64 bit
> > parameters. Maybe we could just put a convert in it for such cases?
> >
>
> yeah, I'd overlooked that this was only changing the 2nd src param..
> u2u32 for 2nd src would make sense
>

For now, that definitely works.


> (arguably we might only want to do that if the 2nd src is 64b, ie. if
> 2nd src is already 16b or 8b no sense to up-convert it to 32b)
>

Yeah, in future, it may help to add some shift variants which take a
smaller src1.


> I'll drop this and make a vtn patch to replace it.
>
> BR,
> -R
>
> >> On Wed, Feb 28, 2018 at 11:51 AM, Rob Clark <robdclark at gmail.com>
> wrote:
> >>>
> >>> From: Karol Herbst <kherbst at redhat.com>
> >>>
> >>> This is a thing for OpenCL kernels.
> >>>
> >>> Signed-off-by: Rob Clark <robdclark at gmail.com>
> >>> ---
> >>>  src/compiler/nir/nir_opcodes.py | 6 +++---
> >>>  1 file changed, 3 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/src/compiler/nir/nir_opcodes.py
> >>> b/src/compiler/nir/nir_opcodes.py
> >>> index 278562b2bd1..c4d2c7805eb 100644
> >>> --- a/src/compiler/nir/nir_opcodes.py
> >>> +++ b/src/compiler/nir/nir_opcodes.py
> >>> @@ -479,9 +479,9 @@ binop("seq", tfloat32, commutative, "(src0 ==
> src1) ?
> >>> 1.0f : 0.0f") # Set on Equ
> >>>  binop("sne", tfloat32, commutative, "(src0 != src1) ? 1.0f : 0.0f") #
> Set
> >>> on Not Equal
> >>>
> >>>
> >>> -opcode("ishl", 0, tint, [0, 0], [tint, tuint32], "", "src0 << src1")
> >>> -opcode("ishr", 0, tint, [0, 0], [tint, tuint32], "", "src0 >> src1")
> >>> -opcode("ushr", 0, tuint, [0, 0], [tuint, tuint32], "", "src0 >> src1")
> >>> +opcode("ishl", 0, tint, [0, 0], [tint, tuint], "", "src0 << src1")
> >>> +opcode("ishr", 0, tint, [0, 0], [tint, tuint], "", "src0 >> src1")
> >>> +opcode("ushr", 0, tuint, [0, 0], [tuint, tuint], "", "src0 >> src1")
> >>>
> >>>  # bitwise logic operators
> >>>  #
> >>> --
> >>> 2.14.3
> >>>
> >>
>
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