On Mon, Mar 02, 2015 at 02:09:29PM -0800, Matt Arsenault wrote: > > > On Mar 2, 2015, at 1:19 PM, Tom Stellard <t...@stellard.net> wrote: > > > > On Mon, Mar 02, 2015 at 10:14:00PM +0100, Marek Olšák wrote: > >> On Mon, Mar 2, 2015 at 10:05 PM, Tom Stellard <t...@stellard.net> wrote: > >>> On Mon, Mar 02, 2015 at 12:54:16PM +0100, Marek Olšák wrote: > >>>> From: Marek Olšák <marek.ol...@amd.com> > >>>> > >>>> --- > >>>> src/gallium/drivers/radeonsi/si_shader.c | 22 ++++++++++++++++------ > >>>> 1 file changed, 16 insertions(+), 6 deletions(-) > >>>> > >>>> diff --git a/src/gallium/drivers/radeonsi/si_shader.c > >>>> b/src/gallium/drivers/radeonsi/si_shader.c > >>>> index b0417ed..f125483 100644 > >>>> --- a/src/gallium/drivers/radeonsi/si_shader.c > >>>> +++ b/src/gallium/drivers/radeonsi/si_shader.c > >>>> @@ -192,6 +192,20 @@ static int get_param_index(unsigned semantic_name, > >>>> unsigned index, > >>>> } > >>>> > >>>> /** > >>>> + * BitField Extract: ((value >> rshift) & ((1 << bitwidth) - 1)) > >>>> + */ > >>> > >>> Ideally, we would just add a pattern for this in the backend and emit > >>> generic > >>> LLVM IR here. This would also make it possible to share the code with > >>> llvmpipe. > >>> > >>> I think the best place to do this would be in > >>> AMDGPUTargetLowering::performDAGCombine(). > >> > >> Why not SIInstructions.td? > >> > > > > Because for patterns like this, I think it is important to match them as > > early as possible, because there may be another optimization which reduces > > the sequence from 5 to 4 instructions which would cause the pattern not to > > match. > > > > -Tom > > > I think the opposite in this case. The basic bit operations have a lot of > existing combines on them, and the computeKnownBits implementations are more > complete. The BFE nodes are not as well understood, and trickier to deal > with. AArch64 and NVPTX both have essentially the same instruction, and they > have a large bit of code to match them in their ISelDAGToDAGs. I’ve wanted to > add a generic BFE node to be matched after legalization, but I haven’t had > time to do it. >
Isn't there a potential for a DAG combine on bit operations, to 'break' the pattern so it can't be recognized? -Tom > -Matt _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
