[Mesa-dev] [PATCH 2/9] radeonsi: use V_BFE for extracting a sample index

[Tom Stellard]

On Thu, Mar 05, 2015 at 05:14:09PM +0100, Marek Olšák wrote:
> Since you acked patch #3, which depends on this, I assume this has your Rb too?
> 

No, I still want to resolved with Matt what to do about intrinsics vs
IR.

-Tom

> Marek
> 
> On Mon, Mar 2, 2015 at 10:05 PM, Tom Stellard <tom at stellard.net> wrote:
> > On Mon, Mar 02, 2015 at 12:54:16PM +0100, Marek Olšák wrote:
> >> From: Marek Olšák <marek.olsak at 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().
> >
> > -Tom
> >
> >> +static LLVMValueRef build_bfe(struct gallivm_state *gallivm,
> >> +                           LLVMValueRef value, LLVMValueRef rshift,
> >> +                           LLVMValueRef bitwidth)
> >> +{
> >> +     LLVMValueRef args[3] = {value, rshift, bitwidth};
> >> +
> >> +     return build_intrinsic(gallivm->builder, "llvm.AMDGPU.bfe.u32",
> >> +                            LLVMInt32TypeInContext(gallivm->context),
> >> +                            args, Elements(args), LLVMReadNoneAttribute);
> >> +}
> >> +
> >> +/**
> >>   * Build an LLVM bytecode indexed load using LLVMBuildGEP + LLVMBuildLoad.
> >>   * It's equivalent to doing a load from &base_ptr[index].
> >>   *
> >> @@ -1721,7 +1735,6 @@ static void tex_fetch_args(
> >>
> >>               /* Initialize some constants. */
> >>               LLVMValueRef four = LLVMConstInt(uint_bld->elem_type, 4, 0);
> >> -             LLVMValueRef F = LLVMConstInt(uint_bld->elem_type, 0xF, 0);
> >>
> >>               /* Apply the formula. */
> >>               LLVMValueRef fmask =
> >> @@ -1734,11 +1747,8 @@ static void tex_fetch_args(
> >>               LLVMValueRef sample_index4 =
> >>                       LLVMBuildMul(gallivm->builder, address[sample_chan], four, "");
> >>
> >> -             LLVMValueRef shifted_fmask =
> >> -                     LLVMBuildLShr(gallivm->builder, fmask, sample_index4, "");
> >> -
> >> -             LLVMValueRef final_sample =
> >> -                     LLVMBuildAnd(gallivm->builder, shifted_fmask, F, "");
> >> +             LLVMValueRef final_sample = build_bfe(gallivm, fmask,
> >> +                                                   sample_index4, four);
> >>
> >>               /* Don't rewrite the sample index if WORD1.DATA_FORMAT of the FMASK
> >>                * resource descriptor is 0 (invalid),
> >> --
> >> 2.1.0
> >>
> >> _______________________________________________
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> >> mesa-dev at lists.freedesktop.org
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