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

[Marek Olšák]

Since you acked patch #3, which depends on this, I assume this has your Rb too?

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
>>
>> _______________________________________________
>> mesa-dev mailing list
>> mesa-dev at lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/mesa-dev