[Mesa-dev] [PATCH] r600g/llvm: don't export more colors than the number of CBs

[Vadim Girlin]

On 08/24/2013 02:31 PM, Marek Olšák wrote:
> Like Christoph said, COLOR0 (if available) must always be exported for
> alpha test.

Are there any piglit tests for that? I didn't see any regressions with 
this patch (at least on evergreen), possibly I messed up the testing 
somehow. Also I think old backend uses the same logic.

Vadim

>
> Marek
>
> On Sat, Aug 24, 2013 at 3:30 AM, Vadim Girlin <vadimgirlin at gmail.com> wrote:
>> Currently llvm backend always exports at least one color in pixel
>> shader even if no color buffers are enabled. With depth/stencil exports
>> this can result in the following code:
>>
>> EXPORT             PIXEL 0     R0.xyzw  VPM
>> EXPORT             PIXEL 61    R1.x___  VPM
>> EXPORT_DONE        PIXEL 61    R0._x__  VPM  EOP
>>
>> AFAIU with zero color buffers no memory is reserved for colors in the export
>> ring and all exports in this example actually write to the same location.
>> The code above still works fine in this particular case, because correct
>> values are written last, but reordering can break it (especially with SB
>> which tends to reorder the exports).
>>
>> Signed-off-by: Vadim Girlin <vadimgirlin at gmail.com>
>> ---
>>
>> This fixes regressions with LLVM+SB, so I consider it as a prerequisite
>> for enabling SB by default. Also it fixes some issues with LLVM backend alone.
>> Tested on evergreen only (I don't have other hw), needs testing on
>> pre-evergreen GPUs.
>>
>>   src/gallium/drivers/r600/r600_llvm.c   | 2 +-
>>   src/gallium/drivers/r600/r600_shader.c | 2 +-
>>   2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/gallium/drivers/r600/r600_llvm.c b/src/gallium/drivers/r600/r600_llvm.c
>> index 03a68e4..d2f4aff 100644
>> --- a/src/gallium/drivers/r600/r600_llvm.c
>> +++ b/src/gallium/drivers/r600/r600_llvm.c
>> @@ -333,8 +333,8 @@ static void llvm_emit_epilogue(struct lp_build_tgsi_context * bld_base)
>>                  } else if (ctx->type == TGSI_PROCESSOR_FRAGMENT) {
>>                          switch (ctx->r600_outputs[i].name) {
>>                          case TGSI_SEMANTIC_COLOR:
>> -                               has_color = true;
>>                                  if ( color_count < ctx->color_buffer_count) {
>> +                                       has_color = true;
>>                                          LLVMValueRef args[3];
>>                                          args[0] = output;
>>                                          if (ctx->fs_color_all) {
>> diff --git a/src/gallium/drivers/r600/r600_shader.c b/src/gallium/drivers/r600/r600_shader.c
>> index fb766c4..85f8469 100644
>> --- a/src/gallium/drivers/r600/r600_shader.c
>> +++ b/src/gallium/drivers/r600/r600_shader.c
>> @@ -1130,7 +1130,7 @@ static int r600_shader_from_tgsi(struct r600_screen *rscreen,
>>                  radeon_llvm_ctx.face_gpr = ctx.face_gpr;
>>                  radeon_llvm_ctx.r600_inputs = ctx.shader->input;
>>                  radeon_llvm_ctx.r600_outputs = ctx.shader->output;
>> -               radeon_llvm_ctx.color_buffer_count = MAX2(key.nr_cbufs , 1);
>> +               radeon_llvm_ctx.color_buffer_count = key.nr_cbufs;
>>                  radeon_llvm_ctx.chip_class = ctx.bc->chip_class;
>>                  radeon_llvm_ctx.fs_color_all = shader->fs_write_all && (rscreen->chip_class >= EVERGREEN);
>>                  radeon_llvm_ctx.stream_outputs = &so;
>> --
>> 1.8.3.1
>>
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