[Mesa-dev] [PATCH] radeonsi: Prevent geometry shader from emitting too many vertices

[Marek Olšák]

I think this patch breaks geometry shaders with LLVM that doesn't
support the kill instruction in GS. All GS piglit tests fail with:

SILowerControlFlow.cpp:296: void
{anonymous}::SILowerControlFlowPass::Kill(llvm::MachineInstr&):
Assertion `MBB.getParent()->getInfo<SIMachineFunctionInfo>()->ShaderType
== ShaderType::PIXEL' failed.

Marek



On Mon, Feb 24, 2014 at 10:03 AM, Michel Dänzer <michel at daenzer.net> wrote:
> From: Michel Daenzer <michel.daenzer at amd.com>
>
> Signed-off-by: Michel Dänzer <michel.daenzer at amd.com>
> ---
>  src/gallium/drivers/radeonsi/si_shader.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/src/gallium/drivers/radeonsi/si_shader.c b/src/gallium/drivers/radeonsi/si_shader.c
> index 54270cd..b22db0b 100644
> --- a/src/gallium/drivers/radeonsi/si_shader.c
> +++ b/src/gallium/drivers/radeonsi/si_shader.c
> @@ -1905,6 +1905,7 @@ static void si_llvm_emit_vertex(
>         LLVMValueRef soffset = LLVMGetParam(si_shader_ctx->radeon_bld.main_fn,
>                                             SI_PARAM_GS2VS_OFFSET);
>         LLVMValueRef gs_next_vertex;
> +       LLVMValueRef can_emit, kill;
>         LLVMValueRef t_list_ptr;
>         LLVMValueRef t_list;
>         LLVMValueRef args[2];
> @@ -1934,6 +1935,21 @@ static void si_llvm_emit_vertex(
>
>         /* Write vertex attribute values to GSVS ring */
>         gs_next_vertex = LLVMBuildLoad(gallivm->builder, si_shader_ctx->gs_next_vertex, "");
> +
> +       /* If this thread has already emitted the declared maximum number of
> +        * vertices, kill it: excessive vertex emissions are not supposed to
> +        * have any effect, and GS threads have no externally observable
> +        * effects other than emitting vertices.
> +        */
> +       can_emit = LLVMBuildICmp(gallivm->builder, LLVMIntULE, gs_next_vertex,
> +                                lp_build_const_int32(gallivm,
> +                                                     shader->gs_max_out_vertices), "");
> +       kill = lp_build_select(&bld_base->base, can_emit,
> +                              lp_build_const_float(gallivm, 1.0f),
> +                              lp_build_const_float(gallivm, -1.0f));
> +       build_intrinsic(gallivm->builder, "llvm.AMDGPU.kill",
> +                       LLVMVoidTypeInContext(gallivm->context), &kill, 1, 0);
> +
>         for (i = 0; i < shader->noutput; i++) {
>                 LLVMValueRef *out_ptr =
>                         si_shader_ctx->radeon_bld.soa.outputs[shader->output[i].index];
> --
> 1.9.0
>
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