[Mesa-dev] [Mesa-stable] [PATCH] radeonsi: add a workaround for bitfield_extract when count is 0

[Marek Olšák]

Do you know what's broken in LLVM? Or is it a problem with the ISA?

Marek

On Fri, Sep 21, 2018 at 10:38 PM, Timothy Arceri <tarceri at itsqueeze.com> wrote:
> This ports the fix from 3d41757788ac. Both LLVM 7 & 8 continue
> to have this problem.
>
> It fixes rendering issues in some menu and loading screens of
> Civ VI which can be seen in the trace from bug 104602.
>
> Note: This does not fix the black triangles on Vega for bug
> 104602.
>
> Cc: mesa-stable at lists.freedesktop.org
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104602
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107276
> ---
>  .../drivers/radeonsi/si_shader_tgsi_alu.c     | 41 ++++++++++++++-----
>  1 file changed, 30 insertions(+), 11 deletions(-)
>
> diff --git a/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c b/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c
> index f54d025aec0..814362bc963 100644
> --- a/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c
> +++ b/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c
> @@ -494,18 +494,37 @@ static void emit_bfe(const struct lp_build_tgsi_action *action,
>                      struct lp_build_emit_data *emit_data)
>  {
>         struct si_shader_context *ctx = si_shader_context(bld_base);
> -       LLVMValueRef bfe_sm5;
> -       LLVMValueRef cond;
> -
> -       bfe_sm5 = ac_build_bfe(&ctx->ac, emit_data->args[0],
> -                              emit_data->args[1], emit_data->args[2],
> -                              emit_data->info->opcode == TGSI_OPCODE_IBFE);
>
> -       /* Correct for GLSL semantics. */
> -       cond = LLVMBuildICmp(ctx->ac.builder, LLVMIntUGE, emit_data->args[2],
> -                            LLVMConstInt(ctx->i32, 32, 0), "");
> -       emit_data->output[emit_data->chan] =
> -               LLVMBuildSelect(ctx->ac.builder, cond, emit_data->args[0], bfe_sm5, "");
> +       if (HAVE_LLVM < 0x0700) {
> +               LLVMValueRef bfe_sm5 =
> +                       ac_build_bfe(&ctx->ac, emit_data->args[0],
> +                                    emit_data->args[1], emit_data->args[2],
> +                                    emit_data->info->opcode == TGSI_OPCODE_IBFE);
> +
> +               /* Correct for GLSL semantics. */
> +               LLVMValueRef cond = LLVMBuildICmp(ctx->ac.builder, LLVMIntUGE, emit_data->args[2],
> +                                                 LLVMConstInt(ctx->i32, 32, 0), "");
> +               emit_data->output[emit_data->chan] =
> +                       LLVMBuildSelect(ctx->ac.builder, cond, emit_data->args[0], bfe_sm5, "");
> +       } else {
> +               /* FIXME: LLVM 7 returns incorrect result when count is 0.
> +                * https://bugs.freedesktop.org/show_bug.cgi?id=107276
> +                */
> +               LLVMValueRef zero = ctx->i32_0;
> +               LLVMValueRef bfe_sm5 =
> +                       ac_build_bfe(&ctx->ac, emit_data->args[0],
> +                                    emit_data->args[1], emit_data->args[2],
> +                                    emit_data->info->opcode == TGSI_OPCODE_IBFE);
> +
> +               /* Correct for GLSL semantics. */
> +               LLVMValueRef cond = LLVMBuildICmp(ctx->ac.builder, LLVMIntUGE, emit_data->args[2],
> +                                                 LLVMConstInt(ctx->i32, 32, 0), "");
> +               LLVMValueRef cond2 = LLVMBuildICmp(ctx->ac.builder, LLVMIntEQ, emit_data->args[2],
> +                                                  zero, "");
> +               bfe_sm5 = LLVMBuildSelect(ctx->ac.builder, cond, emit_data->args[0], bfe_sm5, "");
> +               emit_data->output[emit_data->chan] =
> +                       LLVMBuildSelect(ctx->ac.builder, cond2, zero, bfe_sm5, "");
> +       }
>  }
>
>  /* this is ffs in C */
> --
> 2.17.1
>
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