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

[Timothy Arceri]

On 25/9/18 10:35 am, Marek Olšák wrote:
> Do you know what's broken in LLVM? Or is it a problem with the ISA?

I haven't actually dug any further. Adding Samuel to see if he remembers 
more.

However according to the original bug report this is a regression when 
going from LLVM 6 to LLVM 7. I see the issue on both polaris and vega.

> 
> 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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