[Mesa-dev] [PATCH] state_tracker: Fix bug in conditional discards with native ints.

[Eric Anholt]

Brian Paul <brianp at vmware.com> writes:

> On 09/03/2014 03:04 PM, Eric Anholt wrote:
>> A bool is 0 or ~0, and KILL_IF takes a float arg that's <0 for discard or
>>> = 0 for not.  By negating it, we ended up doing a floating point subtract
>> of (0 - ~0), which ended up as an inf.  To make this actually work, we
>> need to convert the bool to a float.
>> ---
>>   src/mesa/state_tracker/st_glsl_to_tgsi.cpp | 14 ++++++++++++--
>>   1 file changed, 12 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
>> index dd9c84f..62e4101 100644
>> --- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
>> +++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
>> @@ -3091,8 +3091,18 @@ glsl_to_tgsi_visitor::visit(ir_discard *ir)
>>   {
>>      if (ir->condition) {
>>         ir->condition->accept(this);
>> -      this->result.negate = ~this->result.negate;
>> -      emit(ir, TGSI_OPCODE_KILL_IF, undef_dst, this->result);
>> +      st_src_reg condition = this->result;
>> +
>> +      /* Convert the bool condition to a float so we can negate. */
>> +      if (native_integers) {
>> +         st_src_reg temp = get_temp(ir->condition->type);
>> +         emit(ir, TGSI_OPCODE_AND, st_dst_reg(temp),
>> +              condition, st_src_reg_for_float(1.0));
>> +         condition = temp;
>> +      }
>> +
>> +      condition.negate = ~condition.negate;
>> +      emit(ir, TGSI_OPCODE_KILL_IF, undef_dst, condition);
>>      } else {
>>         /* unconditional kil */
>>         emit(ir, TGSI_OPCODE_KILL);
>>
>
> Reviewed-by: Brian Paul <brianp at vmware.com>
>
> Tag for stable branches?

I don't think there are any releaseable drivers doing native ints
without control flow in the stable braches -- GLSL discards just don't
work at all if you're hitting this bug.
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