On Fri, Feb 6, 2015 at 4:17 PM, Francisco Jerez <curroje...@riseup.net> wrote:
> Matt Turner <matts...@gmail.com> writes:
>
>> On Fri, Feb 6, 2015 at 6:42 AM, Francisco Jerez <curroje...@riseup.net>
>> wrote:
>>> If the source type differs from the original type of the constant we
>>> need to bit-cast it before propagating, otherwise the original type
>>> information will be lost. If the constant was a vector float there
>>> isn't much we can do, because the result of bit-casting the component
>>> values of a vector float cannot itself be represented as an immediate.
>>> ---
>>> src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp | 10 ++++++++++
>>> 1 file changed, 10 insertions(+)
>>>
>>> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
>>> b/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
>>> index 81567d2..0a961ce 100644
>>> --- a/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
>>> +++ b/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
>>> @@ -113,6 +113,16 @@ try_constant_propagate(struct brw_context *brw,
>>> vec4_instruction *inst,
>>> if (value.file != IMM)
>>> return false;
>>>
>>> + if (value.type == BRW_REGISTER_TYPE_VF) {
>>> + /* The result of bit-casting the component values of a vector float
>>> + * cannot in general be represented as an immediate.
>>> + */
>>> + if (inst->src[arg].type != BRW_REGISTER_TYPE_F)
>>> + return false;
>>> + } else {
>>> + value.type = inst->src[arg].type;
>>> + }
>>> +
>>> if (inst->src[arg].abs) {
>>> if (!brw_abs_immediate(value.type, &value.fixed_hw_reg)) {
>>> return false;
>>
>> Wow. Did you hit this in practice?
>>
> I hit the non-VF case in practice (constant propagation forgetting the
> original type of the source when propagating a bit-cast constant of a
> different type). I haven't seen the VF case in the wild but my addition
> wouldn't have seemed correct without taking vector immediates into
> account somehow.
Okay, I really do need to see an example. is_direct_copy() checks that
the types are suitable already.
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