[Mesa-dev] [PATCH] st/glsl_to_tgsi: drop the merge_registers() pass
Samuel Pitoiset
samuel.pitoiset at gmail.com
Mon Apr 24 21:42:37 UTC 2017
On 04/24/2017 11:22 PM, Rob Clark wrote:
> On Mon, Apr 24, 2017 at 5:18 PM, Samuel Pitoiset
> <samuel.pitoiset at gmail.com> wrote:
>>
>>
>> On 04/24/2017 11:12 PM, Rob Clark wrote:
>>>
>>> so I guess this is likely to hurt pipe drivers that don't (yet?) have
>>> a real compiler backend. (Ie. etnaviv and freedreno/a2xx.) So maybe
>>> it should be optional.
>>
>>
>> I can't say for these drivers, but it seems safer to add an option if this
>> can hurt them. How about PIPE_SHADER_CAP_TGSI_MERGE_REGISTERS?
>
> so we have already PIPE_CAP_GLSL_OPTIMIZE_CONSERVATIVELY .. not sure
> why that is a cap and not a shader-cap, tbh. I guess I'm ok with
> either bikeshed color ;-)
yeah, not sure of the _SHADER_ or not :)
>
> BR,
> -R
>
>
>>
>>>
>>> Also I wonder about the pre-llvm radeon gen's, since sb uses the
>>> actual instruction encoding for IR between tgsi->sb and backend opt
>>> passes.. iirc they have had problems when the tgsi code uses too many
>>> registers.
>>>
>>> BR,
>>> -R
>>>
>>> On Mon, Apr 24, 2017 at 5:01 PM, Samuel Pitoiset
>>> <samuel.pitoiset at gmail.com> wrote:
>>>>
>>>> The main goal of this pass to merge temporary registers in order
>>>> to reduce the total number of registers and also to produce
>>>> optimal TGSI code.
>>>>
>>>> In fact, compilers seem to be confused when temporary variables
>>>> are already merged, maybe because it's done too early in the
>>>> process.
>>>>
>>>> Removing the pass, reduce both the register pressure and the code
>>>> size (TGSI is no longer optimized, but who cares?).
>>>> shader-db results with RadeonSI and Nouveau are interesting.
>>>>
>>>> Nouveau:
>>>>
>>>> total instructions in shared programs : 3931608 -> 3929463 (-0.05%)
>>>> total gprs used in shared programs : 481255 -> 479014 (-0.47%)
>>>> total local used in shared programs : 27481 -> 27381 (-0.36%)
>>>> total bytes used in shared programs : 36031256 -> 36011120 (-0.06%)
>>>>
>>>> local gpr inst bytes
>>>> helped 14 1471 1309 1309
>>>> hurt 1 88 384 384
>>>>
>>>> RadeonSI:
>>>>
>>>> PERCENTAGE DELTAS Shaders SGPRs VGPRs SpillSGPR SpillVGPR
>>>> PrivVGPR Scratch CodeSize MaxWaves Waits
>>>>
>>>> ----------------------------------------------------------------------------------------------------------------------
>>>> All affected 4906 -0.31 % -0.40 % -2.93 % -20.00 %
>>>> . -20.00 % -0.18 % 0.19 % .
>>>>
>>>> ----------------------------------------------------------------------------------------------------------------------
>>>> Total 47109 -0.04 % -0.05 % -1.97 % -7.14 %
>>>> . -0.30 % -0.03 % 0.02 % .
>>>>
>>>> Found by luck while fixing an issue in the TGSI dead code elimination
>>>> pass which affects tex instructions with bindless samplers.
>>>>
>>>> Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
>>>> ---
>>>> src/mesa/state_tracker/st_glsl_to_tgsi.cpp | 62
>>>> ------------------------------
>>>> 1 file changed, 62 deletions(-)
>>>>
>>>> diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
>>>> b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
>>>> index de7fe7837a..d033bdcc5a 100644
>>>> --- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
>>>> +++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
>>>> @@ -565,7 +565,6 @@ public:
>>>> int eliminate_dead_code(void);
>>>>
>>>> void merge_two_dsts(void);
>>>> - void merge_registers(void);
>>>> void renumber_registers(void);
>>>>
>>>> void emit_block_mov(ir_assignment *ir, const struct glsl_type *type,
>>>> @@ -5262,66 +5261,6 @@ glsl_to_tgsi_visitor::merge_two_dsts(void)
>>>> }
>>>> }
>>>>
>>>> -/* Merges temporary registers together where possible to reduce the
>>>> number of
>>>> - * registers needed to run a program.
>>>> - *
>>>> - * Produces optimal code only after copy propagation and dead code
>>>> elimination
>>>> - * have been run. */
>>>> -void
>>>> -glsl_to_tgsi_visitor::merge_registers(void)
>>>> -{
>>>> - int *last_reads = rzalloc_array(mem_ctx, int, this->next_temp);
>>>> - int *first_writes = rzalloc_array(mem_ctx, int, this->next_temp);
>>>> - struct rename_reg_pair *renames = rzalloc_array(mem_ctx, struct
>>>> rename_reg_pair, this->next_temp);
>>>> - int i, j;
>>>> - int num_renames = 0;
>>>> -
>>>> - /* Read the indices of the last read and first write to each temp
>>>> register
>>>> - * into an array so that we don't have to traverse the instruction
>>>> list as
>>>> - * much. */
>>>> - for (i = 0; i < this->next_temp; i++) {
>>>> - last_reads[i] = -1;
>>>> - first_writes[i] = -1;
>>>> - }
>>>> - get_last_temp_read_first_temp_write(last_reads, first_writes);
>>>> -
>>>> - /* Start looking for registers with non-overlapping usages that can
>>>> be
>>>> - * merged together. */
>>>> - for (i = 0; i < this->next_temp; i++) {
>>>> - /* Don't touch unused registers. */
>>>> - if (last_reads[i] < 0 || first_writes[i] < 0) continue;
>>>> -
>>>> - for (j = 0; j < this->next_temp; j++) {
>>>> - /* Don't touch unused registers. */
>>>> - if (last_reads[j] < 0 || first_writes[j] < 0) continue;
>>>> -
>>>> - /* We can merge the two registers if the first write to j is
>>>> after or
>>>> - * in the same instruction as the last read from i. Note that
>>>> the
>>>> - * register at index i will always be used earlier or at the
>>>> same time
>>>> - * as the register at index j. */
>>>> - if (first_writes[i] <= first_writes[j] &&
>>>> - last_reads[i] <= first_writes[j]) {
>>>> - renames[num_renames].old_reg = j;
>>>> - renames[num_renames].new_reg = i;
>>>> - num_renames++;
>>>> -
>>>> - /* Update the first_writes and last_reads arrays with the
>>>> new
>>>> - * values for the merged register index, and mark the newly
>>>> unused
>>>> - * register index as such. */
>>>> - assert(last_reads[j] >= last_reads[i]);
>>>> - last_reads[i] = last_reads[j];
>>>> - first_writes[j] = -1;
>>>> - last_reads[j] = -1;
>>>> - }
>>>> - }
>>>> - }
>>>> -
>>>> - rename_temp_registers(num_renames, renames);
>>>> - ralloc_free(renames);
>>>> - ralloc_free(last_reads);
>>>> - ralloc_free(first_writes);
>>>> -}
>>>> -
>>>> /* Reassign indices to temporary registers by reusing unused indices
>>>> created
>>>> * by optimization passes. */
>>>> void
>>>> @@ -6712,7 +6651,6 @@ get_mesa_program_tgsi(struct gl_context *ctx,
>>>> while (v->eliminate_dead_code());
>>>>
>>>> v->merge_two_dsts();
>>>> - v->merge_registers();
>>>> v->renumber_registers();
>>>>
>>>> /* Write the END instruction. */
>>>> --
>>>> 2.12.2
>>>>
>>>> _______________________________________________
>>>> mesa-dev mailing list
>>>> mesa-dev at lists.freedesktop.org
>>>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
More information about the mesa-dev
mailing list