[Mesa-dev] [PATCH 1/9] tgsi/scan: add a new pass that analyzes tess factor writes
Marek Olšák
maraeo at gmail.com
Thu Sep 7 10:55:30 UTC 2017
We can also say if gl_TessLevel* is written multiple times, then one
these must be true:
- there must not be a barrier between the writes
- gl_TessLevel* writes aren't inside conditional blocks
I see that these games use a barrier in TCS:
- Hitman
- Grid Autosport
- Tomb Raider
All constraints are true for those games. If we do this, it should be
enough: "there must not be a barrier between the writes"
Marek
On Thu, Sep 7, 2017 at 9:13 AM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
> On 06.09.2017 19:03, Marek Olšák wrote:
>>
>> From: Marek Olšák <marek.olsak at amd.com>
>>
>> The pass tries to deduce whether tess factors are always written by
>> invocation 0 (at least).
>>
>> The implication for radeonsi is that it doesn't have to use a barrier
>> near the end of TCS, and doesn't have to use LDS for passing the tess
>> factors to the epilog.
>
>
> What about the following shader snippet, which is particularly nasty on
> purpose:
>
> gl_TessLevelInner = ...;
>
> barrier();
>
> if (gl_InvocationID == 1) {
> gl_TessLevelInner = ...;
> }
>
> The final gl_TessLevelInner must be the one written by invocation 1.
>
> The point is, this would be a nice improvement, but it requires us to check
> that whenever tess factors are written, then that path includes invocation
> 0.
>
> (The written value itself might depend on the invocation ID, but in that
> case, we can do whatever we like, which means we can just take the value
> written by invocation 0.)
>
> I don't think we can determine this easily with the tools we have, and the
> effort is likely not worth it.
>
> Although you could do a very simplistic approximation of "tess factors are
> only written outside of control flow", which is probably reasonably common.
> (Uniform control flow would also work -- but that would require going to the
> LLVM level).
>
> Cheers,
> Nicolai
>
>
>
>> ---
>> src/gallium/auxiliary/tgsi/tgsi_scan.c | 188
>> +++++++++++++++++++++++++++++++++
>> src/gallium/auxiliary/tgsi/tgsi_scan.h | 11 ++
>> 2 files changed, 199 insertions(+)
>>
>> diff --git a/src/gallium/auxiliary/tgsi/tgsi_scan.c
>> b/src/gallium/auxiliary/tgsi/tgsi_scan.c
>> index db87ce3..612a8c6 100644
>> --- a/src/gallium/auxiliary/tgsi/tgsi_scan.c
>> +++ b/src/gallium/auxiliary/tgsi/tgsi_scan.c
>> @@ -930,10 +930,198 @@ tgsi_scan_arrays(const struct tgsi_token *tokens,
>> array->writemask |= dst->Register.WriteMask;
>> }
>> }
>> }
>> }
>> tgsi_parse_free(&parse);
>> return;
>> }
>> +
>> +static void
>> +check_no_subroutines(const struct tgsi_full_instruction *inst)
>> +{
>> + switch (inst->Instruction.Opcode) {
>> + case TGSI_OPCODE_BGNSUB:
>> + case TGSI_OPCODE_ENDSUB:
>> + case TGSI_OPCODE_CAL:
>> + unreachable("subroutines unhandled");
>> + }
>> +}
>> +
>> +static unsigned
>> +get_inst_tessfactor_writemask(const struct tgsi_shader_info *info,
>> + const struct tgsi_full_instruction *inst)
>> +{
>> + unsigned writemask = 0;
>> +
>> + for (unsigned i = 0; i < inst->Instruction.NumDstRegs; i++) {
>> + const struct tgsi_full_dst_register *dst = &inst->Dst[i];
>> +
>> + if (dst->Register.File == TGSI_FILE_OUTPUT &&
>> + !dst->Register.Indirect) {
>> + unsigned name = info->output_semantic_name[dst->Register.Index];
>> +
>> + if (name == TGSI_SEMANTIC_TESSINNER)
>> + writemask |= dst->Register.WriteMask;
>> + else if (name == TGSI_SEMANTIC_TESSOUTER)
>> + writemask |= dst->Register.WriteMask << 4;
>> + }
>> + }
>> + return writemask;
>> +}
>> +
>> +static unsigned
>> +get_block_tessfactor_writemask(const struct tgsi_shader_info *info,
>> + struct tgsi_parse_context *parse,
>> + unsigned end_opcode)
>> +{
>> + struct tgsi_full_instruction *inst;
>> + unsigned writemask = 0;
>> +
>> + do {
>> + tgsi_parse_token(parse);
>> + assert(parse->FullToken.Token.Type == TGSI_TOKEN_TYPE_INSTRUCTION);
>> + inst = &parse->FullToken.FullInstruction;
>> + check_no_subroutines(inst);
>> +
>> + /* Recursively process nested blocks. */
>> + switch (inst->Instruction.Opcode) {
>> + case TGSI_OPCODE_IF:
>> + case TGSI_OPCODE_UIF:
>> + writemask |=
>> + get_block_tessfactor_writemask(info, parse,
>> TGSI_OPCODE_ENDIF);
>> + continue;
>> +
>> + case TGSI_OPCODE_BGNLOOP:
>> + writemask |=
>> + get_block_tessfactor_writemask(info, parse,
>> TGSI_OPCODE_ENDLOOP);
>> + continue;
>> + }
>> +
>> + writemask |= get_inst_tessfactor_writemask(info, inst);
>> + } while (inst->Instruction.Opcode != end_opcode);
>> +
>> + return writemask;
>> +}
>> +
>> +static void
>> +get_if_block_tessfactor_writemask(const struct tgsi_shader_info *info,
>> + struct tgsi_parse_context *parse,
>> + unsigned *upper_block_tf_writemask,
>> + unsigned *cond_block_tf_writemask)
>> +{
>> + struct tgsi_full_instruction *inst;
>> + unsigned then_tessfactor_writemask = 0;
>> + unsigned else_tessfactor_writemask = 0;
>> + bool is_then = true;
>> +
>> + do {
>> + tgsi_parse_token(parse);
>> + assert(parse->FullToken.Token.Type == TGSI_TOKEN_TYPE_INSTRUCTION);
>> + inst = &parse->FullToken.FullInstruction;
>> + check_no_subroutines(inst);
>> +
>> + switch (inst->Instruction.Opcode) {
>> + case TGSI_OPCODE_ELSE:
>> + is_then = false;
>> + continue;
>> +
>> + /* Recursively process nested blocks. */
>> + case TGSI_OPCODE_IF:
>> + case TGSI_OPCODE_UIF:
>> + get_if_block_tessfactor_writemask(info, parse,
>> + is_then ?
>> &then_tessfactor_writemask :
>> +
>> &else_tessfactor_writemask,
>> + cond_block_tf_writemask);
>> + continue;
>> +
>> + case TGSI_OPCODE_BGNLOOP:
>> + *cond_block_tf_writemask |=
>> + get_block_tessfactor_writemask(info, parse,
>> TGSI_OPCODE_ENDLOOP);
>> + continue;
>> + }
>> +
>> + /* Process an instruction in the current block. */
>> + unsigned writemask = get_inst_tessfactor_writemask(info, inst);
>> +
>> + if (writemask) {
>> + if (is_then)
>> + then_tessfactor_writemask |= writemask;
>> + else
>> + else_tessfactor_writemask |= writemask;
>> + }
>> + } while (inst->Instruction.Opcode != TGSI_OPCODE_ENDIF);
>> +
>> + if (then_tessfactor_writemask || else_tessfactor_writemask) {
>> + /* If both statements write the same tess factor channels,
>> + * we can say that the upper block writes them too. */
>> + *upper_block_tf_writemask |= then_tessfactor_writemask &
>> + else_tessfactor_writemask;
>> + *cond_block_tf_writemask |= then_tessfactor_writemask |
>> + else_tessfactor_writemask;
>> + }
>> +}
>> +
>> +void
>> +tgsi_scan_tess_ctrl(const struct tgsi_token *tokens,
>> + const struct tgsi_shader_info *info,
>> + struct tgsi_tessctrl_info *out)
>> +{
>> + memset(out, 0, sizeof(*out));
>> +
>> + if (info->processor != PIPE_SHADER_TESS_CTRL)
>> + return;
>> +
>> + struct tgsi_parse_context parse;
>> + if (tgsi_parse_init(&parse, tokens) != TGSI_PARSE_OK) {
>> + debug_printf("tgsi_parse_init() failed in tgsi_scan_arrays()!\n");
>> + return;
>> + }
>> +
>> + /* The pass works as follows:
>> + * If all codepaths write tess factors, we can say that all
>> invocations
>> + * define tess factors, therefore invocation 0 defines tess factors.
>> + *
>> + * Each tess factor channel is tracked separately.
>> + */
>> + unsigned main_block_tf_writemask = 0;
>> + unsigned cond_block_tf_writemask = 0;
>> +
>> + while (!tgsi_parse_end_of_tokens(&parse)) {
>> + tgsi_parse_token(&parse);
>> +
>> + if (parse.FullToken.Token.Type != TGSI_TOKEN_TYPE_INSTRUCTION)
>> + continue;
>> +
>> + struct tgsi_full_instruction *inst =
>> &parse.FullToken.FullInstruction;
>> + check_no_subroutines(inst);
>> +
>> + /* Process nested blocks. */
>> + switch (inst->Instruction.Opcode) {
>> + case TGSI_OPCODE_IF:
>> + case TGSI_OPCODE_UIF:
>> + get_if_block_tessfactor_writemask(info, &parse,
>> + &main_block_tf_writemask,
>> + &cond_block_tf_writemask);
>> + continue;
>> +
>> + case TGSI_OPCODE_BGNLOOP:
>> + cond_block_tf_writemask |=
>> + get_block_tessfactor_writemask(info, &parse,
>> TGSI_OPCODE_ENDIF);
>> + continue;
>> + }
>> +
>> + main_block_tf_writemask |= get_inst_tessfactor_writemask(info,
>> inst);
>> + }
>> +
>> + /* If there is a conditional block that writes a tess factor channel
>> that
>> + * the main block doesn't write, we can't say (we're not sure) that
>> + * invocation 0 writes it.
>> + */
>> + out->invoc0_tessfactors_are_def =
>> + main_block_tf_writemask &&
>> + !(cond_block_tf_writemask & ~main_block_tf_writemask);
>> +
>> + tgsi_parse_free(&parse);
>> +}
>> diff --git a/src/gallium/auxiliary/tgsi/tgsi_scan.h
>> b/src/gallium/auxiliary/tgsi/tgsi_scan.h
>> index 857434f..ff64789 100644
>> --- a/src/gallium/auxiliary/tgsi/tgsi_scan.h
>> +++ b/src/gallium/auxiliary/tgsi/tgsi_scan.h
>> @@ -181,30 +181,41 @@ struct tgsi_array_info
>> /** Whether an array with this ID was declared. */
>> bool declared;
>> /** The OR of all writemasks used to write to this array. */
>> ubyte writemask;
>> /** The range with which the array was declared. */
>> struct tgsi_declaration_range range;
>> };
>> +struct tgsi_tessctrl_info
>> +{
>> + /** Whether all codepaths of invocation 0 write tess factors. */
>> + bool invoc0_tessfactors_are_def;
>> +};
>> +
>> extern void
>> tgsi_scan_shader(const struct tgsi_token *tokens,
>> struct tgsi_shader_info *info);
>> void
>> tgsi_scan_arrays(const struct tgsi_token *tokens,
>> unsigned file,
>> unsigned max_array_id,
>> struct tgsi_array_info *arrays);
>> +void
>> +tgsi_scan_tess_ctrl(const struct tgsi_token *tokens,
>> + const struct tgsi_shader_info *info,
>> + struct tgsi_tessctrl_info *out);
>> +
>> static inline bool
>> tgsi_is_bindless_image_file(unsigned file)
>> {
>> return file != TGSI_FILE_IMAGE &&
>> file != TGSI_FILE_MEMORY &&
>> file != TGSI_FILE_BUFFER;
>> }
>> #ifdef __cplusplus
>> } // extern "C"
>>
>
>
> --
> Lerne, wie die Welt wirklich ist,
> Aber vergiss niemals, wie sie sein sollte.
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