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intel/fs: Remove unnecessary HALT_TARGET in opt_redundant_halt()

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This means the pass has to walk all the instructions but it was doing
that in a bunch of cases anyway when it didn't have a HALT_TARGET.
However, removing HALT_TARGET frees up the scheduler a bit because
HALT_TARGET is considered a scheduling barrier.  The shader-db results
are kind-of a wash but we're about to add HALT_TARGET unconditionally so
we want to be able to get rid of it.

Shader-db results on Ice Lake:

    total instructions in shared programs: 19935623 -> 19935623 (0.00%)
    instructions in affected programs: 0 -> 0
    helped: 0
    HURT: 0

    total cycles in shared programs: 976758472 -> 976766135 (<.01%)
    cycles in affected programs: 11097707 -> 11105370 (0.07%)
    helped: 1750
    HURT: 875
    helped stats (abs) min: 1 max: 866 x̄: 26.39 x̃: 4
    helped stats (rel) min: <.01% max: 39.24% x̄: 1.25% x̃: 0.46%
    HURT stats (abs)   min: 1 max: 1678 x̄: 61.54 x̃: 10
    HURT stats (rel)   min: <.01% max: 65.69% x̄: 1.86% x̃: 0.42%
    95% mean confidence interval for cycles value: -2.48 8.32
    95% mean confidence interval for cycles %-change: -0.40% -0.03%
    Inconclusive result (value mean confidence interval includes 0).

    LOST:   62
    GAINED: 46

All of the lost/gained programs are SIMD32 fragment shaders.

Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5071>
This commit is contained in:
Jason Ekstrand 2020-12-01 09:48:30 -06:00
parent f9d549b2bf
commit 4a7f0aa2e0
1 changed files with 17 additions and 5 deletions
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22
src/intel/compiler/brw_fs.cpp
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@ -3033,24 +3033,36 @@ fs_visitor::opt_redundant_halt()
{
bool progress = false;
bblock_t *last_bblock = cfg->blocks[cfg->num_blocks - 1];
unsigned halt_count = 0;
fs_inst *halt_target = NULL;
foreach_inst_in_block_reverse(fs_inst, inst, last_bblock) {
bblock_t *halt_target_block = NULL;
foreach_block_and_inst(block, fs_inst, inst, cfg) {
if (inst->opcode == BRW_OPCODE_HALT)
halt_count++;
if (inst->opcode == SHADER_OPCODE_HALT_TARGET) {
halt_target = inst;
halt_target_block = block;
break;
}
}
if (!halt_target)
if (!halt_target) {
assert(halt_count == 0);
return false;
}
/* Delete any HALTs immediately before the halt target. */
for (fs_inst *prev = (fs_inst *) halt_target->prev;
!prev->is_head_sentinel() && prev->opcode == BRW_OPCODE_HALT;
prev = (fs_inst *) halt_target->prev) {
prev->remove(last_bblock);
prev->remove(halt_target_block);
halt_count--;
progress = true;
}
if (halt_count == 0) {
halt_target->remove(halt_target_block);
progress = true;
}