On Tuesday, February 24, 2015 12:20:08 PM Eric Anholt wrote:
> Kenneth Graunke <kenn...@whitecape.org> writes:
>
> > With the previous optimization in place, some shaders wind up with
> > multiple discard jumps in a row, or jumps directly to the next
> > instruction. We can remove those.
> >
> > Without NIR on Haswell:
> > total instructions in shared programs: 5777258 -> 5775872 (-0.02%)
> > instructions in affected programs: 20312 -> 18926 (-6.82%)
> > helped: 716
> >
> > With NIR on Haswell:
> > total instructions in shared programs: 5773163 -> 5771785 (-0.02%)
> > instructions in affected programs: 21040 -> 19662 (-6.55%)
> > helped: 717
> >
> > v2: Use the CFG rather than the old instructions list. Presumably
> > the placeholder halt will be in the last basic block.
> >
> > Signed-off-by: Kenneth Graunke <kenn...@whitecape.org>
> > ---
> > src/mesa/drivers/dri/i965/brw_fs.cpp | 42
> > ++++++++++++++++++++++++++++++++++++
> > src/mesa/drivers/dri/i965/brw_fs.h | 1 +
> > 2 files changed, 43 insertions(+)
> >
> > diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp
> > b/src/mesa/drivers/dri/i965/brw_fs.cpp
> > index 9df1650..21e1e82 100644
> > --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
> > @@ -2558,6 +2558,47 @@ fs_visitor::opt_register_renaming()
> > return progress;
> > }
> >
> > +/**
> > + * Remove redundant or useless discard jumps.
> > + *
> > + * For example, we can eliminate jumps in the following sequence:
> > + *
> > + * discard-jump (redundant with the next jump)
> > + * discard-jump (useless; jumps to the next instruction)
> > + * placeholder-halt
> > + */
> > +bool
> > +fs_visitor::opt_redundant_discard_jumps()
> > +{
> > + bool progress = false;
> > +
> > + bblock_t *last_bblock = cfg->blocks[cfg->num_blocks - 1];
> > +
> > + fs_inst *placeholder_halt = NULL;
> > + foreach_inst_in_block_reverse(fs_inst, inst, last_bblock) {
> > + if (inst->opcode == FS_OPCODE_PLACEHOLDER_HALT) {
> > + placeholder_halt = inst;
> > + break;
> > + }
> > + }
> > +
> > + if (!placeholder_halt)
> > + return false;
> > +
> > + /* Delete any HALTs immediately before the placeholder halt. */
> > + for (fs_inst *prev = (fs_inst *) placeholder_halt->prev;
> > + prev->opcode == FS_OPCODE_DISCARD_JUMP;
> > + prev = (fs_inst *) placeholder_halt->prev) {
> > + prev->remove(last_bblock);
> > + progress = true;
> > + }
>
> My only question in this series was "what if the placeholder halt is the
> first instruction in the block?" Shouldn't you be checking for a start
> sentinel?
Yep. It's certainly not common. But void main() {} hits that case.
I've changed the loop condition to:
!prev->is_head_sentinel() && prev->opcode == FS_OPCODE_DISCARD_JUMP;
> Other than that, this series is:
>
> Reviewed-by: Eric Anholt <e...@anholt.net>
>
> and I look forward to using the NIR intrinsic in my TGSI support.
Thanks!
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