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aco: don't do divergent break+discard

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If the shader does:
loop {
   if (divergent)
      discard
   else
      a()
   b()
}
then a()'s block will dominate b()'s block in the logical CFG, but not the
linear CFG. This will cause value numbering to try to combine SLAU from
a() and b().

This didn't happen with break/continue because sanitize_if() would move
a() out of the branch. Using sanitize_if() to fix this doesn't look easy,
because discards are not control flow instructions in NIR.

No fossil-db changes.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7216>
This commit is contained in:
Rhys Perry 2020-10-19 11:03:34 +01:00 • committed by Marge Bot
parent d4503a9020
commit 72b307a338
1 changed files with 6 additions and 34 deletions
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40
src/amd/compiler/aco_instruction_selection.cpp
View file

@ -5263,8 +5263,7 @@ void visit_discard(isel_context* ctx, nir_intrinsic_instr *instr)
bool divergent = ctx->cf_info.parent_if.is_divergent ||
ctx->cf_info.parent_loop.has_divergent_continue;
if (ctx->block->loop_nest_depth &&
((nir_instr_is_last(&instr->instr) && !divergent) || divergent)) {
if (ctx->block->loop_nest_depth && (nir_instr_is_last(&instr->instr) && !divergent)) {
/* we handle discards the same way as jump instructions */
append_logical_end(ctx->block);
@ -5272,39 +5271,12 @@ void visit_discard(isel_context* ctx, nir_intrinsic_instr *instr)
Block *linear_target = ctx->cf_info.parent_loop.exit;
ctx->block->kind |= block_kind_discard;
if (!divergent) {
/* uniform discard - loop ends here */
assert(nir_instr_is_last(&instr->instr));
ctx->block->kind |= block_kind_uniform;
ctx->cf_info.has_branch = true;
bld.branch(aco_opcode::p_branch, bld.hint_vcc(bld.def(s2)));
add_linear_edge(ctx->block->index, linear_target);
return;
}
/* we add a break right behind the discard() instructions */
ctx->block->kind |= block_kind_break;
unsigned idx = ctx->block->index;
ctx->cf_info.parent_loop.has_divergent_branch = true;
ctx->cf_info.nir_to_aco[instr->instr.block->index] = idx;
/* remove critical edges from linear CFG */
/* uniform discard - loop ends here */
assert(nir_instr_is_last(&instr->instr));
ctx->block->kind |= block_kind_uniform;
ctx->cf_info.has_branch = true;
bld.branch(aco_opcode::p_branch, bld.hint_vcc(bld.def(s2)));
Block* break_block = ctx->program->create_and_insert_block();
break_block->loop_nest_depth = ctx->cf_info.loop_nest_depth;
break_block->kind |= block_kind_uniform;
add_linear_edge(idx, break_block);
add_linear_edge(break_block->index, linear_target);
bld.reset(break_block);
bld.branch(aco_opcode::p_branch, bld.hint_vcc(bld.def(s2)));
Block* continue_block = ctx->program->create_and_insert_block();
continue_block->loop_nest_depth = ctx->cf_info.loop_nest_depth;
add_linear_edge(idx, continue_block);
append_logical_start(continue_block);
ctx->block = continue_block;
add_linear_edge(ctx->block->index, linear_target);
return;
}