Why not do the more general thing, and evaluate the condition in every block dominated by the then and else blocks? That should handle the loop and non-loop cases.
On Thu, Jul 19, 2018 at 8:06 AM, Timothy Arceri <tarc...@itsqueeze.com> wrote: > Since we know what side of the branch we ended up on we can just > replace the use with a constant. > > All helped shaders are from Unreal Engine 4 besides one shader from > Dirt Showdown. > > V2: make sure we do evaluation when condition is used in else with > a single block (we were checking for blocks < the last else > block rather than <=) > > shader-db results SKL: > > total instructions in shared programs: 13219725 -> 13219643 (<.01%) > instructions in affected programs: 28917 -> 28835 (-0.28%) > helped: 45 > HURT: 0 > > total cycles in shared programs: 529335971 -> 529334604 (<.01%) > cycles in affected programs: 216209 -> 214842 (-0.63%) > helped: 45 > HURT: 4 > > Cc: Ian Romanick <i...@freedesktop.org> > > fix if condition eval for else with a single block > --- > src/compiler/nir/nir_opt_if.c | 121 ++++++++++++++++++++++++++++++++++ > 1 file changed, 121 insertions(+) > > diff --git a/src/compiler/nir/nir_opt_if.c b/src/compiler/nir/nir_opt_if.c > index a52de120ad6..4ed919887ce 100644 > --- a/src/compiler/nir/nir_opt_if.c > +++ b/src/compiler/nir/nir_opt_if.c > @@ -348,6 +348,86 @@ opt_if_loop_terminator(nir_if *nif) > return true; > } > > +static void > +replace_if_condition_use_with_const(nir_src *use, unsigned nir_boolean, > + void *mem_ctx, bool if_condition) > +{ > + /* Create const */ > + nir_load_const_instr *load = nir_load_const_instr_create(mem_ctx, 1, 32); > + load->value.u32[0] = nir_boolean; > + > + if (if_condition) { > + nir_instr_insert_before_cf(&use->parent_if->cf_node, &load->instr); > + } else if (use->parent_instr->type == nir_instr_type_phi) { > + nir_phi_instr *cond_phi = nir_instr_as_phi(use->parent_instr); > + > + bool UNUSED found = false; > + nir_foreach_phi_src(phi_src, cond_phi) { > + if (phi_src->src.ssa == use->ssa) { > + nir_instr_insert_before_block(phi_src->pred, &load->instr); > + found = true; > + break; > + } > + } > + assert(found); > + } else { > + nir_instr_insert_before(use->parent_instr, &load->instr); > + } > + > + /* Rewrite use to use const */ > + nir_src new_src = nir_src_for_ssa(&load->def); > + > + if (if_condition) > + nir_if_rewrite_condition(use->parent_if, new_src); > + else > + nir_instr_rewrite_src(use->parent_instr, use, new_src); > +} > + > +static bool > +evaluate_condition_use(nir_if *nif, nir_src *use_src, void *mem_ctx, > + bool if_condition) > +{ > + bool progress = false; > + > + nir_block *first_then = nir_if_first_then_block(nif); > + if (use_src->parent_instr->block->index > first_then->index) { > + nir_block *first_else = nir_if_first_else_block(nif); > + if (use_src->parent_instr->block->index < first_else->index) { > + replace_if_condition_use_with_const(use_src, NIR_TRUE, mem_ctx, > + if_condition); > + > + progress = true; > + } else if (use_src->parent_instr->block->index <= > + nir_if_last_else_block(nif)->index) { > + replace_if_condition_use_with_const(use_src, NIR_FALSE, mem_ctx, > + if_condition); > + > + progress = true; > + } > + } > + > + return progress; > +} > + > +static bool > +opt_if_evaluate_condition_use(nir_if *nif, void *mem_ctx) > +{ > + bool progress = false; > + > + /* Evaluate any uses of the if condition inside the if branches */ > + assert(nif->condition.is_ssa); > + nir_foreach_use_safe(use_src, nif->condition.ssa) { > + progress |= evaluate_condition_use(nif, use_src, mem_ctx, false); > + } > + > + nir_foreach_if_use_safe(use_src, nif->condition.ssa) { > + if (use_src->parent_if != nif) > + progress |= evaluate_condition_use(nif, use_src, mem_ctx, true); > + } > + > + return progress; > +} > + > static bool > opt_if_cf_list(nir_builder *b, struct exec_list *cf_list) > { > @@ -381,6 +461,41 @@ opt_if_cf_list(nir_builder *b, struct exec_list *cf_list) > return progress; > } > > +/** > + * These optimisations depend on nir_metadata_block_index and therefore must > + * not do anything to cause the metadata to become invalid. > + */ > +static bool > +opt_if_safe_cf_list(nir_builder *b, struct exec_list *cf_list, void *mem_ctx) > +{ > + bool progress = false; > + foreach_list_typed(nir_cf_node, cf_node, node, cf_list) { > + switch (cf_node->type) { > + case nir_cf_node_block: > + break; > + > + case nir_cf_node_if: { > + nir_if *nif = nir_cf_node_as_if(cf_node); > + progress |= opt_if_safe_cf_list(b, &nif->then_list, mem_ctx); > + progress |= opt_if_safe_cf_list(b, &nif->else_list, mem_ctx); > + progress |= opt_if_evaluate_condition_use(nif, mem_ctx); > + break; > + } > + > + case nir_cf_node_loop: { > + nir_loop *loop = nir_cf_node_as_loop(cf_node); > + progress |= opt_if_safe_cf_list(b, &loop->body, mem_ctx); > + break; > + } > + > + case nir_cf_node_function: > + unreachable("Invalid cf type"); > + } > + } > + > + return progress; > +} > + > bool > nir_opt_if(nir_shader *shader) > { > @@ -393,6 +508,12 @@ nir_opt_if(nir_shader *shader) > nir_builder b; > nir_builder_init(&b, function->impl); > > + void *mem_ctx = ralloc_parent(function->impl); > + > + nir_metadata_require(function->impl, nir_metadata_block_index); > + progress = opt_if_safe_cf_list(&b, &function->impl->body, mem_ctx); > + nir_metadata_preserve(function->impl, nir_metadata_block_index); > + > if (opt_if_cf_list(&b, &function->impl->body)) { > nir_metadata_preserve(function->impl, nir_metadata_none); > > -- > 2.17.1 > > _______________________________________________ > mesa-dev mailing list > mesa-dev@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/mesa-dev _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev