[Mesa-dev] [PATCH V2 01/10] nir: evaluate if condition uses inside the if branches
Connor Abbott
cwabbott0 at gmail.com
Thu Jul 19 02:02:49 UTC 2018
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 <tarceri at 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 <idr at 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
>
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