Module: Mesa Branch: master Commit: e3e929f8c342b32dc8f5296adf8fb337866fa40a URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=e3e929f8c342b32dc8f5296adf8fb337866fa40a
Author: Samuel Pitoiset <[email protected]> Date: Wed May 30 14:21:42 2018 +0200 nir: implement the GLSL equivalent of if simplication in nir_opt_if This pass turns: if (cond) { } else { do_work(); } into: if (!cond) { do_work(); } else { } Here's the vkpipeline-db stats (from affected shaders) on Polaris10: Totals from affected shaders: SGPRS: 17272 -> 17296 (0.14 %) VGPRS: 18712 -> 18740 (0.15 %) Spilled SGPRs: 1179 -> 1142 (-3.14 %) Code Size: 1503364 -> 1515176 (0.79 %) bytes Max Waves: 916 -> 911 (-0.55 %) This pass only affects Serious Sam 2017 (Vulkan) on my side. The stats are not really good for now. Some shaders look quite dumb but this will be improved with further NIR passes, like ifs combination. Signed-off-by: Samuel Pitoiset <[email protected]> Reviewed-by: Timothy Arceri <[email protected]> Reviewed-by: Ian Romanick <[email protected]> --- src/compiler/nir/nir_opt_if.c | 97 ++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 92 insertions(+), 5 deletions(-) diff --git a/src/compiler/nir/nir_opt_if.c b/src/compiler/nir/nir_opt_if.c index 68dacea770..b03657a424 100644 --- a/src/compiler/nir/nir_opt_if.c +++ b/src/compiler/nir/nir_opt_if.c @@ -22,6 +22,7 @@ */ #include "nir.h" +#include "nir/nir_builder.h" #include "nir_control_flow.h" /** @@ -201,7 +202,89 @@ opt_peel_loop_initial_if(nir_loop *loop) } static bool -opt_if_cf_list(struct exec_list *cf_list) +is_block_empty(nir_block *block) +{ + return nir_cf_node_is_last(&block->cf_node) && + exec_list_is_empty(&block->instr_list); +} + +/** + * This optimization turns: + * + * if (cond) { + * } else { + * do_work(); + * } + * + * into: + * + * if (!cond) { + * do_work(); + * } else { + * } + */ +static bool +opt_if_simplification(nir_builder *b, nir_if *nif) +{ + /* Only simplify if the then block is empty and the else block is not. */ + if (!is_block_empty(nir_if_first_then_block(nif)) || + is_block_empty(nir_if_first_else_block(nif))) + return false; + + /* Make sure the condition is a comparison operation. */ + nir_instr *src_instr = nif->condition.ssa->parent_instr; + if (src_instr->type != nir_instr_type_alu) + return false; + + nir_alu_instr *alu_instr = nir_instr_as_alu(src_instr); + if (!nir_alu_instr_is_comparison(alu_instr)) + return false; + + /* Insert the inverted instruction and rewrite the condition. */ + b->cursor = nir_after_instr(&alu_instr->instr); + + nir_ssa_def *new_condition = + nir_inot(b, &alu_instr->dest.dest.ssa); + + nir_if_rewrite_condition(nif, nir_src_for_ssa(new_condition)); + + /* Grab pointers to the last then/else blocks for fixing up the phis. */ + nir_block *then_block = nir_if_last_then_block(nif); + nir_block *else_block = nir_if_last_else_block(nif); + + /* Walk all the phis in the block immediately following the if statement and + * swap the blocks. + */ + nir_block *after_if_block = + nir_cf_node_as_block(nir_cf_node_next(&nif->cf_node)); + + nir_foreach_instr(instr, after_if_block) { + if (instr->type != nir_instr_type_phi) + continue; + + nir_phi_instr *phi = nir_instr_as_phi(instr); + + foreach_list_typed(nir_phi_src, src, node, &phi->srcs) { + if (src->pred == else_block) { + src->pred = then_block; + } else if (src->pred == then_block) { + src->pred = else_block; + } + } + } + + /* Finally, move the else block to the then block. */ + nir_cf_list tmp; + nir_cf_extract(&tmp, nir_before_cf_list(&nif->else_list), + nir_after_cf_list(&nif->else_list)); + nir_cf_reinsert(&tmp, nir_before_cf_list(&nif->then_list)); + nir_cf_delete(&tmp); + + return true; +} + +static bool +opt_if_cf_list(nir_builder *b, struct exec_list *cf_list) { bool progress = false; foreach_list_typed(nir_cf_node, cf_node, node, cf_list) { @@ -211,14 +294,15 @@ opt_if_cf_list(struct exec_list *cf_list) case nir_cf_node_if: { nir_if *nif = nir_cf_node_as_if(cf_node); - progress |= opt_if_cf_list(&nif->then_list); - progress |= opt_if_cf_list(&nif->else_list); + progress |= opt_if_cf_list(b, &nif->then_list); + progress |= opt_if_cf_list(b, &nif->else_list); + progress |= opt_if_simplification(b, nif); break; } case nir_cf_node_loop: { nir_loop *loop = nir_cf_node_as_loop(cf_node); - progress |= opt_if_cf_list(&loop->body); + progress |= opt_if_cf_list(b, &loop->body); progress |= opt_peel_loop_initial_if(loop); break; } @@ -240,7 +324,10 @@ nir_opt_if(nir_shader *shader) if (function->impl == NULL) continue; - if (opt_if_cf_list(&function->impl->body)) { + nir_builder b; + nir_builder_init(&b, function->impl); + + if (opt_if_cf_list(&b, &function->impl->body)) { nir_metadata_preserve(function->impl, nir_metadata_none); /* If that made progress, we're no longer really in SSA form. We _______________________________________________ mesa-commit mailing list [email protected] https://lists.freedesktop.org/mailman/listinfo/mesa-commit
