diff options
| -rw-r--r-- | src/compiler/nir/nir_opt_if.c | 97 |
1 files 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 |