/* * Copyright © 2015 Connor Abbott * * Permission is hereby granted, free of charge, to any person obtaining a * copy of this software and associated documentation files (the "Software"), * to deal in the Software without restriction, including without limitation * the rights to use, copy, modify, merge, publish, distribute, sublicense, * and/or sell copies of the Software, and to permit persons to whom the * Software is furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice (including the next * paragraph) shall be included in all copies or substantial portions of the * Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS * IN THE SOFTWARE. * * Authors: * Connor Abbott (cwabbott0@gmail.com) * */ #include "nir.h" #include "nir_builder.h" static nir_alu_instr * get_parent_mov(nir_ssa_def *ssa) { if (ssa->parent_instr->type != nir_instr_type_alu) return NULL; nir_alu_instr *alu = nir_instr_as_alu(ssa->parent_instr); return (alu->op == nir_op_mov) ? alu : NULL; } static bool matching_mov(nir_alu_instr *mov1, nir_ssa_def *ssa) { if (!mov1) return false; nir_alu_instr *mov2 = get_parent_mov(ssa); return mov2 && nir_alu_srcs_equal(mov1, mov2, 0, 0); } /* * This is a pass for removing phi nodes that look like: * a = phi(b, b, b, ...) * * Note that we can't ignore undef sources here, or else we may create a * situation where the definition of b isn't dominated by its uses. We're * allowed to do this since the definition of b must dominate all of the * phi node's predecessors, which means it must dominate the phi node as well * as all of the phi node's uses. In essence, the phi node acts as a copy * instruction. b can't be another phi node in the same block, since the only * time when phi nodes can source other phi nodes defined in the same block is * at the loop header, and in that case one of the sources of the phi has to * be from before the loop and that source can't be b. */ static bool remove_phis_block(nir_block *block, nir_builder *b) { bool progress = false; nir_foreach_instr_safe(instr, block) { if (instr->type != nir_instr_type_phi) break; nir_phi_instr *phi = nir_instr_as_phi(instr); nir_ssa_def *def = NULL; nir_alu_instr *mov = NULL; bool srcs_same = true; nir_foreach_phi_src(src, phi) { assert(src->src.is_ssa); /* For phi nodes at the beginning of loops, we may encounter some * sources from backedges that point back to the destination of the * same phi, i.e. something like: * * a = phi(a, b, ...) * * We can safely ignore these sources, since if all of the normal * sources point to the same definition, then that definition must * still dominate the phi node, and the phi will still always take * the value of that definition. */ if (src->src.ssa == &phi->dest.ssa) continue; if (def == NULL) { def = src->src.ssa; mov = get_parent_mov(def); } else { if (src->src.ssa != def && !matching_mov(mov, src->src.ssa)) { srcs_same = false; break; } } } if (!srcs_same) continue; if (!def) { /* In this case, the phi had no sources. So turn it into an undef. */ b->cursor = nir_after_phis(block); def = nir_ssa_undef(b, phi->dest.ssa.num_components, phi->dest.ssa.bit_size); } else if (mov) { /* If the sources were all movs from the same source with the same * swizzle, then we can't just pick a random move because it may not * dominate the phi node. Instead, we need to emit our own move after * the phi which uses the shared source, and rewrite uses of the phi * to use the move instead. This is ok, because while the movs may * not all dominate the phi node, their shared source does. */ b->cursor = nir_after_phis(block); def = nir_mov_alu(b, mov->src[0], def->num_components); } assert(phi->dest.is_ssa); nir_ssa_def_rewrite_uses(&phi->dest.ssa, nir_src_for_ssa(def)); nir_instr_remove(instr); progress = true; } return progress; } bool nir_opt_remove_phis_block(nir_block *block) { nir_builder b; nir_builder_init(&b, nir_cf_node_get_function(&block->cf_node)); return remove_phis_block(block, &b); } static bool nir_opt_remove_phis_impl(nir_function_impl *impl) { bool progress = false; nir_builder bld; nir_builder_init(&bld, impl); nir_foreach_block(block, impl) { progress |= remove_phis_block(block, &bld); } if (progress) { nir_metadata_preserve(impl, nir_metadata_block_index | nir_metadata_dominance); } else { #ifndef NDEBUG impl->valid_metadata &= ~nir_metadata_not_properly_reset; #endif } return progress; } bool nir_opt_remove_phis(nir_shader *shader) { bool progress = false; nir_foreach_function(function, shader) if (function->impl) progress = nir_opt_remove_phis_impl(function->impl) || progress; return progress; }