| /* |
| * 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" |
| |
| /* |
| * 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, void *state) |
| { |
| bool *progress = state; |
| |
| nir_foreach_instr_safe(block, instr) { |
| if (instr->type != nir_instr_type_phi) |
| break; |
| |
| nir_phi_instr *phi = nir_instr_as_phi(instr); |
| |
| nir_ssa_def *def = NULL; |
| bool srcs_same = true; |
| |
| nir_foreach_phi_src(phi, src) { |
| 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; |
| } else { |
| if (src->src.ssa != def) { |
| srcs_same = false; |
| break; |
| } |
| } |
| } |
| |
| if (!srcs_same) |
| continue; |
| |
| /* We must have found at least one definition, since there must be at |
| * least one forward edge. |
| */ |
| assert(def != NULL); |
| |
| 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 true; |
| } |
| |
| static bool |
| remove_phis_impl(nir_function_impl *impl) |
| { |
| bool progress = false; |
| |
| nir_foreach_block(impl, remove_phis_block, &progress); |
| |
| if (progress) { |
| nir_metadata_preserve(impl, nir_metadata_block_index | |
| nir_metadata_dominance); |
| } |
| |
| return progress; |
| } |
| |
| bool |
| nir_opt_remove_phis(nir_shader *shader) |
| { |
| bool progress = false; |
| |
| nir_foreach_function(shader, function) |
| if (function->impl) |
| progress = remove_phis_impl(function->impl) || progress; |
| |
| return progress; |
| } |
| |