| /* |
| * Copyright © 2018 Intel Corporation |
| * |
| * 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. |
| */ |
| |
| #include "nir.h" |
| #include "nir_builder.h" |
| #include "nir_deref.h" |
| |
| #include "util/u_dynarray.h" |
| |
| /** |
| * Elimination of dead writes based on derefs. |
| * |
| * Dead writes are stores and copies that write to a deref, which then gets |
| * another write before it was used (read or sourced for a copy). Those |
| * writes can be removed since they don't affect anything. |
| * |
| * For derefs that refer to a memory area that can be read after the program, |
| * the last write is considered used. The presence of certain instructions |
| * may also cause writes to be considered used, e.g. memory barrier (in this case |
| * the value must be written as other thread might use it). |
| * |
| * The write mask for store instructions is considered, so it is possible that |
| * a store is removed because of the combination of other stores overwritten |
| * its value. |
| */ |
| |
| /* Entry for unused_writes arrays. */ |
| struct write_entry { |
| /* If NULL indicates the entry is free to be reused. */ |
| nir_intrinsic_instr *intrin; |
| nir_component_mask_t mask; |
| nir_deref_instr *dst; |
| }; |
| |
| static void |
| clear_unused_for_modes(struct util_dynarray *unused_writes, nir_variable_mode modes) |
| { |
| util_dynarray_foreach_reverse(unused_writes, struct write_entry, entry) { |
| if (nir_deref_mode_may_be(entry->dst, modes)) |
| *entry = util_dynarray_pop(unused_writes, struct write_entry); |
| } |
| } |
| |
| static void |
| clear_unused_for_read(struct util_dynarray *unused_writes, nir_deref_instr *src) |
| { |
| util_dynarray_foreach_reverse(unused_writes, struct write_entry, entry) { |
| if (nir_compare_derefs(src, entry->dst) & nir_derefs_may_alias_bit) |
| *entry = util_dynarray_pop(unused_writes, struct write_entry); |
| } |
| } |
| |
| static bool |
| update_unused_writes(struct util_dynarray *unused_writes, |
| nir_intrinsic_instr *intrin, |
| nir_deref_instr *dst, nir_component_mask_t mask) |
| { |
| bool progress = false; |
| |
| /* This pass assumes that destination of copies and stores are derefs that |
| * end in a vector or scalar (it is OK to have wildcards or indirects for |
| * arrays). |
| */ |
| assert(glsl_type_is_vector_or_scalar(dst->type)); |
| |
| /* Find writes that are unused and can be removed. */ |
| util_dynarray_foreach_reverse(unused_writes, struct write_entry, entry) { |
| nir_deref_compare_result comp = nir_compare_derefs(dst, entry->dst); |
| if (comp & nir_derefs_a_contains_b_bit) { |
| entry->mask &= ~mask; |
| if (entry->mask == 0) { |
| nir_instr_remove(&entry->intrin->instr); |
| *entry = util_dynarray_pop(unused_writes, struct write_entry); |
| progress = true; |
| } |
| } |
| } |
| |
| /* Add the new write to the unused array. */ |
| struct write_entry new_entry = { |
| .intrin = intrin, |
| .mask = mask, |
| .dst = dst, |
| }; |
| |
| util_dynarray_append(unused_writes, struct write_entry, new_entry); |
| |
| return progress; |
| } |
| |
| static bool |
| remove_dead_write_vars_local(void *mem_ctx, nir_shader *shader, nir_block *block) |
| { |
| bool progress = false; |
| |
| struct util_dynarray unused_writes; |
| util_dynarray_init(&unused_writes, mem_ctx); |
| |
| nir_foreach_instr_safe(instr, block) { |
| if (instr->type == nir_instr_type_call) { |
| clear_unused_for_modes(&unused_writes, nir_var_shader_out | |
| nir_var_shader_temp | |
| nir_var_function_temp | |
| nir_var_mem_ssbo | |
| nir_var_mem_shared | |
| nir_var_mem_global); |
| continue; |
| } |
| |
| if (instr->type != nir_instr_type_intrinsic) |
| continue; |
| |
| nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr); |
| switch (intrin->intrinsic) { |
| case nir_intrinsic_control_barrier: |
| case nir_intrinsic_group_memory_barrier: |
| case nir_intrinsic_memory_barrier: { |
| clear_unused_for_modes(&unused_writes, nir_var_shader_out | |
| nir_var_mem_ssbo | |
| nir_var_mem_shared | |
| nir_var_mem_global); |
| break; |
| } |
| |
| case nir_intrinsic_memory_barrier_buffer: |
| clear_unused_for_modes(&unused_writes, nir_var_mem_ssbo | |
| nir_var_mem_global); |
| break; |
| |
| case nir_intrinsic_memory_barrier_shared: |
| clear_unused_for_modes(&unused_writes, nir_var_mem_shared); |
| break; |
| |
| case nir_intrinsic_memory_barrier_tcs_patch: |
| clear_unused_for_modes(&unused_writes, nir_var_shader_out); |
| break; |
| |
| case nir_intrinsic_scoped_barrier: { |
| if (nir_intrinsic_memory_semantics(intrin) & NIR_MEMORY_RELEASE) { |
| clear_unused_for_modes(&unused_writes, |
| nir_intrinsic_memory_modes(intrin)); |
| } |
| break; |
| } |
| |
| case nir_intrinsic_emit_vertex: |
| case nir_intrinsic_emit_vertex_with_counter: { |
| clear_unused_for_modes(&unused_writes, nir_var_shader_out); |
| break; |
| } |
| |
| case nir_intrinsic_execute_callable: |
| case nir_intrinsic_rt_execute_callable: { |
| /* Mark payload as it can be used by the callee */ |
| nir_deref_instr *src = nir_src_as_deref(intrin->src[1]); |
| clear_unused_for_read(&unused_writes, src); |
| break; |
| } |
| |
| case nir_intrinsic_trace_ray: |
| case nir_intrinsic_rt_trace_ray: { |
| /* Mark payload as it can be used by the callees */ |
| nir_deref_instr *src = nir_src_as_deref(intrin->src[10]); |
| clear_unused_for_read(&unused_writes, src); |
| break; |
| } |
| |
| case nir_intrinsic_load_deref: { |
| nir_deref_instr *src = nir_src_as_deref(intrin->src[0]); |
| if (nir_deref_mode_must_be(src, nir_var_read_only_modes)) |
| break; |
| clear_unused_for_read(&unused_writes, src); |
| break; |
| } |
| |
| case nir_intrinsic_store_deref: { |
| nir_deref_instr *dst = nir_src_as_deref(intrin->src[0]); |
| |
| if (nir_intrinsic_access(intrin) & ACCESS_VOLATILE) { |
| /* Consider a volatile write to also be a sort of read. This |
| * prevents us from deleting a non-volatile write just before a |
| * volatile write thanks to a non-volatile write afterwards. It's |
| * quite the corner case, but this should be safer and more |
| * predictable for the programmer than allowing two non-volatile |
| * writes to be combined with a volatile write between them. |
| */ |
| clear_unused_for_read(&unused_writes, dst); |
| break; |
| } |
| |
| nir_component_mask_t mask = nir_intrinsic_write_mask(intrin); |
| progress |= update_unused_writes(&unused_writes, intrin, dst, mask); |
| break; |
| } |
| |
| case nir_intrinsic_copy_deref: { |
| nir_deref_instr *src = nir_src_as_deref(intrin->src[1]); |
| nir_deref_instr *dst = nir_src_as_deref(intrin->src[0]); |
| |
| if (nir_intrinsic_dst_access(intrin) & ACCESS_VOLATILE) { |
| clear_unused_for_read(&unused_writes, src); |
| clear_unused_for_read(&unused_writes, dst); |
| break; |
| } |
| |
| /* Self-copy is removed. */ |
| if (nir_compare_derefs(src, dst) & nir_derefs_equal_bit) { |
| nir_instr_remove(instr); |
| progress = true; |
| break; |
| } |
| |
| clear_unused_for_read(&unused_writes, src); |
| nir_component_mask_t mask = (1 << glsl_get_vector_elements(dst->type)) - 1; |
| progress |= update_unused_writes(&unused_writes, intrin, dst, mask); |
| break; |
| } |
| |
| default: |
| break; |
| } |
| } |
| |
| /* All unused writes at the end of the block are kept, since we can't be |
| * sure they'll be overwritten or not with local analysis only. |
| */ |
| |
| return progress; |
| } |
| |
| static bool |
| remove_dead_write_vars_impl(void *mem_ctx, nir_shader *shader, nir_function_impl *impl) |
| { |
| bool progress = false; |
| |
| nir_metadata_require(impl, nir_metadata_block_index); |
| |
| nir_foreach_block(block, impl) |
| progress |= remove_dead_write_vars_local(mem_ctx, shader, block); |
| |
| if (progress) { |
| nir_metadata_preserve(impl, nir_metadata_block_index | |
| nir_metadata_dominance); |
| } else { |
| nir_metadata_preserve(impl, nir_metadata_all); |
| } |
| |
| return progress; |
| } |
| |
| bool |
| nir_opt_dead_write_vars(nir_shader *shader) |
| { |
| void *mem_ctx = ralloc_context(NULL); |
| bool progress = false; |
| |
| nir_foreach_function(function, shader) { |
| if (!function->impl) |
| continue; |
| progress |= remove_dead_write_vars_impl(mem_ctx, shader, function->impl); |
| } |
| |
| ralloc_free(mem_ctx); |
| return progress; |
| } |