/* * Copyright © 2014 Broadcom * * 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. */ /** * @file v3d_opt_dead_code.c * * This is a simple dead code eliminator for SSA values in VIR. * * It walks all the instructions finding what temps are used, then walks again * to remove instructions writing unused temps. * * This is an inefficient implementation if you have long chains of * instructions where the entire chain is dead, but we expect those to have * been eliminated at the NIR level, and here we're just cleaning up small * problems produced by NIR->VIR. */ #include "v3d_compiler.h" static bool debug; static void dce(struct v3d_compile *c, struct qinst *inst) { if (debug) { fprintf(stderr, "Removing: "); vir_dump_inst(c, inst); fprintf(stderr, "\n"); } assert(!v3d_qpu_writes_flags(&inst->qpu)); vir_remove_instruction(c, inst); } static bool has_nonremovable_reads(struct v3d_compile *c, struct qinst *inst) { for (int i = 0; i < vir_get_nsrc(inst); i++) { if (inst->src[i].file == QFILE_VPM) return true; } return false; } static bool can_write_to_null(struct v3d_compile *c, struct qinst *inst) { /* The SFU instructions must write to a physical register. */ if (c->devinfo->ver >= 41 && v3d_qpu_uses_sfu(&inst->qpu)) return false; return true; } static void vir_dce_flags(struct v3d_compile *c, struct qinst *inst) { if (debug) { fprintf(stderr, "Removing flags write from: "); vir_dump_inst(c, inst); fprintf(stderr, "\n"); } assert(inst->qpu.type == V3D_QPU_INSTR_TYPE_ALU); inst->qpu.flags.apf = V3D_QPU_PF_NONE; inst->qpu.flags.mpf = V3D_QPU_PF_NONE; inst->qpu.flags.auf = V3D_QPU_UF_NONE; inst->qpu.flags.muf = V3D_QPU_UF_NONE; } static bool check_last_ldunifa(struct v3d_compile *c, struct qinst *inst, struct qblock *block) { if (!inst->qpu.sig.ldunifa && !inst->qpu.sig.ldunifarf) return false; list_for_each_entry_from(struct qinst, scan_inst, inst->link.next, &block->instructions, link) { /* If we find a new write to unifa, then this was the last * ldunifa in its sequence and is safe to remove. */ if (scan_inst->dst.file == QFILE_MAGIC && scan_inst->dst.index == V3D_QPU_WADDR_UNIFA) { return true; } /* If we find another ldunifa in the same sequence then we * can't remove it. */ if (scan_inst->qpu.sig.ldunifa || scan_inst->qpu.sig.ldunifarf) return false; } return true; } static bool check_first_ldunifa(struct v3d_compile *c, struct qinst *inst, struct qblock *block, struct qinst **unifa) { if (!inst->qpu.sig.ldunifa && !inst->qpu.sig.ldunifarf) return false; list_for_each_entry_from_rev(struct qinst, scan_inst, inst->link.prev, &block->instructions, link) { /* If we find a write to unifa, then this was the first * ldunifa in its sequence and is safe to remove. */ if (scan_inst->dst.file == QFILE_MAGIC && scan_inst->dst.index == V3D_QPU_WADDR_UNIFA) { *unifa = scan_inst; return true; } /* If we find another ldunifa in the same sequence then we * can't remove it. */ if (scan_inst->qpu.sig.ldunifa || scan_inst->qpu.sig.ldunifarf) return false; } unreachable("could not find starting unifa for ldunifa sequence"); } static bool increment_unifa_address(struct v3d_compile *c, struct qblock *block, struct qinst *unifa) { struct qblock *current_block = c->cur_block; if (unifa->qpu.type == V3D_QPU_INSTR_TYPE_ALU && unifa->qpu.alu.mul.op == V3D_QPU_M_MOV) { c->cursor = vir_after_inst(unifa); c->cur_block = block; struct qreg unifa_reg = vir_reg(QFILE_MAGIC, V3D_QPU_WADDR_UNIFA); vir_ADD_dest(c, unifa_reg, unifa->src[0], vir_uniform_ui(c, 4u)); vir_remove_instruction(c, unifa); c->cur_block = current_block; return true; } if (unifa->qpu.type == V3D_QPU_INSTR_TYPE_ALU && unifa->qpu.alu.add.op == V3D_QPU_A_ADD) { c->cursor = vir_after_inst(unifa); c->cur_block = block; struct qreg unifa_reg = vir_reg(QFILE_MAGIC, V3D_QPU_WADDR_UNIFA); struct qreg tmp = vir_ADD(c, unifa->src[1], vir_uniform_ui(c, 4u)); vir_ADD_dest(c, unifa_reg, unifa->src[0], tmp); vir_remove_instruction(c, unifa); c->cur_block = current_block; return true; } return false; } bool vir_opt_dead_code(struct v3d_compile *c) { bool progress = false; bool *used = calloc(c->num_temps, sizeof(bool)); /* Defuse the "are you removing the cursor?" assertion in the core. * You'll need to set up a new cursor for any new instructions after * doing DCE (which we would expect, anyway). */ c->cursor.link = NULL; vir_for_each_inst_inorder(inst, c) { for (int i = 0; i < vir_get_nsrc(inst); i++) { if (inst->src[i].file == QFILE_TEMP) used[inst->src[i].index] = true; } } vir_for_each_block(block, c) { struct qinst *last_flags_write = NULL; vir_for_each_inst_safe(inst, block) { /* If this instruction reads the flags, we can't * remove the flags generation for it. */ if (v3d_qpu_reads_flags(&inst->qpu)) last_flags_write = NULL; if (inst->dst.file != QFILE_NULL && !(inst->dst.file == QFILE_TEMP && !used[inst->dst.index])) { continue; } const bool is_ldunifa = inst->qpu.sig.ldunifa || inst->qpu.sig.ldunifarf; if (vir_has_side_effects(c, inst) && !is_ldunifa) continue; bool is_first_ldunifa = false; bool is_last_ldunifa = false; struct qinst *unifa = NULL; if (is_ldunifa) { is_last_ldunifa = check_last_ldunifa(c, inst, block); is_first_ldunifa = check_first_ldunifa(c, inst, block, &unifa); } if (v3d_qpu_writes_flags(&inst->qpu)) { /* If we obscure a previous flags write, * drop it. */ if (last_flags_write && (inst->qpu.flags.apf != V3D_QPU_PF_NONE || inst->qpu.flags.mpf != V3D_QPU_PF_NONE)) { vir_dce_flags(c, last_flags_write); progress = true; } last_flags_write = inst; } if (v3d_qpu_writes_flags(&inst->qpu) || has_nonremovable_reads(c, inst) || (is_ldunifa && !is_first_ldunifa && !is_last_ldunifa)) { /* If we can't remove the instruction, but we * don't need its destination value, just * remove the destination. The register * allocator would trivially color it and it * wouldn't cause any register pressure, but * it's nicer to read the VIR code without * unused destination regs. */ if (inst->dst.file == QFILE_TEMP && can_write_to_null(c, inst)) { if (debug) { fprintf(stderr, "Removing dst from: "); vir_dump_inst(c, inst); fprintf(stderr, "\n"); } c->defs[inst->dst.index] = NULL; inst->dst.file = QFILE_NULL; progress = true; } continue; } /* If we are removing the first ldunifa in a sequence * we need to update the unifa address. */ if (is_first_ldunifa) { assert(unifa); if (!increment_unifa_address(c, block, unifa)) continue; } assert(inst != last_flags_write); dce(c, inst); progress = true; continue; } } free(used); return progress; }