src/gallium/drivers/r600/sb/sb_if_conversion.cpp

   1 /*
   2  * Copyright 2013 Vadim Girlin <vadimgirlin@gmail.com>
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * on the rights to use, copy, modify, merge, publish, distribute, sub
   8  * license, and/or sell copies of the Software, and to permit persons to whom
   9  * the Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
  18  * THE AUTHOR(S) AND/OR THEIR SUPPLIERS BE LIABLE FOR ANY CLAIM,
  19  * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
  20  * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
  21  * USE OR OTHER DEALINGS IN THE SOFTWARE.
  22  *
  23  * Authors:
  24  *      Vadim Girlin
  25  */
  26
  27 #define IFC_DEBUG 0
  28
  29 #if IFC_DEBUG
  30 #define IFC_DUMP(q) do { q } while (0)
  31 #else
  32 #define IFC_DUMP(q)
  33 #endif
  34
  35 #include "sb_shader.h"
  36 #include "sb_pass.h"
  37
  38 namespace r600_sb {
  39
  40 int if_conversion::run() {
  41
  42         regions_vec &rv = sh.get_regions();
  43
  44         unsigned converted = 0;
  45
  46         for (regions_vec::reverse_iterator N, I = rv.rbegin(), E = rv.rend();
  47                         I != E; I = N) {
  48                 N = I; ++N;
  49
  50                 region_node *r = *I;
  51                 if (run_on(r)) {
  52                         rv.erase(I.base() - 1);
  53                         ++converted;
  54                 }
  55         }
  56         return 0;
  57 }
  58
  59 void if_conversion::convert_kill_instructions(region_node *r,
  60                                               value *em, bool branch,
  61                                               container_node *c) {
  62         value *cnd = NULL;
  63
  64         for (node_iterator I = c->begin(), E = c->end(), N; I != E; I = N) {
  65                 N = I + 1;
  66
  67                 if (!I->is_alu_inst())
  68                         continue;
  69
  70                 alu_node *a = static_cast<alu_node*>(*I);
  71                 unsigned flags = a->bc.op_ptr->flags;
  72
  73                 if (!(flags & AF_KILL))
  74                         continue;
  75
  76                 // ignore predicated or non-const kill instructions
  77                 if (a->pred || !a->src[0]->is_const() || !a->src[1]->is_const())
  78                         continue;
  79
  80                 literal l0 = a->src[0]->literal_value;
  81                 literal l1 = a->src[1]->literal_value;
  82
  83                 expr_handler::apply_alu_src_mod(a->bc, 0, l0);
  84                 expr_handler::apply_alu_src_mod(a->bc, 1, l1);
  85
  86                 if (expr_handler::evaluate_condition(flags, l0, l1)) {
  87                         // kill with constant 'true' condition, we'll convert it to the
  88                         // conditional kill outside of the if-then-else block
  89
  90                         a->remove();
  91
  92                         if (!cnd) {
  93                                 cnd = get_select_value_for_em(sh, em);
  94                         } else {
  95                                 // more than one kill with the same condition, just remove it
  96                                 continue;
  97                         }
  98
  99                         r->insert_before(a);
 100                         a->bc.set_op(branch ? ALU_OP2_KILLE_INT : ALU_OP2_KILLNE_INT);
 101
 102                         a->src[0] = cnd;
 103                         a->src[1] = sh.get_const_value(0);
 104                         // clear modifiers
 105                         memset(&a->bc.src[0], 0, sizeof(bc_alu_src));
 106                         memset(&a->bc.src[1], 0, sizeof(bc_alu_src));
 107                 } else {
 108                         // kill with constant 'false' condition, this shouldn't happen
 109                         // but remove it anyway
 110                         a->remove();
 111                 }
 112         }
 113 }
 114
 115 bool if_conversion::check_and_convert(region_node *r) {
 116
 117         depart_node *nd1 = static_cast<depart_node*>(r->first);
 118         if (!nd1->is_depart() || nd1->target != r)
 119                 return false;
 120         if_node *nif = static_cast<if_node*>(nd1->first);
 121         if (!nif->is_if())
 122                 return false;
 123         depart_node *nd2 = static_cast<depart_node*>(nif->first);
 124         if (!nd2->is_depart() || nd2->target != r)
 125                 return false;
 126
 127         value* &em = nif->cond;
 128
 129         node_stats s;
 130
 131         r->collect_stats(s);
 132
 133         IFC_DUMP(
 134                 sblog << "ifcvt: region " << r->region_id << " :\n";
 135                 s.dump();
 136         );
 137
 138         if (s.region_count || s.fetch_count || s.alu_kill_count ||
 139                        s.if_count != 1 || s.repeat_count || s.uses_ar)
 140                 return false;
 141
 142         unsigned real_alu_count = s.alu_count - s.alu_copy_mov_count;
 143
 144         // if_conversion allows to eliminate JUMP-ALU_POP_AFTER or
 145         // JUMP-ALU-ELSE-ALU_POP_AFTER, for now let's assume that 3 CF instructions
 146         // are eliminated. According to the docs, cost of CF instruction is
 147         // equal to ~40 ALU VLIW instructions (instruction groups),
 148         // so we have eliminated cost equal to ~120 groups in total.
 149         // Let's also assume that we have avg 3 ALU instructions per group,
 150         // This means that potential eliminated cost is about 360 single alu inst.
 151         // On the other hand, we are speculatively executing conditional code now,
 152         // so we are increasing the cost in some cases. In the worst case, we'll
 153         // have to execute real_alu_count additional alu instructions instead of
 154         // jumping over them. Let's assume for now that average added cost is
 155         //
 156         // (0.9 * real_alu_count)
 157         //
 158         // So we should perform if_conversion if
 159         //
 160         // (0.9 * real_alu_count) < 360, or
 161         //
 162         // real_alu_count < 400
 163         //
 164         // So if real_alu_count is more than 400, than we think that if_conversion
 165         // doesn't make sense.
 166
 167         // FIXME: We can use more precise heuristic, taking into account sizes of
 168         // the branches and their probability instead of total size.
 169         // Another way to improve this is to consider the number of the groups
 170         // instead of the number of instructions (taking into account actual VLIW
 171         // packing).
 172         // (Currently we don't know anything about packing at this stage, but
 173         // probably we can make some more precise estimations anyway)
 174
 175         if (real_alu_count > 400)
 176                 return false;
 177
 178         IFC_DUMP( sblog << "if_cvt: processing...\n"; );
 179
 180         value *select = get_select_value_for_em(sh, em);
 181
 182         if (!select)
 183                 return false;
 184
 185         for (node_iterator I = r->phi->begin(), E = r->phi->end(); I != E; ++I) {
 186                 node *n = *I;
 187
 188                 alu_node *ns = convert_phi(select, n);
 189
 190                 if (ns)
 191                         r->insert_after(ns);
 192         }
 193
 194         nd2->expand();
 195         nif->expand();
 196         nd1->expand();
 197         r->expand();
 198
 199         return true;
 200 }
 201
 202 bool if_conversion::run_on(region_node* r) {
 203
 204         if (r->dep_count() != 2 || r->rep_count() != 1)
 205                 return false;
 206
 207         depart_node *nd1 = static_cast<depart_node*>(r->first);
 208         if (!nd1->is_depart())
 209                 return false;
 210         if_node *nif = static_cast<if_node*>(nd1->first);
 211         if (!nif->is_if())
 212                 return false;
 213         depart_node *nd2 = static_cast<depart_node*>(nif->first);
 214         if (!nd2->is_depart())
 215                 return false;
 216
 217         value* &em = nif->cond;
 218
 219         convert_kill_instructions(r, em, true, nd2);
 220         convert_kill_instructions(r, em, false, nd1);
 221
 222         if (check_and_convert(r))
 223                 return true;
 224
 225         if (nd2->empty() && nif->next) {
 226                 // empty true branch, non-empty false branch
 227                 // we'll invert it to get rid of 'else'
 228
 229                 assert(em && em->def);
 230
 231                 alu_node *predset = static_cast<alu_node*>(em->def);
 232
 233                 // create clone of PREDSET instruction with inverted condition.
 234                 // PREDSET has 3 dst operands in our IR (value written to gpr,
 235                 // predicate value and exec mask value), we'll split it such that
 236                 // new PREDSET will define exec mask value only, and two others will
 237                 // be defined in the old PREDSET (if they are not used then DCE will
 238                 // simply remove old PREDSET).
 239
 240                 alu_node *newpredset = sh.clone(predset);
 241                 predset->insert_after(newpredset);
 242
 243                 predset->dst[2] = NULL;
 244
 245                 newpredset->dst[0] = NULL;
 246                 newpredset->dst[1] = NULL;
 247
 248                 em->def = newpredset;
 249
 250                 unsigned cc = newpredset->bc.op_ptr->flags & AF_CC_MASK;
 251                 unsigned cmptype = newpredset->bc.op_ptr->flags & AF_CMP_TYPE_MASK;
 252                 bool swapargs = false;
 253
 254                 cc = invert_setcc_condition(cc, swapargs);
 255
 256                 if (swapargs) {
 257                         std::swap(newpredset->src[0], newpredset->src[1]);
 258                         std::swap(newpredset->bc.src[0], newpredset->bc.src[1]);
 259                 }
 260
 261                 unsigned newopcode = get_predsetcc_op(cc, cmptype);
 262                 newpredset->bc.set_op(newopcode);
 263
 264                 // move the code from the 'false' branch ('else') to the 'true' branch
 265                 nd2->move(nif->next, NULL);
 266
 267                 // swap phi operands
 268                 for (node_iterator I = r->phi->begin(), E = r->phi->end(); I != E;
 269                                 ++I) {
 270                         node *p = *I;
 271                         assert(p->src.size() == 2);
 272                         std::swap(p->src[0], p->src[1]);
 273                 }
 274         }
 275
 276         return false;
 277 }
 278
 279 alu_node* if_conversion::convert_phi(value* select, node* phi) {
 280         assert(phi->dst.size() == 1 || phi->src.size() == 2);
 281
 282         value *d = phi->dst[0];
 283         value *v1 = phi->src[0];
 284         value *v2 = phi->src[1];
 285
 286         assert(d);
 287
 288         if (!d->is_any_gpr())
 289                 return NULL;
 290
 291         if (v1->is_undef()) {
 292                 if (v2->is_undef()) {
 293                         return NULL;
 294                 } else {
 295                         return sh.create_mov(d, v2);
 296                 }
 297         } else if (v2->is_undef())
 298                 return sh.create_mov(d, v1);
 299
 300         alu_node* n = sh.create_alu();
 301
 302         n->bc.set_op(ALU_OP3_CNDE_INT);
 303         n->dst.push_back(d);
 304         n->src.push_back(select);
 305         n->src.push_back(v1);
 306         n->src.push_back(v2);
 307
 308         return n;
 309 }
 310
 311 } // namespace r600_sb