src/gallium/auxiliary/gallivm/lp_bld_flow.c

   1 /**************************************************************************
   2  *
   3  * Copyright 2009 VMware, Inc.
   4  * All Rights Reserved.
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a
   7  * copy of this software and associated documentation files (the
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  11  * permit persons to whom the Software is furnished to do so, subject to
  12  * the following conditions:
  13  *
  14  * The above copyright notice and this permission notice (including the
  15  * next paragraph) shall be included in all copies or substantial portions
  16  * of the Software.
  17  *
  18  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  19  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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  21  * IN NO EVENT SHALL VMWARE AND/OR ITS SUPPLIERS BE LIABLE FOR
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  23  * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  24  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  25  *
  26  **************************************************************************/
  27
  28 /**
  29  * LLVM control flow build helpers.
  30  *
  31  * @author Jose Fonseca <jfonseca@vmware.com>
  32  */
  33
  34 #include "util/u_debug.h"
  35 #include "util/u_memory.h"
  36
  37 #include "lp_bld_init.h"
  38 #include "lp_bld_type.h"
  39 #include "lp_bld_flow.h"
  40
  41
  42 /**
  43  * Insert a new block, right where builder is pointing to.
  44  *
  45  * This is useful important not only for aesthetic reasons, but also for
  46  * performance reasons, as frequently run blocks should be laid out next to
  47  * each other and fall-throughs maximized.
  48  *
  49  * See also llvm/lib/Transforms/Scalar/BasicBlockPlacement.cpp.
  50  *
  51  * Note: this function has no dependencies on the flow code and could
  52  * be used elsewhere.
  53  */
  54 LLVMBasicBlockRef
  55 lp_build_insert_new_block(struct gallivm_state *gallivm, const char *name)
  56 {
  57    LLVMBasicBlockRef current_block;
  58    LLVMBasicBlockRef next_block;
  59    LLVMBasicBlockRef new_block;
  60
  61    /* get current basic block */
  62    current_block = LLVMGetInsertBlock(gallivm->builder);
  63
  64    /* check if there's another block after this one */
  65    next_block = LLVMGetNextBasicBlock(current_block);
  66    if (next_block) {
  67       /* insert the new block before the next block */
  68       new_block = LLVMInsertBasicBlockInContext(gallivm->context, next_block, name);
  69    }
  70    else {
  71       /* append new block after current block */
  72       LLVMValueRef function = LLVMGetBasicBlockParent(current_block);
  73       new_block = LLVMAppendBasicBlockInContext(gallivm->context, function, name);
  74    }
  75
  76    return new_block;
  77 }
  78
  79
  80 /**
  81  * Begin a "skip" block.  Inside this block we can test a condition and
  82  * skip to the end of the block if the condition is false.
  83  */
  84 void
  85 lp_build_flow_skip_begin(struct lp_build_skip_context *skip,
  86                          struct gallivm_state *gallivm)
  87 {
  88    skip->gallivm = gallivm;
  89    /* create new basic block */
  90    skip->block = lp_build_insert_new_block(gallivm, "skip");
  91 }
  92
  93
  94 /**
  95  * Insert code to test a condition and branch to the end of the current
  96  * skip block if the condition is true.
  97  */
  98 void
  99 lp_build_flow_skip_cond_break(struct lp_build_skip_context *skip,
 100                               LLVMValueRef cond)
 101 {
 102    LLVMBasicBlockRef new_block;
 103
 104    new_block = lp_build_insert_new_block(skip->gallivm, "");
 105
 106    /* if cond is true, goto skip->block, else goto new_block */
 107    LLVMBuildCondBr(skip->gallivm->builder, cond, skip->block, new_block);
 108
 109    LLVMPositionBuilderAtEnd(skip->gallivm->builder, new_block);
 110 }
 111
 112
 113 void
 114 lp_build_flow_skip_end(struct lp_build_skip_context *skip)
 115 {
 116    /* goto block */
 117    LLVMBuildBr(skip->gallivm->builder, skip->block);
 118    LLVMPositionBuilderAtEnd(skip->gallivm->builder, skip->block);
 119 }
 120
 121
 122 /**
 123  * Check if the mask predicate is zero.  If so, jump to the end of the block.
 124  */
 125 void
 126 lp_build_mask_check(struct lp_build_mask_context *mask)
 127 {
 128    LLVMBuilderRef builder = mask->skip.gallivm->builder;
 129    LLVMValueRef value;
 130    LLVMValueRef cond;
 131
 132    value = lp_build_mask_value(mask);
 133
 134    /*
 135     * XXX this doesn't quite generate the most efficient code possible, if
 136     * the masks are vectors which have all bits set to the same value
 137     * in each element.
 138     * movmskps/pmovmskb would be more efficient to get the required value
 139     * into ordinary reg (certainly with 8 floats).
 140     * Not sure if llvm could figure that out on its own.
 141     */
 142
 143    /* cond = (mask == 0) */
 144    cond = LLVMBuildICmp(builder,
 145                         LLVMIntEQ,
 146                         LLVMBuildBitCast(builder, value, mask->reg_type, ""),
 147                         LLVMConstNull(mask->reg_type),
 148                         "");
 149
 150    /* if cond, goto end of block */
 151    lp_build_flow_skip_cond_break(&mask->skip, cond);
 152 }
 153
 154
 155 /**
 156  * Begin a section of code which is predicated on a mask.
 157  * \param mask  the mask context, initialized here
 158  * \param flow  the flow context
 159  * \param type  the type of the mask
 160  * \param value  storage for the mask
 161  */
 162 void
 163 lp_build_mask_begin(struct lp_build_mask_context *mask,
 164                     struct gallivm_state *gallivm,
 165                     struct lp_type type,
 166                     LLVMValueRef value)
 167 {
 168    memset(mask, 0, sizeof *mask);
 169
 170    mask->reg_type = LLVMIntTypeInContext(gallivm->context, type.width * type.length);
 171    mask->var = lp_build_alloca(gallivm,
 172                                lp_build_int_vec_type(gallivm, type),
 173                                "execution_mask");
 174
 175    LLVMBuildStore(gallivm->builder, value, mask->var);
 176
 177    lp_build_flow_skip_begin(&mask->skip, gallivm);
 178 }
 179
 180
 181 LLVMValueRef
 182 lp_build_mask_value(struct lp_build_mask_context *mask)
 183 {
 184    return LLVMBuildLoad(mask->skip.gallivm->builder, mask->var, "");
 185 }
 186
 187
 188 /**
 189  * Update boolean mask with given value (bitwise AND).
 190  * Typically used to update the quad's pixel alive/killed mask
 191  * after depth testing, alpha testing, TGSI_OPCODE_KILL_IF, etc.
 192  */
 193 void
 194 lp_build_mask_update(struct lp_build_mask_context *mask,
 195                      LLVMValueRef value)
 196 {
 197    value = LLVMBuildAnd(mask->skip.gallivm->builder,
 198                         lp_build_mask_value(mask),
 199                         value, "");
 200    LLVMBuildStore(mask->skip.gallivm->builder, value, mask->var);
 201 }
 202
 203
 204 /**
 205  * End section of code which is predicated on a mask.
 206  */
 207 LLVMValueRef
 208 lp_build_mask_end(struct lp_build_mask_context *mask)
 209 {
 210    lp_build_flow_skip_end(&mask->skip);
 211    return lp_build_mask_value(mask);
 212 }
 213
 214
 215
 216 void
 217 lp_build_loop_begin(struct lp_build_loop_state *state,
 218                     struct gallivm_state *gallivm,
 219                     LLVMValueRef start)
 220
 221 {
 222    LLVMBuilderRef builder = gallivm->builder;
 223
 224    state->block = lp_build_insert_new_block(gallivm, "loop_begin");
 225
 226    state->counter_var = lp_build_alloca(gallivm, LLVMTypeOf(start), "loop_counter");
 227    state->gallivm = gallivm;
 228
 229    LLVMBuildStore(builder, start, state->counter_var);
 230
 231    LLVMBuildBr(builder, state->block);
 232
 233    LLVMPositionBuilderAtEnd(builder, state->block);
 234
 235    state->counter = LLVMBuildLoad(builder, state->counter_var, "");
 236 }
 237
 238
 239 void
 240 lp_build_loop_end_cond(struct lp_build_loop_state *state,
 241                        LLVMValueRef end,
 242                        LLVMValueRef step,
 243                        LLVMIntPredicate llvm_cond)
 244 {
 245    LLVMBuilderRef builder = state->gallivm->builder;
 246    LLVMValueRef next;
 247    LLVMValueRef cond;
 248    LLVMBasicBlockRef after_block;
 249
 250    if (!step)
 251       step = LLVMConstInt(LLVMTypeOf(end), 1, 0);
 252
 253    next = LLVMBuildAdd(builder, state->counter, step, "");
 254
 255    LLVMBuildStore(builder, next, state->counter_var);
 256
 257    cond = LLVMBuildICmp(builder, llvm_cond, next, end, "");
 258
 259    after_block = lp_build_insert_new_block(state->gallivm, "loop_end");
 260
 261    LLVMBuildCondBr(builder, cond, after_block, state->block);
 262
 263    LLVMPositionBuilderAtEnd(builder, after_block);
 264
 265    state->counter = LLVMBuildLoad(builder, state->counter_var, "");
 266 }
 267
 268 void
 269 lp_build_loop_force_set_counter(struct lp_build_loop_state *state,
 270                           LLVMValueRef end)
 271 {
 272    LLVMBuilderRef builder = state->gallivm->builder;
 273    LLVMBuildStore(builder, end, state->counter_var);
 274 }
 275
 276 void
 277 lp_build_loop_force_reload_counter(struct lp_build_loop_state *state)
 278 {
 279    LLVMBuilderRef builder = state->gallivm->builder;
 280    state->counter = LLVMBuildLoad(builder, state->counter_var, "");
 281 }
 282
 283 void
 284 lp_build_loop_end(struct lp_build_loop_state *state,
 285                   LLVMValueRef end,
 286                   LLVMValueRef step)
 287 {
 288    lp_build_loop_end_cond(state, end, step, LLVMIntNE);
 289 }
 290
 291 /**
 292  * Creates a c-style for loop,
 293  * contrasts lp_build_loop as this checks condition on entry
 294  * e.g. for(i = start; i cmp_op end; i += step)
 295  * \param state      the for loop state, initialized here
 296  * \param gallivm    the gallivm state
 297  * \param start      starting value of iterator
 298  * \param cmp_op     comparison operator used for comparing current value with end value
 299  * \param end        value used to compare against iterator
 300  * \param step       value added to iterator at end of each loop
 301  */
 302 void
 303 lp_build_for_loop_begin(struct lp_build_for_loop_state *state,
 304                         struct gallivm_state *gallivm,
 305                         LLVMValueRef start,
 306                         LLVMIntPredicate cmp_op,
 307                         LLVMValueRef end,
 308                         LLVMValueRef step)
 309 {
 310    LLVMBuilderRef builder = gallivm->builder;
 311
 312    assert(LLVMTypeOf(start) == LLVMTypeOf(end));
 313    assert(LLVMTypeOf(start) == LLVMTypeOf(step));
 314
 315    state->begin = lp_build_insert_new_block(gallivm, "loop_begin");
 316    state->step  = step;
 317    state->counter_var = lp_build_alloca(gallivm, LLVMTypeOf(start), "loop_counter");
 318    state->gallivm = gallivm;
 319    state->cond = cmp_op;
 320    state->end = end;
 321
 322    LLVMBuildStore(builder, start, state->counter_var);
 323    LLVMBuildBr(builder, state->begin);
 324
 325    LLVMPositionBuilderAtEnd(builder, state->begin);
 326    state->counter = LLVMBuildLoad(builder, state->counter_var, "");
 327
 328    state->body = lp_build_insert_new_block(gallivm, "loop_body");
 329    LLVMPositionBuilderAtEnd(builder, state->body);
 330 }
 331
 332 /**
 333  * End the for loop.
 334  */
 335 void
 336 lp_build_for_loop_end(struct lp_build_for_loop_state *state)
 337 {
 338    LLVMValueRef next, cond;
 339    LLVMBuilderRef builder = state->gallivm->builder;
 340
 341    next = LLVMBuildAdd(builder, state->counter, state->step, "");
 342    LLVMBuildStore(builder, next, state->counter_var);
 343    LLVMBuildBr(builder, state->begin);
 344
 345    state->exit = lp_build_insert_new_block(state->gallivm, "loop_exit");
 346
 347    /*
 348     * We build the comparison for the begin block here,
 349     * if we build it earlier the output llvm ir is not human readable
 350     * as the code produced is not in the standard begin -> body -> end order.
 351     */
 352    LLVMPositionBuilderAtEnd(builder, state->begin);
 353    cond = LLVMBuildICmp(builder, state->cond, state->counter, state->end, "");
 354    LLVMBuildCondBr(builder, cond, state->body, state->exit);
 355
 356    LLVMPositionBuilderAtEnd(builder, state->exit);
 357 }
 358
 359
 360 /*
 361   Example of if/then/else building:
 362
 363      int x;
 364      if (cond) {
 365         x = 1 + 2;
 366      }
 367      else {
 368         x = 2 + 3;
 369      }
 370
 371   Is built with:
 372
 373      // x needs an alloca variable
 374      x = lp_build_alloca(builder, type, "x");
 375
 376
 377      lp_build_if(ctx, builder, cond);
 378         LLVMBuildStore(LLVMBuildAdd(1, 2), x);
 379      lp_build_else(ctx);
 380         LLVMBuildStore(LLVMBuildAdd(2, 3). x);
 381      lp_build_endif(ctx);
 382
 383  */
 384
 385
 386
 387 /**
 388  * Begin an if/else/endif construct.
 389  */
 390 void
 391 lp_build_if(struct lp_build_if_state *ifthen,
 392             struct gallivm_state *gallivm,
 393             LLVMValueRef condition)
 394 {
 395    LLVMBasicBlockRef block = LLVMGetInsertBlock(gallivm->builder);
 396
 397    memset(ifthen, 0, sizeof *ifthen);
 398    ifthen->gallivm = gallivm;
 399    ifthen->condition = condition;
 400    ifthen->entry_block = block;
 401
 402    /* create endif/merge basic block for the phi functions */
 403    ifthen->merge_block = lp_build_insert_new_block(gallivm, "endif-block");
 404
 405    /* create/insert true_block before merge_block */
 406    ifthen->true_block =
 407       LLVMInsertBasicBlockInContext(gallivm->context,
 408                                     ifthen->merge_block,
 409                                     "if-true-block");
 410
 411    /* successive code goes into the true block */
 412    LLVMPositionBuilderAtEnd(gallivm->builder, ifthen->true_block);
 413 }
 414
 415
 416 /**
 417  * Begin else-part of a conditional
 418  */
 419 void
 420 lp_build_else(struct lp_build_if_state *ifthen)
 421 {
 422    LLVMBuilderRef builder = ifthen->gallivm->builder;
 423
 424    /* Append an unconditional Br(anch) instruction on the true_block */
 425    LLVMBuildBr(builder, ifthen->merge_block);
 426
 427    /* create/insert false_block before the merge block */
 428    ifthen->false_block =
 429       LLVMInsertBasicBlockInContext(ifthen->gallivm->context,
 430                                     ifthen->merge_block,
 431                                     "if-false-block");
 432
 433    /* successive code goes into the else block */
 434    LLVMPositionBuilderAtEnd(builder, ifthen->false_block);
 435 }
 436
 437
 438 /**
 439  * End a conditional.
 440  */
 441 void
 442 lp_build_endif(struct lp_build_if_state *ifthen)
 443 {
 444    LLVMBuilderRef builder = ifthen->gallivm->builder;
 445
 446    /* Insert branch to the merge block from current block */
 447    LLVMBuildBr(builder, ifthen->merge_block);
 448
 449    /*
 450     * Now patch in the various branch instructions.
 451     */
 452
 453    /* Insert the conditional branch instruction at the end of entry_block */
 454    LLVMPositionBuilderAtEnd(builder, ifthen->entry_block);
 455    if (ifthen->false_block) {
 456       /* we have an else clause */
 457       LLVMBuildCondBr(builder, ifthen->condition,
 458                       ifthen->true_block, ifthen->false_block);
 459    }
 460    else {
 461       /* no else clause */
 462       LLVMBuildCondBr(builder, ifthen->condition,
 463                       ifthen->true_block, ifthen->merge_block);
 464    }
 465
 466    /* Resume building code at end of the ifthen->merge_block */
 467    LLVMPositionBuilderAtEnd(builder, ifthen->merge_block);
 468 }
 469
 470
 471 static LLVMBuilderRef
 472 create_builder_at_entry(struct gallivm_state *gallivm)
 473 {
 474    LLVMBuilderRef builder = gallivm->builder;
 475    LLVMBasicBlockRef current_block = LLVMGetInsertBlock(builder);
 476    LLVMValueRef function = LLVMGetBasicBlockParent(current_block);
 477    LLVMBasicBlockRef first_block = LLVMGetEntryBasicBlock(function);
 478    LLVMValueRef first_instr = LLVMGetFirstInstruction(first_block);
 479    LLVMBuilderRef first_builder = LLVMCreateBuilderInContext(gallivm->context);
 480
 481    if (first_instr) {
 482       LLVMPositionBuilderBefore(first_builder, first_instr);
 483    } else {
 484       LLVMPositionBuilderAtEnd(first_builder, first_block);
 485    }
 486
 487    return first_builder;
 488 }
 489
 490
 491 /**
 492  * Allocate a scalar (or vector) variable.
 493  *
 494  * Although not strictly part of control flow, control flow has deep impact in
 495  * how variables should be allocated.
 496  *
 497  * The mem2reg optimization pass is the recommended way to dealing with mutable
 498  * variables, and SSA. It looks for allocas and if it can handle them, it
 499  * promotes them, but only looks for alloca instructions in the entry block of
 500  * the function. Being in the entry block guarantees that the alloca is only
 501  * executed once, which makes analysis simpler.
 502  *
 503  * See also:
 504  * - http://www.llvm.org/docs/tutorial/OCamlLangImpl7.html#memory
 505  */
 506 LLVMValueRef
 507 lp_build_alloca(struct gallivm_state *gallivm,
 508                 LLVMTypeRef type,
 509                 const char *name)
 510 {
 511    LLVMBuilderRef builder = gallivm->builder;
 512    LLVMBuilderRef first_builder = create_builder_at_entry(gallivm);
 513    LLVMValueRef res;
 514
 515    res = LLVMBuildAlloca(first_builder, type, name);
 516    LLVMBuildStore(builder, LLVMConstNull(type), res);
 517
 518    LLVMDisposeBuilder(first_builder);
 519
 520    return res;
 521 }
 522
 523
 524 /**
 525  * Like lp_build_alloca, but do not zero-initialize the variable.
 526  */
 527 LLVMValueRef
 528 lp_build_alloca_undef(struct gallivm_state *gallivm,
 529                       LLVMTypeRef type,
 530                       const char *name)
 531 {
 532    LLVMBuilderRef first_builder = create_builder_at_entry(gallivm);
 533    LLVMValueRef res;
 534
 535    res = LLVMBuildAlloca(first_builder, type, name);
 536
 537    LLVMDisposeBuilder(first_builder);
 538
 539    return res;
 540 }
 541
 542
 543 /**
 544  * Allocate an array of scalars/vectors.
 545  *
 546  * mem2reg pass is not capable of promoting structs or arrays to registers, but
 547  * we still put it in the first block anyway as failure to put allocas in the
 548  * first block may prevent the X86 backend from successfully align the stack as
 549  * required.
 550  *
 551  * Also the scalarrepl pass is supposedly more powerful and can promote
 552  * arrays in many cases.
 553  *
 554  * See also:
 555  * - http://www.llvm.org/docs/tutorial/OCamlLangImpl7.html#memory
 556  */
 557 LLVMValueRef
 558 lp_build_array_alloca(struct gallivm_state *gallivm,
 559                       LLVMTypeRef type,
 560                       LLVMValueRef count,
 561                       const char *name)
 562 {
 563    LLVMBuilderRef first_builder = create_builder_at_entry(gallivm);
 564    LLVMValueRef res;
 565
 566    res = LLVMBuildArrayAlloca(first_builder, type, count, name);
 567
 568    LLVMDisposeBuilder(first_builder);
 569
 570    return res;
 571 }