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
   8  * "Software"), to deal in the Software without restriction, including
   9  * without limitation the rights to use, copy, modify, merge, publish,
  10  * distribute, sub license, and/or sell copies of the Software, and to
  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
  20  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
  21  * IN NO EVENT SHALL VMWARE AND/OR ITS SUPPLIERS BE LIABLE FOR
  22  * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  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_KIL, 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
 269 void
 270 lp_build_loop_end(struct lp_build_loop_state *state,
 271                   LLVMValueRef end,
 272                   LLVMValueRef step)
 273 {
 274    lp_build_loop_end_cond(state, end, step, LLVMIntNE);
 275 }
 276
 277 /**
 278  * Creates a c-style for loop,
 279  * contrasts lp_build_loop as this checks condition on entry
 280  * e.g. for(i = start; i cmp_op end; i += step)
 281  * \param state      the for loop state, initialized here
 282  * \param gallivm    the gallivm state
 283  * \param start      starting value of iterator
 284  * \param cmp_op     comparison operator used for comparing current value with end value
 285  * \param end        value used to compare against iterator
 286  * \param step       value added to iterator at end of each loop
 287  */
 288 void
 289 lp_build_for_loop_begin(struct lp_build_for_loop_state *state,
 290                         struct gallivm_state *gallivm,
 291                         LLVMValueRef start,
 292                         LLVMIntPredicate cmp_op,
 293                         LLVMValueRef end,
 294                         LLVMValueRef step)
 295 {
 296    LLVMBuilderRef builder = gallivm->builder;
 297
 298    assert(LLVMTypeOf(start) == LLVMTypeOf(end));
 299    assert(LLVMTypeOf(start) == LLVMTypeOf(step));
 300
 301    state->begin = lp_build_insert_new_block(gallivm, "loop_begin");
 302    state->step  = step;
 303    state->counter_var = lp_build_alloca(gallivm, LLVMTypeOf(start), "loop_counter");
 304    state->gallivm = gallivm;
 305    state->cond = cmp_op;
 306    state->end = end;
 307
 308    LLVMBuildStore(builder, start, state->counter_var);
 309    LLVMBuildBr(builder, state->begin);
 310
 311    LLVMPositionBuilderAtEnd(builder, state->begin);
 312    state->counter = LLVMBuildLoad(builder, state->counter_var, "");
 313
 314    state->body = lp_build_insert_new_block(gallivm, "loop_body");
 315    LLVMPositionBuilderAtEnd(builder, state->body);
 316 }
 317
 318 /**
 319  * End the for loop.
 320  */
 321 void
 322 lp_build_for_loop_end(struct lp_build_for_loop_state *state)
 323 {
 324    LLVMValueRef next, cond;
 325    LLVMBuilderRef builder = state->gallivm->builder;
 326
 327    next = LLVMBuildAdd(builder, state->counter, state->step, "");
 328    LLVMBuildStore(builder, next, state->counter_var);
 329    LLVMBuildBr(builder, state->begin);
 330
 331    state->exit = lp_build_insert_new_block(state->gallivm, "loop_exit");
 332
 333    /*
 334     * We build the comparison for the begin block here,
 335     * if we build it earlier the output llvm ir is not human readable
 336     * as the code produced is not in the standard begin -> body -> end order.
 337     */
 338    LLVMPositionBuilderAtEnd(builder, state->begin);
 339    cond = LLVMBuildICmp(builder, state->cond, state->counter, state->end, "");
 340    LLVMBuildCondBr(builder, cond, state->body, state->exit);
 341
 342    LLVMPositionBuilderAtEnd(builder, state->exit);
 343 }
 344
 345
 346 /*
 347   Example of if/then/else building:
 348
 349      int x;
 350      if (cond) {
 351         x = 1 + 2;
 352      }
 353      else {
 354         x = 2 + 3;
 355      }
 356
 357   Is built with:
 358
 359      // x needs an alloca variable
 360      x = lp_build_alloca(builder, type, "x");
 361
 362
 363      lp_build_if(ctx, builder, cond);
 364         LLVMBuildStore(LLVMBuildAdd(1, 2), x);
 365      lp_build_else(ctx);
 366         LLVMBuildStore(LLVMBuildAdd(2, 3). x);
 367      lp_build_endif(ctx);
 368
 369  */
 370
 371
 372
 373 /**
 374  * Begin an if/else/endif construct.
 375  */
 376 void
 377 lp_build_if(struct lp_build_if_state *ifthen,
 378             struct gallivm_state *gallivm,
 379             LLVMValueRef condition)
 380 {
 381    LLVMBasicBlockRef block = LLVMGetInsertBlock(gallivm->builder);
 382
 383    memset(ifthen, 0, sizeof *ifthen);
 384    ifthen->gallivm = gallivm;
 385    ifthen->condition = condition;
 386    ifthen->entry_block = block;
 387
 388    /* create endif/merge basic block for the phi functions */
 389    ifthen->merge_block = lp_build_insert_new_block(gallivm, "endif-block");
 390
 391    /* create/insert true_block before merge_block */
 392    ifthen->true_block =
 393       LLVMInsertBasicBlockInContext(gallivm->context,
 394                                     ifthen->merge_block,
 395                                     "if-true-block");
 396
 397    /* successive code goes into the true block */
 398    LLVMPositionBuilderAtEnd(gallivm->builder, ifthen->true_block);
 399 }
 400
 401
 402 /**
 403  * Begin else-part of a conditional
 404  */
 405 void
 406 lp_build_else(struct lp_build_if_state *ifthen)
 407 {
 408    LLVMBuilderRef builder = ifthen->gallivm->builder;
 409
 410    /* Append an unconditional Br(anch) instruction on the true_block */
 411    LLVMBuildBr(builder, ifthen->merge_block);
 412
 413    /* create/insert false_block before the merge block */
 414    ifthen->false_block =
 415       LLVMInsertBasicBlockInContext(ifthen->gallivm->context,
 416                                     ifthen->merge_block,
 417                                     "if-false-block");
 418
 419    /* successive code goes into the else block */
 420    LLVMPositionBuilderAtEnd(builder, ifthen->false_block);
 421 }
 422
 423
 424 /**
 425  * End a conditional.
 426  */
 427 void
 428 lp_build_endif(struct lp_build_if_state *ifthen)
 429 {
 430    LLVMBuilderRef builder = ifthen->gallivm->builder;
 431
 432    /* Insert branch to the merge block from current block */
 433    LLVMBuildBr(builder, ifthen->merge_block);
 434
 435    /*
 436     * Now patch in the various branch instructions.
 437     */
 438
 439    /* Insert the conditional branch instruction at the end of entry_block */
 440    LLVMPositionBuilderAtEnd(builder, ifthen->entry_block);
 441    if (ifthen->false_block) {
 442       /* we have an else clause */
 443       LLVMBuildCondBr(builder, ifthen->condition,
 444                       ifthen->true_block, ifthen->false_block);
 445    }
 446    else {
 447       /* no else clause */
 448       LLVMBuildCondBr(builder, ifthen->condition,
 449                       ifthen->true_block, ifthen->merge_block);
 450    }
 451
 452    /* Resume building code at end of the ifthen->merge_block */
 453    LLVMPositionBuilderAtEnd(builder, ifthen->merge_block);
 454 }
 455
 456
 457 /**
 458  * Allocate a scalar (or vector) variable.
 459  *
 460  * Although not strictly part of control flow, control flow has deep impact in
 461  * how variables should be allocated.
 462  *
 463  * The mem2reg optimization pass is the recommended way to dealing with mutable
 464  * variables, and SSA. It looks for allocas and if it can handle them, it
 465  * promotes them, but only looks for alloca instructions in the entry block of
 466  * the function. Being in the entry block guarantees that the alloca is only
 467  * executed once, which makes analysis simpler.
 468  *
 469  * See also:
 470  * - http://www.llvm.org/docs/tutorial/OCamlLangImpl7.html#memory
 471  */
 472 LLVMValueRef
 473 lp_build_alloca(struct gallivm_state *gallivm,
 474                 LLVMTypeRef type,
 475                 const char *name)
 476 {
 477    LLVMBuilderRef builder = gallivm->builder;
 478    LLVMBasicBlockRef current_block = LLVMGetInsertBlock(builder);
 479    LLVMValueRef function = LLVMGetBasicBlockParent(current_block);
 480    LLVMBasicBlockRef first_block = LLVMGetEntryBasicBlock(function);
 481    LLVMValueRef first_instr = LLVMGetFirstInstruction(first_block);
 482    LLVMBuilderRef first_builder = LLVMCreateBuilderInContext(gallivm->context);
 483    LLVMValueRef res;
 484
 485    if (first_instr) {
 486       LLVMPositionBuilderBefore(first_builder, first_instr);
 487    } else {
 488       LLVMPositionBuilderAtEnd(first_builder, first_block);
 489    }
 490
 491    res = LLVMBuildAlloca(first_builder, type, name);
 492    LLVMBuildStore(builder, LLVMConstNull(type), res);
 493
 494    LLVMDisposeBuilder(first_builder);
 495
 496    return res;
 497 }
 498
 499
 500 /**
 501  * Allocate an array of scalars/vectors.
 502  *
 503  * mem2reg pass is not capable of promoting structs or arrays to registers, but
 504  * we still put it in the first block anyway as failure to put allocas in the
 505  * first block may prevent the X86 backend from successfully align the stack as
 506  * required.
 507  *
 508  * Also the scalarrepl pass is supposedly more powerful and can promote
 509  * arrays in many cases.
 510  *
 511  * See also:
 512  * - http://www.llvm.org/docs/tutorial/OCamlLangImpl7.html#memory
 513  */
 514 LLVMValueRef
 515 lp_build_array_alloca(struct gallivm_state *gallivm,
 516                       LLVMTypeRef type,
 517                       LLVMValueRef count,
 518                       const char *name)
 519 {
 520    LLVMBuilderRef builder = gallivm->builder;
 521    LLVMBasicBlockRef current_block = LLVMGetInsertBlock(builder);
 522    LLVMValueRef function = LLVMGetBasicBlockParent(current_block);
 523    LLVMBasicBlockRef first_block = LLVMGetEntryBasicBlock(function);
 524    LLVMValueRef first_instr = LLVMGetFirstInstruction(first_block);
 525    LLVMBuilderRef first_builder = LLVMCreateBuilderInContext(gallivm->context);
 526    LLVMValueRef res;
 527
 528    if (first_instr) {
 529       LLVMPositionBuilderBefore(first_builder, first_instr);
 530    } else {
 531       LLVMPositionBuilderAtEnd(first_builder, first_block);
 532    }
 533
 534    res = LLVMBuildArrayAlloca(first_builder, type, count, name);
 535
 536    LLVMDisposeBuilder(first_builder);
 537
 538    return res;
 539 }