src/gallium/drivers/llvmpipe/lp_bld_pack.c

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  27
  28
  29 /**
  30  * @file
  31  * Helper functions for packing/unpacking.
  32  *
  33  * Pack/unpacking is necessary for conversion between types of different
  34  * bit width.
  35  *
  36  * They are also commonly used when an computation needs higher
  37  * precision for the intermediate values. For example, if one needs the
  38  * function:
  39  *
  40  *   c = compute(a, b);
  41  *
  42  * to use more precision for intermediate results then one should implement it
  43  * as:
  44  *
  45  *   LLVMValueRef
  46  *   compute(LLVMBuilderRef builder struct lp_type type, LLVMValueRef a, LLVMValueRef b)
  47  *   {
  48  *      struct lp_type wide_type = lp_wider_type(type);
  49  *      LLVMValueRef al, ah, bl, bh, cl, ch, c;
  50  *
  51  *      lp_build_unpack2(builder, type, wide_type, a, &al, &ah);
  52  *      lp_build_unpack2(builder, type, wide_type, b, &bl, &bh);
  53  *
  54  *      cl = compute_half(al, bl);
  55  *      ch = compute_half(ah, bh);
  56  *
  57  *      c = lp_build_pack2(bld->builder, wide_type, type, cl, ch);
  58  *
  59  *      return c;
  60  *   }
  61  *
  62  * where compute_half() would do the computation for half the elements with
  63  * twice the precision.
  64  *
  65  * @author Jose Fonseca <jfonseca@vmware.com>
  66  */
  67
  68
  69 #include "util/u_debug.h"
  70 #include "util/u_math.h"
  71 #include "util/u_cpu_detect.h"
  72
  73 #include "lp_bld_type.h"
  74 #include "lp_bld_const.h"
  75 #include "lp_bld_intr.h"
  76 #include "lp_bld_arit.h"
  77 #include "lp_bld_pack.h"
  78
  79
  80 /**
  81  * Build shuffle vectors that match PUNPCKLxx and PUNPCKHxx instructions.
  82  */
  83 static LLVMValueRef
  84 lp_build_const_unpack_shuffle(unsigned n, unsigned lo_hi)
  85 {
  86    LLVMValueRef elems[LP_MAX_VECTOR_LENGTH];
  87    unsigned i, j;
  88
  89    assert(n <= LP_MAX_VECTOR_LENGTH);
  90    assert(lo_hi < 2);
  91
  92    /* TODO: cache results in a static table */
  93
  94    for(i = 0, j = lo_hi*n/2; i < n; i += 2, ++j) {
  95       elems[i + 0] = LLVMConstInt(LLVMInt32Type(), 0 + j, 0);
  96       elems[i + 1] = LLVMConstInt(LLVMInt32Type(), n + j, 0);
  97    }
  98
  99    return LLVMConstVector(elems, n);
 100 }
 101
 102
 103 /**
 104  * Build shuffle vectors that match PACKxx instructions.
 105  */
 106 static LLVMValueRef
 107 lp_build_const_pack_shuffle(unsigned n)
 108 {
 109    LLVMValueRef elems[LP_MAX_VECTOR_LENGTH];
 110    unsigned i;
 111
 112    assert(n <= LP_MAX_VECTOR_LENGTH);
 113
 114    /* TODO: cache results in a static table */
 115
 116    for(i = 0; i < n; ++i)
 117       elems[i] = LLVMConstInt(LLVMInt32Type(), 2*i, 0);
 118
 119    return LLVMConstVector(elems, n);
 120 }
 121
 122
 123 /**
 124  * Interleave vector elements.
 125  *
 126  * Matches the PUNPCKLxx and PUNPCKHxx SSE instructions.
 127  */
 128 LLVMValueRef
 129 lp_build_interleave2(LLVMBuilderRef builder,
 130                      struct lp_type type,
 131                      LLVMValueRef a,
 132                      LLVMValueRef b,
 133                      unsigned lo_hi)
 134 {
 135    LLVMValueRef shuffle;
 136
 137    shuffle = lp_build_const_unpack_shuffle(type.length, lo_hi);
 138
 139    return LLVMBuildShuffleVector(builder, a, b, shuffle, "");
 140 }
 141
 142
 143 /**
 144  * Double the bit width.
 145  *
 146  * This will only change the number of bits the values are represented, not the
 147  * values themselves.
 148  */
 149 void
 150 lp_build_unpack2(LLVMBuilderRef builder,
 151                  struct lp_type src_type,
 152                  struct lp_type dst_type,
 153                  LLVMValueRef src,
 154                  LLVMValueRef *dst_lo,
 155                  LLVMValueRef *dst_hi)
 156 {
 157    LLVMValueRef msb;
 158    LLVMTypeRef dst_vec_type;
 159
 160    assert(!src_type.floating);
 161    assert(!dst_type.floating);
 162    assert(dst_type.width == src_type.width * 2);
 163    assert(dst_type.length * 2 == src_type.length);
 164
 165    if(dst_type.sign && src_type.sign) {
 166       /* Replicate the sign bit in the most significant bits */
 167       msb = LLVMBuildAShr(builder, src, lp_build_int_const_scalar(src_type, src_type.width - 1), "");
 168    }
 169    else
 170       /* Most significant bits always zero */
 171       msb = lp_build_zero(src_type);
 172
 173    /* Interleave bits */
 174    if(util_cpu_caps.little_endian) {
 175       *dst_lo = lp_build_interleave2(builder, src_type, src, msb, 0);
 176       *dst_hi = lp_build_interleave2(builder, src_type, src, msb, 1);
 177    }
 178    else {
 179       *dst_lo = lp_build_interleave2(builder, src_type, msb, src, 0);
 180       *dst_hi = lp_build_interleave2(builder, src_type, msb, src, 1);
 181    }
 182
 183    /* Cast the result into the new type (twice as wide) */
 184
 185    dst_vec_type = lp_build_vec_type(dst_type);
 186
 187    *dst_lo = LLVMBuildBitCast(builder, *dst_lo, dst_vec_type, "");
 188    *dst_hi = LLVMBuildBitCast(builder, *dst_hi, dst_vec_type, "");
 189 }
 190
 191
 192 /**
 193  * Expand the bit width.
 194  *
 195  * This will only change the number of bits the values are represented, not the
 196  * values themselves.
 197  */
 198 void
 199 lp_build_unpack(LLVMBuilderRef builder,
 200                 struct lp_type src_type,
 201                 struct lp_type dst_type,
 202                 LLVMValueRef src,
 203                 LLVMValueRef *dst, unsigned num_dsts)
 204 {
 205    unsigned num_tmps;
 206    unsigned i;
 207
 208    /* Register width must remain constant */
 209    assert(src_type.width * src_type.length == dst_type.width * dst_type.length);
 210
 211    /* We must not loose or gain channels. Only precision */
 212    assert(src_type.length == dst_type.length * num_dsts);
 213
 214    num_tmps = 1;
 215    dst[0] = src;
 216
 217    while(src_type.width < dst_type.width) {
 218       struct lp_type tmp_type = src_type;
 219
 220       tmp_type.width *= 2;
 221       tmp_type.length /= 2;
 222
 223       for(i = num_tmps; i--; ) {
 224          lp_build_unpack2(builder, src_type, tmp_type, dst[i], &dst[2*i + 0], &dst[2*i + 1]);
 225       }
 226
 227       src_type = tmp_type;
 228
 229       num_tmps *= 2;
 230    }
 231
 232    assert(num_tmps == num_dsts);
 233 }
 234
 235
 236 /**
 237  * Non-interleaved pack.
 238  *
 239  * This will move values as
 240  *
 241  *   lo =   __ l0 __ l1 __ l2 __..  __ ln
 242  *   hi =   __ h0 __ h1 __ h2 __..  __ hn
 243  *   res =  l0 l1 l2 .. ln h0 h1 h2 .. hn
 244  *
 245  * This will only change the number of bits the values are represented, not the
 246  * values themselves.
 247  *
 248  * It is assumed the values are already clamped into the destination type range.
 249  * Values outside that range will produce undefined results. Use
 250  * lp_build_packs2 instead.
 251  */
 252 LLVMValueRef
 253 lp_build_pack2(LLVMBuilderRef builder,
 254                struct lp_type src_type,
 255                struct lp_type dst_type,
 256                LLVMValueRef lo,
 257                LLVMValueRef hi)
 258 {
 259    LLVMTypeRef src_vec_type = lp_build_vec_type(src_type);
 260    LLVMTypeRef dst_vec_type = lp_build_vec_type(dst_type);
 261    LLVMValueRef shuffle;
 262    LLVMValueRef res;
 263
 264    dst_vec_type = lp_build_vec_type(dst_type);
 265
 266    assert(!src_type.floating);
 267    assert(!dst_type.floating);
 268    assert(src_type.width == dst_type.width * 2);
 269    assert(src_type.length * 2 == dst_type.length);
 270
 271    if(util_cpu_caps.has_sse2 && src_type.width * src_type.length == 128) {
 272       switch(src_type.width) {
 273       case 32:
 274          if(dst_type.sign) {
 275             res = lp_build_intrinsic_binary(builder, "llvm.x86.sse2.packssdw.128", src_vec_type, lo, hi);
 276          }
 277          else {
 278             if (util_cpu_caps.has_sse4_1) {
 279                /* PACKUSDW is the only instrinsic with a consistent signature */
 280                return lp_build_intrinsic_binary(builder, "llvm.x86.sse41.packusdw", dst_vec_type, lo, hi);
 281             }
 282             else {
 283                assert(0);
 284                return LLVMGetUndef(dst_vec_type);
 285             }
 286          }
 287          break;
 288
 289       case 16:
 290          if(dst_type.sign)
 291             res = lp_build_intrinsic_binary(builder, "llvm.x86.sse2.packsswb.128", src_vec_type, lo, hi);
 292          else
 293             res = lp_build_intrinsic_binary(builder, "llvm.x86.sse2.packuswb.128", src_vec_type, lo, hi);
 294          break;
 295
 296       default:
 297          assert(0);
 298          return LLVMGetUndef(dst_vec_type);
 299          break;
 300       }
 301
 302       res = LLVMBuildBitCast(builder, res, dst_vec_type, "");
 303       return res;
 304    }
 305
 306    lo = LLVMBuildBitCast(builder, lo, dst_vec_type, "");
 307    hi = LLVMBuildBitCast(builder, hi, dst_vec_type, "");
 308
 309    shuffle = lp_build_const_pack_shuffle(dst_type.length);
 310
 311    res = LLVMBuildShuffleVector(builder, lo, hi, shuffle, "");
 312
 313    return res;
 314 }
 315
 316
 317
 318 /**
 319  * Non-interleaved pack and saturate.
 320  *
 321  * Same as lp_build_pack2 but will saturate values so that they fit into the
 322  * destination type.
 323  */
 324 LLVMValueRef
 325 lp_build_packs2(LLVMBuilderRef builder,
 326                 struct lp_type src_type,
 327                 struct lp_type dst_type,
 328                 LLVMValueRef lo,
 329                 LLVMValueRef hi)
 330 {
 331    boolean clamp;
 332
 333    assert(!src_type.floating);
 334    assert(!dst_type.floating);
 335    assert(src_type.sign == dst_type.sign);
 336    assert(src_type.width == dst_type.width * 2);
 337    assert(src_type.length * 2 == dst_type.length);
 338
 339    clamp = TRUE;
 340
 341    /* All X86 SSE non-interleaved pack instructions take signed inputs and
 342     * saturate them, so no need to clamp for those cases. */
 343    if(util_cpu_caps.has_sse2 &&
 344       src_type.width * src_type.length == 128 &&
 345       src_type.sign)
 346       clamp = FALSE;
 347
 348    if(clamp) {
 349       struct lp_build_context bld;
 350       unsigned dst_bits = dst_type.sign ? dst_type.width - 1 : dst_type.width;
 351       LLVMValueRef dst_max = lp_build_int_const_scalar(src_type, ((unsigned long long)1 << dst_bits) - 1);
 352       lp_build_context_init(&bld, builder, src_type);
 353       lo = lp_build_min(&bld, lo, dst_max);
 354       hi = lp_build_min(&bld, hi, dst_max);
 355       /* FIXME: What about lower bound? */
 356    }
 357
 358    return lp_build_pack2(builder, src_type, dst_type, lo, hi);
 359 }
 360
 361
 362 /**
 363  * Truncate the bit width.
 364  *
 365  * TODO: Handle saturation consistently.
 366  */
 367 LLVMValueRef
 368 lp_build_pack(LLVMBuilderRef builder,
 369               struct lp_type src_type,
 370               struct lp_type dst_type,
 371               boolean clamped,
 372               const LLVMValueRef *src, unsigned num_srcs)
 373 {
 374    LLVMValueRef (*pack2)(LLVMBuilderRef builder,
 375                          struct lp_type src_type,
 376                          struct lp_type dst_type,
 377                          LLVMValueRef lo,
 378                          LLVMValueRef hi);
 379    LLVMValueRef tmp[LP_MAX_VECTOR_LENGTH];
 380    unsigned i;
 381
 382
 383    /* Register width must remain constant */
 384    assert(src_type.width * src_type.length == dst_type.width * dst_type.length);
 385
 386    /* We must not loose or gain channels. Only precision */
 387    assert(src_type.length * num_srcs == dst_type.length);
 388
 389    if(clamped)
 390       pack2 = &lp_build_pack2;
 391    else
 392       pack2 = &lp_build_packs2;
 393
 394    for(i = 0; i < num_srcs; ++i)
 395       tmp[i] = src[i];
 396
 397    while(src_type.width > dst_type.width) {
 398       struct lp_type tmp_type = src_type;
 399
 400       tmp_type.width /= 2;
 401       tmp_type.length *= 2;
 402
 403       /* Take in consideration the sign changes only in the last step */
 404       if(tmp_type.width == dst_type.width)
 405          tmp_type.sign = dst_type.sign;
 406
 407       num_srcs /= 2;
 408
 409       for(i = 0; i < num_srcs; ++i)
 410          tmp[i] = pack2(builder, src_type, tmp_type, tmp[2*i + 0], tmp[2*i + 1]);
 411
 412       src_type = tmp_type;
 413    }
 414
 415    assert(num_srcs == 1);
 416
 417    return tmp[0];
 418 }