src/gallium/auxiliary/gallivm/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_const_int_vec(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 #if HAVE_LLVM < 0x0207
 260    LLVMTypeRef src_vec_type = lp_build_vec_type(src_type);
 261 #endif
 262    LLVMTypeRef dst_vec_type = lp_build_vec_type(dst_type);
 263    LLVMValueRef shuffle;
 264    LLVMValueRef res;
 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 #if HAVE_LLVM >= 0x0207
 276             res = lp_build_intrinsic_binary(builder, "llvm.x86.sse2.packssdw.128", dst_vec_type, lo, hi);
 277 #else
 278             res = lp_build_intrinsic_binary(builder, "llvm.x86.sse2.packssdw.128", src_vec_type, lo, hi);
 279 #endif
 280          }
 281          else {
 282             if (util_cpu_caps.has_sse4_1) {
 283                return lp_build_intrinsic_binary(builder, "llvm.x86.sse41.packusdw", dst_vec_type, lo, hi);
 284             }
 285             else {
 286                assert(0);
 287                return LLVMGetUndef(dst_vec_type);
 288             }
 289          }
 290          break;
 291
 292       case 16:
 293          if(dst_type.sign)
 294 #if HAVE_LLVM >= 0x0207
 295             res = lp_build_intrinsic_binary(builder, "llvm.x86.sse2.packsswb.128", dst_vec_type, lo, hi);
 296 #else
 297             res = lp_build_intrinsic_binary(builder, "llvm.x86.sse2.packsswb.128", src_vec_type, lo, hi);
 298 #endif
 299          else
 300 #if HAVE_LLVM >= 0x0207
 301             res = lp_build_intrinsic_binary(builder, "llvm.x86.sse2.packuswb.128", dst_vec_type, lo, hi);
 302 #else
 303             res = lp_build_intrinsic_binary(builder, "llvm.x86.sse2.packuswb.128", src_vec_type, lo, hi);
 304 #endif
 305          break;
 306
 307       default:
 308          assert(0);
 309          return LLVMGetUndef(dst_vec_type);
 310          break;
 311       }
 312
 313       res = LLVMBuildBitCast(builder, res, dst_vec_type, "");
 314       return res;
 315    }
 316
 317    lo = LLVMBuildBitCast(builder, lo, dst_vec_type, "");
 318    hi = LLVMBuildBitCast(builder, hi, dst_vec_type, "");
 319
 320    shuffle = lp_build_const_pack_shuffle(dst_type.length);
 321
 322    res = LLVMBuildShuffleVector(builder, lo, hi, shuffle, "");
 323
 324    return res;
 325 }
 326
 327
 328
 329 /**
 330  * Non-interleaved pack and saturate.
 331  *
 332  * Same as lp_build_pack2 but will saturate values so that they fit into the
 333  * destination type.
 334  */
 335 LLVMValueRef
 336 lp_build_packs2(LLVMBuilderRef builder,
 337                 struct lp_type src_type,
 338                 struct lp_type dst_type,
 339                 LLVMValueRef lo,
 340                 LLVMValueRef hi)
 341 {
 342    boolean clamp;
 343
 344    assert(!src_type.floating);
 345    assert(!dst_type.floating);
 346    assert(src_type.sign == dst_type.sign);
 347    assert(src_type.width == dst_type.width * 2);
 348    assert(src_type.length * 2 == dst_type.length);
 349
 350    clamp = TRUE;
 351
 352    /* All X86 SSE non-interleaved pack instructions take signed inputs and
 353     * saturate them, so no need to clamp for those cases. */
 354    if(util_cpu_caps.has_sse2 &&
 355       src_type.width * src_type.length == 128 &&
 356       src_type.sign)
 357       clamp = FALSE;
 358
 359    if(clamp) {
 360       struct lp_build_context bld;
 361       unsigned dst_bits = dst_type.sign ? dst_type.width - 1 : dst_type.width;
 362       LLVMValueRef dst_max = lp_build_const_int_vec(src_type, ((unsigned long long)1 << dst_bits) - 1);
 363       lp_build_context_init(&bld, builder, src_type);
 364       lo = lp_build_min(&bld, lo, dst_max);
 365       hi = lp_build_min(&bld, hi, dst_max);
 366       /* FIXME: What about lower bound? */
 367    }
 368
 369    return lp_build_pack2(builder, src_type, dst_type, lo, hi);
 370 }
 371
 372
 373 /**
 374  * Truncate the bit width.
 375  *
 376  * TODO: Handle saturation consistently.
 377  */
 378 LLVMValueRef
 379 lp_build_pack(LLVMBuilderRef builder,
 380               struct lp_type src_type,
 381               struct lp_type dst_type,
 382               boolean clamped,
 383               const LLVMValueRef *src, unsigned num_srcs)
 384 {
 385    LLVMValueRef (*pack2)(LLVMBuilderRef builder,
 386                          struct lp_type src_type,
 387                          struct lp_type dst_type,
 388                          LLVMValueRef lo,
 389                          LLVMValueRef hi);
 390    LLVMValueRef tmp[LP_MAX_VECTOR_LENGTH];
 391    unsigned i;
 392
 393
 394    /* Register width must remain constant */
 395    assert(src_type.width * src_type.length == dst_type.width * dst_type.length);
 396
 397    /* We must not loose or gain channels. Only precision */
 398    assert(src_type.length * num_srcs == dst_type.length);
 399
 400    if(clamped)
 401       pack2 = &lp_build_pack2;
 402    else
 403       pack2 = &lp_build_packs2;
 404
 405    for(i = 0; i < num_srcs; ++i)
 406       tmp[i] = src[i];
 407
 408    while(src_type.width > dst_type.width) {
 409       struct lp_type tmp_type = src_type;
 410
 411       tmp_type.width /= 2;
 412       tmp_type.length *= 2;
 413
 414       /* Take in consideration the sign changes only in the last step */
 415       if(tmp_type.width == dst_type.width)
 416          tmp_type.sign = dst_type.sign;
 417
 418       num_srcs /= 2;
 419
 420       for(i = 0; i < num_srcs; ++i)
 421          tmp[i] = pack2(builder, src_type, tmp_type, tmp[2*i + 0], tmp[2*i + 1]);
 422
 423       src_type = tmp_type;
 424    }
 425
 426    assert(num_srcs == 1);
 427
 428    return tmp[0];
 429 }