/* * Copyright © 2015 Intel Corporation * * Permission is hereby granted, free of charge, to any person obtaining a * copy of this software and associated documentation files (the "Software"), * to deal in the Software without restriction, including without limitation * the rights to use, copy, modify, merge, publish, distribute, sublicense, * and/or sell copies of the Software, and to permit persons to whom the * Software is furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice (including the next * paragraph) shall be included in all copies or substantial portions of the * Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS * IN THE SOFTWARE. * */ #include "nir.h" #include "nir_builder.h" #include "c99_math.h" /* * Lowers some unsupported double operations, using only: * * - pack/unpackDouble2x32 * - conversion to/from single-precision * - double add, mul, and fma * - conditional select * - 32-bit integer and floating point arithmetic */ /* Creates a double with the exponent bits set to a given integer value */ static nir_ssa_def * set_exponent(nir_builder *b, nir_ssa_def *src, nir_ssa_def *exp) { /* Split into bits 0-31 and 32-63 */ nir_ssa_def *lo = nir_unpack_64_2x32_split_x(b, src); nir_ssa_def *hi = nir_unpack_64_2x32_split_y(b, src); /* The exponent is bits 52-62, or 20-30 of the high word, so set the exponent * to 1023 */ nir_ssa_def *new_hi = nir_bfi(b, nir_imm_int(b, 0x7ff00000), exp, hi); /* recombine */ return nir_pack_64_2x32_split(b, lo, new_hi); } static nir_ssa_def * get_exponent(nir_builder *b, nir_ssa_def *src) { /* get bits 32-63 */ nir_ssa_def *hi = nir_unpack_64_2x32_split_y(b, src); /* extract bits 20-30 of the high word */ return nir_ubitfield_extract(b, hi, nir_imm_int(b, 20), nir_imm_int(b, 11)); } /* Return infinity with the sign of the given source which is +/-0 */ static nir_ssa_def * get_signed_inf(nir_builder *b, nir_ssa_def *zero) { nir_ssa_def *zero_hi = nir_unpack_64_2x32_split_y(b, zero); /* The bit pattern for infinity is 0x7ff0000000000000, where the sign bit * is the highest bit. Only the sign bit can be non-zero in the passed in * source. So we essentially need to OR the infinity and the zero, except * the low 32 bits are always 0 so we can construct the correct high 32 * bits and then pack it together with zero low 32 bits. */ nir_ssa_def *inf_hi = nir_ior(b, nir_imm_int(b, 0x7ff00000), zero_hi); return nir_pack_64_2x32_split(b, nir_imm_int(b, 0), inf_hi); } /* * Generates the correctly-signed infinity if the source was zero, and flushes * the result to 0 if the source was infinity or the calculated exponent was * too small to be representable. */ static nir_ssa_def * fix_inv_result(nir_builder *b, nir_ssa_def *res, nir_ssa_def *src, nir_ssa_def *exp) { /* If the exponent is too small or the original input was infinity/NaN, * force the result to 0 (flush denorms) to avoid the work of handling * denorms properly. Note that this doesn't preserve positive/negative * zeros, but GLSL doesn't require it. */ res = nir_bcsel(b, nir_ior(b, nir_ige(b, nir_imm_int(b, 0), exp), nir_feq(b, nir_fabs(b, src), nir_imm_double(b, INFINITY))), nir_imm_double(b, 0.0f), res); /* If the original input was 0, generate the correctly-signed infinity */ res = nir_bcsel(b, nir_fne(b, src, nir_imm_double(b, 0.0f)), res, get_signed_inf(b, src)); return res; } static nir_ssa_def * lower_rcp(nir_builder *b, nir_ssa_def *src) { /* normalize the input to avoid range issues */ nir_ssa_def *src_norm = set_exponent(b, src, nir_imm_int(b, 1023)); /* cast to float, do an rcp, and then cast back to get an approximate * result */ nir_ssa_def *ra = nir_f2f64(b, nir_frcp(b, nir_f2f32(b, src_norm))); /* Fixup the exponent of the result - note that we check if this is too * small below. */ nir_ssa_def *new_exp = nir_isub(b, get_exponent(b, ra), nir_isub(b, get_exponent(b, src), nir_imm_int(b, 1023))); ra = set_exponent(b, ra, new_exp); /* Do a few Newton-Raphson steps to improve precision. * * Each step doubles the precision, and we started off with around 24 bits, * so we only need to do 2 steps to get to full precision. The step is: * * x_new = x * (2 - x*src) * * But we can re-arrange this to improve precision by using another fused * multiply-add: * * x_new = x + x * (1 - x*src) * * See https://en.wikipedia.org/wiki/Division_algorithm for more details. */ ra = nir_ffma(b, nir_fneg(b, ra), nir_ffma(b, ra, src, nir_imm_double(b, -1)), ra); ra = nir_ffma(b, nir_fneg(b, ra), nir_ffma(b, ra, src, nir_imm_double(b, -1)), ra); return fix_inv_result(b, ra, src, new_exp); } static nir_ssa_def * lower_sqrt_rsq(nir_builder *b, nir_ssa_def *src, bool sqrt) { /* We want to compute: * * 1/sqrt(m * 2^e) * * When the exponent is even, this is equivalent to: * * 1/sqrt(m) * 2^(-e/2) * * and then the exponent is odd, this is equal to: * * 1/sqrt(m * 2) * 2^(-(e - 1)/2) * * where the m * 2 is absorbed into the exponent. So we want the exponent * inside the square root to be 1 if e is odd and 0 if e is even, and we * want to subtract off e/2 from the final exponent, rounded to negative * infinity. We can do the former by first computing the unbiased exponent, * and then AND'ing it with 1 to get 0 or 1, and we can do the latter by * shifting right by 1. */ nir_ssa_def *unbiased_exp = nir_isub(b, get_exponent(b, src), nir_imm_int(b, 1023)); nir_ssa_def *even = nir_iand(b, unbiased_exp, nir_imm_int(b, 1)); nir_ssa_def *half = nir_ishr(b, unbiased_exp, nir_imm_int(b, 1)); nir_ssa_def *src_norm = set_exponent(b, src, nir_iadd(b, nir_imm_int(b, 1023), even)); nir_ssa_def *ra = nir_f2f64(b, nir_frsq(b, nir_f2f32(b, src_norm))); nir_ssa_def *new_exp = nir_isub(b, get_exponent(b, ra), half); ra = set_exponent(b, ra, new_exp); /* * The following implements an iterative algorithm that's very similar * between sqrt and rsqrt. We start with an iteration of Goldschmit's * algorithm, which looks like: * * a = the source * y_0 = initial (single-precision) rsqrt estimate * * h_0 = .5 * y_0 * g_0 = a * y_0 * r_0 = .5 - h_0 * g_0 * g_1 = g_0 * r_0 + g_0 * h_1 = h_0 * r_0 + h_0 * * Now g_1 ~= sqrt(a), and h_1 ~= 1/(2 * sqrt(a)). We could continue * applying another round of Goldschmit, but since we would never refer * back to a (the original source), we would add too much rounding error. * So instead, we do one last round of Newton-Raphson, which has better * rounding characteristics, to get the final rounding correct. This is * split into two cases: * * 1. sqrt * * Normally, doing a round of Newton-Raphson for sqrt involves taking a * reciprocal of the original estimate, which is slow since it isn't * supported in HW. But we can take advantage of the fact that we already * computed a good estimate of 1/(2 * g_1) by rearranging it like so: * * g_2 = .5 * (g_1 + a / g_1) * = g_1 + .5 * (a / g_1 - g_1) * = g_1 + (.5 / g_1) * (a - g_1^2) * = g_1 + h_1 * (a - g_1^2) * * The second term represents the error, and by splitting it out we can get * better precision by computing it as part of a fused multiply-add. Since * both Newton-Raphson and Goldschmit approximately double the precision of * the result, these two steps should be enough. * * 2. rsqrt * * First off, note that the first round of the Goldschmit algorithm is * really just a Newton-Raphson step in disguise: * * h_1 = h_0 * (.5 - h_0 * g_0) + h_0 * = h_0 * (1.5 - h_0 * g_0) * = h_0 * (1.5 - .5 * a * y_0^2) * = (.5 * y_0) * (1.5 - .5 * a * y_0^2) * * which is the standard formula multiplied by .5. Unlike in the sqrt case, * we don't need the inverse to do a Newton-Raphson step; we just need h_1, * so we can skip the calculation of g_1. Instead, we simply do another * Newton-Raphson step: * * y_1 = 2 * h_1 * r_1 = .5 - h_1 * y_1 * a * y_2 = y_1 * r_1 + y_1 * * Where the difference from Goldschmit is that we calculate y_1 * a * instead of using g_1. Doing it this way should be as fast as computing * y_1 up front instead of h_1, and it lets us share the code for the * initial Goldschmit step with the sqrt case. * * Putting it together, the computations are: * * h_0 = .5 * y_0 * g_0 = a * y_0 * r_0 = .5 - h_0 * g_0 * h_1 = h_0 * r_0 + h_0 * if sqrt: * g_1 = g_0 * r_0 + g_0 * r_1 = a - g_1 * g_1 * g_2 = h_1 * r_1 + g_1 * else: * y_1 = 2 * h_1 * r_1 = .5 - y_1 * (h_1 * a) * y_2 = y_1 * r_1 + y_1 * * For more on the ideas behind this, see "Software Division and Square * Root Using Goldschmit's Algorithms" by Markstein and the Wikipedia page * on square roots * (https://en.wikipedia.org/wiki/Methods_of_computing_square_roots). */ nir_ssa_def *one_half = nir_imm_double(b, 0.5); nir_ssa_def *h_0 = nir_fmul(b, one_half, ra); nir_ssa_def *g_0 = nir_fmul(b, src, ra); nir_ssa_def *r_0 = nir_ffma(b, nir_fneg(b, h_0), g_0, one_half); nir_ssa_def *h_1 = nir_ffma(b, h_0, r_0, h_0); nir_ssa_def *res; if (sqrt) { nir_ssa_def *g_1 = nir_ffma(b, g_0, r_0, g_0); nir_ssa_def *r_1 = nir_ffma(b, nir_fneg(b, g_1), g_1, src); res = nir_ffma(b, h_1, r_1, g_1); } else { nir_ssa_def *y_1 = nir_fmul(b, nir_imm_double(b, 2.0), h_1); nir_ssa_def *r_1 = nir_ffma(b, nir_fneg(b, y_1), nir_fmul(b, h_1, src), one_half); res = nir_ffma(b, y_1, r_1, y_1); } if (sqrt) { /* Here, the special cases we need to handle are * 0 -> 0 and * +inf -> +inf */ res = nir_bcsel(b, nir_ior(b, nir_feq(b, src, nir_imm_double(b, 0.0)), nir_feq(b, src, nir_imm_double(b, INFINITY))), src, res); } else { res = fix_inv_result(b, res, src, new_exp); } return res; } static nir_ssa_def * lower_trunc(nir_builder *b, nir_ssa_def *src) { nir_ssa_def *unbiased_exp = nir_isub(b, get_exponent(b, src), nir_imm_int(b, 1023)); nir_ssa_def *frac_bits = nir_isub(b, nir_imm_int(b, 52), unbiased_exp); /* * Decide the operation to apply depending on the unbiased exponent: * * if (unbiased_exp < 0) * return 0 * else if (unbiased_exp > 52) * return src * else * return src & (~0 << frac_bits) * * Notice that the else branch is a 64-bit integer operation that we need * to implement in terms of 32-bit integer arithmetics (at least until we * support 64-bit integer arithmetics). */ /* Compute "~0 << frac_bits" in terms of hi/lo 32-bit integer math */ nir_ssa_def *mask_lo = nir_bcsel(b, nir_ige(b, frac_bits, nir_imm_int(b, 32)), nir_imm_int(b, 0), nir_ishl(b, nir_imm_int(b, ~0), frac_bits)); nir_ssa_def *mask_hi = nir_bcsel(b, nir_ilt(b, frac_bits, nir_imm_int(b, 33)), nir_imm_int(b, ~0), nir_ishl(b, nir_imm_int(b, ~0), nir_isub(b, frac_bits, nir_imm_int(b, 32)))); nir_ssa_def *src_lo = nir_unpack_64_2x32_split_x(b, src); nir_ssa_def *src_hi = nir_unpack_64_2x32_split_y(b, src); return nir_bcsel(b, nir_ilt(b, unbiased_exp, nir_imm_int(b, 0)), nir_imm_double(b, 0.0), nir_bcsel(b, nir_ige(b, unbiased_exp, nir_imm_int(b, 53)), src, nir_pack_64_2x32_split(b, nir_iand(b, mask_lo, src_lo), nir_iand(b, mask_hi, src_hi)))); } static nir_ssa_def * lower_floor(nir_builder *b, nir_ssa_def *src) { /* * For x >= 0, floor(x) = trunc(x) * For x < 0, * - if x is integer, floor(x) = x * - otherwise, floor(x) = trunc(x) - 1 */ nir_ssa_def *tr = nir_ftrunc(b, src); nir_ssa_def *positive = nir_fge(b, src, nir_imm_double(b, 0.0)); return nir_bcsel(b, nir_ior(b, positive, nir_feq(b, src, tr)), tr, nir_fsub(b, tr, nir_imm_double(b, 1.0))); } static nir_ssa_def * lower_ceil(nir_builder *b, nir_ssa_def *src) { /* if x < 0, ceil(x) = trunc(x) * else if (x - trunc(x) == 0), ceil(x) = x * else, ceil(x) = trunc(x) + 1 */ nir_ssa_def *tr = nir_ftrunc(b, src); nir_ssa_def *negative = nir_flt(b, src, nir_imm_double(b, 0.0)); return nir_bcsel(b, nir_ior(b, negative, nir_feq(b, src, tr)), tr, nir_fadd(b, tr, nir_imm_double(b, 1.0))); } static nir_ssa_def * lower_fract(nir_builder *b, nir_ssa_def *src) { return nir_fsub(b, src, nir_ffloor(b, src)); } static nir_ssa_def * lower_round_even(nir_builder *b, nir_ssa_def *src) { /* Add and subtract 2**52 to round off any fractional bits. */ nir_ssa_def *two52 = nir_imm_double(b, (double)(1ull << 52)); nir_ssa_def *sign = nir_iand(b, nir_unpack_64_2x32_split_y(b, src), nir_imm_int(b, 1ull << 31)); b->exact = true; nir_ssa_def *res = nir_fsub(b, nir_fadd(b, nir_fabs(b, src), two52), two52); b->exact = false; return nir_bcsel(b, nir_flt(b, nir_fabs(b, src), two52), nir_pack_64_2x32_split(b, nir_unpack_64_2x32_split_x(b, res), nir_ior(b, nir_unpack_64_2x32_split_y(b, res), sign)), src); } static nir_ssa_def * lower_mod(nir_builder *b, nir_ssa_def *src0, nir_ssa_def *src1) { /* mod(x,y) = x - y * floor(x/y) * * If the division is lowered, it could add some rounding errors that make * floor() to return the quotient minus one when x = N * y. If this is the * case, we return zero because mod(x, y) output value is [0, y). */ nir_ssa_def *floor = nir_ffloor(b, nir_fdiv(b, src0, src1)); nir_ssa_def *mod = nir_fsub(b, src0, nir_fmul(b, src1, floor)); return nir_bcsel(b, nir_fne(b, mod, src1), mod, nir_imm_double(b, 0.0)); } static nir_ssa_def * lower_doubles_instr_to_soft(nir_builder *b, nir_alu_instr *instr, const nir_shader *softfp64, nir_lower_doubles_options options) { if (!(options & nir_lower_fp64_full_software)) return NULL; assert(instr->dest.dest.is_ssa); const char *name; const struct glsl_type *return_type = glsl_uint64_t_type(); switch (instr->op) { case nir_op_f2i64: if (instr->src[0].src.ssa->bit_size == 64) name = "__fp64_to_int64"; else name = "__fp32_to_int64"; return_type = glsl_int64_t_type(); break; case nir_op_f2u64: if (instr->src[0].src.ssa->bit_size == 64) name = "__fp64_to_uint64"; else name = "__fp32_to_uint64"; break; case nir_op_f2f64: name = "__fp32_to_fp64"; break; case nir_op_f2f32: name = "__fp64_to_fp32"; return_type = glsl_float_type(); break; case nir_op_f2i32: name = "__fp64_to_int"; return_type = glsl_int_type(); break; case nir_op_f2u32: name = "__fp64_to_uint"; return_type = glsl_uint_type(); break; case nir_op_f2b1: case nir_op_f2b32: name = "__fp64_to_bool"; return_type = glsl_bool_type(); break; case nir_op_b2f64: name = "__bool_to_fp64"; break; case nir_op_i2f32: if (instr->src[0].src.ssa->bit_size != 64) return false; name = "__int64_to_fp32"; return_type = glsl_float_type(); break; case nir_op_u2f32: if (instr->src[0].src.ssa->bit_size != 64) return false; name = "__uint64_to_fp32"; return_type = glsl_float_type(); break; case nir_op_i2f64: if (instr->src[0].src.ssa->bit_size == 64) name = "__int64_to_fp64"; else name = "__int_to_fp64"; break; case nir_op_u2f64: if (instr->src[0].src.ssa->bit_size == 64) name = "__uint64_to_fp64"; else name = "__uint_to_fp64"; break; case nir_op_fabs: name = "__fabs64"; break; case nir_op_fneg: name = "__fneg64"; break; case nir_op_fround_even: name = "__fround64"; break; case nir_op_ftrunc: name = "__ftrunc64"; break; case nir_op_ffloor: name = "__ffloor64"; break; case nir_op_ffract: name = "__ffract64"; break; case nir_op_fsign: name = "__fsign64"; break; case nir_op_feq: name = "__feq64"; return_type = glsl_bool_type(); break; case nir_op_fne: name = "__fne64"; return_type = glsl_bool_type(); break; case nir_op_flt: name = "__flt64"; return_type = glsl_bool_type(); break; case nir_op_fge: name = "__fge64"; return_type = glsl_bool_type(); break; case nir_op_fmin: name = "__fmin64"; break; case nir_op_fmax: name = "__fmax64"; break; case nir_op_fadd: name = "__fadd64"; break; case nir_op_fmul: name = "__fmul64"; break; case nir_op_ffma: name = "__ffma64"; break; case nir_op_fsat: name = "__fsat64"; break; default: return false; } nir_function *func = NULL; nir_foreach_function(function, softfp64) { if (strcmp(function->name, name) == 0) { func = function; break; } } if (!func || !func->impl) { fprintf(stderr, "Cannot find function \"%s\"\n", name); assert(func); } nir_ssa_def *params[4] = { NULL, }; nir_variable *ret_tmp = nir_local_variable_create(b->impl, return_type, "return_tmp"); nir_deref_instr *ret_deref = nir_build_deref_var(b, ret_tmp); params[0] = &ret_deref->dest.ssa; assert(nir_op_infos[instr->op].num_inputs + 1 == func->num_params); for (unsigned i = 0; i < nir_op_infos[instr->op].num_inputs; i++) { assert(i + 1 < ARRAY_SIZE(params)); params[i + 1] = nir_mov_alu(b, instr->src[i], 1); } nir_inline_function_impl(b, func->impl, params); return nir_load_deref(b, ret_deref); } nir_lower_doubles_options nir_lower_doubles_op_to_options_mask(nir_op opcode) { switch (opcode) { case nir_op_frcp: return nir_lower_drcp; case nir_op_fsqrt: return nir_lower_dsqrt; case nir_op_frsq: return nir_lower_drsq; case nir_op_ftrunc: return nir_lower_dtrunc; case nir_op_ffloor: return nir_lower_dfloor; case nir_op_fceil: return nir_lower_dceil; case nir_op_ffract: return nir_lower_dfract; case nir_op_fround_even: return nir_lower_dround_even; case nir_op_fmod: return nir_lower_dmod; case nir_op_fsub: return nir_lower_dsub; case nir_op_fdiv: return nir_lower_ddiv; default: return 0; } } struct lower_doubles_data { const nir_shader *softfp64; nir_lower_doubles_options options; }; static bool should_lower_double_instr(const nir_instr *instr, const void *_data) { const struct lower_doubles_data *data = _data; const nir_lower_doubles_options options = data->options; if (instr->type != nir_instr_type_alu) return false; const nir_alu_instr *alu = nir_instr_as_alu(instr); assert(alu->dest.dest.is_ssa); bool is_64 = alu->dest.dest.ssa.bit_size == 64; unsigned num_srcs = nir_op_infos[alu->op].num_inputs; for (unsigned i = 0; i < num_srcs; i++) { is_64 |= (nir_src_bit_size(alu->src[i].src) == 64); } if (!is_64) return false; if (options & nir_lower_fp64_full_software) return true; return options & nir_lower_doubles_op_to_options_mask(alu->op); } static nir_ssa_def * lower_doubles_instr(nir_builder *b, nir_instr *instr, void *_data) { const struct lower_doubles_data *data = _data; const nir_lower_doubles_options options = data->options; nir_alu_instr *alu = nir_instr_as_alu(instr); nir_ssa_def *soft_def = lower_doubles_instr_to_soft(b, alu, data->softfp64, options); if (soft_def) return soft_def; if (!(options & nir_lower_doubles_op_to_options_mask(alu->op))) return NULL; nir_ssa_def *src = nir_mov_alu(b, alu->src[0], alu->dest.dest.ssa.num_components); switch (alu->op) { case nir_op_frcp: return lower_rcp(b, src); case nir_op_fsqrt: return lower_sqrt_rsq(b, src, true); case nir_op_frsq: return lower_sqrt_rsq(b, src, false); case nir_op_ftrunc: return lower_trunc(b, src); case nir_op_ffloor: return lower_floor(b, src); case nir_op_fceil: return lower_ceil(b, src); case nir_op_ffract: return lower_fract(b, src); case nir_op_fround_even: return lower_round_even(b, src); case nir_op_fdiv: case nir_op_fsub: case nir_op_fmod: { nir_ssa_def *src1 = nir_mov_alu(b, alu->src[1], alu->dest.dest.ssa.num_components); switch (alu->op) { case nir_op_fdiv: return nir_fmul(b, src, nir_frcp(b, src1)); case nir_op_fsub: return nir_fadd(b, src, nir_fneg(b, src1)); case nir_op_fmod: return lower_mod(b, src, src1); default: unreachable("unhandled opcode"); } } default: unreachable("unhandled opcode"); } } static bool nir_lower_doubles_impl(nir_function_impl *impl, const nir_shader *softfp64, nir_lower_doubles_options options) { struct lower_doubles_data data = { .softfp64 = softfp64, .options = options, }; bool progress = nir_function_impl_lower_instructions(impl, should_lower_double_instr, lower_doubles_instr, &data); if (progress && (options & nir_lower_fp64_full_software)) { /* SSA and register indices are completely messed up now */ nir_index_ssa_defs(impl); nir_index_local_regs(impl); nir_metadata_preserve(impl, nir_metadata_none); /* And we have deref casts we need to clean up thanks to function * inlining. */ nir_opt_deref_impl(impl); } return progress; } bool nir_lower_doubles(nir_shader *shader, const nir_shader *softfp64, nir_lower_doubles_options options) { bool progress = false; nir_foreach_function(function, shader) { if (function->impl) { progress |= nir_lower_doubles_impl(function->impl, softfp64, options); } } return progress; }