On 19/04/16 23:52, Jason Ekstrand wrote: > On Tue, Apr 12, 2016 at 1:05 AM, Samuel Iglesias Gonsálvez < > sigles...@igalia.com> wrote: > >> From: Connor Abbott <connor.w.abb...@intel.com> >> >> v2: Move to compiler/nir (Iago) >> >> Signed-off-by: Iago Toral Quiroga <ito...@igalia.com> >> --- >> src/compiler/Makefile.sources | 1 + >> src/compiler/nir/nir.h | 7 + >> src/compiler/nir/nir_lower_double_ops.c | 387 >> ++++++++++++++++++++++++++++++++ >> 3 files changed, 395 insertions(+) >> create mode 100644 src/compiler/nir/nir_lower_double_ops.c >> >> diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources >> index 6f09abf..db7ca3b 100644 >> --- a/src/compiler/Makefile.sources >> +++ b/src/compiler/Makefile.sources >> @@ -187,6 +187,7 @@ NIR_FILES = \ >> nir/nir_lower_alu_to_scalar.c \ >> nir/nir_lower_atomics.c \ >> nir/nir_lower_clip.c \ >> + nir/nir_lower_double_ops.c \ >> nir/nir_lower_double_packing.c \ >> nir/nir_lower_global_vars_to_local.c \ >> nir/nir_lower_gs_intrinsics.c \ >> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h >> index ebac750..434d92b 100644 >> --- a/src/compiler/nir/nir.h >> +++ b/src/compiler/nir/nir.h >> @@ -2282,6 +2282,13 @@ void nir_lower_to_source_mods(nir_shader *shader); >> >> bool nir_lower_gs_intrinsics(nir_shader *shader); >> >> +typedef enum { >> + nir_lower_drcp = (1 << 0), >> + nir_lower_dsqrt = (1 << 1), >> + nir_lower_drsq = (1 << 2), >> +} nir_lower_doubles_options; >> + >> +void nir_lower_doubles(nir_shader *shader, nir_lower_doubles_options >> options); >> void nir_lower_double_pack(nir_shader *shader); >> >> bool nir_normalize_cubemap_coords(nir_shader *shader); >> diff --git a/src/compiler/nir/nir_lower_double_ops.c >> b/src/compiler/nir/nir_lower_double_ops.c >> new file mode 100644 >> index 0000000..4cd153c >> --- /dev/null >> +++ b/src/compiler/nir/nir_lower_double_ops.c >> @@ -0,0 +1,387 @@ >> +/* >> + * 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_double_2x32_split_x(b, src); >> + nir_ssa_def *hi = nir_unpack_double_2x32_split_y(b, src); >> + >> + /* The exponent is bits 52-62, or 20-30 of the high word, so set those >> bits >> + * to 1023 >> > > We're not setting them to 1023, we're setting it to exp. >
Right. > >> + */ >> + nir_ssa_def *new_hi = nir_bfi(b, nir_imm_uint(b, 0x7ff00000), >> + exp, hi); >> > > Does this really need a line-wrap? It looks shorter than the comment above. > Right. I will undo the line-wrap. > >> + /* recombine */ >> + return nir_pack_double_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_double_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_split = nir_unpack_double_2x32(b, zero); >> + nir_ssa_def *zero_hi = nir_swizzle(b, zero_split, (unsigned[]) {1}, 1, >> false); >> + >> + /* 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_uint(b, 0x7ff00000), zero_hi); >> + nir_ssa_def *inf_split = nir_vec2(b, nir_imm_int(b, 0), inf_hi); >> + return nir_pack_double_2x32(b, inf_split); >> > > Just make this pack_double(b, nir_vec2(b, )). No need for the temporary. > > Other than that > > Reviewed-by: Jason Ekstrand <ja...@jlekstrand.net> > OK, thanks! Sam > >> +} >> + >> +/* >> + * 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_f2d(b, nir_frcp(b, nir_d2f(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, ra, nir_ffma(b, ra, src, nir_imm_double(b, -1)), ra); >> + ra = nir_ffma(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_f2d(b, nir_frsq(b, nir_d2f(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 void >> +lower_doubles_instr(nir_alu_instr *instr, nir_lower_doubles_options >> options) >> +{ >> + assert(instr->dest.dest.is_ssa); >> + if (instr->dest.dest.ssa.bit_size != 64) >> + return; >> + >> + switch (instr->op) { >> + case nir_op_frcp: >> + if (!(options & nir_lower_drcp)) >> + return; >> + break; >> + >> + case nir_op_fsqrt: >> + if (!(options & nir_lower_dsqrt)) >> + return; >> + break; >> + >> + case nir_op_frsq: >> + if (!(options & nir_lower_drsq)) >> + return; >> + break; >> + >> + default: >> + return; >> + } >> + >> + nir_builder bld; >> + nir_builder_init(&bld, >> nir_cf_node_get_function(&instr->instr.block->cf_node)); >> + bld.cursor = nir_before_instr(&instr->instr); >> + >> + nir_ssa_def *src = nir_fmov_alu(&bld, instr->src[0], >> + instr->dest.dest.ssa.num_components); >> + >> + nir_ssa_def *result; >> + >> + switch (instr->op) { >> + case nir_op_frcp: >> + result = lower_rcp(&bld, src); >> + break; >> + case nir_op_fsqrt: >> + result = lower_sqrt_rsq(&bld, src, true); >> + break; >> + case nir_op_frsq: >> + result = lower_sqrt_rsq(&bld, src, false); >> + break; >> + default: >> + unreachable("unhandled opcode"); >> + } >> + >> + nir_ssa_def_rewrite_uses(&instr->dest.dest.ssa, >> nir_src_for_ssa(result)); >> + nir_instr_remove(&instr->instr); >> +} >> + >> +static bool >> +lower_doubles_block(nir_block *block, void *ctx) >> +{ >> + nir_lower_doubles_options options = *((nir_lower_doubles_options *) >> ctx); >> + >> + nir_foreach_instr_safe(block, instr) { >> + if (instr->type != nir_instr_type_alu) >> + continue; >> + >> + lower_doubles_instr(nir_instr_as_alu(instr), options); >> + } >> + >> + return true; >> +} >> + >> +static void >> +lower_doubles_impl(nir_function_impl *impl, nir_lower_doubles_options >> options) >> +{ >> + nir_foreach_block(impl, lower_doubles_block, &options); >> +} >> + >> +void >> +nir_lower_doubles(nir_shader *shader, nir_lower_doubles_options options) >> +{ >> + nir_foreach_function(shader, function) { >> + if (function->impl) >> + lower_doubles_impl(function->impl, options); >> + } >> +} >> -- >> 2.5.0 >> >> _______________________________________________ >> mesa-dev mailing list >> mesa-dev@lists.freedesktop.org >> https://lists.freedesktop.org/mailman/listinfo/mesa-dev >> > _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev