<div dir="ltr"> <div class="gmail_extra"> <div class="gmail_quote">On Tue, Apr 19, 2016 at 6:45 PM, Connor Abbott <<a href="mailto:cwabbott0@gmail.com" target="_blank">cwabbott0@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5">On Tue, Apr 12, 2016 at 4:05 AM, Samuel Iglesias Gonsálvez <<a href="mailto:siglesias@igalia.com">siglesias@igalia.com</a>> wrote: > From: Connor Abbott <<a href="mailto:connor.w.abbott@intel.com">connor.w.abbott@intel.com</a>> > > v2: Move to compiler/nir (Iago) > > Signed-off-by: Iago Toral Quiroga <<a href="mailto:itoral@igalia.com">itoral@igalia.com</a>> > --- > 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 > + */ > + nir_ssa_def *new_hi = nir_bfi(b, nir_imm_uint(b, 0x7ff00000), > + exp, hi); > + /* 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); </div></div>This should be using nir_unpack_double_2x32_split_y and nir_pack_double_2x32_split, or else it won't scalarize correctly. I'm surprised a piglit test didn't catch this. <div class="HOEnZb"><div class="h5"></div></div></blockquote><div> </div><div>They run alu_to_scalar before lowering double ops (helps with register pressure) so this never gets hit. That said, probably still a good idea so the vector path actually works. </div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5"> > + > + /* 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); > +} > + > +/* > + * 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 <a href="https://en.wikipedia.org/wiki/Division_algorithm" rel="noreferrer" target="_blank">https://en.wikipedia.org/wiki/Division_algorithm</a> 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 > + * (<a href="https://en.wikipedia.org/wiki/Methods_of_computing_square_roots" rel="noreferrer" target="_blank">https://en.wikipedia.org/wiki/Methods_of_computing_square_roots</a>). > + */ > + > + 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 > <a href="mailto:mesa-dev@lists.freedesktop.org">mesa-dev@lists.freedesktop.org</a> > <a href="https://lists.freedesktop.org/mailman/listinfo/mesa-dev" rel="noreferrer" target="_blank">https://lists.freedesktop.org/mailman/listinfo/mesa-dev</a> _______________________________________________ mesa-dev mailing list <a href="mailto:mesa-dev@lists.freedesktop.org">mesa-dev@lists.freedesktop.org</a> <a href="https://lists.freedesktop.org/mailman/listinfo/mesa-dev" rel="noreferrer" target="_blank">https://lists.freedesktop.org/mailman/listinfo/mesa-dev</a> </div></div></blockquote></div> </div></div>