diff options
| -rw-r--r-- | src/compiler/nir/nir_lower_flrp.c | 134 |
1 files changed, 134 insertions, 0 deletions
diff --git a/src/compiler/nir/nir_lower_flrp.c b/src/compiler/nir/nir_lower_flrp.c index 952068ec9cc..c041fefc52b 100644 --- a/src/compiler/nir/nir_lower_flrp.c +++ b/src/compiler/nir/nir_lower_flrp.c @@ -137,6 +137,89 @@ replace_with_fast(struct nir_builder *bld, struct u_vector *dead_flrp, append_flrp_to_dead_list(dead_flrp, alu); } +/** + * Replace flrp(a, b, c) with (b*c ± c) + a + */ +static void +replace_with_expanded_ffma_and_add(struct nir_builder *bld, + struct u_vector *dead_flrp, + struct nir_alu_instr *alu, bool subtract_c) +{ + nir_ssa_def *const a = nir_ssa_for_alu_src(bld, alu, 0); + nir_ssa_def *const b = nir_ssa_for_alu_src(bld, alu, 1); + nir_ssa_def *const c = nir_ssa_for_alu_src(bld, alu, 2); + + nir_ssa_def *const b_times_c = nir_fadd(bld, b, c); + nir_instr_as_alu(b_times_c->parent_instr)->exact = alu->exact; + + nir_ssa_def *inner_sum; + + if (subtract_c) { + nir_ssa_def *const neg_c = nir_fneg(bld, c); + nir_instr_as_alu(neg_c->parent_instr)->exact = alu->exact; + + inner_sum = nir_fadd(bld, b_times_c, neg_c); + } else { + inner_sum = nir_fadd(bld, b_times_c, c); + } + + nir_instr_as_alu(inner_sum->parent_instr)->exact = alu->exact; + + nir_ssa_def *const outer_sum = nir_fadd(bld, inner_sum, a); + nir_instr_as_alu(outer_sum->parent_instr)->exact = alu->exact; + + nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, nir_src_for_ssa(outer_sum)); + + /* DO NOT REMOVE the original flrp yet. Many of the lowering choices are + * based on other uses of the sources. Removing the flrp may cause the + * last flrp in a sequence to make a different, incorrect choice. + */ + append_flrp_to_dead_list(dead_flrp, alu); +} + +/** + * Determines whether a swizzled source is constant w/ all components the same. + * + * The value of the constant is stored in \c result. + * + * \return + * True if all components of the swizzled source are the same constant. + * Otherwise false is returned. + */ +static bool +all_same_constant(const nir_alu_instr *instr, unsigned src, double *result) +{ + nir_const_value *val = nir_src_as_const_value(instr->src[src].src); + + if (!val) + return false; + + const uint8_t *const swizzle = instr->src[src].swizzle; + const unsigned num_components = nir_dest_num_components(instr->dest.dest); + + if (instr->dest.dest.ssa.bit_size == 32) { + const float first = val[swizzle[0]].f32; + + for (unsigned i = 1; i < num_components; i++) { + if (val[swizzle[i]].f32 != first) + return false; + } + + *result = first; + } else { + const double first = val[swizzle[0]].f64; + + for (unsigned i = 1; i < num_components; i++) { + if (val[swizzle[i]].f64 != first) + return false; + } + + *result = first; + } + + return true; +} + static bool sources_are_constants_with_similar_magnitudes(const nir_alu_instr *instr) { @@ -265,6 +348,57 @@ convert_flrp_instruction(nir_builder *bld, return; } + /* + * - If x = 1: + * + * (yt + -t) + 1 + * + * - If x = -1: + * + * (yt + t) - 1 + * + * In both cases, x is used in place of ±1 for simplicity. Both forms + * lend to ffma generation on platforms that support ffma. + */ + double src0_as_constant; + if (all_same_constant(alu, 0, &src0_as_constant)) { + if (src0_as_constant == 1.0) { + replace_with_expanded_ffma_and_add(bld, dead_flrp, alu, + true /* subtract t */); + return; + } else if (src0_as_constant == -1.0) { + replace_with_expanded_ffma_and_add(bld, dead_flrp, alu, + false /* add t */); + return; + } + } + + /* + * - If y = ±1: + * + * x(1 - t) + yt + * + * In this case either the multiply in yt will be eliminated by + * nir_opt_algebraic. If FMA is supported, this results in fma(x, (1 - + * t), ±t) for two instructions. If FMA is not supported, then the cost + * is 3 instructions. We rely on nir_opt_algebraic to generate the FMA + * instructions as well. + * + * Another possible replacement is + * + * -xt + x ± t + * + * Some groupings of this may be better on some platforms in some + * circumstances, bit it is probably dependent on scheduling. Futher + * investigation may be required. + */ + double src1_as_constant; + if ((all_same_constant(alu, 1, &src1_as_constant) && + (src1_as_constant == -1.0 || src1_as_constant == 1.0))) { + replace_with_strict(bld, dead_flrp, alu); + return; + } + if (have_ffma) { if (always_precise) { replace_with_strict_ffma(bld, dead_flrp, alu); |