Mesa (master): nir/flrp: Lower flrp(±1, b, c) and flrp(a, ±1, c) differently
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Tue May 7 06:01:30 UTC 2019
Module: Mesa
Branch: master
Commit: 5b908db604b2f47bb8382047533e556db8d5f52b
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=5b908db604b2f47bb8382047533e556db8d5f52b
Author: Ian Romanick <ian.d.romanick at intel.com>
Date: Tue Aug 21 17:17:24 2018 -0700
nir/flrp: Lower flrp(±1, b, c) and flrp(a, ±1, c) differently
No changes on any other Intel platforms.
v2: Rebase on 424372e5dd5 ("nir: Use the flrp lowering pass instead of
nir_opt_algebraic")
Iron Lake and GM45 had similar results. (Iron Lake shown)
total instructions in shared programs: 8189888 -> 8153912 (-0.44%)
instructions in affected programs: 1199037 -> 1163061 (-3.00%)
helped: 4124
HURT: 10
helped stats (abs) min: 1 max: 40 x̄: 8.73 x̃: 9
helped stats (rel) min: 0.20% max: 86.96% x̄: 4.96% x̃: 3.02%
HURT stats (abs) min: 1 max: 2 x̄: 1.20 x̃: 1
HURT stats (rel) min: 1.06% max: 3.92% x̄: 1.62% x̃: 1.06%
95% mean confidence interval for instructions value: -8.84 -8.56
95% mean confidence interval for instructions %-change: -5.12% -4.77%
Instructions are helped.
total cycles in shared programs: 188606710 -> 188426964 (-0.10%)
cycles in affected programs: 27505596 -> 27325850 (-0.65%)
helped: 4026
HURT: 77
helped stats (abs) min: 2 max: 646 x̄: 44.99 x̃: 46
helped stats (rel) min: <.01% max: 94.58% x̄: 2.35% x̃: 0.85%
HURT stats (abs) min: 2 max: 376 x̄: 17.79 x̃: 6
HURT stats (rel) min: <.01% max: 2.60% x̄: 0.22% x̃: 0.04%
95% mean confidence interval for cycles value: -44.75 -42.87
95% mean confidence interval for cycles %-change: -2.44% -2.17%
Cycles are helped.
LOST: 3
GAINED: 35
Reviewed-by: Matt Turner <mattst88 at gmail.com>
---
src/compiler/nir/nir_lower_flrp.c | 134 ++++++++++++++++++++++++++++++++++++++
1 file changed, 134 insertions(+)
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);
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