Mesa (master): nir: Add lowering for nir_op_bit_count.
Eric Anholt
anholt at kemper.freedesktop.org
Wed Jun 6 20:55:45 UTC 2018
Module: Mesa
Branch: master
Commit: 73953b071365ca64db353023fff78a06b20503a3
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=73953b071365ca64db353023fff78a06b20503a3
Author: Eric Anholt <eric at anholt.net>
Date: Tue May 8 13:04:37 2018 -0700
nir: Add lowering for nir_op_bit_count.
This is basically the same as the GLSL lowering path.
v2: Fix typo in the link
Reviewed-by: Matt Turner <mattst88 at gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>
---
src/compiler/nir/nir.h | 2 ++
src/compiler/nir/nir_lower_alu.c | 36 ++++++++++++++++++++++++++++++++++++
2 files changed, 38 insertions(+)
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index 06154aa990..bb477742dc 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -1913,6 +1913,8 @@ typedef struct nir_shader_compiler_options {
bool lower_bitfield_insert_to_shifts;
/** Lowers bitfield_reverse to shifts. */
bool lower_bitfield_reverse;
+ /** Lowers bit_count to shifts. */
+ bool lower_bit_count;
/** Lowers bfm to shifts and subtracts. */
bool lower_bfm;
/** Lowers ifind_msb to compare and ufind_msb */
diff --git a/src/compiler/nir/nir_lower_alu.c b/src/compiler/nir/nir_lower_alu.c
index ff977f0169..8d1a1d3746 100644
--- a/src/compiler/nir/nir_lower_alu.c
+++ b/src/compiler/nir/nir_lower_alu.c
@@ -94,6 +94,42 @@ lower_alu_instr(nir_alu_instr *instr, nir_builder *b)
}
break;
+ case nir_op_bit_count:
+ if (b->shader->options->lower_bit_count) {
+ /* For more details, see:
+ *
+ * http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
+ */
+ nir_ssa_def *c1 = nir_imm_int(b, 1);
+ nir_ssa_def *c2 = nir_imm_int(b, 2);
+ nir_ssa_def *c4 = nir_imm_int(b, 4);
+ nir_ssa_def *c24 = nir_imm_int(b, 24);
+ nir_ssa_def *c33333333 = nir_imm_int(b, 0x33333333);
+ nir_ssa_def *c55555555 = nir_imm_int(b, 0x55555555);
+ nir_ssa_def *c0f0f0f0f = nir_imm_int(b, 0x0f0f0f0f);
+ nir_ssa_def *c01010101 = nir_imm_int(b, 0x01010101);
+
+ lowered = nir_ssa_for_alu_src(b, instr, 0);
+
+ lowered = nir_isub(b, lowered,
+ nir_iand(b, nir_ushr(b, lowered, c1), c55555555));
+
+ lowered = nir_iadd(b,
+ nir_iand(b, lowered, c33333333),
+ nir_iand(b, nir_ushr(b, lowered, c2), c33333333));
+
+ lowered = nir_ushr(b,
+ nir_imul(b,
+ nir_iand(b,
+ nir_iadd(b,
+ lowered,
+ nir_ushr(b, lowered, c4)),
+ c0f0f0f0f),
+ c01010101),
+ c24);
+ }
+ break;
+
case nir_op_imul_high:
case nir_op_umul_high:
if (b->shader->options->lower_mul_high) {
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