This is basically the same as the GLSL lowering path.
---
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 5b29645a6c48..e424a01c8225 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -1889,6 +1889,8 @@ 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 ff977f016961..4b145db7c8c6 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#CountBitsSetPaallel
+ */
+ 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) {
--
2.17.0
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