void
vec4_gs_visitor::gs_end_primitive()
{
/* We can only do EndPrimitive() functionality when the control data
* consists of cut bits. Fortunately, the only time it isn't is when the
* output type is points, in which case EndPrimitive() is a no-op.
*/
if (gs_prog_data->control_data_format !=
GEN7_GS_CONTROL_DATA_FORMAT_GSCTL_CUT) {
return;
}
if (c->control_data_header_size_bits == 0)
return;
/* Cut bits use one bit per vertex. */
assert(c->control_data_bits_per_vertex == 1);
/* Cut bit n should be set to 1 if EndPrimitive() was called after emitting
* vertex n, 0 otherwise. So all we need to do here is mark bit
* (vertex_count - 1) % 32 in the cut_bits register to indicate that
* EndPrimitive() was called after emitting vertex (vertex_count - 1);
* vec4_gs_visitor::emit_control_data_bits() will take care of the rest.
*
* Note that if EndPrimitve() is called before emitting any vertices, this
* will cause us to set bit 31 of the control_data_bits register to 1.
* That's fine because:
*
* - If max_vertices < 32, then vertex number 31 (zero-based) will never be
* output, so the hardware will ignore cut bit 31.
*
* - If max_vertices == 32, then vertex number 31 is guaranteed to be the
* last vertex, so setting cut bit 31 has no effect (since the primitive
* is automatically ended when the GS terminates).
*
* - If max_vertices > 32, then the ir_emit_vertex visitor will reset the
* control_data_bits register to 0 when the first vertex is emitted.
*/
/* control_data_bits |= 1 << ((vertex_count - 1) % 32) */
src_reg one(this, glsl_type::uint_type);
emit(MOV(dst_reg(one), brw_imm_ud(1u)));
src_reg prev_count(this, glsl_type::uint_type);
emit(ADD(dst_reg(prev_count), this->vertex_count, brw_imm_ud(0xffffffffu)));
src_reg mask(this, glsl_type::uint_type);
/* Note: we're relying on the fact that the GEN SHL instruction only pays
* attention to the lower 5 bits of its second source argument, so on this
* architecture, 1 << (vertex_count - 1) is equivalent to 1 <<
* ((vertex_count - 1) % 32).
*/
emit(SHL(dst_reg(mask), one, prev_count));
emit(OR(dst_reg(this->control_data_bits), this->control_data_bits, mask));
}
/**
* Write out a batch of 32 control data bits from the control_data_bits
* register to the URB.
*
* The current value of the vertex_count register determines which DWORD in
* the URB receives the control data bits. The control_data_bits register is
* assumed to contain the correct data for the vertex that was most recently
* output, and all previous vertices that share the same DWORD.
*
* This function takes care of ensuring that if no vertices have been output
* yet, no control bits are emitted.
*/
void
vec4_gs_visitor::emit_control_data_bits()
{
assert(c->control_data_bits_per_vertex != 0);
/* Since the URB_WRITE_OWORD message operates with 128-bit (vec4 sized)
* granularity, we need to use two tricks to ensure that the batch of 32
* control data bits is written to the appropriate DWORD in the URB. To
* select which vec4 we are writing to, we use the "slot {0,1} offset"
* fields of the message header. To select which DWORD in the vec4 we are
* writing to, we use the channel mask fields of the message header. To
* avoid penalizing geometry shaders that emit a small number of vertices
* with extra bookkeeping, we only do each of these tricks when
* c->prog_data.control_data_header_size_bits is large enough to make it
* necessary.
*
* Note: this means that if we're outputting just a single DWORD of control
* data bits, we'll actually replicate it four times since we won't do any
* channel masking. But that's not a problem since in this case the
* hardware only pays attention to the first DWORD.
*/
enum brw_urb_write_flags urb_write_flags = BRW_URB_WRITE_OWORD;
if (c->control_data_header_size_bits > 32)
urb_write_flags = urb_write_flags | BRW_URB_WRITE_USE_CHANNEL_MASKS;
if (c->control_data_header_size_bits > 128)
urb_write_flags = urb_write_flags | BRW_URB_WRITE_PER_SLOT_OFFSET;
/* If vertex_count is 0, then no control data bits have been accumulated
* yet, so we should do nothing.
*/
emit(CMP(dst_null_d(), this->vertex_count, 0u, BRW_CONDITIONAL_NEQ));
emit(IF(BRW_PREDICATE_NORMAL));
{
/* If we are using either channel masks or a per-slot offset, then we
* need to figure out which DWORD we are trying to write to, using the
* formula:
*
* dword_index = (vertex_count - 1) * bits_per_vertex / 32
*
* Since bits_per_vertex is a power of two, and is known at compile
* time, this can be optimized to:
*
* dword_index = (vertex_count - 1) >> (6 - log2(bits_per_vertex))
*/
src_reg dword_index(this, glsl_type::uint_type);
if (urb_write_flags) {
src_reg prev_count(this, glsl_type::uint_type);
emit(ADD(dst_reg(prev_count), this->vertex_count, 0xffffffffu));
unsigned log2_bits_per_vertex =
_mesa_fls(c->control_data_bits_per_vertex);
emit(SHR(dst_reg(dword_index), prev_count,
(uint32_t) (6 - log2_bits_per_vertex)));
}
/* Start building the URB write message. The first MRF gets a copy of
* R0.
*/
int base_mrf = 1;
dst_reg mrf_reg(MRF, base_mrf);
src_reg r0(retype(brw_vec8_grf(0, 0), BRW_REGISTER_TYPE_UD));
vec4_instruction *inst = emit(MOV(mrf_reg, r0));
inst->force_writemask_all = true;
if (urb_write_flags & BRW_URB_WRITE_PER_SLOT_OFFSET) {
/* Set the per-slot offset to dword_index / 4, to that we'll write to
* the appropriate OWORD within the control data header.
*/
src_reg per_slot_offset(this, glsl_type::uint_type);
emit(SHR(dst_reg(per_slot_offset), dword_index, 2u));
emit(GS_OPCODE_SET_WRITE_OFFSET, mrf_reg, per_slot_offset, 1u);
}
if (urb_write_flags & BRW_URB_WRITE_USE_CHANNEL_MASKS) {
/* Set the channel masks to 1 << (dword_index % 4), so that we'll
* write to the appropriate DWORD within the OWORD. We need to do
* this computation with force_writemask_all, otherwise garbage data
* from invocation 0 might clobber the mask for invocation 1 when
* GS_OPCODE_PREPARE_CHANNEL_MASKS tries to OR the two masks
* together.
*/
src_reg channel(this, glsl_type::uint_type);
inst = emit(AND(dst_reg(channel), dword_index, 3u));
inst->force_writemask_all = true;
src_reg one(this, glsl_type::uint_type);
inst = emit(MOV(dst_reg(one), 1u));
inst->force_writemask_all = true;
src_reg channel_mask(this, glsl_type::uint_type);
inst = emit(SHL(dst_reg(channel_mask), one, channel));
inst->force_writemask_all = true;
emit(GS_OPCODE_PREPARE_CHANNEL_MASKS, dst_reg(channel_mask),
channel_mask);
emit(GS_OPCODE_SET_CHANNEL_MASKS, mrf_reg, channel_mask);
}
/* Store the control data bits in the message payload and send it. */
dst_reg mrf_reg2(MRF, base_mrf + 1);
inst = emit(MOV(mrf_reg2, this->control_data_bits));
inst->force_writemask_all = true;
inst = emit(GS_OPCODE_URB_WRITE);
inst->urb_write_flags = urb_write_flags;
/* We need to increment Global Offset by 256-bits to make room for
* Broadwell's extra "Vertex Count" payload at the beginning of the
* URB entry. Since this is an OWord message, Global Offset is counted
* in 128-bit units, so we must set it to 2.
*/
if (brw->gen >= 8)
inst->offset = 2;
inst->base_mrf = base_mrf;
inst->mlen = 2;
}
emit(BRW_OPCODE_ENDIF);
}
