[Mesa-dev] [PATCH 50/74] i965/vec4: Implement SSBO writes
Iago Toral Quiroga
itoral at igalia.com
Thu May 14 07:06:53 PDT 2015
---
src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp | 140 ++++++++++++++++++++++++-
1 file changed, 138 insertions(+), 2 deletions(-)
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
index 5268582..41ca007 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
@@ -25,6 +25,11 @@
#include "brw_cfg.h"
#include "glsl/ir_uniform.h"
#include "program/sampler.h"
+#include "brw_vec4_builder.h"
+#include "brw_vec4_surface_builder.h"
+
+using namespace brw;
+using namespace brw::surface_access;
namespace brw {
@@ -3004,9 +3009,140 @@ vec4_visitor::visit(ir_end_primitive *)
}
void
-vec4_visitor::visit(ir_ssbo_store *)
+vec4_visitor::visit(ir_ssbo_store *ir)
{
- unreachable("not implemented yet");
+ ir_constant *const_uniform_block = ir->block->as_constant();
+ ir_constant *const_offset_ir = ir->offset->as_constant();
+
+ src_reg surf_index;
+ if (const_uniform_block) {
+ unsigned index = prog_data->base.binding_table.ubo_start +
+ const_uniform_block->value.u[0];
+ surf_index = src_reg(index);
+
+ brw_mark_surface_used(&prog_data->base, index);
+ } else {
+ ir->block->accept(this);
+ src_reg block_reg = this->result;
+ surf_index = src_reg(this, glsl_type::uint_type);
+ emit(ADD(dst_reg(surf_index), block_reg,
+ src_reg(prog_data->base.binding_table.ubo_start)));
+
+ brw_mark_surface_used(&prog_data->base,
+ prog_data->base.binding_table.ubo_start +
+ shader_prog->NumUniformBlocks - 1);
+ }
+
+ unsigned const_offset_bytes =
+ const_offset_ir ? const_offset_ir->value.u[0] : 0;
+
+ src_reg offset = src_reg(this, glsl_type::uint_type);
+ ir->offset->accept(this);
+ emit(MOV(dst_reg(offset), this->result));
+
+ src_reg val_reg = src_reg(this, glsl_type::vec4_type);
+ ir->val->accept(this);
+ val_reg.type = this->result.type;
+ emit(MOV(dst_reg(val_reg), this->result));
+
+ /* IvyBridge does not have a native SIMD4x2 untyped write message so untyped
+ * writes will use SIMD8 mode. In order to hide this and keep symmetry across
+ * typed and untyped messages and across hardware platforms, the
+ * current implementation of the untyped messages will transparently convert
+ * the SIMD4x2 payload into an equivalent SIMD8 payload by transposing it
+ * and enabling only channel X on the SEND instruction.
+ *
+ * The above, works well for full vector writes, but not for partial writes
+ * where we want to write some channels and not others, like when we have
+ * code such as v.xyw = vec3(1,2,4). Because the untyped write messages are
+ * quite restrictive with regards to the channel enables we can configure in
+ * the message descriptor (not all combinations are allowed) we cannot simply
+ * implement these scenarios with a single message while keeping the
+ * aforementioned symmetry in the implementation. For now we de decided that
+ * it is better to keep the symmetry to reduce complexity, so in situations
+ * such as the one described we end up emitting two untyped write messages
+ * (one for xy and another for w).
+ *
+ * The code below packs consecutive channels into a single write message,
+ * detects gaps in the vector write and if needed, sends a second message
+ * with the remaining channels. If in the future we decide that we want to
+ * emit a single message at the expense of losing the symmetry in the
+ * implementation we can:
+ *
+ * 1) For IvyBridge: Only use the red channel of the untyped write SIMD8
+ * message payload. In this mode we can write up to 8 offsets and dwords
+ * to the red channel only (for the two vec4s in the SIMD4x2 execution)
+ * and select which of the 8 channels carry data to write by setting the
+ * appropriate writemask in the dst register of the SEND instruction.
+ * It would require to write a new generator opcode specifically for
+ * IvyBridge since we would need to prepare a SIMD8 payload that could
+ * use any channel, not just X.
+ *
+ * 2) For Haswell+: Simply send a single write message but set the writemask
+ * on the dst of the SEND instruction to select the channels we want to
+ * write. It would require to modify the current messages to receive
+ * and honor the writemask provided.
+ */
+ vec4_builder bld(devinfo, mem_ctx, alloc, instructions);
+ bld.set_annotation(current_annotation);
+ bld.set_base_ir(base_ir);
+
+ int swizzle[4] = { 0, 0, 0, 0};
+ int num_channels = 0;
+ unsigned skipped_channels = 0;
+ int num_components = ir->val->type->vector_elements;
+ for (int i = 0; i < num_components; i++) {
+ /* Check if this channel needs to be written. If so, record the
+ * channel we need to take the data from in the swizzle array
+ */
+ int component_mask = 1 << i;
+ int write_test = ir->write_mask & component_mask;
+ if (write_test)
+ swizzle[num_channels++] = i;
+
+ /* If we don't have to write this channel it means we have a gap in the
+ * vector, so write the channels we accumulated until now, if any. Do
+ * the same if this was the last component in the vector.
+ */
+ if (!write_test || i == num_components - 1) {
+ if (num_channels > 0) {
+ /* We have channels to write, so update the offset we need to
+ * write at to skip the channels we skipped, if any.
+ */
+ if (skipped_channels > 0) {
+ if (const_offset_ir) {
+ const_offset_bytes += 4 * skipped_channels;
+ offset = src_reg(const_offset_bytes);
+ } else {
+ emit(ADD(dst_reg(offset), offset,
+ brw_imm_ud(4 * skipped_channels)));
+ }
+ }
+
+ /* Swizzle the data register so we take the data from the channels
+ * we need to write and send the write message. This will write
+ * num_channels consecutive dwords starting at offset.
+ */
+ val_reg.swizzle =
+ BRW_SWIZZLE4(swizzle[0], swizzle[1], swizzle[2], swizzle[3]);
+ emit_untyped_write(bld, surf_index, offset, val_reg,
+ 1 /* dims */, num_channels /* size */,
+ BRW_PREDICATE_NONE);
+
+ /* If we have to do a second write we will have to update the
+ * offset so that we jump over the channels we have just written
+ * now.
+ */
+ skipped_channels = num_channels;
+
+ /* Restart the count for the next write message */
+ num_channels = 0;
+ }
+
+ /* We did not write the current channel, so increase skipped count */
+ skipped_channels++;
+ }
+ }
}
void
--
1.9.1
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