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agx/nir_lower_gs: rework XFB prim calculation

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significant instr count reduction for many outputs in a buffer.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35797>
This commit is contained in:
Alyssa Rosenzweig 2025-04-24 16:43:16 -04:00 • committed by Marge Bot
parent 46e139d453
commit 10554ccad2
1 changed files with 26 additions and 20 deletions
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46
src/asahi/lib/agx_nir_lower_gs.c
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@ -989,38 +989,44 @@ agx_nir_create_pre_gs(struct lower_gs_state *state, struct nir_xfb_info *xfb,
}
if (xfb) {
/* Write XFB addresses */
nir_def *offsets[4] = {NULL};
u_foreach_bit(i, xfb->buffers_written) {
offsets[i] = libagx_setup_xfb_buffer(
b, nir_load_geometry_param_buffer_agx(b), nir_imm_int(b, i));
}
/* Now clamp to the number that XFB captures */
unsigned max_output_end[4] = {0};
for (unsigned i = 0; i < xfb->output_count; ++i) {
nir_xfb_output_info output = xfb->outputs[i];
unsigned buffer = xfb->outputs[i].buffer;
unsigned buffer = output.buffer;
unsigned stream = xfb->buffer_to_stream[buffer];
unsigned stride = xfb->buffers[buffer].stride;
unsigned words_written = util_bitcount(output.component_mask);
unsigned bytes_written = words_written * 4;
unsigned output_end = output.offset + bytes_written;
max_output_end[buffer] = MAX2(max_output_end[buffer], output_end);
}
/* Primitive P will write up to (but not including) offset:
/* Write XFB addresses */
u_foreach_bit(i, xfb->buffers_written) {
nir_def *xfb_offset = libagx_setup_xfb_buffer(
b, nir_load_geometry_param_buffer_agx(b), nir_imm_int(b, i));
unsigned stream = xfb->buffer_to_stream[i];
unsigned stride = xfb->buffers[i].stride;
/* Let output_end = output_offset + output_size.
*
* Primitive P will write up to (but not including) offset:
*
* xfb_offset + ((P - 1) * (verts_per_prim * stride))
* + ((verts_per_prim - 1) * stride)
* + output_offset
* + output_size
* + output_end
*
* Given an XFB buffer of size xfb_size, we get the inequality:
*
* floor(P) <= (stride + xfb_size - xfb_offset - output_offset -
* output_size) // (stride * verts_per_prim)
* To fit all outputs for P, that value must be less than the XFB
* buffer size for the output with maximal output_end, as everything
* else is constant here across outputs within a buffer/primitive:
*
* floor(P) <= (stride + size - xfb_offset - output_end)
* // (stride * verts_per_prim)
*/
nir_def *size = load_geometry_param(b, xfb_size[buffer]);
size = nir_iadd_imm(b, size, stride - output.offset - bytes_written);
size = nir_isub(b, size, offsets[buffer]);
nir_def *size = load_geometry_param(b, xfb_size[i]);
size = nir_iadd_imm(b, size, stride - max_output_end[i]);
size = nir_isub(b, size, xfb_offset);
size = nir_imax(b, size, nir_imm_int(b, 0));
nir_def *max_prims = nir_udiv_imm(b, size, stride * vertices_per_prim);