i965/fs: Add a comment about about an implementation detail.

I was going to fix the code above like the previous commit, but we already
had that covered (otherwise all our uniform access would have been broken,
unlike just pull constants).

Reviewed-by: Kenneth Graunke <[email protected]>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp b/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp
index d1147f544e4..b8936dcfe7d 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp
@@ -310,6 +310,10 @@ fs_visitor::setup_payload_interference(struct ra_graph *g,
        * node.
        */
       for (int j = 0; j < this->virtual_grf_count; j++) {
+         /* Note that we use a <= comparison, unlike virtual_grf_interferes(),
+          * in order to not have to worry about the uniform issue described in
+          * calculate_live_intervals().
+          */
          if (this->virtual_grf_def[j] <= payload_last_use_ip[i] ||
              this->virtual_grf_use[j] <= payload_last_use_ip[i]) {
             ra_add_node_interference(g, first_payload_node + i, j);