[Mesa-dev] [PATCH v2] i965/fs: force pull model for 64-bit GS inputs

[Iago Toral Quiroga]

Triggering the push model when 64-bit inputs are involved is not easy due to
the constrains on the maximum number of registers that we allow for this mode,
however, for GS with 'points' primitive type and just a couple of double
varyings we can trigger this and it just doesn't work because the
implementation is not 64-bit aware at all. For now, let's make sure that we
don't attempt this model whith 64-bit inputs and we always fall back to pull
model for them.

Also, don't enable the VUE handles in the thread payload on the fly when we
find an input for which we need the pull model, this is not safe: if we need
to resort to the pull model we need to account for that when we setup the
thread payload so we compute the first non-payload register properly. If we
didn't do that correctly and we enable it on-the-fly here then we will end up
VUE handles on the first non-payload register which will probably lead to
GPU hangs. Instead, always enable the VUE handles for the pull model so we
can safely use them when needed. The GS is going to resort to pull model
almost in every situation anyway, so this shouldn't make a significant
difference and it makes things easier and safer.

v2: Always enable the VUE handles for pull model, this is easier and safer
    and the GS is going to fallback to pull model almost always anyway (Ken)
---
 src/intel/compiler/brw_fs.cpp     | 30 +++++++++++++++++-------------
 src/intel/compiler/brw_fs_nir.cpp |  4 +++-
 2 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/src/intel/compiler/brw_fs.cpp b/src/intel/compiler/brw_fs.cpp
index eb9b4c38909..1517e87158b 100644
--- a/src/intel/compiler/brw_fs.cpp
+++ b/src/intel/compiler/brw_fs.cpp
@@ -5602,25 +5602,29 @@ fs_visitor::setup_gs_payload()
       payload.num_regs++;
    }
 
+   /* Always enable VUE handles so we can safely use pull model if needed.
+    *
+    * The push model for a GS uses a ton of register space even for trivial
+    * scenarios with just a few inputs, so just make things easier and a bit
+    * safer by always having pull model available.
+    */
+   gs_prog_data->base.include_vue_handles = true;
+
+   /* R3..RN: ICP Handles for each incoming vertex (when using pull model) */
+   payload.num_regs += nir->info.gs.vertices_in;
+
    /* Use a maximum of 24 registers for push-model inputs. */
    const unsigned max_push_components = 24;
 
-   /* If pushing our inputs would take too many registers, reduce the URB read
-    * length (which is in HWords, or 8 registers), and resort to pulling.
+   /* We want to use a maximum of 24 registers for push-model inputs, so make
+    * sure our URB read length (which is in HWords, or 8 registers) respects
+    * that.
     *
     * Note that the GS reads <URB Read Length> HWords for every vertex - so we
-    * have to multiply by VerticesIn to obtain the total storage requirement.
+    * have to account for by VerticesIn to obtain the total storage requirement.
     */
-   if (8 * vue_prog_data->urb_read_length * nir->info.gs.vertices_in >
-       max_push_components || gs_prog_data->invocations > 1) {
-      gs_prog_data->base.include_vue_handles = true;
-
-      /* R3..RN: ICP Handles for each incoming vertex (when using pull model) */
-      payload.num_regs += nir->info.gs.vertices_in;
-
-      vue_prog_data->urb_read_length =
-         ROUND_DOWN_TO(max_push_components / nir->info.gs.vertices_in, 8) / 8;
-   }
+   vue_prog_data->urb_read_length =
+      ROUND_DOWN_TO(max_push_components / nir->info.gs.vertices_in, 8) / 8;
 }
 
 void
diff --git a/src/intel/compiler/brw_fs_nir.cpp b/src/intel/compiler/brw_fs_nir.cpp
index d760946e624..aa57bb9d786 100644
--- a/src/intel/compiler/brw_fs_nir.cpp
+++ b/src/intel/compiler/brw_fs_nir.cpp
@@ -1915,7 +1915,9 @@ fs_visitor::emit_gs_input_load(const fs_reg &dst,
    const unsigned push_reg_count = gs_prog_data->base.urb_read_length * 8;
 
    /* TODO: figure out push input layout for invocations == 1 */
+   /* TODO: make this work with 64-bit inputs */
    if (gs_prog_data->invocations == 1 &&
+       type_sz(dst.type) <= 4 &&
        offset_const != NULL && vertex_const != NULL &&
        4 * (base_offset + offset_const->u32[0]) < push_reg_count) {
       int imm_offset = (base_offset + offset_const->u32[0]) * 4 +
@@ -1928,7 +1930,7 @@ fs_visitor::emit_gs_input_load(const fs_reg &dst,
    }
 
    /* Resort to the pull model.  Ensure the VUE handles are provided. */
-   gs_prog_data->base.include_vue_handles = true;
+   assert(gs_prog_data->base.include_vue_handles);
 
    unsigned first_icp_handle = gs_prog_data->include_primitive_id ? 3 : 2;
    fs_reg icp_handle = bld.vgrf(BRW_REGISTER_TYPE_UD, 1);
-- 
2.11.0