[Mesa-dev] [PATCH] draw: improved handling of undefined inputs

[sroland at vmware.com]

From: Roland Scheidegger <sroland at vmware.com>

Previous attempts to zero initialize all inputs were not really optimal
(though no performance impact was measurable). In fact this is not really
necessary, since we know the max number of inputs used.
Instead, just generate fetch for up to max inputs used by the shader,
directly replacing inputs for which there was no vertex element by zero.
This also cleans up key generation, which previously would have stored
some garbage for these elements.
And also drop the assertion which indicates such bogus usage by a
debug_printf (the whole point of initializing the undefined inputs was to
make this case safe to handle).
---
 src/gallium/auxiliary/draw/draw_llvm.c | 53 ++++++++++++++++++++--------------
 1 file changed, 32 insertions(+), 21 deletions(-)

diff --git a/src/gallium/auxiliary/draw/draw_llvm.c b/src/gallium/auxiliary/draw/draw_llvm.c
index 4270a8f..3b56856 100644
--- a/src/gallium/auxiliary/draw/draw_llvm.c
+++ b/src/gallium/auxiliary/draw/draw_llvm.c
@@ -689,6 +689,11 @@ generate_fetch(struct gallivm_state *gallivm,
    LLVMValueRef ofbit = NULL;
    struct lp_build_if_state if_ctx;
 
+   if (velem->src_format == PIPE_FORMAT_NONE) {
+      *res = lp_build_const_vec(gallivm, lp_float32_vec4_type(), 0);
+      return;
+   }
+
    if (velem->instance_divisor) {
       /* Index is equal to the start instance plus the number of current 
        * instance divided by the divisor. In this case we compute it as:
@@ -1706,12 +1711,6 @@ draw_llvm_generate(struct draw_llvm *llvm, struct draw_llvm_variant *variant,
                       io_itr, io, lp_loop.counter);
 #endif
 
-      for (j = draw->pt.nr_vertex_elements; j < PIPE_MAX_SHADER_INPUTS; j++) {
-         for (i = 0; i < TGSI_NUM_CHANNELS; i++) {
-            inputs[j][i] = lp_build_zero(gallivm, vs_type);
-         }
-      }
-
       for (i = 0; i < vector_length; ++i) {
          LLVMValueRef vert_index =
             LLVMBuildAdd(builder,
@@ -1765,7 +1764,7 @@ draw_llvm_generate(struct draw_llvm *llvm, struct draw_llvm_variant *variant,
             gallivm->builder, true_index_array, true_index,
             lp_build_const_int32(gallivm, i), "");
 
-         for (j = 0; j < draw->pt.nr_vertex_elements; ++j) {
+         for (j = 0; j < key->nr_vertex_elements; ++j) {
             struct pipe_vertex_element *velem = &draw->pt.vertex_element[j];
             LLVMValueRef vb_index =
                lp_build_const_int32(gallivm, velem->vertex_buffer_index);
@@ -1776,7 +1775,7 @@ draw_llvm_generate(struct draw_llvm *llvm, struct draw_llvm_variant *variant,
          }
       }
       convert_to_soa(gallivm, aos_attribs, inputs,
-                     draw->pt.nr_vertex_elements, vs_type);
+                     key->nr_vertex_elements, vs_type);
 
       /* In the paths with elts vertex id has to be unaffected by the
        * index bias and because indices inside our elements array have
@@ -1873,15 +1872,6 @@ draw_llvm_make_variant_key(struct draw_llvm *llvm, char *store)
 
    key->clamp_vertex_color = llvm->draw->rasterizer->clamp_vertex_color; /**/
 
-   /* Presumably all variants of the shader should have the same
-    * number of vertex elements - ie the number of shader inputs.
-    * NOTE: we NEED to store the needed number of needed inputs
-    * here, not the number of provided elements to match keysize
-    * (and the offset of sampler state in the key).
-    */
-   key->nr_vertex_elements = llvm->draw->vs.vertex_shader->info.file_max[TGSI_FILE_INPUT] + 1;
-   assert(key->nr_vertex_elements <= llvm->draw->pt.nr_vertex_elements);
-
    /* will have to rig this up properly later */
    key->clip_xy = llvm->draw->clip_xy;
    key->clip_z = llvm->draw->clip_z;
@@ -1907,13 +1897,34 @@ draw_llvm_make_variant_key(struct draw_llvm *llvm, char *store)
       key->nr_sampler_views = key->nr_samplers;
    }
 
-   draw_sampler = draw_llvm_variant_key_samplers(key);
-
+   /* Presumably all variants of the shader should have the same
+    * number of vertex elements - ie the number of shader inputs.
+    * NOTE: we NEED to store the needed number of needed inputs
+    * here, not the number of provided elements to match keysize
+    * (and the offset of sampler state in the key).
+    * If we have excess number of vertex elements, this is valid,
+    * but the excess ones don't matter.
+    * If we don't have enough vertex elements (which looks not really
+    * valid but we'll handle it gracefully) fill out missing ones with
+    * zero (we'll recognize these later by PIPE_FORMAT_NONE).
+    */
+   key->nr_vertex_elements =
+      llvm->draw->vs.vertex_shader->info.file_max[TGSI_FILE_INPUT] + 1;
+
+   if (llvm->draw->pt.nr_vertex_elements < key->nr_vertex_elements) {
+      debug_printf("draw: vs with %d inputs but only have %d vertex elements\n",
+                   key->nr_vertex_elements, llvm->draw->pt.nr_vertex_elements);
+      memset(key->vertex_element, 0,
+             sizeof(struct pipe_vertex_element) * key->nr_vertex_elements);
+   }
    memcpy(key->vertex_element,
           llvm->draw->pt.vertex_element,
-          sizeof(struct pipe_vertex_element) * key->nr_vertex_elements);
+          sizeof(struct pipe_vertex_element) *
+             MIN2(key->nr_vertex_elements, llvm->draw->pt.nr_vertex_elements));
 
-   memset(draw_sampler, 0, MAX2(key->nr_samplers, key->nr_sampler_views) * sizeof *draw_sampler);
+   draw_sampler = draw_llvm_variant_key_samplers(key);
+   memset(draw_sampler, 0,
+          MAX2(key->nr_samplers, key->nr_sampler_views) * sizeof *draw_sampler);
 
    for (i = 0 ; i < key->nr_samplers; i++) {
       lp_sampler_static_sampler_state(&draw_sampler[i].sampler_state,
-- 
2.7.4