[Mesa-dev] [PATCH 1/3] draw: cleanup and fix instance id computation

[Zack Rusin]

The instance id system value always starts at 0, even if the
specified start instance is larger than 0. Instead of implicitly
setting instance id to instance id plus start instance and then
having to subtract instance id when computing the buffer offsets
lets just set instance id to the proper instance id. This fixes
instance id computation and cleansup buffer offset computation.

Signed-off-by: Zack Rusin <zackr at vmware.com>
---
 src/gallium/auxiliary/draw/draw_llvm.c              |    7 +++----
 src/gallium/auxiliary/draw/draw_pt.c                |    7 ++++---
 src/gallium/auxiliary/translate/translate_generic.c |    3 +--
 src/gallium/auxiliary/translate/translate_sse.c     |    4 ----
 4 files changed, 8 insertions(+), 13 deletions(-)

diff --git a/src/gallium/auxiliary/draw/draw_llvm.c b/src/gallium/auxiliary/draw/draw_llvm.c
index 79e7a9b..a3174b4 100644
--- a/src/gallium/auxiliary/draw/draw_llvm.c
+++ b/src/gallium/auxiliary/draw/draw_llvm.c
@@ -707,15 +707,14 @@ generate_fetch(struct gallivm_state *gallivm,
    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:
-       * index = start_instance + ((instance_id - start_instance) / divisor)
+       * index = start_instance + (instance_id  / divisor)
        */
       LLVMValueRef current_instance;
       index = lp_build_const_int32(gallivm, draw->start_instance);
-      current_instance = LLVMBuildSub(builder, instance_id, index, "");
-      current_instance = LLVMBuildUDiv(builder, current_instance,
+      current_instance = LLVMBuildUDiv(builder, instance_id,
                                        lp_build_const_int32(gallivm, velem->instance_divisor),
                                        "instance_divisor");
-      index = LLVMBuildAdd(builder, index, current_instance, "instance");
+      index = lp_build_uadd_overflow(gallivm, index, current_instance, &ofbit);
    }
 
    stride = lp_build_umul_overflow(gallivm, vb_stride, index, &ofbit);
diff --git a/src/gallium/auxiliary/draw/draw_pt.c b/src/gallium/auxiliary/draw/draw_pt.c
index ccde371..fcc2405 100644
--- a/src/gallium/auxiliary/draw/draw_pt.c
+++ b/src/gallium/auxiliary/draw/draw_pt.c
@@ -542,11 +542,12 @@ draw_vbo(struct draw_context *draw,
     */
 
    for (instance = 0; instance < info->instance_count; instance++) {
-      draw->instance_id = instance + info->start_instance;
+      unsigned instance_idx = instance + info->start_instance;
       draw->start_instance = info->start_instance;
+      draw->instance_id = instance;
       /* check for overflow */
-      if (draw->instance_id < instance ||
-          draw->instance_id < info->start_instance) {
+      if (instance_idx < instance ||
+          instance_idx < draw->start_instance) {
          /* if we overflown just set the instance id to the max */
          draw->instance_id = 0xffffffff;
       }
diff --git a/src/gallium/auxiliary/translate/translate_generic.c b/src/gallium/auxiliary/translate/translate_generic.c
index 96e35b0..fdab0f3 100644
--- a/src/gallium/auxiliary/translate/translate_generic.c
+++ b/src/gallium/auxiliary/translate/translate_generic.c
@@ -625,8 +625,7 @@ static ALWAYS_INLINE void PIPE_CDECL generic_run_one( struct translate_generic *
 
          if (tg->attrib[attr].instance_divisor) {
             index = start_instance;
-            index += (instance_id - start_instance) /
-               tg->attrib[attr].instance_divisor;
+            index += (instance_id  / tg->attrib[attr].instance_divisor);
             /* XXX we need to clamp the index here too, but to a
              * per-array max value, not the draw->pt.max_index value
              * that's being given to us via translate->set_buffer().
diff --git a/src/gallium/auxiliary/translate/translate_sse.c b/src/gallium/auxiliary/translate/translate_sse.c
index a4f7b24..726a9b1 100644
--- a/src/gallium/auxiliary/translate/translate_sse.c
+++ b/src/gallium/auxiliary/translate/translate_sse.c
@@ -1094,10 +1094,6 @@ static boolean init_inputs( struct translate_sse *p,
                struct x86_reg tmp_EDX = p->tmp2_EDX;
                struct x86_reg tmp_ECX = p->src_ECX;
 
-               /* instance_num = instance_id - start_instance */
-               x86_mov(p->func, tmp_EDX, start_instance);
-               x86_sub(p->func, tmp_EAX, tmp_EDX);
-
                /* TODO: Add x86_shr() to rtasm and use it whenever
                 *       instance divisor is power of two.
                 */
-- 
1.7.10.4