draw: cleanup and fix instance id computation

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 <[email protected]>
Reviewed-by: Roland Scheidegger <[email protected]>
Reviewed-by: Brian Paul <[email protected]>
Reviewed-by: Jose Fonseca <[email protected]>

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 79e7a9b6d12..a3174b404c1 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 ccde371ffcd..fcc24057db0 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 96e35b0eb41..fdab0f34a1a 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 a4f7b243c13..726a9b1e34b 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.
                 */