[Mesa-dev] [PATCH 2/2] draw: simplify prim mask construction

[sroland at vmware.com]

From: Roland Scheidegger <sroland at vmware.com>

The code was quite weird, the second comparison was in fact a complete no-op
and we can also do the comparison with the vector directly instead of scalar,
which should not also be faster but it is way more obvious how that mask
is actually going to look like.
(Not sure how many instructions that saves as it turned out the mask wasn't
used in the test geometry shader I used at all after all...)
---
 src/gallium/auxiliary/draw/draw_llvm.c |   32 ++++++++++----------------------
 1 file changed, 10 insertions(+), 22 deletions(-)

diff --git a/src/gallium/auxiliary/draw/draw_llvm.c b/src/gallium/auxiliary/draw/draw_llvm.c
index 68f6369..84e3392 100644
--- a/src/gallium/auxiliary/draw/draw_llvm.c
+++ b/src/gallium/auxiliary/draw/draw_llvm.c
@@ -2040,31 +2040,19 @@ generate_mask_value(struct draw_gs_llvm_variant *variant,
 {
    struct gallivm_state *gallivm = variant->gallivm;
    LLVMBuilderRef builder = gallivm->builder;
-   LLVMValueRef bits[16];
-   struct lp_type  mask_type = lp_int_type(gs_type);
-   struct lp_type mask_elem_type = lp_elem_type(mask_type);
-   LLVMValueRef mask_val = lp_build_const_vec(gallivm,
-                                              mask_type,
-                                              0);
+   struct lp_type mask_type = lp_int_type(gs_type);
+   LLVMValueRef num_prims;
+   LLVMValueRef mask_val = lp_build_const_vec(gallivm, mask_type, 0);
    unsigned i;
 
-   assert(gs_type.length <= Elements(bits));
-
-   for (i = gs_type.length; i >= 1; --i) {
-      int idx = i - 1;
-      LLVMValueRef ind = lp_build_const_int32(gallivm, i);
-      bits[idx] = lp_build_compare(gallivm,
-                                   mask_elem_type, PIPE_FUNC_GEQUAL,
-                                   variant->num_prims, ind);
-   }
-   for (i = 0; i < gs_type.length; ++i) {
-      LLVMValueRef ind = lp_build_const_int32(gallivm, i);
-      mask_val = LLVMBuildInsertElement(builder, mask_val, bits[i], ind, "");
+   num_prims = lp_build_broadcast(gallivm, lp_build_vec_type(gallivm, mask_type),
+                                  variant->num_prims);
+   for (i = 0; i <= gs_type.length; i++) {
+      LLVMValueRef idx = lp_build_const_int32(gallivm, i);
+      mask_val = LLVMBuildInsertElement(builder, mask_val, idx, idx, "");
    }
-   mask_val = lp_build_compare(gallivm,
-                               mask_type, PIPE_FUNC_NOTEQUAL,
-                               mask_val,
-                               lp_build_const_int_vec(gallivm, mask_type, 0));
+   mask_val = lp_build_compare(gallivm, mask_type,
+                               PIPE_FUNC_GREATER, num_prims, mask_val);
 
    return mask_val;
 }
-- 
1.7.9.5