[Mesa-dev] [PATCH] glsl: store read vector in a temp in vec_index_to_cond

[Vincent Lejeune]

Vector indexing on matrixes generates several copy of the
constant matrix, for instance vec=mat4[i][j] generates :
vec=mat4[i].x;
vec=(j==1)?mat4[i].y;
vec=(j==2)?mat4[i].z;
vec=(j==3)?mat4[i].w;
In the case of constant matrixes, the mat4[i] expression generates
copy of the 16 elements of the matrix 4 times ; indirect addressing
also prevents some conservative CSE algorithms (like the one in LLVM)
from factoring the mat4[i] expression.
This patch will make the vec_index_to_cond pass generates :
temp = mat4[i];
vec=temp.x;
vec=(j==1)?temp.y;
vec=(j==2)?temp.z;
vec=(j==3)?temp.w;
---
 src/glsl/lower_vec_index_to_cond_assign.cpp | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/glsl/lower_vec_index_to_cond_assign.cpp b/src/glsl/lower_vec_index_to_cond_assign.cpp
index fce9c34..f8b4131 100644
--- a/src/glsl/lower_vec_index_to_cond_assign.cpp
+++ b/src/glsl/lower_vec_index_to_cond_assign.cpp
@@ -68,9 +68,9 @@ ir_rvalue *
 ir_vec_index_to_cond_assign_visitor::convert_vec_index_to_cond_assign(ir_rvalue *ir)
 {
    ir_dereference_array *orig_deref = ir->as_dereference_array();
-   ir_assignment *assign;
-   ir_variable *index, *var;
-   ir_dereference *deref;
+   ir_assignment *assign, *value_assign;
+   ir_variable *index, *var, *value;
+   ir_dereference *deref, *deref_value;
    int i;
 
    if (!orig_deref)
@@ -95,6 +95,14 @@ ir_vec_index_to_cond_assign_visitor::convert_vec_index_to_cond_assign(ir_rvalue
    assign = new(base_ir) ir_assignment(deref, orig_deref->array_index, NULL);
    list.push_tail(assign);
 
+   /* Store the value inside a temp, thus avoiding matrixes duplication */
+   value = new(base_ir) ir_variable(orig_deref->array->type, "vec_value_tmp",
+				    ir_var_temporary);
+   list.push_tail(value);
+   deref_value = new(base_ir) ir_dereference_variable(value);
+   value_assign = new(base_ir) ir_assignment(deref_value, orig_deref->array);
+   list.push_tail(value_assign);
+
    /* Temporary where we store whichever value we swizzle out. */
    var = new(base_ir) ir_variable(ir->type, "vec_index_tmp_v",
 				  ir_var_temporary);
@@ -117,7 +125,7 @@ ir_vec_index_to_cond_assign_visitor::convert_vec_index_to_cond_assign(ir_rvalue
        * underlying variable.
        */
       ir_rvalue *swizzle =
-	 new(base_ir) ir_swizzle(orig_deref->array->clone(mem_ctx, NULL),
+	 new(base_ir) ir_swizzle(deref_value->clone(mem_ctx, NULL),
 				 i, 0, 0, 0, 1);
 
       deref = new(base_ir) ir_dereference_variable(var);
-- 
1.7.11.7