glsl: Correctly return progress from lower_variable_index_to_cond_assign

lower_variable_index_to_cond_assign runs until it can't make any more
progress.  It then returns the result of the last pass which will
always be false.  This caused the lowering loop in
_mesa_ir_link_shader to end before doing one last round of
lower_if_to_cond_assign.  This caused several if-statements (resulting
from lower_variable_index_to_cond_assign) to be left in the IR.

In addition to this change, lower_variable_index_to_cond_assign should
take a flag indicating whether or not it should even generate
if-statements.  This is easily controlled by
switch_generator::linear_sequence_max_length.  This would generate
much better code on architectures without any flow contol.

Fixes i915 piglit regressions glsl-texcoord-array and
glsl-fs-vec4-indexing-temp-src.

Reviewed-by: Eric Anholt <eric@anholt.net>

diff --git a/src/glsl/lower_variable_index_to_cond_assign.cpp b/src/glsl/lower_variable_index_to_cond_assign.cpp
index 7792e6e624fcc0cbcc138d439209262b07584801..f8e4a1de428a1566bb90d2921d318adc3798df01 100644 (file)
--- a/src/glsl/lower_variable_index_to_cond_assign.cpp
+++ b/src/glsl/lower_variable_index_to_cond_assign.cpp
@@ -525,10 +525,12 @@ lower_variable_index_to_cond_assign(exec_list *instructions,
     * matrix columns of an array of matrix), each pass will only lower one
     * level of indirection.
     */
+   bool progress_ever = false;
    do {
       v.progress = false;
       visit_list_elements(&v, instructions);
+      progress_ever = v.progress || progress_ever;
    } while (v.progress);
 
-   return v.progress;
+   return progress_ever;
 }