[Mesa-dev] [PATCH 4/3] glsl: tidy up IR after loop unrolling

[Timothy Arceri]

c7affbf6875622a enabled GLSLOptimizeConservatively on some
drivers. The idea was to speed up compile times by running
the GLSL IR passes only once each time do_common_optimization()
is called. However loop unrolling can create a big mess and
with large loops can actually case compile times to increase
significantly due to a bunch of redundant if statements being
propagated to other IRs.

Here we make sure to clean things up before moving on.

There was no measureable difference in shader-db compile times,
but it makes compile times of some piglit tests go from a couple
of seconds to basically instant.

The shader-db results seemed positive also:

Totals:
SGPRS: 2829456 -> 2828376 (-0.04 %)
VGPRS: 1720793 -> 1721457 (0.04 %)
Spilled SGPRs: 7707 -> 7707 (0.00 %)
Spilled VGPRs: 33 -> 33 (0.00 %)
Private memory VGPRs: 3140 -> 2060 (-34.39 %)
Scratch size: 3308 -> 2180 (-34.10 %) dwords per thread
Code Size: 79441464 -> 79214616 (-0.29 %) bytes
LDS: 436 -> 436 (0.00 %) blocks
Max Waves: 558670 -> 558571 (-0.02 %)
Wait states: 0 -> 0 (0.00 %)
---
 src/compiler/glsl/glsl_parser_extras.cpp | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/compiler/glsl/glsl_parser_extras.cpp b/src/compiler/glsl/glsl_parser_extras.cpp
index 9cbc2355f9..764c05ad80 100644
--- a/src/compiler/glsl/glsl_parser_extras.cpp
+++ b/src/compiler/glsl/glsl_parser_extras.cpp
@@ -2209,21 +2209,27 @@ do_common_optimization(exec_list *ir, bool linked,
    OPT(lower_vector_insert, ir, false);
    OPT(do_swizzle_swizzle, ir);
    OPT(do_noop_swizzle, ir);
 
    OPT(optimize_split_arrays, ir, linked);
    OPT(optimize_redundant_jumps, ir);
 
    if (options->MaxUnrollIterations) {
       loop_state *ls = analyze_loop_variables(ir);
       if (ls->loop_found) {
-         OPT(unroll_loops, ir, ls, options);
+         bool loop_progress = unroll_loops(ir, ls, options);
+         while (loop_progress) {
+            loop_progress = false;
+            loop_progress |= do_constant_propagation(ir);
+            loop_progress |= do_if_simplification(ir);
+         }
+         progress |= loop_progress;
       }
       delete ls;
    }
 
 #undef OPT
 
    return progress;
 }
 
 extern "C" {
-- 
2.13.5