[Mesa-dev] [PATCH 3/3] glsl: relax loop unrolling restrictions

[Timothy Arceri]

The main reason these restriction exist is because glsl the loop
unrolling pass is super slow with large loops.

be5f27a84d0d fixed things so that expression trees were counted
against the limit, however it left the limit as
max_iterations * 5 which is actually fine for most shaders but
probably over conservative.

This change relaxes the limit to allow more loops to unroll in the
Unigine Superposition benchmark.

Results from Unigine Superposition @ 1920x1080 - High - Fullscreen
On radeonsi (RX480)

Before:

Average: 28.20 Frames Per Second

After:

Average: 28.60 Frames Per Second
---

 The increase is small but it seems to be consistent, I would be
 interested in the results if others were interested in testing it.

 src/compiler/glsl/loop_unroll.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/compiler/glsl/loop_unroll.cpp b/src/compiler/glsl/loop_unroll.cpp
index bc377df..64ebf0f 100644
--- a/src/compiler/glsl/loop_unroll.cpp
+++ b/src/compiler/glsl/loop_unroll.cpp
@@ -350,21 +350,21 @@ loop_unroll_visitor::visit_leave(ir_loop *ir)
    /* Don't try to unroll loops that have zillions of iterations either.
     */
    if (iterations > max_iterations)
       return visit_continue;
 
    /* Don't try to unroll nested loops and loops with a huge body.
     */
    loop_unroll_count count(&ir->body_instructions, ls, options);
 
    bool loop_too_large =
-      count.nested_loop || count.nodes * iterations > max_iterations * 5;
+      count.nested_loop || count.nodes * iterations > max_iterations * 10;
 
    if (loop_too_large && !count.unsupported_variable_indexing &&
        !count.array_indexed_by_induction_var_with_exact_iterations)
       return visit_continue;
 
    /* Note: the limiting terminator contributes 1 to ls->num_loop_jumps.
     * We'll be removing the limiting terminator before we unroll.
     */
    assert(ls->num_loop_jumps > 0);
    unsigned predicted_num_loop_jumps = ls->num_loop_jumps - 1;
-- 
2.9.4