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glsl: Add an optimization pass to flatten simple nested if blocks.

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GLBenchmark 2.7's shaders contain conditional blocks like:

if (x) {
    if (y) {
        ...
    }
}

where the outer conditional's then clause contains exactly one statement
(the nested if) and there are no else clauses.  This can easily be
optimized into:

if (x && y) {
    ...
}

This saves a few instructions in GLBenchmark 2.7:

    total instructions in shared programs: 11833 -> 11649 (-1.55%)
    instructions in affected programs:     8234 -> 8050 (-2.23%)

It also helps CS:GO slightly (-0.05%/-0.22%).  More importantly,
however, it simplifies the control flow graph, which could enable other
optimizations.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
This commit is contained in:
Kenneth Graunke
2013-04-03 23:56:57 -07:00
parent 967514ce68
commit edc52a8f28
4 changed files with 106 additions and 0 deletions
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1
src/glsl/ir_optimization.h
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@@ -82,6 +82,7 @@ bool do_function_inlining(exec_list *instructions);
bool do_lower_jumps(exec_list *instructions, bool pull_out_jumps = true, bool lower_sub_return = true, bool lower_main_return = false, bool lower_continue = false, bool lower_break = false);
bool do_lower_texture_projection(exec_list *instructions);
bool do_if_simplification(exec_list *instructions);
bool opt_flatten_nested_if_blocks(exec_list *instructions);
bool do_discard_simplification(exec_list *instructions);
bool lower_if_to_cond_assign(exec_list *instructions, unsigned max_depth = 0);
bool do_mat_op_to_vec(exec_list *instructions);