On 04/19/2013 06:04 AM, pkucoin wrote:
Hi,
My name is Sida Li and I am a senior student from Peking University in
China. I am interested in the idea that
improved application of GLSL complier optimizations.
I have downloaded the source code and read some parts of the it. First
let me talk about my understanding about the problem.
The loop we try to improve should be in the main.cpp:
do {
progress = do_common_optimization(shader->ir, false, false, 32);
} while (progress);
In the function do_common_optimization, all optimization passes are
called in a certain order. As the loop goes in a few times, some
optimization passes do not contribute to optimizing the code since the
original unoptimized code has been optimized and no more code that can
be optimized by these optimization passes is generated by
other optimization passes. So time spending on these optimization passes
is wasted.
The goal is to find a static ordering, with possible repeats, of
optimization passes that does not compromise the quality of the
generated code. I find it difficult to start because a single
optimization pass or a combo of optimization passes may generate some
code that can be optimized by other optimization pass, which can not be
decided before.
Since I suggested the project, I'll offer some opinions.
There are a few ways to attack this problem, I think. Certain
optimizations can generate opportunities for other optimizations to do
work. For example, copy propagation can "create" dead code. Using this
sort of analysis, it should be possible to come up with an initial
ordering of passes that still uses the "while progress" loop.
Once that is done, it should be possible to instrument the code to see
which optimization passes make progress on each pass. This will let us
know, for example, if do_algebraic never does anything after the first
pass. Then it's a matter of running the compiler on a large set of
shaders and seeing what happens.
Can you give me some advice?
Best regards,
Sida Li
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