On 23/01/2014 22:26, August Oktobar wrote:
Hello, I have seen your mails about peephole optimization, so I wonder
if you could look at this reports
http://bugs.freepascal.org/view.php?id=23595
or perhaps optimize slow array access using operator [] (it is faster
to use pointer arithmetics)
thanks!
1) I am just getting started on this, so I can only answer with limited
knowledge.
@experts, please correct me below, where needed
2) The peephole opt is only something I do "on the side" as it currently is.
From a quick glance, this does not look like something for the peephole
opt.
The peephole opt currently looks at statements that are close together
(follow each other immediately).
I am not sure to which extend (if at all) it would be acceptable to
break that limit (it is doable, question is if desired).
In this specific case:
1) between the "fstpl" and the "mov (half_the_data), %edi" are other
statements.
detecting the connection would either:
- need scanning several statements ahead. This would be slow, because
it had to be done after each storing "something to memory" (so very often)
- keeping state of all the involved registers and memory (do-able /
interesting at least from a theoretical view / but not sure if desired)
2) only half the mem is accessed, and then the other half. That means to
detect the connection between the mem read and the register, it is
needed to analyse 4 statements. Very unlikely to see this in the
peephole opt.
The livelihood of "a[i]" needs to be checked where the code is generated.
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