[fpc-devel] Case block optimisation

[J. Gareth Moreton]

 I'll see what I can do!

 The one thing about my case optimisations here is that they're done at the
node level.  Some parts are platform-independent, but unfortunately,
things like jump table generation have to be implemented for each platform.

 The aint shuffling is a little difficult to test for sure, but what's
worse is the use of TConstExprInt, and not just because of the overhead
involved with reading and writing to them.  I used logic in some places
though, like when I do a sort of for-loop between max_ and hv, I subtracted
1 from each variable (sometimes implicitly) to account for a potential
overflow situation.  It's impossible for it to trigger an underflow
because max_ is greater than min_, and they wouldn't be equal otherwise a
jump table won't even be generated.

 Either way, I'm just enjoying myself with this!

 Gareth aka. Kit

 On Sat 15/12/18 19:55 , Martok listbox at martoks-place.de sent:
 Am 15.12.2018 um 18:08 schrieb J. Gareth Moreton: 
 > So here's something else I've been playing with in the interim... I've
been 
 > working on improving the algorithms used when compiling case blocks. 
It was 
 > driven partly by my binary search idea for certain kinds of case block,
which I 
 > wrote up over here:
http://wiki.freepascal.org/Case_Compiler_Optimization
[1]">http://wiki.freepascal.org/Case_Compiler_Optimization 

 Feel free to include '0033093_Casenode_order.patch' from 
  [2]; 
 It's actually already a bit simpler in your version ;-) 

 The one thing that still bugs me (but I know it's not really seen as a
problem 
 in FPC) is that every platform cg theoretically has to implement all of
that, 
 causing a lot of duplication. 

 I like the use of more expressive intermediate names. But there was a lot
of 
 overflowed-aint-shuffling, are you sure that still works everywhere? 

 Bug 0032115 provides a "nice" test case for things that can go wrong with 
 different word sizes, and is also a good test for the true label count. 

 -- 
 Regards, 
 Martok 

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Links:
------
[1] http://wiki.freepascal.org/Case_Compiler_Optimization
[2] https://bugs.freepascal.org/view.php?id=33093
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