[Bug tree-optimization/35805] [ira] error in start_allocno_priorities, at ira-color.c:1806

Kenneth Zadeck zadeck@naturalbridge.com
Fri Jan 2 18:54:00 GMT 2009

Steven Bosscher wrote:
> On Fri, Jan 2, 2009 at 7:37 PM, Paolo Bonzini <bonzini@gnu.org> wrote:
>>>> At this point, if your patch costs say 0.3%, and removing all traces
>>>> DF_LR_RUN_DCE (instead scheduling a dozen more pass_fast_rtl_dce in
>>>> passes.c) costs 0.5%, I'd rather see the latter, at least it's easier to
>>>> look for opportunities to remove some useless DCE.
>> I'll try to do this for 4.5.
> It might be more worthwhile to just "fix" IRA to use DF_LIVE (which
> Vlad should have done in the first place). Then we wouldn't need
> Kenny's patch and DF_LR_RUN_DCE would still be essentially free.
> Gr.
> Steven
There is the issue of correctness vs rot.   I actually think that one of
the reasons that flow was so bad was that people went down this long
slippery slope of well it is good enough here ... and we really can get
away with it not being right here ... and after a while, all you have is

The problem with this game is that it is not maintainable.   Those kinds
of decisions tend to get forgotten and lost as the personnel supporting
the compiler changes.    Even if it is a fractional percentage slower,
the fact that you do not have to reason about it as the compiler evolves
is actually quite important.  

Thus, I plan to both fix this bug and add another one for vlad to fix
the sets that he uses. 


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