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Re: optimization/8492: [3.3 regression] GCC spins forever compiling loop
> > I think deleting unreachable blocks is cheap enought to do in the case
> > conditional jump was eliminated.
>
> Ok. But then the GCSE code needs to be (at least partially) re-initialized
> because the number of basic blocks may change. I've attached a naive patch I
> wrote some time ago: while fixing the PR (and doing some housekeeping work),
> it introduces many regressions because of this problem.
>
> > Alternatively we may prevent first local cprop pass from modifying CFG.
>
> I don't know enough of the global organization of optimization passes to
> comment. Will the optimizations missed at that point be caught elsewhere ?
Yes, there are examples where removing the conditional would allow more
PRE to happen, but I guess it is not that common. We already disable
the transformation for global CPROP and in fact I am quite surprised
that I didn't the same for local pass. I guess I just forgot about
that.
Honza
>
> --
> Eric Botcazou