bug#62537: Error compiling emacs master with native compilation activated

[Mattias Engdegård]

5 apr. 2023 kl. 19.19 skrev Andrea Corallo <akrl@sdf.org>:

> As we suspected was a bug in the native compiler limplification pass
> triggered by the new LAP emitted.
> 
> fa669c4b17c fixes bootstrap --with-native-compilation=aot here and adds
> a test, is now pushed to master.  In 29 the bug never showed up
> (probably because the new LAP tweak is not it) so I guess it's better to
> leave the code as it is.

Nice! So the bug was that we optimised away switches where all jump targets are 
the same, without considering the fall-through case?

(Perhaps we should do something like that in the LAP optimiser. Wonder how 
common the opportunity is though.)

By the way, the bulk of `comp-jump-table-optimizable` should be equivalent to 
something like

   (apply #'= (hash-table-values jmp-table))

which is arguably clearer and definitely shorter.