-funsafe-loop-optimizations

[Robert Dewar]

David Edelsohn wrote:

> 	While we discuss whether this should be the default or enabled at
> any optimization level, can we agree that users should be able to assert
> with a commandline option that they want less strict induction variable
> semantics?  I hope that we can move forward with an option to address
> these performance regressions and allow users to request this optimzation
> when they *do* want it, along the lines of the draft patch.

My view is that it is just fine to have command line options to modify
standard behavior. I don't even think it is terrible to have the default
be non-standard behavior if there are well defined options to get standard
behavior. I am a little uneasy about the optimization level changing the
semantics, although you can get by this by saying that something is
undefined, in which case it is fair game for optimization levels to
change the behavior.

One absolute requirement for me is that there should be a very precise
semantic definition, preferably in the framework of the semantic level
of the standard, that defines exactly what the modified semantics are
(it is fine of course for this definition to say that bla-bla-bla has
undefined semantics, but it is important that bla-bla-bla be very well
defined).

Happy New Year,
Robert
(who notes there are not too many early morning msgs on the list
this morning :-)