-funsafe-loop-optimizations

[Gabriel Dos Reis]

Robert Dewar <dewar@adacore.com> writes:

| 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.

Yes.  However the proposed transformation is not based on undefined
behviour. There is no overflow for unsigned integer types in C and
C++.  They are modular.  The proposed tranformation is true mutilation
of standard semantics.

-- Gaby