Re: [tree-ssa] Statement with no effect warning

[law at redhat dot com]

In message <jmfzfkwpu8.fsf@desire.geoffk.org>, Geoff Keating writes:
 >Jan Hubicka <jh@suse.cz> writes:
 >
 >> > In message <20031216160527.GN2199@kam.mff.cuni.cz>, Jan Hubicka writes:
 >> >  >Ignore the comments about non-checking bootstrap.  As I've checked
 >> >  >Diego's machines did run earlier than I've commited the patch.  Hope
 >> >  >that all the problems are fixed by now.
 >> > What I'm far more concerned about is the fact that a patch which didn't
 >> > bootstrap was checked into the tree to start with.
 >> 
 >> I see you don't believe, it, but it really did bootstrap.  As I pointed
 >> out already, it only reproduce on disabled checking bootstrap, while I
 >> did bootstrap with checking enabled (the default settings).
 >
 >Can we fix this?  It would be better if it was impossible to write
 >code that will build on a compiler with checking enabled but won't
 >build on a compiler with checking disabled.
What I've typically found with this kind of problem is that with
checking disabled the resulting source code is simplified enough that
suddenly new optimization opportunities are exposed and thus code within
the optimizers is exercised more heavily than before.

Now, one of my goals as I've been working on the SSA optimizers is to get
them to a point where this happens less often by making the optimizers better
at optimizing away useless checking code.

Clearly  we can't make all the checking code go away, but the better the
optimizers are at determining that a particular hunk of checking code is
redundant the more likely we are to not have situations where a checking
bootstrap succeeds and a no-checking bootstrap fails.

jeff