[tree-ssa] CCP and non-destructive folding problems

[law@redhat.com]

In message <1046211609.1695.76.camel@shadowfax>, Diego Novillo writes:
 >On Tue, 2003-02-25 at 15:51, law@redhat.com wrote:
 >
 >> My first checkin handles this correctly to.  If an expression with
 >> constants doesn't fold, then it's VARYING.  Yes we can miss some
 >> optimization opportunities, but they should be rare.
 >> 
 >Well, we won't know until we measure.
I just did.  It found 2 in the gcc testsuite.  One was a trivial oversight
in the CCP code, the other was a rather dubious range testing case that, if
we care should have been handled before we got to the tree-ssa code.

And if this is what we're going to check for, then it can be done pretty
easily, but I don't think it's going to be worth the effort.

 >Could you leave it in exactly for that reason?  If you want, predicate
 >it on #ifdef TREE_CHECKING and/or have it emit a warning instead of
 >abort().
I'd *really* prefer not to.   You're focusing on something that I don't
expect is going to be a real issue.  I really don't like adding useless
code the compiler, especially under a maze of #ifdefs.

jeff