Re: C++ delayed folding branch review

[Jeff Law <law at redhat dot com>]

On 07/30/2015 10:52 AM, Jason Merrill wrote:
> > This hunk is necessary as we don't use canonical-form produced by
> > shorten_compare anymore.  Therefore special operand can occur on
> > right-hand side too.
>
> That seems like a problem, if the middle end is expecting the canonical
> form.  What is your plan for dealing with shorten_compare issues, again?
We want to handle the shorten_compare stuff independently of delayed 
folding if at all possible.  It's a bit of a rats nest.

One of the general problems we have is that shorten_compare also does 
canonicalization and issues warnings.  If we're no longer getting into 
shorten_compare for some code, then that canonicalization isn't being done.

Note, anything outside of the C/C++ front-ends depending on that 
canonicalization done by shorten_compare is, IMHO, broken.

I've extracted a patch from Kai's shorten_compare work to move the 
canonicalization into match.pd *but* that runs into testsuite 
regressions because shorten_compare is also where we emit certain 
warnings for comparisons that are always true/false.

With the canonicalization moved to match.pd, shorten_compare no longer 
recognizes a particular sequence and we lose the warning.  I haven't yet 
found a good place to relocate that warning.  This has been pushed down 
several items in my TODO stack.

Jeff