Re: [PATCH] Fix OMP CAS expansion with separate condition

[Jakub Jelinek <jakub@redhat.com>]

On Thu, May 19, 2022 at 02:13:33PM +0000, Richard Biener wrote:
> > Though, depending on what exactly you allow or disallow, maybe even
> > the im != 0 might not be acceptable.
> > Oh, and if COND_EXPRs can only use some limited set of comparisons, we might
> > need to adjust e.g. arith_overflow_check_p and various other spots in
> > tree-ssa-math-opts.cc and other passes.
> 
> With the changes I have in the queue the !cond_stmt path should be
> effectively dead code (though I don't remove such immediately).
> 
> Not sure what you think the issue with arith_overflow_check_p would be?
> Note this is only about COND_EXPRs in gimple assignments.

Just that there will be more dead code in the compiler.
At least tree-ssa-math-opts.cc in various spots (but I think phiopt too and
other spots I've touched too) are looking for all 3 kinds of comparisons,
GIMPLE_CONDs, comparisons in COND_EXPR first operand and assignments
with tcc_comparison rhs codes and deal with all 3.  If we restrict what
can appear in COND_EXPR first operand in gimple assignments, perhaps we'll
need to only deal with the first and last case and not the COND_EXPR ones.

	Jakub