Re: [PATCH] [PR102501] Adjust jump threading testcases for ppc64* and others.

[Jeff Law <jeffreyalaw@gmail.com>]

On 9/28/2021 10:09 AM, Aldy Hernandez wrote:
> I really don't know what to do here.  This is a bit of whack-o-mole.
> The IL is sufficiently different for various architectures that any
> tweak can cause the number of jump threads to vary.
>
> For the pr7745-2.c testcase, we have less threading candidates because 2
> of them now cross loop boundaries.  Interestingly, this test matches
> "Jumps threaded", not threads registered, so the block copier can
> drop threads at copying time adding further confusion.
>
> For example, we can register N threads, but the old copier can cancel
> N-M threads while updating the CFG for a variety of different reasons
> (removed edges, threading through loop exits, etc).  This makes the
> "Registering jump threads" not to match the total number of threads this
> test checks for with "Jumps threaded".
>
> The pr66752-3.c test OTOH, is just a matter of thread4 eliminating the
> "if".  I had erroneously thought it would always be eliminated by
> thread3, but we really don't care where it gets cleaned up.  All we know
> is that DCE can't depend on the early threaders doing this work, because
> it may cross loop boundaries.  I've chosen thread4 arbitrarily, but we
> could just as easily pick the ".optimized" dump.
>
> Sorry, I'm really at my wits end here.  I don't see any clean path
> forward, except rewrite these tests as gimple IL.  They're close to useless
> as they sit.
>
> OK?
>
> gcc/testsuite/ChangeLog:
>
> 	PR testsuite/102501
> 	* gcc.dg/tree-ssa/pr66752-3.c: Adjust.
> 	* gcc.dg/tree-ssa/pr77445-2.c: Adjust.
Note these were two of the consistent failures on other targets as well.
Jeff