Alan Modra
Mon Feb 1 01:13:00 GMT 2016

On Sun, Jan 31, 2016 at 06:02:35PM -0600, Segher Boessenkool wrote:
> On Mon, Feb 01, 2016 at 08:46:42AM +1030, Alan Modra wrote:
> > The comment says this test is supposed to prevent "a narrower
> > operation than requested", but it actually only allows a larger
> > subreg, not one the same size.  Fix that.
> > 
> > Bootstrapped and regression tested powerpc64-linux.  OK for stage1?
> > 
> > Note that this bug was found when investigating why gcc-6 does not
> > suffer from pr69548, ie. this bug was masking a powerpc backend bug.
> It sounds like you have a testcase, can we see it please?

The testcase in pr69548 will show changes in rtl..

> And, just a missed optimisation, not a bug, right?

Yes, not a bug, and only presumed a missed optimisation.  I don't
actually have a testcase that shows worse code.  All I have is a
comment that makes sense to me, that doesn't agree exactly with the
code, and some understanding how the code may have been accidentally
written the way it is.

Alan Modra
Australia Development Lab, IBM

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