On Mon, 9 May 2016, Marc Glisse wrote:
> On Mon, 9 May 2016, Richard Biener wrote:
>
> > The following patch implements CSEing of "subreg" reads from memory
> > like (from the testcase in the PR)
> >
> > union U { int i[16]; char c; };
> >
> > char foo(int i)
> > {
> > union U u;
> > u.i[0] = i;
> > return u.c;
> > }
> >
> > CSEing u.c as (char)i and thus removing u during GIMPLE optimizations.
> >
> > The patch always goes via generating BIT_FIELD_REFs and letting them
> > be simplified via the match-and-simplify machinery. This means it
> > replaces handling of complex component and vector extracts we've been
> > able to do before.
> >
> > I didn't restrict the kind of BIT_FIELD_REFs much apart from requiring
> > byte-size accesses. I did inspect code generated on powerpc (big-endian)
> > for the testcase though (also to verify any endianess issues) and didn't
> > spot anything wrong (even for non-lowpart "subregs").
>
> I expect this will also fix https://gcc.gnu.org/bugzilla/show_bug.cgi?id=28367
> (reading an element from a vector through a union)?
Yes. Will add the testcase and adjust the ChangeLog entry.
Thanks for the heads-up.
Richard.
