On Tue, Jan 16, 2024 at 11:44 PM Richard Biener <richard.guenther@gmail.com>
wrote:

> > On Tue, Jan 16, 2024 at 11:20 PM Greg McGary <gkm@rivosinc.com> wrote:

> > >

> > > The sign bit of a sign-extending load cannot be known until runtime,

> > > so don't attempt to simplify it in the combiner.

> >
> It feels like this papers over an issue downstream?

While the code comment is true, perhaps it obscures the primary intent,
which is recognition that the pattern (SIGN_EXTEND (mem ...) ) is destined
to expand into a single memory-load instruction and no simplification is
possible, so why waste time with further analysis or transformation? There
are plenty of other conditions that also short circuit to "do nothing" and
this seems just as straightforward as those others. Efforts to catch this
further downstream add gratuitous complexity.

G