[LLVMdev] Dependence Analysis [was: Flow-Sensitive AA]

David Greene dag at cray.com
Fri Aug 22 14:27:51 PDT 2008

On Friday 22 August 2008 16:14, Daniel Berlin wrote:
> On Fri, Aug 22, 2008 at 5:03 PM, Vikram S. Adve <vadve at cs.uiuc.edu> wrote:
> > Thanks!  This is all very interesting, and tells me that LLVM has a
> > way to go to fully support all of these capabilities (if that is the
> > right thing to do, which isn't clear).  OTOH, it looks like a lot of
> > real-world software that is using LLVM already doesn't seem to be
> > affected by the lack of them.
> >
> > Does anyone know of any C/C++ programs that require integer overflow
> > on signed arithmetic (even though it is not strictly allowed by the
> > standard)?
> Yes, see the unending discussion on the gcc mailing list about
> programs we are breaking that led to the introduction of this option.
> My serious suggestion would be to tell any users who require this flag
> to shove it.
> :)

Right on!

> (Otherwise you end up in a very dark place because there are a lot of
> optimizations that make assumptions about overflow when rearranging
> expressions, etc).

Exactly right.  One of my first jobs here was to fix a bunch of overflow 
problems exposed by optimization.  It's now become a tradition to
give this task to any new optimizer employee.  :)


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