[LLVMdev] Minimum Array Size

[Hal Finkel]

On Mon, 10 Sep 2012 17:40:43 -0700
Nick Lewycky <nicholas at mxc.ca> wrote:

> Hal Finkel wrote:
> > Hello,
> >
> > clang currently seems to generate the same code for both:
> >
> > double something_a(char A[const static 256]) {
> >    ...
> > }
> >
> > and for:
> >
> > double something_b(char (*const A)) {
> >    ...
> > }
> >
> > even though in the first case the programmer has told us that the
> > array A is at least 256 bytes in length (and, thus, will not be
> > null). Do we currently have a way to pass this information to LLVM?
> 
> No, but I'm interested in this. C++ references imply that 'n' bytes
> of the pointer may be dereferenced, and we have no way of capturing
> that fact. It would feed into llvm::isSafeToLoadUnconditionally().

At the risk of starting yet another metadata proposal discussion, shall
we add some metadata to describe this? These cases could be handled by
metadata with an integer parameter. Is there a reasonable way of
handling cases like:
void foo(int n, int q[n][n]) { ... } ?

 -Hal

> 
> Nick



-- 
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory