[llvm-dev] Identifying contained loops

[Russell Wallace via llvm-dev]

One of the things I'm trying to do is perform high-level optimizations on
loops, which requires first identifying them. For a simple case, suppose
you have something like

for (size_t i = 0; i != n; ++i)
  ++a[i];

If a is a simple array, that will compile to a single basic block, which is
easy enough to identify.

But the body doesn't need to be a single basic block. It could contain
complex conditions, nested loops, whatever, and for some purposes, it's
still valid to think of it as a single loop that does something to every
element of a.

However, if there are branches into and out of the loop, that's no longer
valid; it might do something to half the elements of the array and leave
the other half untouched, for example.

I don't know what the concept I'm looking for - a loop that is guaranteed
to proceed from beginning to end, with no branches in or out - is usually
called; for the title of this post, I've called it a 'contained' loop.

I can figure out how to identify such, but I'd like to check whether this
has already been done. Are there any existing passes or whatever that use
this concept or identify such loops?
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20151111/88f09d0c/attachment.html>