llvm 3.7.1 spec2006 astar lto failure on aarch64

[resending to llvm-dev for more exposure]

Hi Tom,

The following change does not seem to have made it into 3.7.1:


This change fixes a failure we’re seeing on spec2006.astar when compiled with LTO on aarch64.

The change also has a somewhat complicated history of reversion, so perhaps one of the authors/reviewers I’ve CC’d can chime in on this?

Hi Geoff,

I'm sceptical. It does look convoluted, and a rather large change, but
the case seems reasonably serious.

I'd like the authors and reviewers to make sure they can get a single
patch that applies to 3.7.1 without failures, before we can consider a
merge. This change looks very generic and can change all targets in
unpredictable ways... I'm not sure just running spec on AArch64 would
be enough to prove the change is ok for a point release.