[LLVMdev] Traditional Dataflow Algorithm

[dag at cray.com]

Andrew Trick <atrick at apple.com> writes:

> David was asking for a post-register-rewrite analysis, which I think
> is a totally different problem and best implemented separately by each
> target.  The target knows best which register units are overwritten or
> preserved by an operation. We try to fake it with
> undef/implicit-use/implicit-def, but it isn't reliable. Reaching defs
> just can't be reliably rediscovered in a generic way after we drop
> explicit subregister information.

I don't see why not.  All of the subregister information is exposed in a
generic way through TargetRegisterInfo.

Your statement that undef/implicit-use/implicit-def isn't reliable is
news to me.  It seems unsafe to even provide it if it's incorrect.

                             -David