[LLVMdev] reg_iterator Caveats

David Greene dag at cray.com
Tue Apr 1 08:47:38 PDT 2008

On Monday 31 March 2008 18:55, Chris Lattner wrote:
> On Mon, 31 Mar 2008, Evan Cheng wrote:
> >> I just discovered that def_itterator (and presumably, reg_iterator)
> >> doesn't
> >> include implicit defs, for example at function calls for caller-save
> >> physical
> >> registers.  Guh.  I'm not sure if it should or not, but it's certainly
> >> necessary information in some cases.  Is this expected behavior, or an
> >> oversight?
> reg iterators will return everything that is in the function.  If the
> implicit operands haven't been added to the machieninstrs yet, then they
> won't be returned.

Hmm...this is definitely NOT true in my copy.  During register allocation
these implicit defs are not returned.  By then the instructions are most
definitely fully constructed.  :)

We have a very old copy of llvm.  Is it possible they got added sometime
after reg_iterators were created?

Also, just as a point of information, where would I go to find out if a
physical register is a caller-save or callee-save register?  The closest
thing I can find is in the .td files but no interface is generated (as far
as I can tell) to categorize physical registers according to calling 


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