[LLVMdev] reg_iterator Caveats

David A. Greene greened at obbligato.org
Sun Mar 30 22:42:48 PDT 2008

On Sunday 30 March 2008 01:30:40 pm Chris Lattner wrote:
> On Mar 30, 2008, at 11:17 AM, David Greene wrote:
> > I'm forwarding this to llvmdev so it doesn't get lost in the sea of
> > commits...
> reg_iterators are independent of SSA or not.  The basic issue is that
> if you loop over uses or defs of a register, it will return *all* the
> uses/defs of that register in the current function.  If the value is
> SSA form, it is reasonable to say "give me the first def" and expect
> it to be the only def.  For multiply defined values like physregs,
> this is not true, because the reg can have multiple defs.

Gotcha.  This is exactly what I want.  Thanks for the explanation.

For non-SSA values, is there some indication of which defs reach which
uses?  I don't need this right now but I can imagine using it in the future.


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