Re: [PR tree-optimization/71691] Fix unswitching in presence of maybe-undef SSA_NAMEs (take 2)

[Aldy Hernandez]

On 12/20/2016 09:16 AM, Richard Biener wrote:

You do not handle memory or calls conservatively which means the existing
testcase only needs some obfuscation to become a problem again.  To fix
that before /* Check that any SSA names used to define NAME is also fully
defined.  */ bail out conservatively, like
   if (! is_gimple_assign (def)
      || gimple_assign_single_p (def))
    return true;

I understand the !is_gimple_assign, which will skip over GIMPLE_CALLs 
setting a value, but the "gimple_assign_single_p(def) == true"??

Won't this last one bail on things like e.3_7 = e, or x_77 = y_88? 
Don't we want to follow up the def chain precisely on these?

Thanks.
Aldy