[tree-ssa] Thoughts on live-on-entry variables

[Joern Rennecke]

> an uninitialized variable.  This pass would run at the end of the
> optimization pipeline, which would minimize (eliminate?) false
> positives.

If you manage to get the optimizers to a point that they eliminate
false positives, you will cause quite a stir in computing science.
consider:

int
f (void (*fun)(void))
{
  int u;

  (*fun) ();
  return u;
}

If f is linked statically with a caller that passes a pointer to a
function that doesn't terminate, no warning is issued.
If it is statically linked to a caller that passes a pointer to a
function that terminates, a warning about 'u' being used
uninitialized is issued.  Hence, you have solved the halting problem.

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