[Bug rtl-optimization/47138] backport r158175: replace dominated uses in loop-invariant

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47138

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-01-02 
17:50:02 UTC ---
The rev. doesn't have a testcase (and it didn't fix a bug?).

If you have a testcase that shows this patch fixes a regression it is ok
to backport.  If it fixes a wrong-code bug then it is also ok to backport
if you have a testcase.