[Bug tree-optimization/18501] [4.7/4.8/4.9 Regression] Missing 'used uninitialized' warning (CCP)

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18501

--- Comment #68 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #67)
> *** Bug 59225 has been marked as a duplicate of this bug. ***

PR 59225 gave me an idea. Wouldn't it be possible to keep a PHI node with just
two operands, the constant and the undefined value? If further optimizations
remove the undefined block as unexecutable, then the undefined operand will go
away. Perhaps the problem is that other optimizations do not treat PHI<1,(D)>
as simply 1 and this will result in worse code, although VRP seems to work just
fine with PHI<1,2,(D)>.

Richard, do you see it feasible?