https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101189
--- Comment #2 from Andrew Macleod <amacleod at redhat dot com> ---
We always register relations on outgoing edges from a conditional.
in this case
_2 = -f_6; // f_6 was known to be [4,5]
if (_2 == f_6) // This this was known to fail because _2 was [-5, -4]
goto <bb 8>; [INV]
else
goto <bb 10>; [INV]
<bb 8> :
if (_2 != f_6) // which makes this unreachable code
goto <bb 10>; [INV]
else
goto <bb 9>; [INV]
THe problem is we were registering _2 == f_6 as a relation on the edge 6->8
which would then make the condition on bb_8 false.
We know that _2 != f_6, so the vrp folder was saying this branch was always
taken, and the relation code was prompted that its never taken :-P Its an
unreachable branch, but it was adding an inconsitency.
Instead, if we know an edge cannot be taken, like 6->8, do not register a
relation on that edge.
