use kill_instruction() when killing an OP_PHI during CSE

cse_one_instruction() contains some code to be executed when
an OP_PHI is eliminated. This code is roughly equivalent to
what is done in kill_instruction() for OP_PHI but not complete
since it doesn't recursively try to kill others instructions
which are used only by this OP_PHI.

Fix this and avoid duplicated code by replacing this code by
a call to kill_instruction().

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Christopher Li <sparse@chrisli.org>
1 file changed