Simple if-then-else expressions can often be replaced by an OP_SELECT. This is done in a very generic way by looking not at the test/if part but at OP_PHIs which contain exactly 2 values. An implementation detail makes that the address of valid OP_PHI's sources must not change, so the list holding these values must not be repacked and such. As consequence, when a value need to be removed from the list this value is simply replaced in the list by a VOID. These VOIDs must then be ignored when processing OP_PHI's sources. But for the if-conversion, these VOID are not ignored and are thus considered like any other value which in turn make miss some optimization opportunities. For example code like: int foo(int a) { if (a) return 0; else return 1; return 2; } will be linearized into something like: ... phi.32 %r2 <- %phi1, %phi2, VOID ret.32 %r2 where %phi1 & %phi2 correspond to the 'return 0' & 'return 1' and the VOID correspond to the dead 'return 2'. This code should be trivially be converted to a select but is not because the OP_PHI is considered as having 3 elements instead of 2. Worse, if at some moment we would have a phi list with: phi.32 %r2 <- %phi1, VOID then the optimization would trigger but the corresponding code make the assumption that the pseudos are the target of an OP_PHISOURCE instruction, which VOIDs, of course, are not and a crash should ensue. Fix this by filtering out these VOIDs before checking the conditions of the if-conversion. Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>