Redefinition to remove the possibility of a sentinel sometimes does not

[sstrickl]

Take the following CFG:

B0[graph]:0 {
      v2 <- Constant(#3)
}
B1[function entry]:2
    v3 <- LoadStaticField:10(x)
    v5 <- Constant(#sentinel)
    Branch if StrictCompare:12(===, v3, v5) goto (2, 3)
B2[target]:4
    goto:16 B4
B3[target]:6
    v7 <- Redefinition(v3 ^ T{int?})
    goto:18 B4
B4[join]:8 pred(B2, B3) {
      v9 <- phi(v2, v7) alive
}
    Return:20(v9)

In B3, we would expect that the CompileType for v7 would be T{int?} after type propagation. However, that is not what happens:

B0[graph]:0 {
      v2 <- Constant(#3) T{_Smi}
}
B1[function entry]:2
    v3 <- LoadStaticField:10(x) T{int?~}
    v5 <- Constant(#sentinel) T{Sentinel~}
    Branch if StrictCompare:12(===, v3, v5) goto (2, 3)
B2[target]:4
    goto:16 B4
B3[target]:6
    v7 <- Redefinition(v3 ^ T{int?}) T{int?~}
    goto:18 B4
B4[join]:8 pred(B2, B3) {
      v9 <- phi(v2, v7) alive T{int?~}
}
    Return:20(v9)