convTag

fn convTag(
    self: *Builder,
    signedness: Constant.Cast.Signedness,
    val_ty: Type,
    ty: Type,
) Function.Instruction.Tag {
    assert(val_ty != ty);
    return switch (val_ty.scalarTag(self)) {
        .simple => switch (ty.scalarTag(self)) {
            .simple => switch (std.math.order(val_ty.scalarBits(self), ty.scalarBits(self))) {
                .lt => .fpext,
                .eq => unreachable,
                .gt => .fptrunc,
            },
            .integer => switch (signedness) {
                .unsigned => .fptoui,
                .signed => .fptosi,
                .unneeded => unreachable,
            },
            else => unreachable,
        },
        .integer => switch (ty.scalarTag(self)) {
            .simple => switch (signedness) {
                .unsigned => .uitofp,
                .signed => .sitofp,
                .unneeded => unreachable,
            },
            .integer => switch (std.math.order(val_ty.scalarBits(self), ty.scalarBits(self))) {
                .lt => switch (signedness) {
                    .unsigned => .zext,
                    .signed => .sext,
                    .unneeded => unreachable,
                },
                .eq => unreachable,
                .gt => switch (signedness) {
                    .unsigned => .@"trunc nuw",
                    .signed => .@"trunc nsw",
                    .unneeded => .trunc,
                },
            },
            .pointer => .inttoptr,
            else => unreachable,
        },
        .pointer => switch (ty.scalarTag(self)) {
            .integer => .ptrtoint,
            .pointer => .addrspacecast,
            else => unreachable,
        },
        else => unreachable,
    };
}