getBase

    pub fn getBase(self: Constant, builder: *const Builder) Global.Index {
        var cur = self;
        while (true) switch (cur.unwrap()) {
            .constant => |constant| {
                const item = builder.constant_items.get(constant);
                switch (item.tag) {
                    .ptrtoint,
                    .inttoptr,
                    .bitcast,
                    => cur = builder.constantExtraData(Cast, item.data).val,
                    .getelementptr => cur = builder.constantExtraData(GetElementPtr, item.data).base,
                    .add => {
                        const extra = builder.constantExtraData(Binary, item.data);
                        const lhs_base = extra.lhs.getBase(builder);
                        const rhs_base = extra.rhs.getBase(builder);
                        return if (lhs_base != .none and rhs_base != .none)
                            .none
                        else if (lhs_base != .none) lhs_base else rhs_base;
                    },
                    .sub => {
                        const extra = builder.constantExtraData(Binary, item.data);
                        if (extra.rhs.getBase(builder) != .none) return .none;
                        cur = extra.lhs;
                    },
                    else => return .none,
                }
            },
            .global => |global| switch (global.ptrConst(builder).kind) {
                .alias => |alias| cur = alias.ptrConst(builder).aliasee,
                .variable, .function => return global,
                .replaced => unreachable,
            },
        };
    }