[cfe-dev] static const function locals

[Eli Friedman]

On Mon, Jun 18, 2012 at 10:47 AM, Peter Cooper <peter_cooper at apple.com> wrote:
> Hi all
>
> I'm trying to write an optimization to create constant initializers for static const locals where they are structures, i.e., on this test
>
> struct S {
>        int i;
>        S(int v) : i(v) { }
> };
>
> int foo(int i) {
>        static const S arr[4] = {0,1,2,3};
>        return arr[i].i;
> }
>
> i'm going to change the IR so that instead of a series of stores guarded by __cxa_guard functions, we just have
>
> @_ZZ3fooiE3arr = constant global [4 x %struct.S] [%struct.S { i32 0}, %struct.S { i32 1}, %struct.S { i32 2}, %struct.S { i32 3}]
>
> However, the global has been given a zero initializer which makes doing this change difficult without more analysis than I think is necessary.
>
> So, finally, my question is, can we put an undef initializer on this variable instead of a zero initializer?  I don't know the C++ spec so i'm not sure if i'm missing something.

No; see [stmt.dcl]p4.

-Eli