[llvm-commits] [llvm] r104404 - /llvm/trunk/lib/Target/README.txt

[Duncan Sands]

Hi Chris,

> +Another interesting case is that something related could be used for variables
> +that go const after their ctor has finished.  In these cases, globalopt (which
> +can statically run the constructor) could mark the global const (so it gets put
> +in the readonly section).  A testcase would be:
> +
> +#include<complex>
> +using namespace std;
> +const complex<char>  should_be_in_rodata (42,-42);
> +complex<char>  should_be_in_data (42,-42);
> +complex<char>  should_be_in_bss;
> +
> +Where we currently evaluate the ctors but the globals don't become const because
> +the optimizer doesn't know they "become const" after the ctor is done.  See
> +GCC PR4131 for more examples.

isn't this what the invariant_start intrinsic and friends are for?  Dragonegg
calls them in an analogous situation (to mark trampolines as constant after
they have been initialized), and it works to some extent, though not as well as
I would like.

Ciao,

Duncan.