Re: Functions that are CSEable but not pure

[Jason Merrill]

On 10/04/2012 01:42 PM, Richard Guenther wrote:
So I suppose the testcase that would be "valid" but break with using
pure would be instead
int main()
{
   int x = init_count;
   int *p = get_me();
   if (init_count == x)
     __builtin_abort();
   int *q = get_me();
   if (init_count == x)
     __builtin_abort();
}

here when get_me is pure we CSE init_count over the _first_ call of get_me.

That's OK for C++ thread_local semantics; the initialization is 
specified to happen some time before the first use, so the testcase is 
making an invalid assumption.  This might not be desirable for 
user-written singleton functions, though.

Jason