------- Comment #3 from pluto at agmk dot net 2009-10-28 12:03 -------
(In reply to comment #2)
> 4.3.x and newer gcc says:
>
> pr31043.c:3: warning: 'pi' initialized and declared 'extern'
so, lets get correct testcase:
#ifndef pi_hpp
#define pi_hpp
extern double const pi;
extern double foo();
#endif
#include "pi.hpp"
#include <cmath>
double const pi = M_PI;
double foo() { return pi; }
now, it compiles cleanly with `g++ -Wall -Wextra -O2 -S pi.cpp`
> So, if you don't want to be treated as a constant, write
>
> double pi = M_PI;
>
> and this will generate the code you are looking for:
but in this testcase i don't want to drop const.
> As far as double copy when "double const pi = M_PI;" is used, tree optimizers
> already propagate constant to return, as evident from optimized dump:
>
> foo ()
> {
> <bb 2>:
> return 3.141592653589793115997963468544185161590576171875e+0;
>
> }
>
> And this constant is handled in different way than its shadow in the memory.
could you explain why? they are identicial constants.
-fmerge-constants should do something with this.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31043
