Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."

[Geert Bosch]

On Jan 1, 2007, at 21:14, Ian Lance Taylor wrote:
> [...]
> extern void bar (void);
> void
> foo (int m)
> {
>   int i;
>   for (i = 1; i < m; ++i)
>     {
>       if (i > 0)
>         bar ();
>     }
> }
>
> Here the limit for i without -fwrapv becomes (1, INF].  This enables
> VRP to eliminate the test "i > 0".  With -fwrapv, this test of course
> can not be eliminated.  VRP is the only optimization pass which is
> able to eliminate that test.

We should be able to optimize this even for -fwrapv.
For i = 0, the loop will not execute at all, for other
i, execution will stop when i == m, after m - 1 executions
of the loop body. The condition i > 0 will never be true,
regardless of -fwrapv as there won't be overflow.

  -Grt