On Mon, Jan 28, 2013 at 04:41:31PM +0100, Marc Glisse wrote:
> On Mon, 28 Jan 2013, Jakub Jelinek wrote:
>
> >2013-01-28 Jakub Jelinek <ja...@redhat.com>
> >
> > PR tree-optimization/56125
> > * tree-ssa-math-opts.c (gimple_expand_builtin_pow): Don't optimize
> > pow(x,c) into sqrt(x) * powi(x, n/2) or
> > 1.0 / (sqrt(x) * powi(x, abs(n/2))) if c is an integer or when
> > optimizing for size.
> > Don't optimize pow(x,c) into powi(x, n/3) * powi(cbrt(x), n%3) or
> > 1.0 / (powi(x, abs(n)/3) * powi(cbrt(x), abs(n)%3)) if 2c is an
> > integer.
> >
> > * gcc.dg/pr56125.c: New test.
>
> is there an implicit -lm in the testsuite?
Yes.
> The testcase now generates a library call to pow, like gcc-4.6. This
> is correct, but I am surprised this is considered better than
> leaving the original x/(n*n) unchanged... Should that be a different
> PR?
The function in question is marked as cold, therefore it should be optimized
for size. The call to pow is certainly shorter than the sqrt,
multiplication, division etc.
Jakub
