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[Bug tree-optimization/72785] [7 Regression] kernel build error since r236831
- From: "jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Mon, 07 Nov 2016 14:20:55 +0000
- Subject: [Bug tree-optimization/72785] [7 Regression] kernel build error since r236831
- Auto-submitted: auto-generated
- References: <bug-72785-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72785
--- Comment #14 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to dhowells@redhat.com from comment #13)
> Another possibility, at least for handling ilog2(), could be to provide
> __builtin_ilog2(unsigned long x) as an alternative.
>
> Note that the kernel ilog2() has the property that the result is undefined
> if x==0 (and will jump to ____ilog2_NaN() if x is constant 0).
Ugh, no. Why not just x && (x & -x) == x ? __builtin_ctz (x) : -1
(or ctzl or ctzll depending on what the type is)?