On Tue, 2018-04-17 at 17:07 -0700, Linus Torvalds wrote: > On Tue, Apr 17, 2018 at 4:35 PM, Martin Wilck <mwilck@xxxxxxxx> > wrote: > > Sparse emits errors about ilog2() in array indices because of the > > use of > > __ilog2_32() and __ilog2_64(), > > If sparse warns about it, then presumably gcc with -Wvla warns about > it too? No, it doesn't (gcc 7.3.0). -> https://paste.opensuse.org/27471594 It doesn't even warn on an expression like this: #define SIZE (1<<10) static int foo[ilog2(SIZE)]; sparse 0.5.2 doesn't warn about that either. It emits "error: bad integer constant expression" only if ilog2 is used in an array initializer, like this: #define SIZE (1<<10) #define SUBS (1<<5) static int foo [ilog2(SIZE)] = { [ilog2(SUBS)] = 0, }; So maybe I was wrong, and this is actually a false positive in sparse. > So I suspect that what you'd want is > > #define ilog2(n) \ > __builtin_choose_expr(__is_constexpr(n), \ > const_ilog2(n), \ > __builtin_choose_expr(sizeof(n) <= 4, \ > __ilog2_u32(n), \ > __ilog2_u64(n))) > > or something. Hmm? Do you want me to convert the patch to your approach anyway? Or should I throw this away and report to sparse? Regards and thanks, Martin PS: apologies to all recipients for the broken cc list in my post. -- Dr. Martin Wilck <mwilck@xxxxxxxx>, Tel. +49 (0)911 74053 2107 SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton HRB 21284 (AG Nürnberg)
