On Sat, Aug 4, 2012 at 9:40 AM, Dimitrios Apostolou <ji...@gmx.net> wrote: > On Fri, 3 Aug 2012, Ian Lance Taylor wrote: > >>> 2012-08-04 Dimitrios Apostolou <ji...@gmx.net> >>> >>> * libiberty.h >>> (XOBDELETE,XOBGROW,XOBGROWVEC,XOBSHRINK,XOBSHRINKVEC): New >>> type-safe macros for obstack allocation. >>> (XOBFINISH): Renamed argument to PT since it is a pointer to T. >> >> >>> +/* Type-safe obstack allocator. You must first initialize the obstack >>> with >>> + obstack_init() or _obstack_begin(). >> >> >> This should recommend obstack_init, or obstack_begin, but not >> _obstack_begin. Also obstack_specify_allocation and >> obstack_specify_allocation_with_arg are OK, so really it might be >> better not to list the functions, but simply say "You must first >> initialization the obstack." > > > Grep reveals that 9 out of 10 times we use _obstack_begin(), and we set > alignment to 0 (isn't it suboptimal?).
I'm not sure where you are looking. I only see one call to _obstack_begin in the gcc directory, and it could easily be replaced with a call to obstack_specify_allocation instead. It does set the alignment to 0, but that just directs the obstack code to use the default alignment, which is the alignment of double. I think that should normally be fine. >>> + T: Type, O: Obstack, N: Number of elements, S: raw Size, >> >> >> s/Size/size/ >> >>> +#define XOBSHRINK(O, T) obstack_blank ((O), -1 * sizeof >>> (T)) >>> +#define XOBSHRINKVEC(O, T, N) obstack_blank ((O), -1 * sizeof (T) * >>> (N)) >> >> >> These are hard to use safely. I'm not sure we should define them at all. > > > I've already used XOBSHRINK and it looks clear to me, but I could use > obstack_blank() directly if necessary. I'm a bit concerned because they only work if space has already been allocated, and there is no checking. Also I only see them used in genautomata.c. But I guess it's OK. >>> +#define XOBFINISH(O, PT) ((PT) obstack_finish ((O))) >> >> >> For XOBNEW, etc., we use (T *) rather than (PT). Using (PT) seems >> error-probe--it's the only use of the obstack with a different type >> parameter. Why not use T rather than PT here, and return (T *)? > > > I'd have to change many (about 60) occurences of XOBFINISH if I change that. > I'd go for it if I was sure it's what we want, it can be a separate patch > later on. I'm sorry to ask you to change a lot of code, but it simply doesn't make sense to me to have all but one macro take the type as an argument, and have one macro take a pointer to the type. They really have to be consistent. Ian
