Re: [PATCH][Tree-optimization/PR89772]fold memchr builtins for character not in constant nul-padded string

[JunMa <JunMa at linux dot alibaba dot com>]

在 2019/3/21 下午1:06, Bin.Cheng 写道:
> On Thu, Mar 21, 2019 at 12:57 PM JunMa <JunMa@linux.alibaba.com> wrote:
> > Hi
> > For now, gcc can not fold code like:
> >
> > const char a[5] = "123"
> > __builtin_memchr (a, '7', sizeof a)
> >
> > It tries to avoid folding out of string length although length of a is 5.
> > This is a bit conservative, it's safe to folding memchr/bcmp/memcmp
> > builtins when constant string stores in array with some trailing nuls.
> >
> > This patch folds these cases by exposing additional length of
> > trailing nuls in c_getstr().
> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> I suppose that it's for GCC10?
>
> Thanks,
> bin
Since it's a P3 normal bug, so the patch is for GCC10.
Sorry for the misleading, and thanks for pointing it out.

Regards Jun
> > Regards
> > JunMa
> >
> >
> > gcc/ChangeLog
> >
> > 2019-03-21  Jun Ma <JunMa@linux.alibaba.com>
> >
> >       PR Tree-optimization/89772
> >       * fold-const.c (c_getstr): Add new parameter to get length of
> > additional
> >       trailing nuls after constant string.
> >       * gimple-fold.c (gimple_fold_builtin_memchr): consider trailing nuls in
> >       out-of-bound accesses checking.
> >       * fold-const-call.c (fold_const_call): Likewise.
> >
> >
> > gcc/testsuite/ChangeLog
> >
> > 2019-03-21  Jun Ma <JunMa@linux.alibaba.com>
> >
> >       PR Tree-optimization/89772
> >       * gcc.dg/builtin-memchr-4.c: New test.