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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning
Date: Mon, 26 May 2014 12:42:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Happens on an isolated path where GCC optimized

 if (len)
   ....

 memset (p, val, len);

to

 if (len == 0)
   {
  ....
   memset (p, val, 0);
   }
 else
   {
 .....
   memset (p, val, len);
   }

can happen and there is no good way around that, thus it's a false positive.

It's the

   if (grid->Points)

check that is false when the compiler can compute the 'len' parameter will
be zero.  Maybe that helps you deciding whether it really is a false positive
or not (well, yes, whether you are calling memset with len == 0, which
might be valid, but we warn about it).