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Re: [RFC] Implement Undefined Behavior Sanitizer

From: Segher Boessenkool <segher at kernel dot crashing dot org>
To: Jakub Jelinek <jakub at redhat dot com>
Cc: Marek Polacek <polacek at redhat dot com>, Jason Merrill <jason at redhat dot com>, "Joseph S. Myers" <joseph at codesourcery dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>
Date: Thu, 6 Jun 2013 15:26:19 +0200
Subject: Re: [RFC] Implement Undefined Behavior Sanitizer
References: <20130605175728 dot GD4160 at redhat dot com> <20130605191910 dot GV1493 at tucnak dot redhat dot com> <20130605193508 dot GX1493 at tucnak dot redhat dot com> <20130606060741 dot GY1493 at tucnak dot redhat dot com>

The C++11/C++14 undefined behavior of left signed shift can be tested
similarly, if ((unsigned type for op0's type) op0) >> (precm1 - y)
is greater than one, then it is undefined behavior.
Jason, does

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3675.html#1457

apply just to C++11/C++14, or to C++03 too?


Doesn't DR1457 also leave

   neg << 0

as undefined, where "neg" is a negative value?  That isn't caught by
your "greater than one" expression.


Segher

Follow-Ups:
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References:
- [RFC] Implement Undefined Behavior Sanitizer
  - From: Marek Polacek
- Re: [RFC] Implement Undefined Behavior Sanitizer
  - From: Jakub Jelinek
- Re: [RFC] Implement Undefined Behavior Sanitizer
  - From: Jakub Jelinek
- Re: [RFC] Implement Undefined Behavior Sanitizer
  - From: Jakub Jelinek

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