[LLVMbugs] [Bug 19174] -O1 breaks std::abs

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19174

Benjamin Kramer <benny.kra at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |benny.kra at gmail.com
         Resolution|---                         |INVALID

--- Comment #1 from Benjamin Kramer <benny.kra at gmail.com> ---
On linux, rand() without seed returns 1804289383. Multiplying this by 4
overflows a 32 bit integer, which is undefined behavior. The optimizer can use
that fact to simplify code.

To avoid the undefined behavior you can pass -fwrapv to clang.

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20140325/8f34e290/attachment.html>