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From: "nacitar at ubercpp dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/67980] New: left shift count is negative [-Wshift-count-negative] generated for unreachable code
Date: Thu, 15 Oct 2015 20:25:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67980

            Bug ID: 67980
           Summary: left shift count is negative [-Wshift-count-negative]
                    generated for unreachable code
           Product: gcc
           Version: 5.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nacitar at ubercpp dot com
  Target Milestone: ---

Created attachment 36519
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36519&action=edit
test driver

With -Wall, unreachable code in a constexpr function generates a warning if
written using c++14's expanded constexpr and using actual if statements,
however does not in the case of a ternary-styled c++11 constexpr function.

This can be worked around using template specializations, but certainly this
error shouldn't happen given that these values are all known at compilation
time and it's impossible for that count to ever actually be negative.

This is a simplification of the problem from a larger issue.