[Bug c++/81408] New: Lots of new -Wunsafe-loop-optimizations warnings with 7 compared to 6

["jak at jak-linux dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81408

            Bug ID: 81408
           Summary: Lots of new -Wunsafe-loop-optimizations warnings with
                    7 compared to 6
           Product: gcc
           Version: 7.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jak@jak-linux.org
  Target Milestone: ---

Created attachment 41726
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41726&action=edit
Minimized example

Compiling a recent apt with g++-7 causes a lot more unsafe loop optimizations
warnings than g++ 6 did (134 vs 8). That's a massive regression.

7.1.0 build log:
https://launchpadlibrarian.net/327296659/buildlog_ubuntu-artful-i386.apt_1.5~beta1_BUILDING.txt.gz

6.3.0 build log:
https://launchpadlibrarian.net/326714445/buildlog_ubuntu-artful-i386.apt_1.5~beta1_BUILDING.txt.gz

It seems these are for-each kind of loops.

I attached a simple minimized example from one of the cases mentioned in the
log.