[Bug c++/72769] New: ifstream Optimed Out ?

["roy at chameleon dot ad" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72769

            Bug ID: 72769
           Summary: ifstream Optimed Out ?
           Product: gcc
           Version: 6.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: roy at chameleon dot ad
  Target Milestone: ---

Created attachment 39041
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=39041&action=edit
the ii file

This is my first bug report so be patient!

g++ version is 6.1.1 20160707 [gcc-6-branch revision 238088]
Full compilation flag are those
https://gist.github.com/RoyBellingan/be151f3d22e7e0a50143d5dde622baba

System type is uname --all
Linux linux-gzgr 4.6.2-1-default #1 SMP PREEMPT Fri Jun 10 08:12:44 UTC 2016
(2a68ef0) x86_64 x86_64 x86_64 GNU/Linux

The invocation line is 

g++-6 -save-temps -O2 campaigns/1350_tmp.cpp -std=c++11 -g -o
campaigns/1350_3.so -shared -fPIC -Wall -Wconversion -Wsign-compare
-pedantic-errors -I data/

Output given is
https://gist.github.com/RoyBellingan/7c09b6bf8908f62b9052575bf14cf43d just some
warning of non used variable (this code is create dynamically and loaded via
dlopen)

The .ii file is attached

In short the at line 37937 of the ii file
while (infile >> a){
fails because a is set to 0 WHEN the compiler is invoked with O2 (and also with
O1)

If I use O0 a is assigned the correct value ...

For now a "fix" is to force swap the first line in a std:string (the two empty
line at 37935 & 37936

        unsigned long long a;
        std::ifstream infile("campaigns/1350_ids");
        std::string cry;
        infile >> cry;
        while (infile >> a){
                ids.insert(std::pair<unsigned long long,bool>(a,1));
        }

The 1350_ids file contains a list of id to check some rows are here
https://gist.github.com/RoyBellingan/8dcde8d63001dfcd438ccf9921f60627

Hope is enought!