[Bug ipa/65765] New: Compiling Firefox with GCC 5 leads to broken javascript engine on x86-64

[mh+gcc at glandium dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65765

            Bug ID: 65765
           Summary: Compiling Firefox with GCC 5 leads to broken
                    javascript engine on x86-64
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ipa
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mh+gcc at glandium dot org

Created attachment 35314
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35314&action=edit
reduced.tgz

When building Firefox with GCC 5 [1], some parts of the test suite fail because
of what might be a compiler bug. It seems to be involving
__attribute__((cold)). Dan Gohman got a reduced testcase, attached here.

Unpack and build with g++ -O2 *.cpp, then run a.out.

This doesn't happen at -O1, or with -O2 -Dcold=.

1. GCC 5.1.0-RC-20150412, compiled with "--enable-languages=c,c++ 
--disable-nls --disable-gnu-unique-object --enable-__cxa_atexit
--with-arch-32=pentiumpro".
I've also reproduced with the reduced testcase with a snapshot of 5-20150111
(building Firefox with that snapshot fails for other reasons, unfortunately).