[Bug c/58485] New: [4.9 Regression] GMP test on subnormal fails with LTO and -O3

[vincent-gcc at vinc17 dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58485

            Bug ID: 58485
           Summary: [4.9 Regression] GMP test on subnormal fails with LTO
                    and -O3
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vincent-gcc at vinc17 dot net

When I build GMP with

GNU MP config.status 5.1.2
configured by ./configure, generated by GNU Autoconf 2.69,
  with options "'--disable-shared' 'CC=gcc-snapshot' 'CFLAGS=-march=native -O3
-flto=jobserve -fuse-linker-plugin'"

one of the tests fails:

mpn_get_d wrong on denorm
  n=1
  exp   -1020
  sign  0
  got   =[00 00 00 00 00 00 F0 7F] inf
  want  =[00 00 00 00 00 00 30 00] 8.9002954340288055324e-308

with:

gcc (Debian 20130917-1) 4.9.0 20130917 (experimental) [trunk revision 202647]

This doesn't occur if I replace -O3 by -O2 or if I do not enable LTO.
This doesn't occur either with the same options as above and:

gcc-4.8.real (Debian 4.8.1-10) 4.8.1
gcc-4.7.real (Debian 4.7.3-7) 4.7.3