$ spack spec eigen %intel
Input spec
--------------------------------
eigen%intel

Normalized
--------------------------------
eigen%intel
    ^cmake

Concretized
--------------------------------
eigen@3.2.10%intel@17.0.0 cflags="-axCORE-AVX2,AVX" cxxflags="-axCORE-AVX2,AVX" fflags="-axCORE-AVX2,AVX"~debug+fftw+metis+mpfr+scotch+suitesparse arch=linux-centos6-x86_64
    ^cmake@3.6.1%gcc@6.1.0~doc+ncurses+openssl+ownlibs~qt arch=linux-centos6-x86_64
        ^ncurses@6.0%gcc@6.1.0 arch=linux-centos6-x86_64
        ^openssl@1.0.2j%gcc@6.1.0 arch=linux-centos6-x86_64
            ^zlib@1.2.8%gcc@6.1.0+pic arch=linux-centos6-x86_64
    ^fftw@3.3.5%intel@17.0.0 cflags="-axCORE-AVX2,AVX" cxxflags="-axCORE-AVX2,AVX" fflags="-axCORE-AVX2,AVX"+float+long_double+mpi+openmp~pfft_patches~quad arch=linux-centos6-x86_64
        ^mvapich2@2.2%intel@17.0.0 cflags="-axCORE-AVX2,AVX" cxxflags="-axCORE-AVX2,AVX" fflags="-axCORE-AVX2,AVX"~debug~gforker+hydra~mrail~nemesis~nemesisib~nemesisibtcp+psm~remshell~slurm~sock arch=linux-centos6-x86_64
            ^bison@3.0.4%gcc@6.1.0 arch=linux-centos6-x86_64
                ^m4@1.4.17%gcc@6.1.0+sigsegv arch=linux-centos6-x86_64
                    ^libsigsegv@2.10%gcc@6.1.0 arch=linux-centos6-x86_64
            ^libpciaccess@0.13.4%intel@17.0.0 cflags="-axCORE-AVX2,AVX" cxxflags="-axCORE-AVX2,AVX" fflags="-axCORE-AVX2,AVX" arch=linux-centos6-x86_64
                ^libtool@2.4.6%gcc@6.1.0 arch=linux-centos6-x86_64
                ^pkg-config@0.29.1%gcc@6.1.0+internal_glib arch=linux-centos6-x86_64
                ^util-macros@1.19.0%gcc@6.1.0 arch=linux-centos6-x86_64
    ^gmp@6.1.1%intel@17.0.0 cflags="-axCORE-AVX2,AVX" cxxflags="-axCORE-AVX2,AVX" fflags="-axCORE-AVX2,AVX" arch=linux-centos6-x86_64
    ^metis@5.1.0%intel@17.0.0 cflags="-axCORE-AVX2,AVX" cxxflags="-axCORE-AVX2,AVX" fflags="-axCORE-AVX2,AVX"~debug~gdb~idx64~real64+shared arch=linux-centos6-x86_64
    ^mpfr@3.1.4%intel@17.0.0 cflags="-axCORE-AVX2,AVX" cxxflags="-axCORE-AVX2,AVX" fflags="-axCORE-AVX2,AVX" arch=linux-centos6-x86_64
    ^scotch@6.0.3%intel@17.0.0 cflags="-axCORE-AVX2,AVX" cxxflags="-axCORE-AVX2,AVX" fflags="-axCORE-AVX2,AVX"+compression~esmumps+metis~mpi+shared arch=linux-centos6-x86_64
        ^flex@2.6.1%gcc@6.1.0 arch=linux-centos6-x86_64
            ^gettext@0.19.8.1%gcc@6.1.0+bzip2+curses+git~libunistring+libxml2+tar+xz arch=linux-centos6-x86_64
                ^bzip2@1.0.6%intel@17.0.0 cflags="-axCORE-AVX2,AVX" cxxflags="-axCORE-AVX2,AVX" fflags="-axCORE-AVX2,AVX" arch=linux-centos6-x86_64
                ^libxml2@2.9.4%intel@17.0.0 cflags="-axCORE-AVX2,AVX" cxxflags="-axCORE-AVX2,AVX" fflags="-axCORE-AVX2,AVX"~python arch=linux-centos6-x86_64
                    ^xz@5.2.2%intel@17.0.0 cflags="-axCORE-AVX2,AVX" cxxflags="-axCORE-AVX2,AVX" fflags="-axCORE-AVX2,AVX" arch=linux-centos6-x86_64
                ^tar@1.29%intel@17.0.0 cflags="-axCORE-AVX2,AVX" cxxflags="-axCORE-AVX2,AVX" fflags="-axCORE-AVX2,AVX" arch=linux-centos6-x86_64
            ^help2man@1.47.4%gcc@6.1.0 arch=linux-centos6-x86_64
    ^suite-sparse@4.5.3%intel@17.0.0 cflags="-axCORE-AVX2,AVX" cxxflags="-axCORE-AVX2,AVX" fflags="-axCORE-AVX2,AVX"+fpic+tbb arch=linux-centos6-x86_64
        ^openblas@0.2.19%intel@17.0.0 cflags="-axCORE-AVX2,AVX" cxxflags="-axCORE-AVX2,AVX" fflags="-axCORE-AVX2,AVX"+fpic+openmp+shared arch=linux-centos6-x86_64
        ^tbb@4.4.4%intel@17.0.0 cflags="-axCORE-AVX2,AVX" cxxflags="-axCORE-AVX2,AVX" fflags="-axCORE-AVX2,AVX" arch=linux-centos6-x86_64