[Bug target/57927] New: -march=core-avx2 different than -march=native on INTEL Haswell (i7-4700K)

[vincenzo.innocente at cern dot ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57927

            Bug ID: 57927
           Summary: -march=core-avx2  different than -march=native on
                    INTEL Haswell (i7-4700K)
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vincenzo.innocente at cern dot ch

for instance

mkdir scimark2TMP
cd scimark2TMP
wget http://math.nist.gov/scimark2/scimark2_1c.zip .
unzip scimark2_1c.zip
c++ -S LU.c -O3 -march=native -o LU.native -v
c++ -S LU.c -O3 -march=core-avx2 -o LU.avx2 -v
diff LU.native LU.avx2

if you run the benchmark
gcc -O3 -march=core-avx2 *.c -lm; ./a.out 5 
gcc -O3 -march=native *.c -lm; ./a.out 5 
"core-avx2" is better than "native"