AVX2 vectorization seems to cause to errors in tests

[Harry-Chen]

I tried to compile swift with icc 18 successfully, but encountered some errors when running make check.

If I do not provide any specific CFLAGS when running configuration script, it will automatically use -O3 -ansi-alias -xCORE-AVX2, which leads to:

• FAIL: testMaths
• FAIL: testVoronoi2D
• FAIL: test27cellsStarsPerturbed.sh
• FAIL: test27cellsPerturbed.sh
• FAIL: test27cells.sh

If I use --no-vec, the script will use -O3 -xCORE-AVX2 -ansi-alias -no-simd -no-vec (weird that -xCORE-AVX2 still exists), which leads to:

• FAIL: testMaths
• FAIL: testVoronoi2D
• FAIL: test27cellsStarsPerturbed.sh

If I disable AVX2 by manually specifying --no-optimization and CFLAGS="-O3 -mavx", all tests will pass.

By trying more compiling options I believe that enabling AVX2 does cause these tests to fail. I also read your jenkins build output and found that your CI server does not support AVX2 so that no errors were reported.