https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69564
Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |lto, missed-optimization Status|UNCONFIRMED |NEW Last reconfirmed| |2016-02-01 CC| |hubicka at gcc dot gnu.org, | |rguenth at gcc dot gnu.org Component|lto |c++ Summary|lto makes scimark2 LU |lto and/or C++ make |slower |scimark2 LU slower Ever confirmed|0 |1 --- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> --- Any reason you are using the c++ driver here? I get > gcc-6 -Ofast -flto *.c -lm -B /abuild/rguenther/trunk3-g/gcc > ./a.out ** ** ** SciMark2 Numeric Benchmark, see http://math.nist.gov/scimark ** ** for details. (Results can be submitted to p...@nist.gov) ** ** ** Using 2.00 seconds min time per kenel. Composite Score: 1729.02 FFT Mflops: 1247.04 (N=1024) SOR Mflops: 1537.70 (100 x 100) MonteCarlo: Mflops: 842.21 Sparse matmult Mflops: 1657.86 (N=1000, nz=5000) LU Mflops: 3360.29 (M=100, N=100) > gcc-6 -Ofast *.c -lm -B /abuild/rguenther/trunk3-g/gcc > ./a.out ** ** ** SciMark2 Numeric Benchmark, see http://math.nist.gov/scimark ** ** for details. (Results can be submitted to p...@nist.gov) ** ** ** Using 2.00 seconds min time per kenel. Composite Score: 1645.94 FFT Mflops: 1288.61 (N=1024) SOR Mflops: 1471.29 (100 x 100) MonteCarlo: Mflops: 459.90 Sparse matmult Mflops: 1665.91 (N=1000, nz=5000) LU Mflops: 3343.98 (M=100, N=100) Ok, when using g++ to compile things I _do_ get > g++-6 -Ofast -flto *.c -lm -B /abuild/rguenther/trunk3-g/gcc > ./a.out ** ** ** SciMark2 Numeric Benchmark, see http://math.nist.gov/scimark ** ** for details. (Results can be submitted to p...@nist.gov) ** ** ** Using 2.00 seconds min time per kenel. Composite Score: 1321.43 FFT Mflops: 1261.86 (N=1024) SOR Mflops: 1533.77 (100 x 100) MonteCarlo: Mflops: 850.69 Sparse matmult Mflops: 1669.90 (N=1000, nz=5000) LU Mflops: 1290.93 (M=100, N=100) > g++-6 -Ofast *.c -lm -B /abuild/rguenther/trunk3-g/gcc > ./a.out ** ** ** SciMark2 Numeric Benchmark, see http://math.nist.gov/scimark ** ** for details. (Results can be submitted to p...@nist.gov) ** ** ** Using 2.00 seconds min time per kenel. Composite Score: 1492.12 FFT Mflops: 1279.12 (N=1024) SOR Mflops: 1479.86 (100 x 100) MonteCarlo: Mflops: 433.83 Sparse matmult Mflops: 1637.11 (N=1000, nz=5000) LU Mflops: 2630.71 (M=100, N=100) So even without LTO I get a hit in using C++ to compile LU. Interesting.