[Bug tree-optimization/79390] [7 Regression] 10% performance drop in SciMark2 LU after r242550

[vincenzo.innocente at cern dot ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79390

--- Comment #17 from vincenzo Innocente <vincenzo.innocente at cern dot ch> ---
[innocent@vinavx3 innocent]$ mkdir scimark2TMP
[innocent@vinavx3 innocent]$ cd scimark2TMP
[innocent@vinavx3 scimark2TMP]$ wget
http://math.nist.gov/scimark2/scimark2_1c.zip .
.....
gcc version 7.0.1 20170407 (experimental) [trunk revision 246752] (GCC) 
[innocent@vinavx3 scimark2TMP]$ gcc -Ofast -march=haswell *.c -lm
[innocent@vinavx3 scimark2TMP]$ ./a.out 
**                                                              **
** SciMark2 Numeric Benchmark, see http://math.nist.gov/scimark **
** for details. (Results can be submitted to pozo@nist.gov)     **
**                                                              **
Using       2.00 seconds min time per kenel.
Composite Score:         2783.60
FFT             Mflops:  2325.65    (N=1024)
SOR             Mflops:  2260.36    (100 x 100)
MonteCarlo:     Mflops:   829.14
Sparse matmult  Mflops:  2582.70    (N=1000, nz=5000)
LU              Mflops:  5920.14    (M=100, N=100)
[innocent@vinavx3 scimark2TMP]$ gcc -Ofast -march=haswell *.c -lm
-fno-split-paths 
[innocent@vinavx3 scimark2TMP]$ ./a.out
**                                                              **
** SciMark2 Numeric Benchmark, see http://math.nist.gov/scimark **
** for details. (Results can be submitted to pozo@nist.gov)     **
**                                                              **
Using       2.00 seconds min time per kenel.
Composite Score:         2825.86
FFT             Mflops:  2333.43    (N=1024)
SOR             Mflops:  2260.36    (100 x 100)
MonteCarlo:     Mflops:   829.14
Sparse matmult  Mflops:  2570.04    (N=1000, nz=5000)
LU              Mflops:  6136.33    (M=100, N=100)
[innocent@vinavx3 scimark2TMP]$ gcc -Ofast -march=haswell *.c -lm -fsplit-paths
[innocent@vinavx3 scimark2TMP]$ ./a.out
**                                                              **
** SciMark2 Numeric Benchmark, see http://math.nist.gov/scimark **
** for details. (Results can be submitted to pozo@nist.gov)     **
**                                                              **
Using       2.00 seconds min time per kenel.
Composite Score:         2787.46
FFT             Mflops:  2325.65    (N=1024)
SOR             Mflops:  2260.36    (100 x 100)
MonteCarlo:     Mflops:   832.36
Sparse matmult  Mflops:  2582.70    (N=1000, nz=5000)
LU              Mflops:  5936.23    (M=100, N=100)
[innocent@vinavx3 scimark2TMP]$ pushd ~/code/s7/C
CMSSW_8_0_22/     CMSSW_9_1_0_pre2/ 
[innocent@vinavx3 scimark2TMP]$ pushd ~/code/s7/CMSSW_9_1_0_pre2/
~/code/s7/CMSSW_9_1_0_pre2 /tmp/innocent/scimark2TMP 
[innocent@vinavx3 CMSSW_9_1_0_pre2]$ cmsenv
[innocent@vinavx3 CMSSW_9_1_0_pre2]$ popd
/tmp/innocent/scimark2TMP 
[innocent@vinavx3 scimark2TMP]$ gcc -v
gcc version 6.3.0 (GCC) 
[innocent@vinavx3 scimark2TMP]$ gcc -Ofast -march=haswell *.c -lm 
[innocent@vinavx3 scimark2TMP]$ ./a.out
**                                                              **
** SciMark2 Numeric Benchmark, see http://math.nist.gov/scimark **
** for details. (Results can be submitted to pozo@nist.gov)     **
**                                                              **
Using       2.00 seconds min time per kenel.
Composite Score:         2820.21
FFT             Mflops:  2325.65    (N=1024)
SOR             Mflops:  2260.36    (100 x 100)
MonteCarlo:     Mflops:   810.37
Sparse matmult  Mflops:  2427.26    (N=1000, nz=5000)
LU              Mflops:  6277.39    (M=100, N=100)