[Bug fortran/68829] [5/6/7 Regression] Segfaults with -Ofast due to large array on stack

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68829

--- Comment #6 from Uroš Bizjak <ubizjak at gmail dot com> ---
Polyhedron 11 test_fpu2 currently segfaults on Fedora 25 due to this problem:

[uros@localhost source]$ /ssd/uros/gcc-build/gcc/xgcc -B
/ssd/uros/gcc-build/gcc -S -Ofast -funroll-loops test_fpu2.f90 
[uros@localhost source]$ gfortran test_fpu2.s
[uros@localhost source]$ ulimit -s unlimited
[uros@localhost source]$ ./a.out
  Benchmark running, hopefully as only ACTIVE task
Test1: Gauss  - 1000 ( 250x 250) inverts in  14.892 seconds  Err=0.000000000000
Test2: Crout  - 1000 ( 250x 250) inverts in  16.343 seconds  Err=0.000000000000
Test3: Crout  -    2 (2000x2000) inverts in   9.769 seconds  Err=0.000000000000
Test4: Lapack -    2 (2000x2000) inverts in   7.548 seconds  Err=0.000000000013
                             Total = 48.6 sec

[uros@localhost source]$ ulimit -s 8192
[uros@localhost source]$ ./a.out
  Benchmark running, hopefully as only ACTIVE task
Test1: Gauss  - 1000 ( 250x 250) inverts in  14.810 seconds  Err=0.000000000000
Test2: Crout  - 1000 ( 250x 250) inverts in  16.538 seconds  Err=0.000000000000
Segmentation fault (core dumped)

Also on Suse polyhedron tester [1]:


 6 Apr 2017 15:03:29 gfortran_lin - Compile test_fpu2
command=/gcc/spec/sb-vangelis-head-64/x86_64/install-201704052254/bin/gfortran
-march=native -Ofast -funroll-loops test_fpu2.f90 -static -o test_fpu2

 6 Apr 2017 15:03:42 gfortran_lin - Execute test_fpu2
sh: line 1: 29627 Segmentation fault      ./test_fpu2 >>gfortran_lin.run
test_fpu2 Run #   1   151.34920   151.34920 - Error=100.0000%
sh: line 1: 29633 Segmentation fault      ./test_fpu2 >dummyfile
test_fpu2 Run #   2   150.31599   150.83260 - Error=  0.3425%
sh: line 1: 29639 Segmentation fault      ./test_fpu2 >dummyfile
test_fpu2 Run #   3   150.74271   150.80263 - Error=  0.1988%
sh: line 1: 29645 Segmentation fault      ./test_fpu2 >dummyfile
test_fpu2 Run #   4   150.90080   150.82718 - Error=  0.1415%

[1] https://gcc.opensuse.org/c++bench/pb11/pb11-performance-latest