[Bug fortran/83540] New: [8 Regression] Invalid code with MATMUL, -fno-realloc-lhs -ffrontend-optimize

["anlauf at gmx dot de" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83540

            Bug ID: 83540
           Summary: [8 Regression] Invalid code with MATMUL,
                    -fno-realloc-lhs -ffrontend-optimize
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: anlauf at gmx dot de
  Target Milestone: ---

The following code crashes at runtime:

! Bug with "-fno-realloc-lhs -ffrontend-optimize"
program gfcbug142
  implicit none
  real, allocatable :: b(:,:)
  integer :: n = 5
  allocate (b(n,n))
  call random_number (b)
  print *, shape (matmul (b, transpose (b)))
end program gfcbug142

% gfc-8 -g -fno-realloc-lhs -ffrontend-optimize gfcbug142a.f90 && ./a.out

Program received signal SIGSEGV: Segmentation fault - invalid memory reference.

Backtrace for this error:
#0  0xffffe3ff in ???
#1  0x8048b77 in gfcbug142
        at /work/DWD/git/dace_code/gfcbug142a.f90:8
#2  0x8048dd2 in main
        at /work/DWD/git/dace_code/gfcbug142a.f90:9
Segmentation fault (core dumped)

Adding -fcheck=all:

Fortran runtime error: Incorrect extent in return array in MATMUL intrinsic for
dimension 1: is 0, should be 5

Error termination. Backtrace:
#0  0x8048a7b in gfcbug142
        at /work/DWD/git/dace_code/gfcbug142a.f90:8
#1  0x804950d in main
        at /work/DWD/git/dace_code/gfcbug142a.f90:9