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From: "jellby at yahoo dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug fortran/101841] New: Wrong realloc-lhs warning with matmul and
 -O2
Date: Tue, 10 Aug 2021 08:11:22 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101841

            Bug ID: 101841
           Summary: Wrong realloc-lhs warning with matmul and -O2
           Product: gcc
           Version: 10.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jellby at yahoo dot com
  Target Milestone: ---

I get a warning with this:

program test
real, allocatable :: F(:,:), A(:,:), B(:,:)
allocate(F(10,10), A(10,10), B(10,10))
F(:,:) =3D 1.0
A(:,:) =3D 0.5
B(:,:) =3D 2.0
F(:,:) =3D F-matmul(a,b)
end program test

$ gfortran test.f90 -Wrealloc-lhs -O2

No warning with "F(:,:) =3D matmul(a,b)"

Maybe the warning means that a temporary array is created (although I guess=
 it
wouldn't be needed)? But as far as I can see there should be no reallocation
here.=