[Bug fortran/101841] New: Wrong realloc-lhs warning with matmul and -O2

[Bug fortran/101841] New: Wrong realloc-lhs warning with matmul and -O2

[jellby at yahoo dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101841

            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(:,:) = 1.0
A(:,:) = 0.5
B(:,:) = 2.0
F(:,:) = F-matmul(a,b)
end program test

$ gfortran test.f90 -Wrealloc-lhs -O2

No warning with "F(:,:) = 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.

[Bug fortran/101841] Wrong realloc-lhs warning with matmul and -O2

[anlauf at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101841

anlauf at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
           Priority|P3                          |P4
   Last reconfirmed|                            |2021-08-10

--- Comment #1 from anlauf at gcc dot gnu.org ---
Confirmed.

The warning disappears when frontend-optimization is disabled
(i.e. use -fno-frontend-optimize).

The warning also disappears if you disable the generation of inline
code for matmul by specifying -finline-matmul-limit=0 .