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From: "anlauf at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/99218] matmul on temporary array accesses invalid
 memory (segfault)
Date: Tue, 23 Feb 2021 21:10:33 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99218

anlauf at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |8.4.1

--- Comment #3 from anlauf at gcc dot gnu.org ---
Playing with the reduced testcase:

  fTmp =3D matmul (transpose (G), lambda(::2))

is clean while

  fTmp =3D matmul (transpose (G), lambda(::1))

is not.

It seems we run into a highly optimized code for rank-2 times rank-2.
The following patch fixes the testcase:

diff --git a/libgfortran/m4/matmul_internal.m4
b/libgfortran/m4/matmul_internal.m4
index 13fd7696238..0e96207a0fc 100644
--- a/libgfortran/m4/matmul_internal.m4
+++ b/libgfortran/m4/matmul_internal.m4
@@ -192,7 +192,8 @@ sinclude(`matmul_asm_'rtype_code`.m4')dnl
        }
     }

-  if (rxstride =3D=3D 1 && axstride =3D=3D 1 && bxstride =3D=3D 1)
+  if (rxstride =3D=3D 1 && axstride =3D=3D 1 && bxstride =3D=3D 1
+      && GFC_DESCRIPTOR_RANK (b) !=3D 1)
     {
       /* This block of code implements a tuned matmul, derived from
          Superscalar GEMM-based level 3 BLAS,  Beta version 0.1=