[Bug fortran/100123] New: -ftree-fre gives incorrect result in subroutine with array declared as length 1

[Bug fortran/100123] New: -ftree-fre gives incorrect result in subroutine with array declared as length 1

[johnnorthall263 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100123

            Bug ID: 100123
           Summary: -ftree-fre gives incorrect result in subroutine with
                    array declared as length 1
           Product: gcc
           Version: 10.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: johnnorthall263 at gmail dot com
  Target Milestone: ---

Created attachment 50620
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50620&action=edit
source makefile and output from -save-temps

When compiling a program I found it works fine on -O0 but has problems with -Og
in a number of subroutines.  By trial and error I found that adding
-fno-tree-fre with -Og restores correct execution.  Further investigation of
one subroutine enabled the following simple example to demonstrate the problem.
 The subroutine setmid is designed to set a mid-point grid with option for
repeat boundary condition.  The correct mid-point y-coords are:-
 -1.000000  1.000000  3.000000  5.000000  7.000000  9.000000 11.000000
13.000000
but -Og gives:-
 -1.000000  1.000000  3.000000  5.000000  7.000000  9.000000 11.000000
11.000000
Swapping the order in which the repeat is applied simply shifts the error to
the other side of the grid.  Bizarrely simply changing the declared dimension
of XYM to 2 make it work!

First output from "gfortran -c -v -Wall -Wextra -Og -save-temps setmid.f" is:-

Using built-in specs.
COLLECT_GCC=gfortran
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-suse-linux
Configured with: ../configure --prefix=/usr --infodir=/usr/share/info
--mandir=/usr/share/man --libdir=/usr/lib64 --libexecdir=/usr/lib64
--enable-languages=c,c++,objc,fortran,obj-c++,ada,go,d
--enable-offload-targets=nvptx-none=/usr/nvptx-none,amdgcn-amdhsa=/usr/amdgcn-amdhsa,
--without-cuda-driver --enable-checking=release --disable-werror
--with-gxx-include-dir=/usr/include/c++/10 --enable-ssp --disable-libssp
--disable-libvtv --enable-cet=auto --disable-libcc1 --disable-plugin
--with-bugurl=https://bugs.opensuse.org/ --with-pkgversion='SUSE Linux'
--with-slibdir=/lib64 --with-system-zlib --enable-libstdcxx-allocator=new
--disable-libstdcxx-pch --enable-libphobos
--enable-version-specific-runtime-libs --with-gcc-major-version-only
--enable-linker-build-id --enable-linux-futex --enable-gnu-indirect-function
--program-suffix=-10 --without-system-libunwind --enable-multilib
--with-arch-32=x86-64 --with-tune=generic --build=x86_64-suse-linux
--host=x86_64-suse-linux
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 10.2.1 20200825 [revision c0746a1beb1ba073c7981eb09f55b3d993b32e5c]
(SUSE Linux) 
COLLECT_GCC_OPTIONS='-c' '-v' '-Wall' '-Wextra' '-Og' '-save-temps'
'-mtune=generic' '-march=x86-64'
 /usr/lib64/gcc/x86_64-suse-linux/10/f951 setmid.f -ffixed-form -quiet
-dumpbase setmid.f -mtune=generic -march=x86-64 -auxbase setmid -Og -Wall
-Wextra -version -fintrinsic-modules-path
/usr/lib64/gcc/x86_64-suse-linux/10/finclude -o setmid.s
GNU Fortran (SUSE Linux) version 10.2.1 20200825 [revision
c0746a1beb1ba073c7981eb09f55b3d993b32e5c] (x86_64-suse-linux)
        compiled by GNU C version 10.2.1 20200825 [revision
c0746a1beb1ba073c7981eb09f55b3d993b32e5c], GMP version 6.1.2, MPFR version
4.0.1, MPC version 1.1.0, isl version isl-0.18-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU Fortran2008 (SUSE Linux) version 10.2.1 20200825 [revision
c0746a1beb1ba073c7981eb09f55b3d993b32e5c] (x86_64-suse-linux)
        compiled by GNU C version 10.2.1 20200825 [revision
c0746a1beb1ba073c7981eb09f55b3d993b32e5c], GMP version 6.1.2, MPFR version
4.0.1, MPC version 1.1.0, isl version isl-0.18-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
COLLECT_GCC_OPTIONS='-c' '-v' '-Wall' '-Wextra' '-Og' '-save-temps'
'-mtune=generic' '-march=x86-64'
 /usr/lib64/gcc/x86_64-suse-linux/10/../../../../x86_64-suse-linux/bin/as -v
--64 -o setmid.o setmid.s
GNU assembler version 2.35.1 (x86_64-suse-linux) using BFD version (GNU
Binutils; openSUSE Leap 15.2) 2.35.1.20201123-lp152.4.6
COMPILER_PATH=/usr/lib64/gcc/x86_64-suse-linux/10/:/usr/lib64/gcc/x86_64-suse-linux/10/:/usr/lib64/gcc/x86_64-suse-linux/:/usr/lib64/gcc/x86_64-suse-linux/10/:/usr/lib64/gcc/x86_64-suse-linux/:/usr/lib64/gcc/x86_64-suse-linux/10/../../../../x86_64-suse-linux/bin/
LIBRARY_PATH=/usr/lib64/gcc/x86_64-suse-linux/10/:/usr/lib64/gcc/x86_64-suse-linux/10/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/usr/lib64/gcc/x86_64-suse-linux/10/../../../../x86_64-suse-linux/lib/:/usr/lib64/gcc/x86_64-suse-linux/10/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-c' '-v' '-Wall' '-Wextra' '-Og' '-save-temps'
'-mtune=generic' '-march=x86-64'

I will attach the source file, plus a short main to call it and a print to
display the result.  Also, I believe the output of -save-temps is desirable to
I include that, and also the same for XYM declared as size 2.
I'm sure some will decry the differing array declarations in the subroutine and
calling program - however this is something I used for many years when I worked
on large codes in industry it can be very powerful!
Apologies if I've missed something vital - I'm new to this website. 
John

[Bug fortran/100123] -ftree-fre gives incorrect result in subroutine with array declared as length 1

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100123

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |DUPLICATE
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This code is undefined.
See PR 69360 and why.

*** This bug has been marked as a duplicate of bug 69360 ***