https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91359
Bug ID: 91359
Summary: GFORTRAN [NNNNN RETURN] of .FALSE. logical function X
returns .TRUE. after [if (.not.X) goto NNNNN] -
Warning: spaghetti code
Product: gcc
Version: 5.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: briantcarcich at gmail dot com
Target Milestone: ---
Created attachment 46673
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46673&action=edit
Minimal test case; test_zero.f90 from gfortran -save-temps ... test_zero.f
This error does not appear with G77; I also tried it with GFORTRAN 4.4.7 and it
did not appear there.
I attached a minimal test case (.f90, not .i*, as this is FORTRAN). It was
generated from source file test_zero.f, which has the following contents:
logical function zero()
goto 00002
00001 return
00002 zero = .false.
if (.not.zero) goto 00001
return
end
program test_zero
logical zero
if (zero()) stop 'FAIL: zero() returned .TRUE.'
stop 'OKAY: zero() returned .FALSE.'
end
The simplest commands to produce the bug are preceded by [>] below; the
responses are as shown between the commands:
> gfortran -std=legacy -g -O0 -finit-local-zero -fno-automatic -Wall \
test_zero.f -o test_zero_gfortran.e -save-temps -v
Driving: gfortran -std=legacy -g -O0 -finit-local-zero -fno-automatic -Wall
test_zero.f -o test_zero_gfortran.e -save-temps -v -l gfortran -l m
-shared-libgcc
Using built-in specs.
COLLECT_GCC=gfortran
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
5.4.0-6ubuntu1~16.04.11' --with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs
--enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-5 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --with-system-zlib
--disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-amd64/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686
--with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib
--with-tune=generic --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.11)
COLLECT_GCC_OPTIONS='-std=legacy' '-g' '-O0' '-finit-local-zero'
'-fno-automatic' '-Wall' '-o' 'test_zero_gfortran.e' '-save-temps' '-v'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/5/f951 test_zero.f -ffixed-form -quiet -dumpbase
test_zero.f -mtune=generic -march=x86-64 -auxbase test_zero -g -O0 -Wall
-std=legacy -version -finit-local-zero -fno-automatic -fintrinsic-modules-path
/usr/lib/gcc/x86_64-linux-gnu/5/finclude -o test_zero.s
GNU Fortran (Ubuntu 5.4.0-6ubuntu1~16.04.11) version 5.4.0 20160609
(x86_64-linux-gnu)
compiled by GNU C version 5.4.0 20160609, GMP version 6.1.0, MPFR
version 3.1.4, MPC version 1.0.3
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU Fortran2008 (Ubuntu 5.4.0-6ubuntu1~16.04.11) version 5.4.0 20160609
(x86_64-linux-gnu)
compiled by GNU C version 5.4.0 20160609, GMP version 6.1.0, MPFR
version 3.1.4, MPC version 1.0.3
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
test_zero.f:3:0:
00001 return
^
Warning: control reaches end of non-void function [-Wreturn-type]
COLLECT_GCC_OPTIONS='-std=legacy' '-g' '-O0' '-finit-local-zero'
'-fno-automatic' '-Wall' '-o' 'test_zero_gfortran.e' '-save-temps' '-v'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
as -v --64 -o test_zero.o test_zero.s
GNU assembler version 2.26.1 (x86_64-linux-gnu) using BFD version (GNU Binutils
for Ubuntu) 2.26.1
Reading specs from /usr/lib/gcc/x86_64-linux-gnu/5/libgfortran.spec
rename spec lib to liborig
COLLECT_GCC_OPTIONS='-std=legacy' '-g' '-O0' '-finit-local-zero'
'-fno-automatic' '-Wall' '-o' 'test_zero_gfortran.e' '-save-temps' '-v'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/5/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/5/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-std=legacy' '-g' '-O0' '-finit-local-zero'
'-fno-automatic' '-Wall' '-o' 'test_zero_gfortran.e' '-save-temps' '-v'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/5/collect2 -plugin
/usr/lib/gcc/x86_64-linux-gnu/5/liblto_plugin.so
-plugin-opt=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper
-plugin-opt=-fresolution=test_zero.res -plugin-opt=-pass-through=-lgcc_s
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lquadmath
-plugin-opt=-pass-through=-lm -plugin-opt=-pass-through=-lgcc_s
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lc
-plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc --sysroot=/
--build-id --eh-frame-hdr -m elf_x86_64 --hash-style=gnu --as-needed
-dynamic-linker /lib64/ld-linux-x86-64.so.2 -z relro -o test_zero_gfortran.e
/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/crt1.o
/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/crti.o
/usr/lib/gcc/x86_64-linux-gnu/5/crtbegin.o -L/usr/lib/gcc/x86_64-linux-gnu/5
-L/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu
-L/usr/lib/gcc/x86_64-linux-gnu/5/../../../../lib -L/lib/x86_64-linux-gnu
-L/lib/../lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib
-L/usr/lib/gcc/x86_64-linux-gnu/5/../../.. test_zero.o -lgfortran -lm -lgcc_s
-lgcc -lquadmath -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
/usr/lib/gcc/x86_64-linux-gnu/5/crtend.o
/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/crtn.o
> ./test_zero_gfortran.e
STOP FAIL: zero() returned .TRUE.
>
The problem is likely related to the warning message above; however in the case
of FORTRAN, the code is correct, as suggested by G77 and version 4.4.7 of
GFORTRAN generating a correct solution.
See https://github.com/drbitboy/sftran3_gfortran_bug for more detail and my
attempt at analysis.
Sidebar: with the presence of the spaghetti GOTOs, "refactor the ugly code"
may be the first response, and I do not disagree with the sentiment. N.B.
however two things: 1) ugly or not, AFAICT this code is not being compiled by
GFORTRAN to the FORTRAN standard; 2) this is a minimal test case that
represents a problem in a much larger codebase converted to FORTRAN by the
SFTRAN3 pre-processor, from a time when IF-ENDIF and DO-ENDDO were not part of
any FORTRAN compiler's grammar.
