bug report for g77 (F77 fortran compiler)

[Jerzy Tarasiuk <jt at japc50 dot fuw dot edu dot pl>]

Hello, here is a program which shows the bug.

The compiler version: egcs-g77.1.1.2 (details on end).

Problem: DO has hidden variable which causes it to behave
differently from Fortran standard - terminate the DO loop
prematurely if another loop was executed during the time;
the variable keeps remaing count of loop repeats;
this occurs when jump is done outside the loop range and
then back into the loop (such a construction is allowed
by the standard). Also, the compiler shows warning or
error (depends on order of instructions) when such a jump
is used (the warning is not shown if it is assigned goto).

The program worked OK with every other compiler I seen.

Jerzy Tarasiuk  <jt@fuw.edu.pl>

----------------------------------------------------------
 
	program dotest

C****	DOTEST - show a bug of 'DO' in Linux F77 compiler.
C
C	Jerzy Tarasiuk				09 May 2000
C
	k=0
	l=5
	i=-1
C without the following ASSIGN result is the same,
C but the compiler issues warning in spite it is valid
C in FORTRAN to jump outside DO loop and back jump into it.
	assign 4 to j
	do 4 i=1,l
C the following WRITE is executed 2 times, the DO loop ends
C in spite the value of L is 5 - this is the _BUG_ of F77!
	write(*,1004) 'l',i,k,l
	goto 41
 4	continue
	write(*,1004) 'e',i,k,l
	stop
C can put here instructions change value of K only, the K=1
C is used twice to make final value of K independent of I
C but the result does not depend on the change.
 41	if(i.eq.1) goto j
C for first pass of DO 4 the IF condition is met and return
C to DO 4 loop is done in the line above; for next pass the
C condition is missed and the DO loop below is executed;
C the only result of the loop should be changing of K which
C is irrelevant, but it has also hidden side effect which
C causes the bug: internal loop counter is set to -1, and
C the DO 4 loop is terminated on begin of next pass.
	do 42 k=1,i
 42	continue
	goto j
 1004	format(1x,a1,3h i=,i2,3h k=,i2,3h l=,i2)
	end

------------------------------------------------------------

$ g77 --verbose

g77 version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release) (from FSF-g77 version 0.5.24-19981002)
Driving: g77 -v -c -xf77-version /dev/null -xnone
Reading specs from /usr/lib/gcc-lib/i386-slackware-linux/egcs-2.91.66/specs
gcc version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)
 /usr/lib/gcc-lib/i386-slackware-linux/egcs-2.91.66/cpp -lang-c -v -undef -D__GNUC__=2 -D__GNUC_MINOR__=91 -D__ELF__ -D__unix__ -D__i386__ -D__i386__ -D__linux__ -D__unix -D__i386 -D__linux -Asystem(posix) -D_LANGUAGE_FORTRAN -traditional -Asystem(unix) -Acpu(i386) -Amachine(i386) -Di386 -D__i386 -D__i386__ /dev/null /dev/null
GNU CPP version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release) (i386 Linux/ELF)
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/lib/gcc-lib/i386-slackware-linux/egcs-2.91.66/include
 /usr/include
End of search list.
 /usr/lib/gcc-lib/i386-slackware-linux/egcs-2.91.66/f771 -fnull-version -quiet -dumpbase g77-version.f -version -fversion -o /tmp/ccStiDag.s /dev/null
GNU F77 version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release) (i386-slackware-linux) compiled by GNU C version egcs-2.91.66 19990314 (egcs-1.1.2 release).
GNU Fortran Front End version 0.5.24-19981002
 /usr/i386-slackware-linux/bin/as -V -Qy -o /tmp/ccgtlWDn.o /tmp/ccStiDag.s
GNU assembler version 2.9.1 (i386-slackware-linux), using BFD version 2.9.1.0.25
 /usr/i386-slackware-linux/bin/ld -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 -o /tmp/ccerWHQw /tmp/ccgtlWDn.o /usr/lib/crt1.o /usr/lib/crti.o /usr/lib/gcc-lib/i386-slackware-linux/egcs-2.91.66/crtbegin.o -L/usr/lib/gcc-lib/i386-slackware-linux/egcs-2.91.66 -L/usr/i386-slackware-linux/lib -lg2c -lm -lgcc -lc -lgcc /usr/lib/gcc-lib/i386-slackware-linux/egcs-2.91.66/crtend.o /usr/lib/crtn.o
 /tmp/ccerWHQw
__G77_LIBF77_VERSION__: 0.5.24
@(#)LIBF77 VERSION 19970919
__G77_LIBI77_VERSION__: 0.5.24-19981021
@(#) LIBI77 VERSION pjw,dmg-mods 19980617
__G77_LIBU77_VERSION__: 0.5.24-19990305
@(#) LIBU77 VERSION 19980709

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