https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98490
Bug ID: 98490
Summary: Unexpected out of bounds in array constructor with
implied do loop
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: ffadrique at gmail dot com
Target Milestone: ---
The followinng code, when compiled with -fbounds-check produces a runtime
exception
program test
implicit none
call sub( 'Lorem ipsum' )
contains
subroutine sub( text )
character(len=*), intent(in) :: text
integer :: i
write(*,*) [ ( text(i:i), i = 1, len(text) ) ]
end subroutine sub
end program test
Run time error:
At line 18 of file test.f90
Fortran runtime error: Substring out of bounds: lower bound (-2147483648) of
'text' is less than one
Error termination. Backtrace:
#0 0x7f01d0965d3a
#1 0x7f01d0966849
#2 0x7f01d0966ec6
#3 0x5567acbd1269
#4 0x5567acbd14e6
#5 0x5567acbd151e
#6 0x7f01d077a0b2
#7 0x5567acbd10fd
#8 0xffffffffffffffff
It is clear to me that the automatic variable i is not initialised before
invoking the implied do loop. However, the loop should run between 1 and the
length of the input text as given in the loop controls; not evaluate at the
uninitialised value.
The behaviour is as expected when not compiled with the bound check flag. Also
valgrind is not reporting any invalid memory access. The issue may be
associated to the compilation with the bound check flag (that I need to have
enabled in general). The workaround is straightforward.
I have also checked that if there were several statements like the write one in
the example, I would have to control the initial value of i before each implied
loop to make sure that the initial value is not out of the array in the loop.
i = 1 ! Prevents the exception
write(*,*) [ ( text1(i:i), i = 1, len(text1) ) ] ! text1 of length 20
! Next statement triggers the exception unless i is reset again
write(*,*) [ ( text2(i:i), i = 1, len(text2) ) ] ! text2 of length 10
