Part of original report:
I have recently had the chance to compile some code using -Wconversion and a
loop that may iterate more than 2.2 billion times. There is a compiler warning
of this sort which I cannot resolve:
nell:~/work/bit barnes$ gfortran -Wconversion -o t.x testcase.f
testcase.f:7.16:
do i=1_8,n
1
Warning: Conversion from INTEGER(4) to INTEGER(8) at (1)
---
program testcase
implicit none
integer(8) i,n
n=1_8
do i=1_8,n
enddo
end
---
The only variables in the testcase are 8-byte integers, yet I get that
conversion warning. I skimmed the gfortran bugzilla and did not notice
anything similar. If the loop is executed 2.2 billion times (n=2 200 000
000_8), it does run each instance, so I know the do loop is not being truncated
at the limit of a 4-byte integer.
---
nell:~/work/bit barnes$ gfortran -v
Using built-in specs.
Target: i686-apple-darwin8
Configured with: ../gcc-4.2.2/configure --prefix=/sw --prefix=/sw/lib/gcc4.2
--mandir=/sw/share/man --infodir=/sw/share/info
--enable-languages=c,c++,fortran,objc,java --with-arch=nocona
--with-tune=generic --host=i686-apple-darwin8 --with-gmp=/sw
--with-libiconv-prefix=/sw --with-system-zlib --x-includes=/usr/X11R6/include
--x-libraries=/usr/X11R6/lib
Thread model: posix
gcc version 4.2.2
Part of reply from Tobias Burnus (he asked me to file a bug report):
The problem is that the iterator step variable is INTEGER(4) [implicitly added
"1_4" ("gfc_int_expr (1);")]:
do i = 1_8, n, 1_4
Something like the following should work:
Index: gcc/fortran/match.c
===================================================================
--- gcc/fortran/match.c (revision 131912)
+++ gcc/fortran/match.c (working copy)
@@ -958,6 +965,8 @@ gfc_match_iterator (gfc_iterator *iter,
if (gfc_match_char (',') != MATCH_YES)
{
e3 = gfc_int_expr (1);
+ if (var->ts.type == BT_INTEGER)
+ e3->ts.kind = var->ts.kind;
goto done;
}
--
Summary: spurious warning using -Wconversion, a do loop, and 8
byte integers
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: bcbarnes at gmail dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35003
