===================================================================
@@ -2252,6 +2252,7 @@ typedef struct
int warn_align_commons;
int warn_real_q_constant;
int warn_unused_dummy_argument;
+ int warn_zerotrip;
int warn_realloc_lhs;
int warn_realloc_lhs_all;
int warn_compare_reals;
===================================================================
@@ -954,6 +954,12 @@ This option is implied by @option{-Wextra}.
Warn if the pointer in a pointer assignment might be longer than the its
target. This option is implied by @option{-Wall}.
+@item -Wzerotrip
+@opindex @code{Wzerotrip}
+Warn if a @code{DO} loop is known to execute zero times at compile
+time. This option is on by default and can be deactivated by
+@option{-Wno-zerotrip}.
+
@item -Werror
@opindex @code{Werror}
@cindex warnings, to errors
===================================================================
@@ -293,6 +293,10 @@ Wunused-dummy-argument
Fortran Warning
Warn about unused dummy arguments.
+Wzerotrip
+Fortran Warning
+Warn about zero-trip DO loops
+
cpp
Fortran Negative(nocpp)
Enable preprocessing
===================================================================
@@ -109,6 +109,7 @@ gfc_init_options (unsigned int decoded_options_cou
gfc_option.warn_align_commons = 1;
gfc_option.warn_real_q_constant = 0;
gfc_option.warn_unused_dummy_argument = 0;
+ gfc_option.warn_zerotrip = 1;
gfc_option.warn_realloc_lhs = 0;
gfc_option.warn_realloc_lhs_all = 0;
gfc_option.warn_compare_reals = 0;
@@ -747,6 +748,10 @@ gfc_handle_option (size_t scode, const char *arg,
gfc_option.warn_unused_dummy_argument = value;
break;
+ case OPT_Wzerotrip:
+ gfc_option.warn_zerotrip = value;
+ break;
+
case OPT_fall_intrinsics:
gfc_option.flag_all_intrinsics = 1;
break;
===================================================================
@@ -6282,8 +6282,10 @@ gfc_resolve_iterator (gfc_iterator *iter, bool rea
sgn = mpfr_sgn (iter->step->value.real);
cmp = mpfr_cmp (iter->end->value.real, iter->start->value.real);
}
- if ((sgn > 0 && cmp < 0) || (sgn < 0 && cmp > 0))
- gfc_warning ("DO loop at %L will be executed zero times",
+ if (gfc_option.warn_zerotrip &&
+ ((sgn > 0 && cmp < 0) || (sgn < 0 && cmp > 0)))
+ gfc_warning ("DO loop at %L will be executed zero times"
+ " (use -Wno-zerotrip to suppress)",
&iter->step->where);
}
Hello world, the rather self-explanatory patch implements the -Wzerotrip option. The positive form is not really useful, because the option is on by default (so the default behavior is not changed). The negative form of the option, -Wno-zerotrip, suppresses the warning. I have also added information of how to suppress the warning in the message. Alternatively, it is also possible to only activate the warning if it is set explicitly, or with -Wall. I can easily change the patch to do so, if that turns out to be the consensus (I have no strong opinion on the matter either way) Regression-tested. OK for trunk? Thomas 2013-08-03 Thomas Koenig <tkoenig@gcc.gnu.org> PR fortran/56666 * gfortran.h (gfc_option_t): Add warn_zerotrip. * invoke.texi (-Wzerotrip): Document option. * lang.opt (Wzerotrip): Add. * options.c (gfc_init_options): Initialize warn_zerotrip. (gfc_handle_option): Handle OPT_Wzerotrip. * resolve.c (gfc_resolve_iterator): Honor gfc_option.warn_zerotrip; update error message to show how to suppress the warning. 2013-08-03 Thomas Koenig <tkoenig@gcc.gnu.org> PR fortran/56666 * gfortran.dg/do_check_10.f90: New test.