re PR fortran/56666 (Suppression flag for " DO loop at (1) will be executed zero times")

2013-08-12  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.
	(set_Wall): Add handling of 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.

2013-08-12  Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/56666
	* gfortran.dg/do_check_10.f90:  New test.
	* gfortran.dg/array_constructor_11.f90:  Add -Wzerotrip to dg-options.
	* gfortran.dg/array_constructor_18.f90:  Likewise.
	* gfortran.dg/array_constructor_22.f90:  Likewise.
	* gfortran.dg/coarray_15.f90:  Likewise.
	* gfortran.dg/do_1.f90:  Add -Wall to dg-options.
	* gfortran.dg/do_3.F90:  Add -Wzerotrip to dg-options.
	* gfortran.dg/do_check_5.f90:  Add -Wall to gd-options.

From-SVN: r201658

6 files changed, 33 insertions, 2 deletions

diff --git a/gcc/fortran/ChangeLog b/gcc/fortran/ChangeLog
index c1adb88..ba34ac1 100644
--- a/gcc/fortran/ChangeLog
+++ b/gcc/fortran/ChangeLog
@@ -1,3 +1,16 @@
+2013-08-12  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.
+	(set_Wall): Add handling of 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.
+
 2013-08-09  Janus Weil  <janus@gcc.gnu.org>
 
 	* gfortran.h (gfc_get_code): Modified prototype.
diff --git a/gcc/fortran/gfortran.h b/gcc/fortran/gfortran.h
index 5c617ca..691aa8c 100644
--- a/gcc/fortran/gfortran.h
+++ b/gcc/fortran/gfortran.h
@@ -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;
diff --git a/gcc/fortran/invoke.texi b/gcc/fortran/invoke.texi
index 3af57a3..69bec27 100644
--- a/gcc/fortran/invoke.texi
+++ b/gcc/fortran/invoke.texi
@@ -954,6 +954,11 @@ 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 implied by @option{-Wall}.
+
 @item -Werror
 @opindex @code{Werror}
 @cindex warnings, to errors
diff --git a/gcc/fortran/lang.opt b/gcc/fortran/lang.opt
index 61f77b4..4f79934 100644
--- a/gcc/fortran/lang.opt
+++ b/gcc/fortran/lang.opt
@@ -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
diff --git a/gcc/fortran/options.c b/gcc/fortran/options.c
index 908b47e..3a9c508 100644
--- a/gcc/fortran/options.c
+++ b/gcc/fortran/options.c
@@ -109,6 +109,7 @@ gfc_init_options (unsigned int decoded_options_count,
   gfc_option.warn_align_commons = 1;
   gfc_option.warn_real_q_constant = 0;
   gfc_option.warn_unused_dummy_argument = 0;
+  gfc_option.warn_zerotrip = 0;
   gfc_option.warn_realloc_lhs = 0;
   gfc_option.warn_realloc_lhs_all = 0;
   gfc_option.warn_compare_reals = 0;
@@ -466,6 +467,7 @@ set_Wall (int setting)
   gfc_option.warn_real_q_constant = setting;
   gfc_option.warn_unused_dummy_argument = setting;
   gfc_option.warn_target_lifetime = setting;
+  gfc_option.warn_zerotrip = setting;
 
   warn_return_type = setting;
   warn_uninitialized = setting;
@@ -747,6 +749,10 @@ gfc_handle_option (size_t scode, const char *arg, int value,
       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;
diff --git a/gcc/fortran/resolve.c b/gcc/fortran/resolve.c
index 837bf15..067288d 100644
--- a/gcc/fortran/resolve.c
+++ b/gcc/fortran/resolve.c
@@ -6281,8 +6281,10 @@ gfc_resolve_iterator (gfc_iterator *iter, bool real_ok, bool own_scope)
 	  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);
     }