[fortran] Warning for feal / complex equality / inequality comparisons

Index: testsuite/gfortran.dg/bessel_5.f90
===================================================================
--- testsuite/gfortran.dg/bessel_5.f90	(Revision 190442)
+++ testsuite/gfortran.dg/bessel_5.f90	(Arbeitskopie)
@@ -1,5 +1,5 @@ 
 ! { dg-do run }
-! { dg-options "-Wall -fno-range-check" }
+! { dg-options "-Wall -fno-range-check -Wno-compare-reals" }
 !
 ! PR fortran/36158 - Transformational BESSEL_JN/YN
 ! PR fortran/33197 - F2008 math functions
Index: fortran/gfortran.h
===================================================================
--- fortran/gfortran.h	(Revision 190442)
+++ fortran/gfortran.h	(Arbeitskopie)
@@ -2225,6 +2225,7 @@  typedef struct
   int warn_unused_dummy_argument;
   int warn_realloc_lhs;
   int warn_realloc_lhs_all;
+  int warn_compare_reals;
   int max_errors;
 
   int flag_all_intrinsics;
Index: fortran/lang.opt
===================================================================
--- fortran/lang.opt	(Revision 190442)
+++ fortran/lang.opt	(Arbeitskopie)
@@ -218,6 +218,10 @@  Wcharacter-truncation
 Fortran Warning
 Warn about truncated character expressions
 
+Wcompare-reals
+Fortran Warning
+Warn about equality comparisons involving REAL or COMPLEX expressions
+
 Wconversion
 Fortran Warning
 ; Documented in C
Index: fortran/invoke.texi
===================================================================
--- fortran/invoke.texi	(Revision 190442)
+++ fortran/invoke.texi	(Arbeitskopie)
@@ -726,10 +726,11 @@  warnings.
 @cindex warnings, all
 Enables commonly used warning options pertaining to usage that
 we recommend avoiding and that we believe are easy to avoid.
-This currently includes @option{-Waliasing}, @option{-Wampersand}, 
-@option{-Wconversion}, @option{-Wsurprising}, @option{-Wintrinsics-std},
-@option{-Wno-tabs}, @option{-Wintrinsic-shadow}, @option{-Wline-truncation},
-@option{-Wreal-q-constant} and @option{-Wunused}.
+This currently includes @option{-Waliasing}, @option{-Wampersand},
+@option{-Wconversion}, @option{-Wcompare-reals}, @option{-Wsurprising},
+@option{-Wintrinsics-std}, @option{-Wno-tabs}, @option{-Wintrinsic-shadow},
+@option{-Wline-truncation}, @option{-Wreal-q-constant} and
+@option{-Wunused}.
 
 @item -Waliasing
 @opindex @code{Waliasing}
@@ -935,6 +936,11 @@  a scalar.  See also @option{-frealloc-lhs}.
 Warn when the compiler inserts code to for allocation or reallocation of an
 allocatable variable; this includes scalars and derived types.
 
+@item -Wcompare-reals
+@opindex @code{Wcompare-reals}
+Warn when comparing real or complex types for equality or inequality.
+Enabled by @option{-Wall}.
+
 @item -Werror
 @opindex @code{Werror}
 @cindex warnings, to errors
Index: fortran/resolve.c
===================================================================
--- fortran/resolve.c	(Revision 190442)
+++ fortran/resolve.c	(Arbeitskopie)
@@ -4034,6 +4034,27 @@  resolve_operator (gfc_expr *e)
 
 	  e->ts.type = BT_LOGICAL;
 	  e->ts.kind = gfc_default_logical_kind;
+
+	  if (gfc_option.warn_compare_reals)
+	    {
+	      gfc_intrinsic_op op = e->value.op.op;
+	      
+	      if ((op1->ts.type == BT_REAL || op1->ts.type == BT_COMPLEX)
+		  && (op == INTRINSIC_EQ || op == INTRINSIC_EQ_OS
+		      || op == INTRINSIC_NE || op == INTRINSIC_NE_OS))
+		{
+		  bool equality;
+
+		  equality = op == INTRINSIC_EQ || op == INTRINSIC_EQ_OS;
+		  
+		  /* Type conversion has made sure that the types
+		     of op1 and op2 agree.  */
+		  gfc_warning ("%s comparison for %s at %L",
+			       equality ? "Equality" : "Inequality",
+			       gfc_typename (&op1->ts), &op1->where);
+		}
+	    }
+
 	  break;
 	}
 
Index: fortran/options.c
===================================================================
--- fortran/options.c	(Revision 190442)
+++ fortran/options.c	(Arbeitskopie)
@@ -113,6 +113,7 @@  gfc_init_options (unsigned int decoded_options_cou
   gfc_option.warn_unused_dummy_argument = 0;
   gfc_option.warn_realloc_lhs = 0;
   gfc_option.warn_realloc_lhs_all = 0;
+  gfc_option.warn_compare_reals = 0;
   gfc_option.max_errors = 25;
 
   gfc_option.flag_all_intrinsics = 0;
@@ -473,6 +474,7 @@  set_Wall (int setting)
   gfc_option.warn_character_truncation = setting;
   gfc_option.warn_real_q_constant = setting;
   gfc_option.warn_unused_dummy_argument = setting;
+  gfc_option.warn_compare_reals = setting;
 
   warn_return_type = setting;
   warn_switch = setting;
@@ -638,6 +640,10 @@  gfc_handle_option (size_t scode, const char *arg,
       gfc_option.warn_character_truncation = value;
       break;
 
+    case OPT_Wcompare_reals:
+      gfc_option.warn_compare_reals = value;
+      break;
+
     case OPT_Wconversion:
       gfc_option.gfc_warn_conversion = value;
       break;