arith.c (gfc_arith_divide): With -Winteger-division...

2015-07-01  Thomas Koenig  <tkoenig@gcc.gnu.org>

	* arith.c (gfc_arith_divide):  With -Winteger-division,
	warn about contant integer division if there is a non-zero
	remainder.
	* invoke.texi:  Document -Winteger-division.
	* lang.opt:  Add -Winteger-division.

2015-07-01  Thomas Koenig  <tkoenig@gcc.gnu.org>

	* gfortran.dg/warn_conversion_8.f90:  New test.

From-SVN: r225262

gcc/fortran/ChangeLog

+2015-07-01  Thomas Koenig  <tkoenig@gcc.gnu.org>
+
+	* arith.c (gfc_arith_divide):  With -Winteger-division,
+	warn about contant integer division if there is a non-zero
+	remainder.
+	* invoke.texi:  Document -Winteger-division.
+	* lang.opt:  Add -Winteger-division.
+
 2015-06-25  Andrew MacLeod  <amacleod@redhat.com>
 
 	* f95-lang.c: Remove ipa-ref.h and plugin-api.h from include list.

gcc/fortran/arith.c

@@ -731,8 +731,28 @@ gfc_arith_divide (gfc_expr *op1, gfc_expr *op2, gfc_expr **resultp)
 	  break;
 	}
 
-      mpz_tdiv_q (result->value.integer, op1->value.integer,
-		  op2->value.integer);
+      if (warn_integer_division)
+	{
+	  mpz_t r;
+	  mpz_init (r);
+	  mpz_tdiv_qr (result->value.integer, r, op1->value.integer,
+		       op2->value.integer);
+
+	  if (mpz_cmp_si (r, 0) != 0)
+	    {
+	      char *p;
+	      p = mpz_get_str (NULL, 10, result->value.integer);
+	      gfc_warning_now (OPT_Winteger_division, "Integer division "
+			       "truncated to constant %qs at %L", p,
+			       &op1->where);
+	      free (p);
+	    }
+	  mpz_clear (r);
+	}
+      else
+	mpz_tdiv_q (result->value.integer, op1->value.integer,
+		    op2->value.integer);
+
       break;
 
     case BT_REAL:

gcc/fortran/invoke.texi

@@ -745,7 +745,7 @@ This currently includes @option{-Waliasing}, @option{-Wampersand},
 @option{-Wconversion}, @option{-Wsurprising}, @option{-Wc-binding-type},
 @option{-Wintrinsics-std}, @option{-Wno-tabs}, @option{-Wintrinsic-shadow},
 @option{-Wline-truncation}, @option{-Wtarget-lifetime},
-@option{-Wreal-q-constant} and @option{-Wunused}.
+@option{-Winteger-division}, @option{-Wreal-q-constant} and @option{-Wunused}.
 
 @item -Waliasing
 @opindex @code{Waliasing}
@@ -844,6 +844,13 @@ check that the declared interfaces are consistent across program units.
 Warn if a procedure is called that has neither an explicit interface
 nor has been declared as @code{EXTERNAL}.
 
+@item -Winteger-division
+@opindex @code{Winteger-division}
+@cindex warnings, integer division
+@cindex warnings, division of integers
+Warn if a constant integer division truncates it result.
+As an example, 3/5 evaluates to 0.
+
 @item -Wintrinsics-std
 @opindex @code{Wintrinsics-std}
 @cindex warnings, non-standard intrinsics

gcc/fortran/lang.opt

@@ -249,6 +249,10 @@ Wimplicit-procedure
 Fortran Warning Var(warn_implicit_procedure)
 Warn about called procedures not explicitly declared
 
+Winteger-division
+Fortran Warning Var(warn_integer_division) LangEnabledBy(Fortran,Wall)
+Warn about constant integer divisions with truncated results
+
 Wline-truncation
 Fortran Warning Var(warn_line_truncation) LangEnabledBy(Fortran,Wall) Init(-1)
 Warn about truncated source lines

gcc/testsuite/ChangeLog

+2015-07-01  Thomas Koenig  <tkoenig@gcc.gnu.org>
+
+	* gfortran.dg/warn_conversion_8.f90:  New test.
+
 2015-07-01  Bernd Edlinger  <bernd.edlinger@hotmail.de>
 
 	PR rtl-optimization/61047

gcc/testsuite/gfortran.dg/warn_conversion_8.f90

+! { dg-do compile }
+! { dg-options "-Winteger-division" }
+program main
+  integer, parameter :: n = 23
+  integer, parameter :: m = n*(n+1)/2  ! No warning
+  integer, parameter :: i = n*(n+1)/17 ! { dg-warning "Integer division truncated to constant" }
+  print *, 3/5 ! { dg-warning "Integer division truncated to constant" }
+end program main