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[patch, fortran] PR 47359 - warnings for constant conversion


Hello world,

please find attached a rather lengthy patch, which attempts to deal
with warnings for conversions in Fortran once and for all (one can
hope ... :-)

The patch has two parts.

One part moves all the checking for conversion into the
gfc_<type>2<type> functions.  The checks are made much more
extensive; for example, integer conversions to real are also
checked because they can change the value.

There is one change in behavior:  Previosly, when a value
which did not change on a narrowing conversion was detected
with -Wconversion, it was not reported with -Wconversion-extra,
but there was a warning if only -Wconversion-extra was specified.

This patch changes that behavior so that -Wconversion and
-Wconversion-extra emit the same warning if the value is changed,
but that -Wconversion-extra, if specified alone, will emit
a warning anyway.

The second part catches the case when the user supplies more
digits than appropriate for the number.  More often than not,
this is a KIND error.

For the second part (which can also be committed separately)
I am not sure if the -Wconversion-extra flag is the right one.
I shied away from specifying YANF (Yet Another New Flag), but
I could do so if the consensus is that this is better.  It
might also be possible to invent another name for this option,
and maybe enable this with -Wsurprising.

Regression-tested.  Comments?  OK for trunk?

	Thomas

2015-05-31  Thomas Koenig  <tkoenig@netcologne.de>

        PR fortran/47359
        * arith.c (eval_intrinsic_op): Set warn flag for
        gfc_type_convert_binary if -Wconversion or -Wconversion-extra
        are set.
        (wprecision_real_real): New function.
        (wprecision_int_real): New function.
        (gfc_int2int): If -fno-range-check and -Wconversion are specified
        and it is a narrowing conversion, warn.
        (gfc_int2real): If there is a change in value for the conversion,
        warn.
        (gfc_int2complex):  Likewise.
        (gfc_real2int): If there is a fractional part to the real number,
        warn with -Wconversion, otherwise warn with -Wconversion-extra.
        (gfc_real2real): Emit warning if the constant was changed by
        conversion with either -Wconversion or -Wconversion-extra.  With
        -Wconversion-extra, warn if no warning was issued earlier.
        (gfc_real2complex):  Likewise.
        (gfc_complex2int): For -Wconversion or -Wconversion-extra, if
        there was an imaginary part, warn; otherwise, warn for change in
        value.  Warn with -Wconversion-extra if no other warning was
        issued.
        (gfc_complex2real): For -Wconversion or -Wconversion-extra, if
        there was an imaginary part, warn; otherwise, warn for change in
        value. Warn with -Wconversion-extra if no other warning was
        issued.
        (gfc_complex2complex):  For -Wconversion, warn if the value of
        either the real or the imaginary part was changed.  Warn for
        -Wconversion-extra if no prior warning was issued.
        * expr.c (gfc_check_assign):  Remove check for change in value.
        * primary.c (match_real_constant): For -Wconversion-extra, check
        against a number in which the last non-zero digit has been
        replaced with a zero.  If the number compares equal, warn.

2015-05-31  Thomas Koenig  <tkoenig@netcologne.de>

        PR fortran/47359
        * gfortran.dg/array_constructor_type_17.f03: Adjust error message.
        * gfortran.dg/warn_conversion.f90: Add warning for change in value
        for assignment.
        * gfortran.dg/warn_conversion_3.f90: Add warnings.
        * gfortran.dg/warn_conversion_5.f90: New test.
        * gfortran.dg/warn_conversion_6.f90: New test.
        * gfortran.dg/warn_conversion_7.f90: New test.
! { dg-do compile }
! { dg-options "-Wconversion" }
! PR 47359 - additional warnings for conversions.
program main
  implicit none
  complex(kind=4) :: c4
  complex(kind=8) :: c8
  real(kind=4) :: r4
  real(kind=8) :: r8
  complex(kind=4), parameter :: c4p = (1.0, -4.)
  complex, parameter :: c8w = (1.0_8, -4.2_8) ! { dg-warning "Change of value in conversion" }
  complex (kind=8), parameter :: c8p = (1.0_8, -4.2_8)
  integer :: i

  c4 = c8p ! { dg-warning "Change of value in conversion" }
  c4 = 2**26 + 1 ! { dg-warning "Change of value in conversion" }
  c4 = 1.3d0     ! { dg-warning "Change of value in conversion" }
  c4 = c8p       ! { dg-warning "Change of value in conversion" }
  c4 = (1.2, 1000000001) ! { dg-warning "Change of value in conversion" }
  r4 = (2**26 + 1) * 2.3 ! { dg-warning "Change of value in conversion" }
  r4 = 2.4d0 ! { dg-warning "Change of value" }
  r4 = c4p ! { dg-warning "Non-zero imaginary part" }
  r4 = r4 + 2.3d0 ! { dg-warning "Possible change of value in conversion" }
  r8 = 2_8**62 - 1_8 ! { dg-warning "Change of value in conversion" }
  i = c4p ! { dg-warning "Non-zero imaginary part" }
  i = 42 + 1.3 ! { dg-warning "Change of value in conversion" }
  i = (1.2, 0.) ! { dg-warning "Change of value in conversion" }
  c4 = 1.2       ! no warning
  c4 = -3.25d0   ! no warning
  c4 = -42       ! no warning
  c8 = 2**26 + 1 ! no warning
  i = 22.        ! no warning
  i = (35., 0.)  ! no warning
  r4 = 2.5d0     ! no warning
  r4 = 235       ! no warning
  r8 = 2.3       ! no warning
end program main
! { dg-do compile }
! { dg-options "-Wconversion -Wconversion-extra" }
! PR 47359 - additional warnings for conversions.
program main
  implicit none
  real(kind=8) :: a,b
  complex(kind=8) :: c
  integer :: i
  real(kind=4) :: r
  a = 0.13              ! { dg-warning "Conversion" }
  print *,0.1_8 ** 0.2  ! { dg-warning "Conversion" }
  b = a/0.13            ! { dg-warning "Conversion" }
  i = 12345.            ! { dg-warning "Conversion" }
  i = (1., 23.)         ! { dg-warning "Non-zero imaginary part" }
  r = (1., 23.)         ! { dg-warning "Non-zero imaginary part" }
  b = 0.&                 ! { dg-warning "Possible change of value" }
       &5_8*c             ! { dg-warning "Conversion" }
  c = 0.3               ! { dg-warning "Conversion" }
  a = 0.5               ! { dg-warning "Conversion" }
end program main
  
! { dg-do compile }
! { dg-options "-Wconversion-extra -Wconversion" }
program main
  implicit none
  double precision, parameter :: pi = &  ! { dg-warning "Conversion" }
       & 3.1415829535897932     ! { dg-warning "Non-significant digits" }
end program main
Index: fortran/arith.c
===================================================================
--- fortran/arith.c	(Revision 223876)
+++ fortran/arith.c	(Arbeitskopie)
@@ -1521,7 +1521,7 @@ eval_intrinsic (gfc_intrinsic_op op,
       temp.value.op.op1 = op1;
       temp.value.op.op2 = op2;
 
-      gfc_type_convert_binary (&temp, 0);
+      gfc_type_convert_binary (&temp, warn_conversion || warn_conversion_extra);
 
       if (op == INTRINSIC_EQ || op == INTRINSIC_NE
 	  || op == INTRINSIC_GE || op == INTRINSIC_GT
@@ -1949,7 +1949,43 @@ arith_error (arith rc, gfc_typespec *from, gfc_typ
      NaN, etc.  */
 }
 
+/* Returns true if significant bits were lost when converting real
+   constant r from from_kind to to_kind.  */
 
+static bool
+wprecision_real_real (mpfr_t r, int from_kind, int to_kind)
+{
+  mpfr_t rv, diff;
+  bool ret;
+
+  gfc_set_model_kind (to_kind);
+  mpfr_init (rv);
+  gfc_set_model_kind (from_kind);
+  mpfr_init (diff);
+
+  mpfr_set (rv, r, GFC_RND_MODE);
+  mpfr_sub (diff, rv, r, GFC_RND_MODE);
+
+  ret = ! mpfr_zero_p (diff);
+  mpfr_clear (rv);
+  mpfr_clear (diff);
+  return ret;
+}
+
+/* Return true if conversion from an integer to a real loses precision.  */
+
+static bool
+wprecision_int_real (mpz_t n, mpfr_t r)
+{
+  mpz_t i;
+  mpz_init (i);
+  mpfr_get_z (i, r, GFC_RND_MODE);
+  mpz_sub (i, i, n);
+  return mpz_cmp_si (i, 0) != 0;
+  mpz_clear (i);
+
+}
+
 /* Convert integers to integers.  */
 
 gfc_expr *
@@ -1985,8 +2021,12 @@ gfc_int2int (gfc_expr *src, int kind)
       k = gfc_validate_kind (BT_INTEGER, kind, false);
       gfc_convert_mpz_to_signed (result->value.integer,
 				 gfc_integer_kinds[k].bit_size);
+
+      if (warn_conversion && kind < src->ts.kind)
+	gfc_warning_now (OPT_Wconversion, "Conversion from %qs to %qs at %L",
+			 gfc_typename (&src->ts), gfc_typename (&result->ts),
+			 &src->where);
     }
-
   return result;
 }
 
@@ -2010,6 +2050,14 @@ gfc_int2real (gfc_expr *src, int kind)
       return NULL;
     }
 
+  if (warn_conversion
+      && wprecision_int_real (src->value.integer, result->value.real))
+    gfc_warning_now (OPT_Wconversion, "Change of value in conversion "
+		     "from %qs to %qs at %L",
+		     gfc_typename (&src->ts),
+		     gfc_typename (&result->ts),
+		     &src->where);
+
   return result;
 }
 
@@ -2034,6 +2082,15 @@ gfc_int2complex (gfc_expr *src, int kind)
       return NULL;
     }
 
+  if (warn_conversion
+      && wprecision_int_real (src->value.integer,
+			      mpc_realref (result->value.complex)))
+      gfc_warning_now (OPT_Wconversion, "Change of value in conversion "
+		       "from %qs to %qs at %L",
+		       gfc_typename (&src->ts),
+		       gfc_typename (&result->ts),
+		       &src->where);
+
   return result;
 }
 
@@ -2045,6 +2102,7 @@ gfc_real2int (gfc_expr *src, int kind)
 {
   gfc_expr *result;
   arith rc;
+  bool did_warn = false;
 
   result = gfc_get_constant_expr (BT_INTEGER, kind, &src->where);
 
@@ -2057,6 +2115,28 @@ gfc_real2int (gfc_expr *src, int kind)
       return NULL;
     }
 
+  /* If there was a fractional part, warn about this.  */
+
+  if (warn_conversion)
+    {
+      mpfr_t f;
+      mpfr_init (f);
+      mpfr_frac (f, src->value.real, GFC_RND_MODE);
+      if (mpfr_cmp_si (f, 0) != 0)
+	{
+	  gfc_warning_now (OPT_Wconversion, "Change of value in conversion "
+			   "from %qs to %qs at %L", gfc_typename (&src->ts),
+			   gfc_typename (&result->ts), &src->where);
+	  did_warn = true;
+	}
+    }
+  if (!did_warn && warn_conversion_extra)
+    {
+      gfc_warning_now (OPT_Wconversion_extra, "Conversion from %qs to %qs "
+		       "at %L", gfc_typename (&src->ts),
+		       gfc_typename (&result->ts), &src->where);
+    }
+
   return result;
 }
 
@@ -2068,6 +2148,7 @@ gfc_real2real (gfc_expr *src, int kind)
 {
   gfc_expr *result;
   arith rc;
+  bool did_warn = false;
 
   result = gfc_get_constant_expr (BT_REAL, kind, &src->where);
 
@@ -2088,6 +2169,33 @@ gfc_real2real (gfc_expr *src, int kind)
       return NULL;
     }
 
+  /* As a special bonus, don't warn about REAL values which are not changed by
+     the conversion if -Wconversion is specified and -Wconversion-extra is
+     not.  */
+
+  if ((warn_conversion || warn_conversion_extra) && src->ts.kind > kind)
+    {
+      int w = warn_conversion ? OPT_Wconversion : OPT_Wconversion_extra;
+      
+      /* Calculate the difference between the constant and the rounded
+	 value and check it against zero.  */
+
+      if (wprecision_real_real (src->value.real, src->ts.kind, kind))
+	{
+	  gfc_warning_now (w, "Change of value in conversion from "
+			   "%qs to %qs at %L",
+			   gfc_typename (&src->ts), gfc_typename (&result->ts),
+			   &src->where);
+	  /* Make sure the conversion warning is not emitted again.  */
+	  did_warn = true;
+	}
+    }
+
+    if (!did_warn && warn_conversion_extra)
+      gfc_warning_now (OPT_Wconversion_extra, "Conversion from %qs to %qs "
+		       "at %L", gfc_typename(&src->ts),
+		       gfc_typename(&result->ts), &src->where);
+
   return result;
 }
 
@@ -2099,6 +2207,7 @@ gfc_real2complex (gfc_expr *src, int kind)
 {
   gfc_expr *result;
   arith rc;
+  bool did_warn = false;
 
   result = gfc_get_constant_expr (BT_COMPLEX, kind, &src->where);
 
@@ -2119,6 +2228,26 @@ gfc_real2complex (gfc_expr *src, int kind)
       return NULL;
     }
 
+  if ((warn_conversion || warn_conversion_extra) && src->ts.kind > kind)
+    {
+      int w = warn_conversion ? OPT_Wconversion : OPT_Wconversion_extra;
+
+      if (wprecision_real_real (src->value.real, src->ts.kind, kind))
+	{
+	  gfc_warning_now (w, "Change of value in conversion from "
+			   "%qs to %qs at %L",
+			   gfc_typename (&src->ts), gfc_typename (&result->ts),
+			   &src->where);
+	  /* Make sure the conversion warning is not emitted again.  */
+	  did_warn = true;
+	}
+    }
+
+  if (!did_warn && warn_conversion_extra)
+    gfc_warning_now (OPT_Wconversion_extra, "Conversion from %qs to %qs "
+		     "at %L", gfc_typename(&src->ts),
+		     gfc_typename(&result->ts), &src->where);
+
   return result;
 }
 
@@ -2130,6 +2259,7 @@ gfc_complex2int (gfc_expr *src, int kind)
 {
   gfc_expr *result;
   arith rc;
+  bool did_warn = false;
 
   result = gfc_get_constant_expr (BT_INTEGER, kind, &src->where);
 
@@ -2143,6 +2273,43 @@ gfc_complex2int (gfc_expr *src, int kind)
       return NULL;
     }
 
+  if (warn_conversion || warn_conversion_extra)
+    {
+      int w = warn_conversion ? OPT_Wconversion : OPT_Wconversion_extra;
+
+      /* See if we discarded an imaginary part.  */
+      if (mpfr_cmp_si (mpc_imagref (src->value.complex), 0) != 0)
+	{
+	  gfc_warning_now (w, "Non-zero imaginary part discarded "
+			   "in conversion from %qs to %qs at %L",
+			   gfc_typename(&src->ts), gfc_typename (&result->ts),
+			   &src->where);
+	  did_warn = true;
+	}
+
+      else {
+	mpfr_t f;
+
+	mpfr_init (f);
+	mpfr_frac (f, src->value.real, GFC_RND_MODE);
+	if (mpfr_cmp_si (f, 0) != 0)
+	  {
+	    gfc_warning_now (w, "Change of value in conversion from "
+			     "%qs to %qs at %L", gfc_typename (&src->ts),
+			     gfc_typename (&result->ts), &src->where);
+	    did_warn = true;
+	  }
+	mpfr_clear (f);
+      }
+
+      if (!did_warn && warn_conversion_extra)
+	{
+	  gfc_warning_now (OPT_Wconversion_extra, "Conversion from %qs to %qs "
+			   "at %L", gfc_typename (&src->ts),
+			   gfc_typename (&result->ts), &src->where);
+	}
+    }
+
   return result;
 }
 
@@ -2154,6 +2321,7 @@ gfc_complex2real (gfc_expr *src, int kind)
 {
   gfc_expr *result;
   arith rc;
+  bool did_warn = false;
 
   result = gfc_get_constant_expr (BT_REAL, kind, &src->where);
 
@@ -2174,6 +2342,41 @@ gfc_complex2real (gfc_expr *src, int kind)
       return NULL;
     }
 
+  if (warn_conversion || warn_conversion_extra)
+    {
+      int w = warn_conversion ? OPT_Wconversion : OPT_Wconversion_extra;
+
+      /* See if we discarded an imaginary part.  */
+      if (mpfr_cmp_si (mpc_imagref (src->value.complex), 0) != 0)
+	{
+	  gfc_warning_now (w, "Non-zero imaginary part discarded "
+			   "in conversion from %qs to %qs at %L",
+			   gfc_typename(&src->ts), gfc_typename (&result->ts),
+			   &src->where);
+	  did_warn = true;
+	}
+
+      /* Calculate the difference between the real constant and the rounded
+	 value and check it against zero.  */
+      
+      if (kind > src->ts.kind
+	  && wprecision_real_real (mpc_realref (src->value.complex),
+				   src->ts.kind, kind))
+	{
+	  gfc_warning_now (w, "Change of value in conversion from "
+			   "%qs to %qs at %L",
+			   gfc_typename (&src->ts), gfc_typename (&result->ts),
+			   &src->where);
+	  /* Make sure the conversion warning is not emitted again.  */
+	  did_warn = true;
+	}
+    }
+
+  if (!did_warn && warn_conversion_extra)
+    gfc_warning_now (OPT_Wconversion, "Conversion from %qs to %qs at %L",
+		     gfc_typename(&src->ts), gfc_typename (&result->ts),
+		     &src->where);
+
   return result;
 }
 
@@ -2185,6 +2388,7 @@ gfc_complex2complex (gfc_expr *src, int kind)
 {
   gfc_expr *result;
   arith rc;
+  bool did_warn = false;
 
   result = gfc_get_constant_expr (BT_COMPLEX, kind, &src->where);
 
@@ -2220,6 +2424,26 @@ gfc_complex2complex (gfc_expr *src, int kind)
       return NULL;
     }
 
+  if ((warn_conversion || warn_conversion_extra) && src->ts.kind > kind
+      && (wprecision_real_real (mpc_realref (src->value.complex),
+				src->ts.kind, kind)
+	  || wprecision_real_real (mpc_imagref (src->value.complex),
+				   src->ts.kind, kind)))
+    {
+      int w = warn_conversion ? OPT_Wconversion : OPT_Wconversion_extra;
+
+      gfc_warning_now (w, "Change of value in conversion from "
+		       " %qs to %qs at %L",
+		       gfc_typename (&src->ts), gfc_typename (&result->ts),
+		       &src->where);
+      did_warn = true;
+    }
+
+  if (!did_warn && warn_conversion_extra && src->ts.kind != kind)
+    gfc_warning_now (OPT_Wconversion_extra, "Conversion from %qs to %qs "
+		     "at %L", gfc_typename(&src->ts),
+		     gfc_typename (&result->ts), &src->where);
+
   return result;
 }
 
Index: fortran/expr.c
===================================================================
--- fortran/expr.c	(Revision 223876)
+++ fortran/expr.c	(Arbeitskopie)
@@ -3247,55 +3247,6 @@ gfc_check_assign (gfc_expr *lvalue, gfc_expr *rval
 	}
     }
 
-  /*  Warn about type-changing conversions for REAL or COMPLEX constants.
-      If lvalue and rvalue are mixed REAL and complex, gfc_compare_types
-      will warn anyway, so there is no need to to so here.  */
-
-  if (rvalue->expr_type == EXPR_CONSTANT && lvalue->ts.type == rvalue->ts.type
-      && (lvalue->ts.type == BT_REAL || lvalue->ts.type == BT_COMPLEX))
-    {
-      if (lvalue->ts.kind < rvalue->ts.kind && warn_conversion)
-	{
-	  /* As a special bonus, don't warn about REAL rvalues which are not
-	     changed by the conversion if -Wconversion is specified.  */
-	  if (rvalue->ts.type == BT_REAL && mpfr_number_p (rvalue->value.real))
-	    {
-	      /* Calculate the difference between the constant and the rounded
-		 value and check it against zero.  */
-	      mpfr_t rv, diff;
-	      gfc_set_model_kind (lvalue->ts.kind);
-	      mpfr_init (rv);
-	      gfc_set_model_kind (rvalue->ts.kind);
-	      mpfr_init (diff);
-
-	      mpfr_set (rv, rvalue->value.real, GFC_RND_MODE);
-	      mpfr_sub (diff, rv, rvalue->value.real, GFC_RND_MODE);
-
-	      if (!mpfr_zero_p (diff))
-		gfc_warning (OPT_Wconversion, 
-			     "Change of value in conversion from "
-			     " %qs to %qs at %L", gfc_typename (&rvalue->ts),
-			     gfc_typename (&lvalue->ts), &rvalue->where);
-
-	      mpfr_clear (rv);
-	      mpfr_clear (diff);
-	    }
-	  else
-	    gfc_warning (OPT_Wconversion,
-			 "Possible change of value in conversion from %qs "
-			 "to %qs at %L", gfc_typename (&rvalue->ts),
-			 gfc_typename (&lvalue->ts), &rvalue->where);
-
-	}
-      else if (warn_conversion_extra && lvalue->ts.kind > rvalue->ts.kind)
-	{
-	  gfc_warning (OPT_Wconversion_extra,
-		       "Conversion from %qs to %qs at %L",
-		       gfc_typename (&rvalue->ts),
-		       gfc_typename (&lvalue->ts), &rvalue->where);
-	}
-    }
-
   if (gfc_compare_types (&lvalue->ts, &rvalue->ts))
     return true;
 
Index: fortran/intrinsic.c
===================================================================
--- fortran/intrinsic.c	(Revision 223876)
+++ fortran/intrinsic.c	(Arbeitskopie)
@@ -4695,15 +4695,18 @@ gfc_convert_type_warn (gfc_expr *expr, gfc_typespe
 	  /* Larger kinds can hold values of smaller kinds without problems.
 	     Hence, only warn if target kind is smaller than the source
 	     kind - or if -Wconversion-extra is specified.  */
-	  if (warn_conversion && from_ts.kind > ts->kind)
-	    gfc_warning_now (OPT_Wconversion, "Possible change of value in "
-			     "conversion from %s to %s at %L",
-			     gfc_typename (&from_ts), gfc_typename (ts),
-			     &expr->where);
-	  else if (warn_conversion_extra)
-	    gfc_warning_now (OPT_Wconversion_extra, "Conversion from %s to %s "
-			     "at %L", gfc_typename (&from_ts),
-			     gfc_typename (ts), &expr->where);
+	  if (expr->expr_type != EXPR_CONSTANT)
+	    {
+	      if (warn_conversion && from_ts.kind > ts->kind)
+		gfc_warning_now (OPT_Wconversion, "Possible change of value in "
+				 "conversion from %s to %s at %L",
+				 gfc_typename (&from_ts), gfc_typename (ts),
+				 &expr->where);
+	      else if (warn_conversion_extra)
+		gfc_warning_now (OPT_Wconversion_extra, "Conversion from %s to %s "
+				 "at %L", gfc_typename (&from_ts),
+				 gfc_typename (ts), &expr->where);
+	    }
 	}
       else if ((from_ts.type == BT_REAL && ts->type == BT_INTEGER)
 	       || (from_ts.type == BT_COMPLEX && ts->type == BT_INTEGER)
@@ -4711,7 +4714,7 @@ gfc_convert_type_warn (gfc_expr *expr, gfc_typespe
 	{
 	  /* Conversion from REAL/COMPLEX to INTEGER or COMPLEX to REAL
 	     usually comes with a loss of information, regardless of kinds.  */
-	  if (warn_conversion)
+	  if (warn_conversion && expr->expr_type != EXPR_CONSTANT)
 	    gfc_warning_now (OPT_Wconversion, "Possible change of value in "
 			     "conversion from %s to %s at %L",
 			     gfc_typename (&from_ts), gfc_typename (ts),
Index: fortran/primary.c
===================================================================
--- fortran/primary.c	(Revision 223876)
+++ fortran/primary.c	(Arbeitskopie)
@@ -736,6 +736,58 @@ done:
       gfc_internal_error ("gfc_range_check() returned bad value");
     }
 
+  /* Warn about trailing digits which suggest the user added too many
+     trailing digits, which may cause the appearance of higher pecision
+     than the kind kan support.
+
+     This is done by replacing the rightmost non-zero digit with zero
+     and comparing with the original value.  If these are equal, we
+     assume the user supplied more digits than intended (or forgot to
+     convert to the correct kind).
+  */
+
+  if (warn_conversion_extra)
+    {
+      mpfr_t r;
+      char *c, *p;
+      bool did_break;
+
+      c = strchr (buffer, 'e');
+      if (c == NULL)
+	c = buffer + strlen(buffer);
+
+      did_break = false;
+      for (p = c - 1; p >= buffer; p--)
+	{
+	  if (*p == '.')
+	    continue;
+	  
+	  if (*p != '0')
+	    {
+	      *p = '0';
+	      did_break = true;
+	      break;
+	    }
+	}
+
+      if (did_break)
+	{
+	  mpfr_init (r);
+	  mpfr_set_str (r, buffer, 10, GFC_RND_MODE);
+	  if (negate)
+	    mpfr_neg (r, r, GFC_RND_MODE);
+
+	  mpfr_sub (r, r, e->value.real, GFC_RND_MODE);
+
+	  if (mpfr_cmp_ui (r, 0) == 0)
+	    gfc_warning (OPT_Wconversion_extra, "Non-significant digits "
+			 "in %qs number at %C, maybe incorrect KIND",
+			 gfc_typename (&e->ts));
+
+	  mpfr_clear (r);
+	}
+    }
+
   *result = e;
   return MATCH_YES;
 
Index: testsuite/gfortran.dg/array_constructor_type_17.f03
===================================================================
--- testsuite/gfortran.dg/array_constructor_type_17.f03	(Revision 223876)
+++ testsuite/gfortran.dg/array_constructor_type_17.f03	(Arbeitskopie)
@@ -8,5 +8,5 @@ PROGRAM test
   IMPLICIT NONE
 
   INTEGER(KIND=4) :: arr(1)
-  arr = (/ INTEGER(KIND=4) :: HUGE(0_8) /) ! { dg-warning "conversion from" }
+  arr = (/ INTEGER(KIND=4) :: HUGE(0_8) /) ! { dg-warning "Conversion" }
 END PROGRAM test
Index: testsuite/gfortran.dg/warn_conversion.f90
===================================================================
--- testsuite/gfortran.dg/warn_conversion.f90	(Revision 223876)
+++ testsuite/gfortran.dg/warn_conversion.f90	(Arbeitskopie)
@@ -18,7 +18,7 @@ SUBROUTINE pr27866c4
   integer(kind=4) :: i4
   i4 = 2.3              ! { dg-warning "conversion" }
   i1 = 500              ! { dg-error "overflow" }
-  a = 2**26-1           ! assignment INTEGER(4) to REAL(4) - no warning
+  a = 2**26-1           ! { dg-warning "Change of value in conversion" }
   b = 1d999             ! { dg-error "overflow" }
 
   a = i4                ! assignment INTEGER(4) to REAL(4) - no warning
Index: testsuite/gfortran.dg/warn_conversion_3.f90
===================================================================
--- testsuite/gfortran.dg/warn_conversion_3.f90	(Revision 223876)
+++ testsuite/gfortran.dg/warn_conversion_3.f90	(Arbeitskopie)
@@ -7,8 +7,8 @@ program main
   complex(8), parameter :: z = cmplx (0.5, 0.5)  ! { dg-warning "Conversion" }
   real :: r1, r2
   r1 = 2.3d0 ! { dg-warning "Change of value in conversion" }
-  r2 = 2.5d0 ! No warning because the value does not change
+  r2 = 2.5d0 ! { dg-warning "Conversion" }
   d1 = .13 ! { dg-warning "Conversion" }
   d2 = .13d0
-  d1 = z     ! { dg-warning "change of value in conversion" }
+  d1 = z     ! { dg-warning "Non-zero imaginary part" }
 end program main

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