re PR tree-optimization/88074 (g++ hangs on math expression)

	PR middle-end/88074
	* simplify.c (simplify_transformation_to_array): Run post_op
	immediately after processing corresponding row, rather than at the
	end.
	(norm2_scale): New variable.
	(add_squared): Rename to ...
	(norm2_add_squared): ... this.  Scale down operand and/or result
	if needed.
	(do_sqrt): Rename to ...
	(norm2_do_sqrt): ... this.  Handle the result == e case.  Scale up
	result and clear norm2_scale.
	(gfc_simplify_norm2): Clear norm2_scale.  Change add_squared to
	norm2_add_squared and &do_sqrt to norm2_do_sqrt.  Scale up result
	and clear norm2_scale again.

From-SVN: r268962

gcc/fortran/ChangeLog

+2019-02-16  Jakub Jelinek  <jakub@redhat.com>
+
+	PR middle-end/88074
+	* simplify.c (simplify_transformation_to_array): Run post_op
+	immediately after processing corresponding row, rather than at the
+	end.
+	(norm2_scale): New variable.
+	(add_squared): Rename to ...
+	(norm2_add_squared): ... this.  Scale down operand and/or result
+	if needed.
+	(do_sqrt): Rename to ...
+	(norm2_do_sqrt): ... this.  Handle the result == e case.  Scale up
+	result and clear norm2_scale.
+	(gfc_simplify_norm2): Clear norm2_scale.  Change add_squared to
+	norm2_add_squared and &do_sqrt to norm2_do_sqrt.  Scale up result
+	and clear norm2_scale again.
+
 2019-02-17  Thomas Koenig  <tkoenig@gcc.gnu.org>
 
 	PR fortran/71066

gcc/fortran/simplify.c

@@ -636,6 +636,9 @@ simplify_transformation_to_array (gfc_expr *result, gfc_expr *array, gfc_expr *d
 	if (*src)
 	  *dest = op (*dest, gfc_copy_expr (*src));
 
+      if (post_op)
+	*dest = post_op (*dest, *dest);
+
       count[0]++;
       base += sstride[0];
       dest += dstride[0];
@@ -671,10 +674,7 @@ simplify_transformation_to_array (gfc_expr *result, gfc_expr *array, gfc_expr *d
   result_ctor = gfc_constructor_first (result->value.constructor);
   for (i = 0; i < resultsize; ++i)
     {
-      if (post_op)
-	result_ctor->expr = post_op (result_ctor->expr, resultvec[i]);
-      else
-	result_ctor->expr = resultvec[i];
+      result_ctor->expr = resultvec[i];
       result_ctor = gfc_constructor_next (result_ctor);
     }
 
@@ -6048,9 +6048,10 @@ gfc_simplify_idnint (gfc_expr *e)
   return simplify_nint ("IDNINT", e, NULL);
 }
 
+static int norm2_scale;
 
 static gfc_expr *
-add_squared (gfc_expr *result, gfc_expr *e)
+norm2_add_squared (gfc_expr *result, gfc_expr *e)
 {
   mpfr_t tmp;
 
@@ -6059,8 +6060,45 @@ add_squared (gfc_expr *result, gfc_expr *e)
 	      && result->expr_type == EXPR_CONSTANT);
 
   gfc_set_model_kind (result->ts.kind);
+  int index = gfc_validate_kind (BT_REAL, result->ts.kind, false);
+  mpfr_exp_t exp;
+  if (mpfr_regular_p (result->value.real))
+    {
+      exp = mpfr_get_exp (result->value.real);
+      /* If result is getting close to overflowing, scale down.  */
+      if (exp >= gfc_real_kinds[index].max_exponent - 4
+	  && norm2_scale <= gfc_real_kinds[index].max_exponent - 2)
+	{
+	  norm2_scale += 2;
+	  mpfr_div_ui (result->value.real, result->value.real, 16,
+		       GFC_RND_MODE);
+	}
+    }
+
   mpfr_init (tmp);
-  mpfr_pow_ui (tmp, e->value.real, 2, GFC_RND_MODE);
+  if (mpfr_regular_p (e->value.real))
+    {
+      exp = mpfr_get_exp (e->value.real);
+      /* If e**2 would overflow or close to overflowing, scale down.  */
+      if (exp - norm2_scale >= gfc_real_kinds[index].max_exponent / 2 - 2)
+	{
+	  int new_scale = gfc_real_kinds[index].max_exponent / 2 + 4;
+	  mpfr_set_ui (tmp, 1, GFC_RND_MODE);
+	  mpfr_set_exp (tmp, new_scale - norm2_scale);
+	  mpfr_div (result->value.real, result->value.real, tmp, GFC_RND_MODE);
+	  mpfr_div (result->value.real, result->value.real, tmp, GFC_RND_MODE);
+	  norm2_scale = new_scale;
+	}
+    }
+  if (norm2_scale)
+    {
+      mpfr_set_ui (tmp, 1, GFC_RND_MODE);
+      mpfr_set_exp (tmp, norm2_scale);
+      mpfr_div (tmp, e->value.real, tmp, GFC_RND_MODE);
+    }
+  else
+    mpfr_set (tmp, e->value.real, GFC_RND_MODE);
+  mpfr_pow_ui (tmp, tmp, 2, GFC_RND_MODE);
   mpfr_add (result->value.real, result->value.real, tmp,
 	    GFC_RND_MODE);
   mpfr_clear (tmp);
@@ -6070,14 +6108,26 @@ add_squared (gfc_expr *result, gfc_expr *e)
 
 
 static gfc_expr *
-do_sqrt (gfc_expr *result, gfc_expr *e)
+norm2_do_sqrt (gfc_expr *result, gfc_expr *e)
 {
   gcc_assert (e->ts.type == BT_REAL && e->expr_type == EXPR_CONSTANT);
   gcc_assert (result->ts.type == BT_REAL
 	      && result->expr_type == EXPR_CONSTANT);
 
-  mpfr_set (result->value.real, e->value.real, GFC_RND_MODE);
+  if (result != e)
+    mpfr_set (result->value.real, e->value.real, GFC_RND_MODE);
   mpfr_sqrt (result->value.real, result->value.real, GFC_RND_MODE);
+  if (norm2_scale && mpfr_regular_p (result->value.real))
+    {
+      mpfr_t tmp;
+      mpfr_init (tmp);
+      mpfr_set_ui (tmp, 1, GFC_RND_MODE);
+      mpfr_set_exp (tmp, norm2_scale);
+      mpfr_mul (result->value.real, result->value.real, tmp, GFC_RND_MODE);
+      mpfr_clear (tmp);
+    }
+  norm2_scale = 0;
+
   return result;
 }
 
@@ -6100,15 +6150,27 @@ gfc_simplify_norm2 (gfc_expr *e, gfc_expr *dim)
   if (size_zero)
     return result;
 
+  norm2_scale = 0;
   if (!dim || e->rank == 1)
     {
       result = simplify_transformation_to_scalar (result, e, NULL,
-						  add_squared);
+						  norm2_add_squared);
       mpfr_sqrt (result->value.real, result->value.real, GFC_RND_MODE);
+      if (norm2_scale && mpfr_regular_p (result->value.real))
+	{
+	  mpfr_t tmp;
+	  mpfr_init (tmp);
+	  mpfr_set_ui (tmp, 1, GFC_RND_MODE);
+	  mpfr_set_exp (tmp, norm2_scale);
+	  mpfr_mul (result->value.real, result->value.real, tmp, GFC_RND_MODE);
+	  mpfr_clear (tmp);
+	}
+      norm2_scale = 0;
     }
   else
     result = simplify_transformation_to_array (result, e, dim, NULL,
-					       add_squared, &do_sqrt);
+					       norm2_add_squared,
+					       norm2_do_sqrt);
 
   return result;
 }