Fortran: error recovery while simplifying expressions [PR103707,PR106987]

When an exception is encountered during simplification of arithmetic
expressions, the result may depend on whether range-checking is active
(-frange-check) or not.  However, the code path in the front-end should
stay the same for "soft" errors for which the exception is triggered by the
check, while "hard" errors should always terminate the simplification, so
that error recovery is independent of the flag.  Separation of arithmetic
error codes into "hard" and "soft" errors shall be done consistently via
is_hard_arith_error().

	PR fortran/103707
	PR fortran/106987

gcc/fortran/ChangeLog:

	* arith.cc (is_hard_arith_error): New helper function to determine
	whether an arithmetic error is "hard" or not.
	(check_result): Use it.
	(gfc_arith_divide): Set "Division by zero" only for regular
	numerators of real and complex divisions.
	(reduce_unary): Use is_hard_arith_error to determine whether a hard
	or (recoverable) soft error was encountered.  Terminate immediately
	on hard error, otherwise remember code of first soft error.
	(reduce_binary_ac): Likewise.
	(reduce_binary_ca): Likewise.
	(reduce_binary_aa): Likewise.

gcc/testsuite/ChangeLog:

	* gfortran.dg/pr99350.f90:
	* gfortran.dg/arithmetic_overflow_3.f90: New test.

3 files changed, 143 insertions, 41 deletions

diff --git a/gcc/fortran/arith.cc b/gcc/fortran/arith.cc
index d17d1aa..b373c25 100644
--- a/gcc/fortran/arith.cc
+++ b/gcc/fortran/arith.cc
@@ -130,6 +130,30 @@ gfc_arith_error (arith code)
 }
 
 
+/* Check if a certain arithmetic error code is severe enough to prevent
+   further simplification, as opposed to errors thrown by the range check
+   (e.g. overflow) or arithmetic exceptions that are tolerated with
+   -fno-range-check.  */
+
+static bool
+is_hard_arith_error (arith code)
+{
+  switch (code)
+    {
+    case ARITH_OK:
+    case ARITH_OVERFLOW:
+    case ARITH_UNDERFLOW:
+    case ARITH_NAN:
+    case ARITH_DIV0:
+    case ARITH_ASYMMETRIC:
+      return false;
+
+    default:
+      return true;
+    }
+}
+
+
 /* Get things ready to do math.  */
 
 void
@@ -579,10 +603,10 @@ check_result (arith rc, gfc_expr *x, gfc_expr *r, gfc_expr **rp)
       val = ARITH_OK;
     }
 
-  if (val == ARITH_OK || val == ARITH_OVERFLOW)
-    *rp = r;
-  else
+  if (is_hard_arith_error (val))
     gfc_free_expr (r);
+  else
+    *rp = r;
 
   return val;
 }
@@ -792,23 +816,26 @@ gfc_arith_divide (gfc_expr *op1, gfc_expr *op2, gfc_expr **resultp)
       break;
 
     case BT_REAL:
-      if (mpfr_sgn (op2->value.real) == 0 && flag_range_check == 1)
-	{
-	  rc = ARITH_DIV0;
-	  break;
-	}
+      /* Set "Division by zero" only for regular numerator.  */
+      if (flag_range_check == 1
+	  && mpfr_zero_p (op2->value.real)
+	  && mpfr_regular_p (op1->value.real))
+	rc = ARITH_DIV0;
 
       mpfr_div (result->value.real, op1->value.real, op2->value.real,
 	       GFC_RND_MODE);
       break;
 
     case BT_COMPLEX:
-      if (mpc_cmp_si_si (op2->value.complex, 0, 0) == 0
-	  && flag_range_check == 1)
-	{
-	  rc = ARITH_DIV0;
-	  break;
-	}
+      /* Set "Division by zero" only for regular numerator.  */
+      if (flag_range_check == 1
+	  && mpfr_zero_p (mpc_realref (op2->value.complex))
+	  && mpfr_zero_p (mpc_imagref (op2->value.complex))
+	  && ((mpfr_regular_p (mpc_realref (op1->value.complex))
+	       && mpfr_number_p (mpc_imagref (op1->value.complex)))
+	      || (mpfr_regular_p (mpc_imagref (op1->value.complex))
+		  && mpfr_number_p (mpc_realref (op1->value.complex)))))
+	rc = ARITH_DIV0;
 
       gfc_set_model (mpc_realref (op1->value.complex));
       if (mpc_cmp_si_si (op2->value.complex, 0, 0) == 0)
@@ -1323,7 +1350,6 @@ reduce_unary (arith (*eval) (gfc_expr *, gfc_expr **), gfc_expr *op,
   gfc_constructor *c;
   gfc_expr *r;
   arith rc;
-  bool ov = false;
 
   if (op->expr_type == EXPR_CONSTANT)
     return eval (op, result);
@@ -1335,19 +1361,22 @@ reduce_unary (arith (*eval) (gfc_expr *, gfc_expr **), gfc_expr *op,
   head = gfc_constructor_copy (op->value.constructor);
   for (c = gfc_constructor_first (head); c; c = gfc_constructor_next (c))
     {
-      rc = reduce_unary (eval, c->expr, &r);
+      arith rc_tmp = reduce_unary (eval, c->expr, &r);
 
-      /* Remember any overflow encountered during reduction and continue,
-	 but terminate on serious errors.  */
-      if (rc == ARITH_OVERFLOW)
-	ov = true;
-      else if (rc != ARITH_OK)
-	break;
+      /* Remember first recoverable ("soft") error encountered during
+	 reduction and continue, but terminate on serious errors.  */
+      if (is_hard_arith_error (rc_tmp))
+	{
+	  rc = rc_tmp;
+	  break;
+	}
+      else if (rc_tmp != ARITH_OK && rc == ARITH_OK)
+	rc = rc_tmp;
 
       gfc_replace_expr (c->expr, r);
     }
 
-  if (rc != ARITH_OK && rc != ARITH_OVERFLOW)
+  if (is_hard_arith_error (rc))
     gfc_constructor_free (head);
   else
     {
@@ -1368,7 +1397,7 @@ reduce_unary (arith (*eval) (gfc_expr *, gfc_expr **), gfc_expr *op,
       *result = r;
     }
 
-  return ov ? ARITH_OVERFLOW : rc;
+  return rc;
 }
 
 
@@ -1384,22 +1413,31 @@ reduce_binary_ac (arith (*eval) (gfc_expr *, gfc_expr *, gfc_expr **),
   head = gfc_constructor_copy (op1->value.constructor);
   for (c = gfc_constructor_first (head); c; c = gfc_constructor_next (c))
     {
+      arith rc_tmp;
+
       gfc_simplify_expr (c->expr, 0);
 
       if (c->expr->expr_type == EXPR_CONSTANT)
-        rc = eval (c->expr, op2, &r);
+	rc_tmp = eval (c->expr, op2, &r);
       else if (c->expr->expr_type != EXPR_ARRAY)
-	rc = ARITH_NOT_REDUCED;
+	rc_tmp = ARITH_NOT_REDUCED;
       else
-	rc = reduce_binary_ac (eval, c->expr, op2, &r);
+	rc_tmp = reduce_binary_ac (eval, c->expr, op2, &r);
 
-      if (rc != ARITH_OK)
-	break;
+      /* Remember first recoverable ("soft") error encountered during
+	 reduction and continue, but terminate on serious errors.  */
+      if (is_hard_arith_error (rc_tmp))
+	{
+	  rc = rc_tmp;
+	  break;
+	}
+      else if (rc_tmp != ARITH_OK && rc == ARITH_OK)
+	rc = rc_tmp;
 
       gfc_replace_expr (c->expr, r);
     }
 
-  if (rc != ARITH_OK)
+  if (is_hard_arith_error (rc))
     gfc_constructor_free (head);
   else
     {
@@ -1438,22 +1476,31 @@ reduce_binary_ca (arith (*eval) (gfc_expr *, gfc_expr *, gfc_expr **),
   head = gfc_constructor_copy (op2->value.constructor);
   for (c = gfc_constructor_first (head); c; c = gfc_constructor_next (c))
     {
+      arith rc_tmp;
+
       gfc_simplify_expr (c->expr, 0);
 
       if (c->expr->expr_type == EXPR_CONSTANT)
-	rc = eval (op1, c->expr, &r);
+	rc_tmp = eval (op1, c->expr, &r);
       else if (c->expr->expr_type != EXPR_ARRAY)
-	rc = ARITH_NOT_REDUCED;
+	rc_tmp = ARITH_NOT_REDUCED;
       else
-	rc = reduce_binary_ca (eval, op1, c->expr, &r);
+	rc_tmp = reduce_binary_ca (eval, op1, c->expr, &r);
 
-      if (rc != ARITH_OK)
-	break;
+      /* Remember first recoverable ("soft") error encountered during
+	 reduction and continue, but terminate on serious errors.  */
+      if (is_hard_arith_error (rc_tmp))
+	{
+	  rc = rc_tmp;
+	  break;
+	}
+      else if (rc_tmp != ARITH_OK && rc == ARITH_OK)
+	rc = rc_tmp;
 
       gfc_replace_expr (c->expr, r);
     }
 
-  if (rc != ARITH_OK)
+  if (is_hard_arith_error (rc))
     gfc_constructor_free (head);
   else
     {
@@ -1503,10 +1550,17 @@ reduce_binary_aa (arith (*eval) (gfc_expr *, gfc_expr *, gfc_expr **),
        c && d;
        c = gfc_constructor_next (c), d = gfc_constructor_next (d))
     {
-      rc = reduce_binary (eval, c->expr, d->expr, &r);
+      arith rc_tmp = reduce_binary (eval, c->expr, d->expr, &r);
 
-      if (rc != ARITH_OK)
-	break;
+      /* Remember first recoverable ("soft") error encountered during
+	 reduction and continue, but terminate on serious errors.  */
+      if (is_hard_arith_error (rc_tmp))
+	{
+	  rc = rc_tmp;
+	  break;
+	}
+      else if (rc_tmp != ARITH_OK && rc == ARITH_OK)
+	rc = rc_tmp;
 
       gfc_replace_expr (c->expr, r);
     }
@@ -1514,7 +1568,7 @@ reduce_binary_aa (arith (*eval) (gfc_expr *, gfc_expr *, gfc_expr **),
   if (rc == ARITH_OK && (c || d))
     rc = ARITH_INCOMMENSURATE;
 
-  if (rc != ARITH_OK)
+  if (is_hard_arith_error (rc))
     gfc_constructor_free (head);
   else
     {
diff --git a/gcc/testsuite/gfortran.dg/arithmetic_overflow_3.f90 b/gcc/testsuite/gfortran.dg/arithmetic_overflow_3.f90
new file mode 100644
index 0000000..4dc5527
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/arithmetic_overflow_3.f90
@@ -0,0 +1,48 @@
+! { dg-do compile }
+! { dg-additional-options "-frange-check" }
+!
+! PR fortran/103707
+! PR fortran/106987
+!
+! Check error recovery on arithmetic exceptions
+
+program p
+  implicit none
+  integer, parameter :: a(3) = [30,31,32]
+  integer, parameter :: e(1) = 2
+  print *, 2 ** a       ! { dg-error "Arithmetic overflow" }
+  print *, e ** 31      ! { dg-error "Arithmetic overflow" }
+end
+
+! { dg-prune-output "Result of exponentiation" }
+
+subroutine s
+  implicit none
+  real, parameter :: inf = real (z'7F800000')
+  real, parameter :: nan = real (z'7FC00000')
+
+  ! Unary operators
+  print *, -[inf,nan]           ! { dg-error "Arithmetic overflow" }
+  print *, -[nan,inf]           ! { dg-error "Arithmetic NaN" }
+
+  ! Binary operators
+  print *, [1.]/[0.]            ! { dg-error "Division by zero" }
+  print *, [0.]/[0.]            ! { dg-error "Arithmetic NaN" }
+  print *, 0. / [(0.,0.)]       ! { dg-error "Arithmetic NaN" }
+  print *, [1.,0.]/[0.,0.]      ! { dg-error "Division by zero" }
+  print *, [(1.,1.)]/[0.]       ! { dg-error "Division by zero" }
+  print *, [(1.,0.)]/[0.]       ! { dg-error "Division by zero" }
+  print *, [(0.,0.)]/[0.]       ! { dg-error "Arithmetic NaN" }
+  print *, - [1./0.]/[0.]       ! { dg-error "Division by zero" }
+  print *, - [ 1/0 ] * 1        ! { dg-error "Division by zero" }
+
+  ! Binary operators, exceptional input
+  print *, 1. / nan             ! { dg-error "Arithmetic NaN" }
+  print *, [inf] / inf          ! { dg-error "Arithmetic NaN" }
+  print *, inf + [nan]          ! { dg-error "Arithmetic NaN" }
+  print *, [(1.,0.)]/[(nan,0.)] ! { dg-error "Arithmetic NaN" }
+  print *, [(1.,0.)]/[(0.,nan)] ! { dg-error "Arithmetic NaN" }
+  print *, [(1.,0.)]/[(inf,0.)] ! OK
+  print *, [nan,inf] / (0.)     ! { dg-error "Arithmetic NaN" }
+  print *, [inf,nan] / (0.)     ! { dg-error "Arithmetic overflow" }
+end
diff --git a/gcc/testsuite/gfortran.dg/pr99350.f90 b/gcc/testsuite/gfortran.dg/pr99350.f90
index 7f751b9..ec19881 100644
--- a/gcc/testsuite/gfortran.dg/pr99350.f90
+++ b/gcc/testsuite/gfortran.dg/pr99350.f90
@@ -7,7 +7,7 @@ program p
       character(:), pointer :: a
    end type
    type(t) :: z
-   character((0.)/0), target :: c = 'abc' ! { dg-error "Division by zero" }
+   character((0.)/0), target :: c = 'abc' ! { dg-error "Arithmetic NaN" }
    z%a => c
 ! The associate statement was not needed to trigger the ICE.
    associate (y => z%a)