2019-09-18 Thomas Koenig <tkoenig@gcc.gnu.org>

    Backport from trunk
    PR fortran/91550
    * frontend-passes.c (do_subscript): If step equals
    zero, a previuos error has been reported; do nothing
    in this case.
    * resolve.c (gfc_resolve_iterator): Move error checking
    after type conversion.

2019-09-18  Thomas Koenig  <tkoenig@gcc.gnu.org>

    Backport from trunk
    PR fortran/91550
    * gfortran.dg/do_subscript_6.f90: New test.



git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/gcc-9-branch@275891 138bc75d-0d04-0410-961f-82ee72b054a4

5 files changed, 52 insertions, 16 deletions

diff --git a/gcc/fortran/ChangeLog b/gcc/fortran/ChangeLog
index 44c13940625..74b86623a2c 100644
--- a/gcc/fortran/ChangeLog
+++ b/gcc/fortran/ChangeLog
@@ -1,3 +1,13 @@
+2019-09-18  Thomas Koenig  <tkoenig@gcc.gnu.org>
+
+	Backport from trunk
+	PR fortran/91550
+	* frontend-passes.c (do_subscript): If step equals
+	zero, a previuos error has been reported; do nothing
+	in this case.
+	* resolve.c (gfc_resolve_iterator): Move error checking
+	after type conversion.
+
 2019-09-15  Thomas Koenig  <tkoenig@gcc.gnu.org>
 
 	Backport from trunk
diff --git a/gcc/fortran/frontend-passes.c b/gcc/fortran/frontend-passes.c
index 08503ea5d1d..e6786635788 100644
--- a/gcc/fortran/frontend-passes.c
+++ b/gcc/fortran/frontend-passes.c
@@ -2580,6 +2580,7 @@ do_subscript (gfc_expr **e)
 	      bool have_do_start, have_do_end;
 	      bool error_not_proven;
 	      int warn;
+	      int sgn;
 
 	      dl = lp->c;
 	      if (dl == NULL)
@@ -2608,7 +2609,16 @@ do_subscript (gfc_expr **e)
 		 Do not warn in this case.  */
 
 	      if (dl->ext.iterator->step->expr_type == EXPR_CONSTANT)
-		mpz_init_set (do_step, dl->ext.iterator->step->value.integer);
+		{
+		  sgn = mpz_cmp_ui (dl->ext.iterator->step->value.integer, 0);
+		  /* This can happen, but then the error has been
+		     reported previusly.  */
+		  if (sgn == 0)
+		    continue;
+
+		  mpz_init_set (do_step, dl->ext.iterator->step->value.integer);
+		}
+
 	      else
 		continue;
 
@@ -2634,9 +2644,8 @@ do_subscript (gfc_expr **e)
 	      /* No warning inside a zero-trip loop.  */
 	      if (have_do_start && have_do_end)
 		{
-		  int sgn, cmp;
+		  int cmp;
 
-		  sgn = mpz_cmp_ui (do_step, 0);
 		  cmp = mpz_cmp (do_end, do_start);
 		  if ((sgn > 0 && cmp < 0) || (sgn < 0 && cmp > 0))
 		    break;
diff --git a/gcc/fortran/resolve.c b/gcc/fortran/resolve.c
index 9647ef2c46a..2d2d32e1733 100644
--- a/gcc/fortran/resolve.c
+++ b/gcc/fortran/resolve.c
@@ -7059,19 +7059,6 @@ gfc_resolve_iterator (gfc_iterator *iter, bool real_ok, bool own_scope)
 				  "Step expression in DO loop"))
     return false;
 
-  if (iter->step->expr_type == EXPR_CONSTANT)
-    {
-      if ((iter->step->ts.type == BT_INTEGER
-	   && mpz_cmp_ui (iter->step->value.integer, 0) == 0)
-	  || (iter->step->ts.type == BT_REAL
-	      && mpfr_sgn (iter->step->value.real) == 0))
-	{
-	  gfc_error ("Step expression in DO loop at %L cannot be zero",
-		     &iter->step->where);
-	  return false;
-	}
-    }
-
   /* Convert start, end, and step to the same type as var.  */
   if (iter->start->ts.kind != iter->var->ts.kind
       || iter->start->ts.type != iter->var->ts.type)
@@ -7085,6 +7072,19 @@ gfc_resolve_iterator (gfc_iterator *iter, bool real_ok, bool own_scope)
       || iter->step->ts.type != iter->var->ts.type)
     gfc_convert_type (iter->step, &iter->var->ts, 1);
 
+  if (iter->step->expr_type == EXPR_CONSTANT)
+    {
+      if ((iter->step->ts.type == BT_INTEGER
+	   && mpz_cmp_ui (iter->step->value.integer, 0) == 0)
+	  || (iter->step->ts.type == BT_REAL
+	      && mpfr_sgn (iter->step->value.real) == 0))
+	{
+	  gfc_error ("Step expression in DO loop at %L cannot be zero",
+		     &iter->step->where);
+	  return false;
+	}
+    }
+
   if (iter->start->expr_type == EXPR_CONSTANT
       && iter->end->expr_type == EXPR_CONSTANT
       && iter->step->expr_type == EXPR_CONSTANT)
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 6bb23d64b98..cd500d0b1c7 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2019-09-18  Thomas Koenig  <tkoenig@gcc.gnu.org>
+
+	Backport from trunk
+	PR fortran/91550
+	* gfortran.dg/do_subscript_6.f90: New test.
+
 2019-09-15  Thomas Koenig  <tkoenig@gcc.gnu.org>
 
 	Backport from trunk
diff --git a/gcc/testsuite/gfortran.dg/do_subscript_6.f90 b/gcc/testsuite/gfortran.dg/do_subscript_6.f90
new file mode 100644
index 00000000000..d78b9d39056
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/do_subscript_6.f90
@@ -0,0 +1,11 @@
+! { dg-do compile }
+! { dg-options "-std=legacy" }
+! PR 91550 - this used to cause an ICE
+! Test case by Gerhard Steinmetz
+program p
+   real :: a(3)
+   integer :: i
+   do i = 1, 3, .1 ! { dg-error "cannot be zero" }
+      a(i) = i
+   end do
+end