[Ada] Fix segfault on elaboration of empty 1-element array at -O

[Eric Botcazou]

This is another rather obscure case where the elaboration of an empty array 
whose base type is an array type of length at most 1 goes awry when the code 
is compiled with optimization.

Tested on x86-64/Linux, applied on the mainline, 10 and 9 branches.


2020-11-11  Eric Botcazou  <ebotca...@adacore.com>

        * gcc-interface/trans.c (can_be_lower_p): Remove.
        (Regular_Loop_to_gnu): Add ENTRY_COND unconditionally if
        BOTTOM_COND is non-zero.


2020-11-11  Eric Botcazou  <ebotca...@adacore.com>

        * gnat.dg/opt89.adb: New test.

-- 
Eric Botcazou
diff --git a/gcc/ada/gcc-interface/trans.c b/gcc/ada/gcc-interface/trans.c
index d0663a2d69b..065fcd2f956 100644
--- a/gcc/ada/gcc-interface/trans.c
+++ b/gcc/ada/gcc-interface/trans.c
@@ -2814,38 +2814,6 @@ can_equal_max_val_p (tree val, tree type, bool reverse)
   return can_equal_min_or_max_val_p (val, type, !reverse);
 }
 
-/* Return true if VAL1 can be lower than VAL2.  */
-
-static bool
-can_be_lower_p (tree val1, tree val2)
-{
-  if (TREE_CODE (val1) == NOP_EXPR)
-    {
-      tree type = TREE_TYPE (TREE_OPERAND (val1, 0));
-      if (can_be_lower_p (TYPE_MAX_VALUE (type), TYPE_MIN_VALUE (type)))
-	return true;
-
-      val1 = TYPE_MIN_VALUE (type);
-    }
-
-  if (TREE_CODE (val1) != INTEGER_CST)
-    return true;
-
-  if (TREE_CODE (val2) == NOP_EXPR)
-    {
-      tree type = TREE_TYPE (TREE_OPERAND (val2, 0));
-      if (can_be_lower_p (TYPE_MAX_VALUE (type), TYPE_MIN_VALUE (type)))
-	return true;
-
-      val2 = TYPE_MAX_VALUE (type);
-    }
-
-  if (TREE_CODE (val2) != INTEGER_CST)
-    return true;
-
-  return tree_int_cst_lt (val1, val2);
-}
-
 /* Replace EXPR1 and EXPR2 by invariant expressions if possible.  Return
    true if both expressions have been replaced and false otherwise.  */
 
@@ -3126,19 +3094,16 @@ Regular_Loop_to_gnu (Node_Id gnat_node, tree *gnu_cond_expr_p)
 	}
 
       /* If we use the BOTTOM_COND, we can turn the test into an inequality
-	 test but we may have to add ENTRY_COND to protect the empty loop.  */
+	 test but we have to add ENTRY_COND to protect the empty loop.  */
       if (LOOP_STMT_BOTTOM_COND_P (gnu_loop_stmt))
 	{
 	  test_code = NE_EXPR;
-	  if (can_be_lower_p (gnu_high, gnu_low))
-	    {
-	      gnu_cond_expr
-		= build3 (COND_EXPR, void_type_node,
-			  build_binary_op (LE_EXPR, boolean_type_node,
-					   gnu_low, gnu_high),
-			  NULL_TREE, alloc_stmt_list ());
-	      set_expr_location_from_node (gnu_cond_expr, gnat_iter_scheme);
-	    }
+	  gnu_cond_expr
+	    = build3 (COND_EXPR, void_type_node,
+		      build_binary_op (LE_EXPR, boolean_type_node,
+				       gnu_low, gnu_high),
+		      NULL_TREE, alloc_stmt_list ());
+	  set_expr_location_from_node (gnu_cond_expr, gnat_iter_scheme);
 	}
 
       /* Open a new nesting level that will surround the loop to declare the

-- { dg-do run }
-- { dg-options "-O" }

procedure Opt89 is

  type Rec is record
    I : Integer := 3;
  end record;

  subtype Index is Natural range 0..0;

  type Arr is array (Index range <>) of Rec;

  X : Arr (0 .. -1);

begin
  null;
end;