[PATCH] Fix internal error on small array with negative lower bound

[Eric Botcazou via Gcc-patches]

Hi,

Ada supports arrays with negative indices, although the internal index type is
sizetype like in other languages, which is unsigned.  This means that negative
values are represented by very large numbers, which works with a bit of care.
The attached test exposes a small loophole in output_constructor_bitfield.

Tested on x86-64/Linux, OK for the mainline?


2023-05-18  Eric Botcazou <ebotca...@adacore.com>

        * varasm.cc (output_constructor_bitfield): Call tree_to_uhwi instead
        of tree_to_shwi on array indices.  Minor tweaks.


2023-05-18  Eric Botcazou <ebotca...@adacore.com>

        * gnat.dg/specs/array6.ads: New test.

-- 
Eric Botcazou
diff --git a/gcc/varasm.cc b/gcc/varasm.cc
index 2256194d934..478cbfe6736 100644
--- a/gcc/varasm.cc
+++ b/gcc/varasm.cc
@@ -5585,19 +5585,18 @@ output_constructor_bitfield (oc_local_state *local, unsigned int bit_offset)
 
   /* Relative index of this element if this is an array component.  */
   HOST_WIDE_INT relative_index
-    = (!local->field
-       ? (local->index
-	  ? (tree_to_shwi (local->index)
-	     - tree_to_shwi (local->min_index))
-	  : local->last_relative_index + 1)
-       : 0);
+    = (local->field
+       ? 0
+       : (local->index
+	  ? tree_to_uhwi (local->index) - tree_to_uhwi (local->min_index)
+	  : local->last_relative_index + 1));
 
   /* Bit position of this element from the start of the containing
      constructor.  */
   HOST_WIDE_INT constructor_relative_ebitpos
-      = (local->field
-	 ? int_bit_position (local->field)
-	 : ebitsize * relative_index);
+    = (local->field
+       ? int_bit_position (local->field)
+       : ebitsize * relative_index);
 
   /* Bit position of this element from the start of a possibly ongoing
      outer byte buffer.  */

-- { dg-do compile }

package Array6 is 

  type Range_Type is range -10 ..  10;
  type Array_Type is array (Range_Type range <> ) of Short_Short_Integer;

  type Record_Type is record 
    A : Array_Type(-2..4);
  end record ;

  Rec : Record_Type := (A => (others => -1));

end Array6;