[gcc r12-1627] [Ada] Error issued on string literal assigned to fixed-lower-bound array

[Pierre-Marie de Rodat <pmderodat@gcc.gnu.org>]

https://gcc.gnu.org/g:f44441d80fa8523a2e1b294b8563180202879727

commit r12-1627-gf44441d80fa8523a2e1b294b8563180202879727
Author: Gary Dismukes <dismukes@adacore.com>
Date:   Thu Mar 18 20:23:04 2021 -0400

    [Ada] Error issued on string literal assigned to fixed-lower-bound array
    
    gcc/ada/
    
            * exp_util.adb (Expand_Sliding_Conversion): Move test of
            Is_Fixed_Lower_Bound_Subtype to an assertion. Exclude string
            literals from sliding expansion.

Diff:
---
 gcc/ada/exp_util.adb | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/gcc/ada/exp_util.adb b/gcc/ada/exp_util.adb
index 19b8c656e2c..ed1a016be48 100644
--- a/gcc/ada/exp_util.adb
+++ b/gcc/ada/exp_util.adb
@@ -5323,7 +5323,8 @@ package body Exp_Util is
    procedure Expand_Sliding_Conversion (N : Node_Id; Arr_Typ : Entity_Id) is
 
       pragma Assert (Is_Array_Type (Arr_Typ)
-                      and then not Is_Constrained (Arr_Typ));
+                      and then not Is_Constrained (Arr_Typ)
+                      and then Is_Fixed_Lower_Bound_Array_Subtype (Arr_Typ));
 
       Constraints : List_Id;
       Index       : Node_Id := First_Index (Arr_Typ);
@@ -5342,7 +5343,10 @@ package body Exp_Util is
       All_FLBs_Match : Boolean := True;
 
    begin
-      if Is_Fixed_Lower_Bound_Array_Subtype (Arr_Typ) then
+      --  Sliding should never be needed for string literals, because they have
+      --  their bounds set according to the applicable index constraint.
+
+      if Nkind (N) /= N_String_Literal then
          Constraints := New_List;
 
          Act_Subt  := Get_Actual_Subtype (N);