[gcc r13-297] [Ada] Reset Reachable field when mutating label into loop entity

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

https://gcc.gnu.org/g:470fff3d8e48ede98f0a74a1beb9eafc7452f4b4

commit r13-297-g470fff3d8e48ede98f0a74a1beb9eafc7452f4b4
Author: Piotr Trojanek <trojanek@adacore.com>
Date:   Fri Jan 28 18:12:18 2022 +0100

    [Ada] Reset Reachable field when mutating label into loop entity
    
    An entity flag Reachable now only applies to E_Label entities and needs
    to be explicitly reset when mutating labels into loop entities. Only
    needed to prevent cascaded errors when compiling a malicious ACATS test
    with -gnatq (try semantics, even if parse errors).
    
    Cleanup related to detection of uninitialized scalars with GOTO
    statements.
    
    gcc/ada/
    
            * sem_ch5.adb (Analyze_Statements): Only clear Reachable flag on
            proper label entities.

Diff:
---
 gcc/ada/sem_ch5.adb | 1 +
 1 file changed, 1 insertion(+)

diff --git a/gcc/ada/sem_ch5.adb b/gcc/ada/sem_ch5.adb
index f8e6d0c3e30..a0f22060007 100644
--- a/gcc/ada/sem_ch5.adb
+++ b/gcc/ada/sem_ch5.adb
@@ -4012,6 +4012,7 @@ package body Sem_Ch5 is
 
             if Ekind (Ent) = E_Label then
                Reinit_Field_To_Zero (Ent, F_Enclosing_Scope);
+               Reinit_Field_To_Zero (Ent, F_Reachable);
                Mutate_Ekind (Ent, E_Loop);
 
                if Nkind (Parent (Ent)) = N_Implicit_Label_Declaration then