ada: Incorrect constant folding in postcondition involving 'Old

The following patch fixes an issue in the compiler whereby certain flavors of
access comparisons may be incorrectly constant-folded out of contract
expressions - notably in postcondition expressions featuring a reference to
'Old.

gcc/ada/

	* checks.adb (Install_Null_Excluding_Check): Avoid non-null
	optimizations when assertions are enabled.

1 files changed, 12 insertions, 1 deletions

diff --git a/gcc/ada/checks.adb b/gcc/ada/checks.adb
index 9f3c679..0d47296 100644
--- a/gcc/ada/checks.adb
+++ b/gcc/ada/checks.adb
@@ -8437,7 +8437,18 @@ package body Checks is
               Right_Opnd => Make_Null (Loc)),
           Reason => CE_Access_Check_Failed));
 
-      Mark_Non_Null;
+      --  Mark the entity of N "non-null" except when assertions are enabled -
+      --  since expansion becomes much more complicated (especially when it
+      --  comes to contracts) due to the generation of wrappers and wholesale
+      --  moving of declarations and statements which may happen.
+
+      --  Additionally, it is assumed that extra checks will exist with
+      --  assertions enabled so some potentially redundant checks are
+      --  acceptable.
+
+      if not Assertions_Enabled then
+         Mark_Non_Null;
+      end if;
    end Install_Null_Excluding_Check;
 
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