[gcc r13-1430] [Ada] Avoid unwanted warnings for statically-known-successful assertions

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

https://gcc.gnu.org/g:f7c05e82037356ac4610e9e5d1365b345a17d0f7

commit r13-1430-gf7c05e82037356ac4610e9e5d1365b345a17d0f7
Author: Steve Baird <baird@adacore.com>
Date:   Tue May 24 14:09:14 2022 -0700

    [Ada] Avoid unwanted warnings for statically-known-successful assertions
    
    The -gnatwc switch enables warnings for test condition outcomes that are
    known at compile time. Such warnings are unlikely to be useful in the
    case of an assertion expression (or a subexpression thereof), so do not
    generate them in that case.
    
    gcc/ada/
    
            * sem_warn.adb (Warn_On_Constant_Valid_Condition): Do not
            generate a warning if the expression in question is an assertion
            expression, or a subexpression thereof. But do call
            Test_Comparison so that it can generate warnings for the cases
            that it generates warnings for.
            * sem_prag.ads: Modify Assertion_Expression_Pragma constant so
            that the predicate Sem_Util.In_Assertion_Expression_Pragma
            returns True for the expression of a Compile_Time_Error pragma.

Diff:
---
 gcc/ada/sem_prag.ads | 1 +
 gcc/ada/sem_warn.adb | 9 +++++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/gcc/ada/sem_prag.ads b/gcc/ada/sem_prag.ads
index 0a1ad5bedf1..e8a65ce5011 100644
--- a/gcc/ada/sem_prag.ads
+++ b/gcc/ada/sem_prag.ads
@@ -135,6 +135,7 @@ package Sem_Prag is
       Pragma_Assert_And_Cut            => True,
       Pragma_Assume                    => True,
       Pragma_Check                     => True,
+      Pragma_Compile_Time_Error        => True,
       Pragma_Contract_Cases            => True,
       Pragma_Default_Initial_Condition => True,
       Pragma_Initial_Condition         => True,
diff --git a/gcc/ada/sem_warn.adb b/gcc/ada/sem_warn.adb
index b23be725437..1d73f21e7de 100644
--- a/gcc/ada/sem_warn.adb
+++ b/gcc/ada/sem_warn.adb
@@ -3401,9 +3401,14 @@ package body Sem_Warn is
             False_Result => False_Result);
 
          --  Warn on a possible evaluation to False / True in the presence of
-         --  invalid values.
+         --  invalid values. But issue no warning for an assertion expression
+         --  (or a subexpression thereof); in particular, we don't want a
+         --  warning about an assertion that will always succeed.
 
-         if True_Result then
+         if In_Assertion_Expression_Pragma (Op) then
+            null;
+
+         elsif True_Result then
             Error_Msg_N
               ("condition can only be False if invalid values present?c?", Op);