[gcc r13-497] [Ada] Fix proof of double arithmetic units

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

https://gcc.gnu.org/g:c1e007985fef1389ba09f5b558aa4e7b9f03783f

commit r13-497-gc1e007985fef1389ba09f5b558aa4e7b9f03783f
Author: Yannick Moy <moy@adacore.com>
Date:   Fri Mar 11 11:54:53 2022 +0100

    [Ada] Fix proof of double arithmetic units
    
    Proof of an assertion is not automatic anymore. Add two assertions
    before it to guide the prover.
    
    gcc/ada/
    
            * libgnat/s-aridou.adb (Double_Divide): Add intermediate
            assertions.

Diff:
---
 gcc/ada/libgnat/s-aridou.adb | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/gcc/ada/libgnat/s-aridou.adb b/gcc/ada/libgnat/s-aridou.adb
index ffb6f4ca269..08cbed7cefc 100644
--- a/gcc/ada/libgnat/s-aridou.adb
+++ b/gcc/ada/libgnat/s-aridou.adb
@@ -941,11 +941,13 @@ is
          else
             T2 := Yhi * Zlo;
             pragma Assert (Big (T2) = Big (Double_Uns'(Yhi * Zlo)));
+            pragma Assert (Big_0 = Big (Double_Uns'(Ylo * Zhi)));
          end if;
 
       else
          T2 := Ylo * Zhi;
          pragma Assert (Big (T2) = Big (Double_Uns'(Ylo * Zhi)));
+         pragma Assert (Big_0 = Big (Double_Uns'(Yhi * Zlo)));
       end if;
 
       T1 := Ylo * Zlo;