[gcc(refs/users/aoliva/heads/testme)] testsuite: tolerate compare_exchange_weak spurious failure

[Alexandre Oliva]

https://gcc.gnu.org/g:594bb2a6c8cf25da6a2981204cc25603100346dc

commit 594bb2a6c8cf25da6a2981204cc25603100346dc
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Tue Mar 10 04:38:07 2026 -0300

    testsuite: tolerate compare_exchange_weak spurious failure
    
    compare_exchange_weak is allowed to fail spuriously, and we're
    actually hitting such spurious failures quite often on ppc-vx7r2,
    presumably when random interrupts hit between ll and sc.
    
    Tolerate one such failure, hopefully that will suffice.
    
    
    for  libstdc++-v3/ChangeLog
    
            * testsuite/29_atomics/atomic/compare_exchange_padding.cc:
            Tolerate one compare_exchange_weak spurious failure.

Diff:
---
 libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc b/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc
index d9c7b90c1a5c..3fc2f6b4f803 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc
@@ -37,8 +37,8 @@ main ()
   fill_struct(n);
   n.c = 'b';
   n.s = 71;
-  // padding cleared on compexchg
-  VERIFY( as.compare_exchange_weak(s, n) );
+  // padding cleared on compexchg.  tolerate one spurious _weak failure.
+  VERIFY( as.compare_exchange_weak(s, n) || as.compare_exchange_weak(s, n) );
   VERIFY( as.compare_exchange_strong(n, s) );
   return 0;
 }