testsuite: tolerate compare_exchange_weak spurious failure

[Alexandre Oliva]

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.

Regstrapped on x86_64-linux-gnu, also tested with gcc-15 for ppc-vx7r2.
Ok to install?


for  libstdc++-v3/ChangeLog

	* testsuite/29_atomics/atomic/compare_exchange_padding.cc:
	Tolerate one compare_exchange_weak spurious failure.
---
 .../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 d9c7b90c1a5c1..3fc2f6b4f8031 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;
 }

-- 
Alexandre Oliva, happy hacker            https://blog.lx.oliva.nom.br/
Free Software Activist     FSFLA co-founder     GNU Toolchain Engineer
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