From: LLVM Packaging Team <pkg-llvm-team@lists.alioth.debian.org>
Date: Sat, 7 Nov 2020 14:53:51 +0000 (+0000)
Subject: libcxx-test-fix-lockfree-test-for-i386
X-Git-Tag: archive/raspbian/1%11.0.0-5+rpi1~28
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=167ba472f3bd91f16b2b6a533d8245f41ec4d9e7;p=llvm-toolchain-11.git

libcxx-test-fix-lockfree-test-for-i386

Lock is_always_lock free test fails on i386 because std::atomic is aligned

Lock is_always_lock free test fails on i386 because std::atomic is aligned
to 8 bytes while long long is aligned to 4 bytes. clang can't generate inline
code for unaligned 8 byte atomics even tough instruction set and gcc support
it.

That makes it expected thaqt ATOMIC_LLONG_LOCK_FREE and
std::atomic<long long>::is_always_lock_free don't match on i386. Correct test
for std::atomic<long long> is to check if target cpu support cmpxchg8 instruction.
To set instruction support one can check __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8 define.

Bug: https://llvm.org/bugs/show_bug.cgi?id=19355


Gbp-Pq: Topic libcxx
Gbp-Pq: Name libcxx-test-fix-lockfree-test-for-i386.patch
---

diff --git a/libcxx/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp b/libcxx/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp
index 34a068918..824704189 100644
--- a/libcxx/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp
@@ -21,6 +21,14 @@
 # error Feature test macro missing.
 #endif
 
+#if defined(__i386__) && defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_8)
+/* Fix for clang setting __GCC_ATOMIC_LLONG_LOCK_FREE incorecctly for x86
+ * https://llvm.org/bugs/show_bug.cgi?id=19355
+ */
+#undef ATOMIC_LLONG_LOCK_FREE
+#define ATOMIC_LLONG_LOCK_FREE 2
+#endif
+
 template <typename T> void checkAlwaysLockFree() {
   if (std::atomic<T>::is_always_lock_free)
     assert(std::atomic<T>().is_lock_free());