From: LLVM Packaging Team <pkg-llvm-team@lists.alioth.debian.org>
Date: Wed, 17 Oct 2018 09:00:09 +0000 (+0100)
Subject: libcxx-test-fix-lockfree-test-for-i386
X-Git-Tag: archive/raspbian/1%7-6+rpi1~13
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=5527a989481f9445e07cd45c5f158f74dc05816c;p=llvm-toolchain-7.git

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

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: 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 7a8d4c1f4..5cd0e2d2c 100644
--- a/libcxx/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp
@@ -20,6 +20,14 @@
 # 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());