[libc++] Use __builtin_expect and __builtin_assume in _LIBCPP_ASSERT

Since we expect the condition to be true most of the time, we might
as well tell the compiler. And when assertions are disabled, we
might as well tell the compiler that it's allowed to assume that
the condition holds.

Differential Revision: https://reviews.llvm.org/D122397

Author: ldionne

libcxx/include/__assert

@@ -34,9 +34,20 @@
 #endif
 
 #if _LIBCPP_ENABLE_ASSERTIONS
-# define _LIBCPP_ASSERT(expression, message) ((expression) ? (void)0 : ::std::__libcpp_assertion_handler(__FILE__, __LINE__, #expression, message))
+# define _LIBCPP_ASSERT(expression, message)                                        \
+    (__builtin_expect(static_cast<bool>(expression), 1) ?                           \
+      (void)0 :                                                                     \
+      ::std::__libcpp_assertion_handler(__FILE__, __LINE__, #expression, message))
 #else
-# define _LIBCPP_ASSERT(x, m) ((void)0)
+# if __has_builtin(__builtin_assume)
+#   define _LIBCPP_ASSERT(expression, message)                                      \
+      (_LIBCPP_DIAGNOSTIC_PUSH                                                      \
+      _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wassume")                                  \
+      __builtin_assume(static_cast<bool>(expression))                               \
+      _LIBCPP_DIAGNOSTIC_POP)
+# else
+#   define _LIBCPP_ASSERT(expression, message) ((void)0)
+# endif
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD

libcxx/test/libcxx/assertions/single_expression.sh.cpp

@@ -0,0 +1,34 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// Make sure that _LIBCPP_ASSERT is a single expression. This is useful so we can use
+// it in places that require an expression, such as in a constructor initializer list.
+
+// RUN: %{build} -Wno-macro-redefined -D_LIBCPP_ENABLE_ASSERTIONS=1
+// RUN: %{run}
+
+// RUN: %{build} -Wno-macro-redefined -D_LIBCPP_ENABLE_ASSERTIONS=0
+// RUN: %{run}
+
+// We flag uses of the assertion handler in older dylibs at compile-time to avoid runtime
+// failures when back-deploying.
+// UNSUPPORTED: use_system_cxx_lib && target={{.+}}-apple-macosx{{10.9|10.10|10.11|10.12|10.13|10.14|10.15|11|12}}
+
+#include <__assert>
+#include <cassert>
+
+void f() {
+  int i = (_LIBCPP_ASSERT(true, "message"), 3);
+  assert(i == 3);
+  return _LIBCPP_ASSERT(true, "message");
+}
+
+int main(int, char**) {
+  f();
+  return 0;
+}

libcxx/test/libcxx/containers/sequences/vector/robust_against_adl.pass.cpp

@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03
-// UNSUPPORTED: debug_level=0, debug_level=1, libcpp-has-assertions
 
 // <vector>
 
@@ -41,7 +40,9 @@ int main(int, char**)
     v.erase(v.begin());
     v.erase(v.begin(), v.end());
 #if TEST_STD_VER >= 14
-    v.swap(w);
+    // TODO: vector::swap is not robust against ADL because we compare allocators, and that
+    //       triggers ADL when looking up operator==.
+    // v.swap(w);
 #endif
     return 0;
 }