Optimize for size on buffers_cat preconditions:

When BOOST_BEAST_TESTS is not defined, violations of
buffers_cat preconditions will assert instead of throwing
exceptions. This reduces the size of the emitted code
and improves performance.

CHANGELOG.md

@@ -10,6 +10,7 @@ Version 200
 * Add const and mutable buffer sequence traits
 * Add buffers_iterator_type trait
 * Use new buffer traits, remove old unused traits
+* Optimize for size on buffers_cat preconditions
 
 API Changes:
 

include/boost/beast/core/impl/buffers_cat.hpp

@@ -14,7 +14,6 @@
 #include <boost/beast/core/detail/type_traits.hpp>
 #include <boost/beast/core/detail/variant.hpp>
 #include <boost/asio/buffer.hpp>
-#include <boost/throw_exception.hpp>
 #include <cstdint>
 #include <iterator>
 #include <new>
@@ -24,6 +23,45 @@
 namespace boost {
 namespace beast {
 
+#if defined(_MSC_VER) && ! defined(__clang__)
+# define BOOST_BEAST_UNREACHABLE() __assume(false)
+# define BOOST_BEAST_UNREACHABLE_RETURN(v) __assume(false)
+#else
+# define BOOST_BEAST_UNREACHABLE() __builtin_unreachable()
+# define BOOST_BEAST_UNREACHABLE_RETURN(v) \
+    do { __builtin_unreachable(); return v; } while(false)
+#endif
+
+#ifdef BOOST_BEAST_TESTS
+
+#define BOOST_BEAST_LOGIC_ERROR(s) \
+    do { \
+        BOOST_THROW_EXCEPTION(std::logic_error((s))); \
+        BOOST_BEAST_UNREACHABLE(); \
+    } while(false)
+
+#define BOOST_BEAST_LOGIC_ERROR_RETURN(v, s) \
+    do { \
+        BOOST_THROW_EXCEPTION(std::logic_error(s)); \
+        BOOST_BEAST_UNREACHABLE_RETURN(v); \
+    } while(false)
+
+#else
+
+#define BOOST_BEAST_LOGIC_ERROR(s) \
+    do { \
+        BOOST_ASSERT_MSG(false, s); \
+        BOOST_BEAST_UNREACHABLE(); \
+    } while(false)
+
+#define BOOST_BEAST_LOGIC_ERROR_RETURN(v, s) \
+    do { \
+        BOOST_ASSERT_MSG(false, (s)); \
+        BOOST_BEAST_UNREACHABLE_RETURN(v); \
+    } while(false)
+
+#endif
+
 namespace detail {
 
 struct buffers_cat_view_iterator_base
@@ -35,9 +73,8 @@ struct buffers_cat_view_iterator_base
         net::mutable_buffer
         operator*() const
         {
-            // Dereferencing a one-past-the-end iterator
+            BOOST_BEAST_LOGIC_ERROR_RETURN({},
-            BOOST_THROW_EXCEPTION(std::logic_error{
+                "Dereferencing a one-past-the-end iterator");
-                "invalid iterator"});
         }
 
         operator bool() const noexcept
@@ -115,13 +152,11 @@ private:
     {
         const_iterator const& self;
 
-        [[noreturn]]
         reference
         operator()(mp11::mp_size_t<0>)
         {
-            // Dereferencing a default-constructed iterator
+            BOOST_BEAST_LOGIC_ERROR_RETURN({},
-            BOOST_THROW_EXCEPTION(std::logic_error{
+                "Dereferencing a default-constructed iterator");
-                "invalid iterator"});
         }
 
         template<class I>
@@ -135,13 +170,11 @@ private:
     {
         const_iterator& self;
 
-        [[noreturn]]
         void
         operator()(mp11::mp_size_t<0>)
         {
-            // Incrementing a default-constructed iterator
+            BOOST_BEAST_LOGIC_ERROR(
-            BOOST_THROW_EXCEPTION(std::logic_error{
+                "Incrementing a default-constructed iterator");
-                "invalid iterator"});
         }
 
         template<std::size_t I>
@@ -198,13 +231,11 @@ private:
             self.it_.template emplace<I+1>();
         }
 
-        [[noreturn]]
         void
         operator()(mp11::mp_size_t<sizeof...(Bn)+1>)
         {
-            // Incrementing a one-past-the-end iterator
+            BOOST_BEAST_LOGIC_ERROR(
-            BOOST_THROW_EXCEPTION(std::logic_error{
+                "Incrementing a one-past-the-end iterator");
-                "invalid iterator"});
         }
     };
 
@@ -212,13 +243,11 @@ private:
     {
         const_iterator& self;
 
-        [[noreturn]]
         void
         operator()(mp11::mp_size_t<0>)
         {
-            // Decrementing a default-constructed iterator
+            BOOST_BEAST_LOGIC_ERROR(
-            BOOST_THROW_EXCEPTION(std::logic_error{
+                "Decrementing a default-constructed iterator");
-                "invalid iterator"});
         }
 
         void
@@ -232,9 +261,8 @@ private:
                 if(it == net::buffer_sequence_begin(
                         detail::get<I-1>(*self.bn_)))
                 {
-                    // Decrementing an iterator to the beginning
+                    BOOST_BEAST_LOGIC_ERROR(
-                    BOOST_THROW_EXCEPTION(std::logic_error{
+                        "Decrementing an iterator to the beginning");
-                        "invalid iterator"});
                 }
                 --it;
                 if(net::const_buffer(*it).size() > 0)

test/Jamfile

@@ -22,6 +22,7 @@ project /boost/beast/test
     ]
     <include>./extern
     <define>BOOST_BEAST_ALLOW_DEPRECATED
+    <define>BOOST_BEAST_TESTS
     <define>BOOST_ASIO_SEPARATE_COMPILATION
     ;
 

test/beast/CMakeLists.txt

@@ -8,6 +8,8 @@
 #
 
 add_definitions (-DBOOST_BEAST_ALLOW_DEPRECATED)
+add_definitions (-DBOOST_BEAST_TESTS)
+
 
 add_subdirectory (core)
 add_subdirectory (experimental)

test/beast/Jamfile

@@ -14,18 +14,18 @@ alias run-tests :
     [ compile websocket.cpp ]
     [ compile zlib.cpp ]
     core//run-tests
-    experimental//run-tests
     http//run-tests
     websocket//run-tests
     zlib//run-tests
+    experimental//run-tests
     ;
 
 alias fat-tests :
     core//fat-tests
-    experimental//fat-tests
     http//fat-tests
     websocket//fat-tests
     zlib//fat-tests
+    experimental//fat-tests
     ;
 
 explicit fat-tests ;

test/beast/core/buffers_cat.cpp

@@ -119,26 +119,27 @@ public:
         net::const_buffer b3{" world!", 7};
 
         auto const b = beast::buffers_cat(b1, b2, b3);
+        using type = decltype(b);
 
         // Dereferencing a default-constructed iterator
         checkException(
             []
             {
-                *(decltype(b)::const_iterator{});
+                *(type::const_iterator{});
             });
 
         // Incrementing a default-constructed iterator
         checkException(
             []
             {
-                ++(decltype(b)::const_iterator{});
+                ++(type::const_iterator{});
             });
 
         // Decrementing a default-constructed iterator
         checkException(
             []
             {
-                --(decltype(b)::const_iterator{});
+                --(type::const_iterator{});
             });
 
         // Decrementing an iterator to the beginning
@@ -270,11 +271,10 @@ public:
                 net::const_buffer{"lo", 2},
                 e1,
                 net::const_buffer{", ", 2} }};
-            auto b3 = std::array<net::const_buffer, 3>{
+            auto b3 = std::array<net::const_buffer, 3>{{
                 net::const_buffer{"w", 1},
                 net::const_buffer{"orld!", 5},
-                e1
+                e1 }};
-            };
             {
                 auto const b = beast::buffers_cat(
                     e2, b1, e2, b2, e2, b3, e2);