Build: Add a check for __attribute__((__always_inline__)).

All even remotely relevant GCC and Clang versions support this
attribute. The test is useful to detect support in compilers that
don't define __GNUC__ or __clang__, for example, Solaris Studio.

CMakeLists.txt

@@ -829,6 +829,10 @@ calculation if supported by the system" ON)
     endif()
 endif()
 
+# Check for __attribute__((__always_inline__)) support.
+tuklib_check_func_attribute_always_inline(HAVE_FUNC_ATTRIBUTE_ALWAYS_INLINE)
+tuklib_add_definition_if(liblzma HAVE_FUNC_ATTRIBUTE_ALWAYS_INLINE)
+
 # Symbol visibility support:
 #
 # The C_VISIBILITY_PRESET property takes care of adding the compiler

cmake/tuklib_gnu_c_attributes.cmake

@@ -39,6 +39,14 @@ function(tuklib_check_attribute CODE RESULT)
                                        ": unknown attribute")
 endfunction()
 
+function(tuklib_check_func_attribute_always_inline RESULT)
+    tuklib_check_attribute("
+            __attribute__((__always_inline__))
+            static inline int my_inline_func(int x) { return x + 1; }
+            void my_func(void) { return my_inline_func(123); }
+        " "${RESULT}")
+endfunction()
+
 function(tuklib_check_func_attribute_constructor RESULT)
     tuklib_check_attribute("
             __attribute__((__constructor__))

configure.ac

@@ -844,6 +844,11 @@ AC_ARG_ENABLE([ifunc], [AS_HELP_STRING([--disable-ifunc],
 	[], [enable_ifunc=yes])
 AS_IF([test "x$enable_ifunc" = xyes], [AX_GCC_FUNC_ATTRIBUTE([ifunc])])
 
+# GCC >= 3.2 and Clang support the attribute always_inline but a few other
+# compilers support it too. So it's better to check for the support here
+# instead of just checking if __GNUC__ or __clang__ is defined.
+AX_GCC_FUNC_ATTRIBUTE([always_inline])
+
 
 ###############################################################################
 # Checks for library functions.