How to detect LLVM and its version through #define directives?

Question

The question is quite clear I think. I\'m trying to write a compiler detection header to be able to include in the application information on which compiler was used and whi

Answer 1

Note that if you're using llvm to hack on bytecode, and thus #includeing llvm include files, you can check the macros in llvm/Config/llvm-config.h. And concretely:

/* Major version of the LLVM API */
#define LLVM_VERSION_MAJOR 3

/* Minor version of the LLVM API */
#define LLVM_VERSION_MINOR 8

/* Patch version of the LLVM API */
#define LLVM_VERSION_PATCH 0

/* LLVM version string */
#define LLVM_VERSION_STRING "3.8.0"

Answer 2

Take a look at the Pre-defined Compiler Macros page, select Compilers->Clang. There is information on many other macros for standards, compilers, libraries, OS, architectures and more.

Answer 3

I agree that the best choice is to use has feature macroses, not version macroses. Example with boost:

#include <boost/config.hpp>

#if defined(BOOST_NO_CXX11_NOEXCEPT)
 #if defined(BOOST_MSVC)
  #define MY_NOEXCEPT throw()
 #else
  #define MY_NOEXCEPT
 #endif
#else
 #define MY_NOEXCEPT noexcept
#endif

void my_noexcept_function() MY_NOEXCEPT; // it's example, use BOOST_NOEXCEPT (:

But anyway, if you need compiler version, you can use boost.predef:

#include <iostream>
#include <boost/predef.h>

int main() {
#if (BOOST_COMP_CLANG)
  std::cout << BOOST_COMP_CLANG_NAME << "-" << BOOST_COMP_CLANG << std::endl;
#else
  std::cout << "Unknown compiler" << std::endl;
#endif
  return 0;
}

Output examples:

Clang-30400000
Clang-50000000

Answer 4

For clang, you shouldn't test its version number, you should check for features you want with feature checking macros.

Answer 5

Everyone who has answered that the right thing do it is to use feature detection macros like __has_feature, __has_builtin, etc., is right. If that's possible for your use case, that's what you should do.

That said, there are times when clang doesn't expose anything specific to what you're trying to check. For example, there is no way to tell if a particular SSE/AVX or NEON function is available (and yes, new ones are added from time to time; the instructions the CPU supports are fixed, but sometimes new functions using existing instructions are added to plug a hole in the API). Or maybe there was a bug and clang was generating incorrect machine code. We actually run into these types of issues a fairly often in the SIMDe project.

Unfortunately you can't rely on __clang_major__/__clang_minor__/__clang_patchlevel__. Vendors like Apple take clang and repackage it as their own compiler with their own version numbers, and when they do they generally also change the __clang_*__ versions to match their compiler version, not upstream clang's. For example, Apple clang 4.0 is really a repackaged clang 3.1, but they set __clang_major__ to 4 and __clang_minor__ to 0.

The best solution I've found is to use the feature detection code to detect completely unrelated features which just so happen to be added in the same version as what you really want to detect. I've been doing this for a while, but earlier today I finally put together a header to keep all that logic in one place. It's part of SIMDe, but has no dependencies whatsoever and is public domain (CC0). I'll probably forget to update this answer with any improvements in the future, so please check the repo for the current version, but here is what it looks like right now:

#if !defined(SIMDE_DETECT_CLANG_H)
#define SIMDE_DETECT_CLANG_H 1

#if defined(__clang__) && !defined(SIMDE_DETECT_CLANG_VERSION)
#  if __has_warning("-Wimplicit-const-int-float-conversion")
#    define SIMDE_DETECT_CLANG_VERSION 110000
#  elif __has_warning("-Wmisleading-indentation")
#    define SIMDE_DETECT_CLANG_VERSION 100000
#  elif defined(__FILE_NAME__)
#    define SIMDE_DETECT_CLANG_VERSION 90000
#  elif __has_warning("-Wextra-semi-stmt") || __has_builtin(__builtin_rotateleft32)
#    define SIMDE_DETECT_CLANG_VERSION 80000
#  elif __has_warning("-Wc++98-compat-extra-semi")
#    define SIMDE_DETECT_CLANG_VERSION 70000
#  elif __has_warning("-Wpragma-pack")
#    define SIMDE_DETECT_CLANG_VERSION 60000
#  elif __has_warning("-Wasm-ignored-qualifier")
#    define SIMDE_DETECT_CLANG_VERSION 50000
#  elif __has_attribute(diagnose_if)
#    define SIMDE_DETECT_CLANG_VERSION 40000
#  elif __has_warning("-Wcomma")
#    define SIMDE_DETECT_CLANG_VERSION 30900
#  elif __has_warning("-Wmicrosoft")
#    define SIMDE_DETECT_CLANG_VERSION 30800
#  else
#    define SIMDE_DETECT_CLANG_VERSION 1
#  endif
#endif /* defined(__clang__) && !defined(SIMDE_DETECT_CLANG_VERSION) */

#if defined(SIMDE_DETECT_CLANG_VERSION)
#  define SIMDE_DETECT_CLANG_VERSION_CHECK(major, minor, revision) (SIMDE_DETECT_CLANG_VERSION >= ((major * 10000) + (minor * 1000) + (revision)))
#  define SIMDE_DETECT_CLANG_VERSION_NOT(major, minor, revision) SIMDE_DETECT_CLANG_VERSION_CHECK(major, minor, revision)
#else
#  define SIMDE_DETECT_CLANG_VERSION_CHECK(major, minor, revision) (0)
#  define SIMDE_DETECT_CLANG_VERSION_NOT(major, minor, revision) (1)
#endif

#endif /* !defined(SIMDE_DETECT_CLANG_H) */

Answer 6

The __llvm__ and __clang__ macros are the official way to check for an LLVM compiler (llvm-gcc or clang) or clang, respectively.

__has_feature and __has_builtin are the recommended way of checking for optional compiler features when using clang, they are documented here.

Note that you can find a list of the builtin compiler macros for gcc, llvm-gcc, and clang using:

echo | clang -dM -E -

This preprocesses an empty string and spits out all macros defined by the compiler.