[llvm-exegesis] Guard `__builtin_thread_pointer` behind a configure check

[zero9178]

Summary

Due to arguably a bug in GCC[0], using __has_builtin is not sufficient to check whether __builtin_thread_pointer can actually be compiled by GCC. This makes it impossible to compile LLVM with llvm-exegesis enabled with e.g. GCC 10 as it does have the builtin, but no implementation for architectures such as x86.

This patch works around this issue by making it a cmake configure check whether the builtin can be compiled and used, rather than relying on the broken preprocessor macro.

[0] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96952, demonstration: https://godbolt.org/z/9z5nWM6Ef

[MaskRay]

This is unfortunate... LG, but I'll defer to llvm-exegesis reviewers for a second opinion.

llvm/cmake/config-ix.cmake

68

LLVM style uses void *

[zero9178]

Fix code style

[aidengrossman]

LGTM. Definitely not ideal, but we want code that works rather than code that is aesthetically pleasing.

llvm/cmake/config-ix.cmake

 if( WIN32 AND NOT CYGWIN )
   # We consider Cygwin as another Unix
   set(PURE_WINDOWS 1)
 endif()
 
 include(CheckIncludeFile)
 include(CheckLibraryExists)
 include(CheckSymbolExists)
 include(CheckCXXSymbolExists)
 include(CheckFunctionExists)
 include(CheckStructHasMember)
 include(CheckCCompilerFlag)
+include(CheckCSourceCompiles)
 include(CMakePushCheckState)
 
 include(CheckCompilerVersion)
 include(CheckProblematicConfigurations)
 include(HandleLLVMStdlib)
 
 if( UNIX AND NOT (APPLE OR BEOS OR HAIKU) )
   # Used by check_symbol_exists:

 check_include_file(sys/types.h HAVE_SYS_TYPES_H)
 check_include_file(sysexits.h HAVE_SYSEXITS_H)
 check_include_file(termios.h HAVE_TERMIOS_H)
 check_include_file(unistd.h HAVE_UNISTD_H)
 check_include_file(valgrind/valgrind.h HAVE_VALGRIND_VALGRIND_H)
 check_include_file(fenv.h HAVE_FENV_H)
 check_symbol_exists(FE_ALL_EXCEPT "fenv.h" HAVE_DECL_FE_ALL_EXCEPT)
 check_symbol_exists(FE_INEXACT "fenv.h" HAVE_DECL_FE_INEXACT)
+check_c_source_compiles("
+        void *foo() {
+          return __builtin_thread_pointer();
+        }
+        int main(void) { return 0; }"
+        HAVE_BUILTIN_THREAD_POINTER)
 
 check_include_file(mach/mach.h HAVE_MACH_MACH_H)
 check_include_file(CrashReporterClient.h HAVE_CRASHREPORTERCLIENT_H)
 if(APPLE)
-  include(CheckCSourceCompiles)
-  CHECK_C_SOURCE_COMPILES("
+  check_c_source_compiles("
      static const char *__crashreporter_info__ = 0;
      asm(\".desc ___crashreporter_info__, 0x10\");
      int main(void) { return 0; }"
     HAVE_CRASHREPORTER_INFO)
 endif()
 
 if(${CMAKE_SYSTEM_NAME} STREQUAL "Linux")
   check_include_file(linux/magic.h HAVE_LINUX_MAGIC_H)

llvm/include/llvm/Config/config.h.cmake

 /* Define to the default GlobalISel coverage file prefix */
 #cmakedefine LLVM_GISEL_COV_PREFIX "${LLVM_GISEL_COV_PREFIX}"
 
 /* Whether Timers signpost passes in Xcode Instruments */
 #cmakedefine01 LLVM_SUPPORT_XCODE_SIGNPOSTS
 
 #cmakedefine HAVE_PROC_PID_RUSAGE 1
 
+#cmakedefine HAVE_BUILTIN_THREAD_POINTER ${HAVE_BUILTIN_THREAD_POINTER}
+
 #endif

llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp

 #endif
 #include <sys/mman.h>
 #include <sys/ptrace.h>
 #include <sys/socket.h>
 #include <sys/syscall.h>
 #include <sys/wait.h>
 #include <unistd.h>
 
-#if defined(__GLIBC__) && __has_include(<sys/rseq.h>) && __has_builtin(__builtin_thread_pointer)
+#if defined(__GLIBC__) && __has_include(<sys/rseq.h>) && defined(HAVE_BUILTIN_THREAD_POINTER)
 #include <sys/rseq.h>
 #ifdef RSEQ_SIG
 #define GLIBC_INITS_RSEQ
 #endif
 #endif
 #endif
 
 namespace llvm {