GraphWriter: detect graph viewer programs at runtime

Replace the crufty build-time configure checks for program paths with
equivalent runtime logic.

This lets users install graphing tools as needed without having to reconfigure
and rebuild LLVM, while eliminating a long chain of inappropriate compile
dependencies that included GUI programs and the windowing system.

Additional features:

 * Support the OS X 'open' command to view graphs generated by any of the
   Graphviz utilities. This is an alternative to the Graphviz OS X UI which is
   no longer available on Mountain Lion.

 * Produce informative log output upon failure to indicate which programs can
   be installed to view graphs.

Ping me if this doesn't work for your particular environment.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210001 91177308-0d34-0410-b5e6-96231b3b80d8

9 files changed, 137 insertions, 374 deletions

diff --git a/autoconf/configure.ac b/autoconf/configure.ac
index 08f756c921..a1c2ac52e2 100644
--- a/autoconf/configure.ac
+++ b/autoconf/configure.ac
@@ -1282,16 +1282,6 @@ AC_PATH_PROG(TAR,  [tar],  [gtar])
 AC_PATH_PROG(BINPWD,[pwd],  [pwd])
 
 dnl Looking for misc. graph plotting software
-AC_PATH_PROG(GRAPHVIZ, [Graphviz], [echo Graphviz])
-if test "$GRAPHVIZ" != "echo Graphviz" ; then
-  AC_DEFINE([HAVE_GRAPHVIZ],[1],[Define if the Graphviz program is available])
-  dnl If we're targeting for mingw we should emit windows paths, not msys
-  if test "$llvm_cv_os_type" = "MingW" ; then
-    GRAPHVIZ=`echo $GRAPHVIZ | sed 's/^\/\([[A-Za-z]]\)\//\1:\//' `
-  fi
-  AC_DEFINE_UNQUOTED([LLVM_PATH_GRAPHVIZ],"$GRAPHVIZ${EXEEXT}",
-   [Define to path to Graphviz program if found or 'echo Graphviz' otherwise])
-fi
 AC_PATH_PROG(DOT, [dot], [echo dot])
 if test "$DOT" != "echo dot" ; then
   AC_DEFINE([HAVE_DOT],[1],[Define if the dot program is available])
@@ -1302,76 +1292,6 @@ if test "$DOT" != "echo dot" ; then
   AC_DEFINE_UNQUOTED([LLVM_PATH_DOT],"$DOT${EXEEXT}",
    [Define to path to dot program if found or 'echo dot' otherwise])
 fi
-AC_PATH_PROG(FDP, [fdp], [echo fdp])
-if test "$FDP" != "echo fdp" ; then
-  AC_DEFINE([HAVE_FDP],[1],[Define if the neat program is available])
-  dnl If we're targeting for mingw we should emit windows paths, not msys
-  if test "$llvm_cv_os_type" = "MingW" ; then
-    FDP=`echo $FDP | sed 's/^\/\([[A-Za-z]]\)\//\1:\//' `
-  fi
-  AC_DEFINE_UNQUOTED([LLVM_PATH_FDP],"$FDP${EXEEXT}",
-   [Define to path to fdp program if found or 'echo fdp' otherwise])
-fi
-AC_PATH_PROG(NEATO, [neato], [echo neato])
-if test "$NEATO" != "echo neato" ; then
-  AC_DEFINE([HAVE_NEATO],[1],[Define if the neat program is available])
-  dnl If we're targeting for mingw we should emit windows paths, not msys
-  if test "$llvm_cv_os_type" = "MingW" ; then
-    NEATO=`echo $NEATO | sed 's/^\/\([[A-Za-z]]\)\//\1:\//' `
-  fi
-  AC_DEFINE_UNQUOTED([LLVM_PATH_NEATO],"$NEATO${EXEEXT}",
-   [Define to path to neato program if found or 'echo neato' otherwise])
-fi
-AC_PATH_PROG(TWOPI, [twopi], [echo twopi])
-if test "$TWOPI" != "echo twopi" ; then
-  AC_DEFINE([HAVE_TWOPI],[1],[Define if the neat program is available])
-  dnl If we're targeting for mingw we should emit windows paths, not msys
-  if test "$llvm_cv_os_type" = "MingW" ; then
-    TWOPI=`echo $TWOPI | sed 's/^\/\([[A-Za-z]]\)\//\1:\//' `
-  fi
-  AC_DEFINE_UNQUOTED([LLVM_PATH_TWOPI],"$TWOPI${EXEEXT}",
-   [Define to path to twopi program if found or 'echo twopi' otherwise])
-fi
-AC_PATH_PROG(CIRCO, [circo], [echo circo])
-if test "$CIRCO" != "echo circo" ; then
-  AC_DEFINE([HAVE_CIRCO],[1],[Define if the neat program is available])
-  dnl If we're targeting for mingw we should emit windows paths, not msys
-  if test "$llvm_cv_os_type" = "MingW" ; then
-    CIRCO=`echo $CIRCO | sed 's/^\/\([[A-Za-z]]\)\//\1:\//' `
-  fi
-  AC_DEFINE_UNQUOTED([LLVM_PATH_CIRCO],"$CIRCO${EXEEXT}",
-   [Define to path to circo program if found or 'echo circo' otherwise])
-fi
-AC_PATH_PROGS(GV, [gv gsview32], [echo gv])
-if test "$GV" != "echo gv" ; then
-  AC_DEFINE([HAVE_GV],[1],[Define if the gv program is available])
-  dnl If we're targeting for mingw we should emit windows paths, not msys
-  if test "$llvm_cv_os_type" = "MingW" ; then
-    GV=`echo $GV | sed 's/^\/\([[A-Za-z]]\)\//\1:\//' `
-  fi
-  AC_DEFINE_UNQUOTED([LLVM_PATH_GV],"$GV${EXEEXT}",
-   [Define to path to gv program if found or 'echo gv' otherwise])
-fi
-AC_PATH_PROG(DOTTY, [dotty], [echo dotty])
-if test "$DOTTY" != "echo dotty" ; then
-  AC_DEFINE([HAVE_DOTTY],[1],[Define if the dotty program is available])
-  dnl If we're targeting for mingw we should emit windows paths, not msys
-  if test "$llvm_cv_os_type" = "MingW" ; then
-    DOTTY=`echo $DOTTY | sed 's/^\/\([[A-Za-z]]\)\//\1:\//' `
-  fi
-  AC_DEFINE_UNQUOTED([LLVM_PATH_DOTTY],"$DOTTY${EXEEXT}",
-   [Define to path to dotty program if found or 'echo dotty' otherwise])
-fi
-AC_PATH_PROGS(XDOT, [xdot xdot.py], [echo xdot])
-if test "$XDOT" != "echo xdot" ; then
-  AC_DEFINE([HAVE_XDOT],[1],[Define if the xdot program is available])
-  dnl If we're targeting for mingw we should emit windows paths, not msys
-  if test "$llvm_cv_os_type" = "MingW" ; then
-    XDOT=`echo $XDOT | sed 's/^\/\([[A-Za-z]]\)\//\1:\//' `
-  fi
-  AC_DEFINE_UNQUOTED([LLVM_PATH_XDOT],"$XDOT${EXEEXT}",
-   [Define to path to xdot program if found or 'echo xdot' otherwise])
-fi
 
 dnl Find the install program
 AC_PROG_INSTALL
diff --git a/cmake/config-ix.cmake b/cmake/config-ix.cmake
index 1325e790c8..2af3fe3c5e 100755
--- a/cmake/config-ix.cmake
+++ b/cmake/config-ix.cmake
@@ -252,15 +252,9 @@ function(llvm_find_program name)
   endif(LLVM_PATH_${NAME})
 endfunction()
 
-llvm_find_program(gv)
-llvm_find_program(circo)
-llvm_find_program(twopi)
-llvm_find_program(neato)
-llvm_find_program(fdp)
-llvm_find_program(dot)
-llvm_find_program(dotty)
-llvm_find_program(xdot xdot.py)
-llvm_find_program(Graphviz)
+if (LLVM_ENABLE_DOXYGEN)
+  llvm_find_program(dot)
+endif ()
 
 if( LLVM_ENABLE_FFI )
   find_path(FFI_INCLUDE_PATH ffi.h PATHS ${FFI_INCLUDE_DIR})
diff --git a/docs/ProgrammersManual.rst b/docs/ProgrammersManual.rst
index 7e46ac4e8e..8d9668e4ee 100644
--- a/docs/ProgrammersManual.rst
+++ b/docs/ProgrammersManual.rst
@@ -545,14 +545,15 @@ methods.  Within GDB, for example, you can usually use something like ``call
 DAG.viewGraph()`` to pop up a window.  Alternatively, you can sprinkle calls to
 these functions in your code in places you want to debug.
 
-Getting this to work requires a small amount of configuration.  On Unix systems
+Getting this to work requires a small amount of setup.  On Unix systems
 with X11, install the `graphviz <http://www.graphviz.org>`_ toolkit, and make
 sure 'dot' and 'gv' are in your path.  If you are running on Mac OS X, download
 and install the Mac OS X `Graphviz program
 <http://www.pixelglow.com/graphviz/>`_ and add
 ``/Applications/Graphviz.app/Contents/MacOS/`` (or wherever you install it) to
-your path.  Once in your system and path are set up, rerun the LLVM configure
-script and rebuild LLVM to enable this functionality.
+your path. The programs need not be present when configuring, building or
+running LLVM and can simply be installed when needed during an active debug
+session.
 
 ``SelectionDAG`` has been extended to make it easier to locate *interesting*
 nodes in large complex graphs.  From gdb, if you ``call DAG.setGraphColor(node,
diff --git a/include/llvm/Config/config.h.cmake b/include/llvm/Config/config.h.cmake
index ea1e75a76a..969e384bcb 100644
--- a/include/llvm/Config/config.h.cmake
+++ b/include/llvm/Config/config.h.cmake
@@ -45,9 +45,6 @@
 /* Define to 1 if you have the `ceilf' function. */
 #cmakedefine HAVE_CEILF ${HAVE_CEILF}
 
-/* Define if the neat program is available */
-#cmakedefine HAVE_CIRCO ${HAVE_CIRCO}
-
 /* Define to 1 if you have the `closedir' function. */
 #cmakedefine HAVE_CLOSEDIR ${HAVE_CLOSEDIR}
 
@@ -80,12 +77,6 @@
 /* Define if dlopen() is available on this platform. */
 #cmakedefine HAVE_DLOPEN ${HAVE_DLOPEN}
 
-/* Define if the dot program is available */
-#cmakedefine HAVE_DOT ${HAVE_DOT}
-
-/* Define if the dotty program is available */
-#cmakedefine HAVE_DOTTY ${HAVE_DOTTY}
-
 /* Define if you have the _dyld_func_lookup function. */
 #undef HAVE_DYLD
 
@@ -98,9 +89,6 @@
 /* Define to 1 if you have the <fcntl.h> header file. */
 #cmakedefine HAVE_FCNTL_H ${HAVE_FCNTL_H}
 
-/* Define if the neat program is available */
-#cmakedefine HAVE_FDP ${HAVE_FDP}
-
 /* Define to 1 if you have the <fenv.h> header file. */
 #cmakedefine HAVE_FENV_H ${HAVE_FENV_H}
 
@@ -161,12 +149,6 @@
 /* Define to 1 if you have the `gettimeofday' function. */
 #cmakedefine HAVE_GETTIMEOFDAY ${HAVE_GETTIMEOFDAY}
 
-/* Define if the Graphviz program is available */
-#cmakedefine HAVE_GRAPHVIZ ${HAVE_GRAPHVIZ}
-
-/* Define if the gv program is available */
-#cmakedefine HAVE_GV ${HAVE_GV}
-
 /* Define to 1 if the system has the type `int64_t'. */
 #cmakedefine HAVE_INT64_T ${HAVE_INT64_T}
 
@@ -271,9 +253,6 @@
 /* Define to 1 if you have the `nearbyintf' function. */
 #cmakedefine HAVE_NEARBYINTF ${HAVE_NEARBYINTF}
 
-/* Define if the neat program is available */
-#cmakedefine HAVE_NEATO ${HAVE_NEATO}
-
 /* Define to 1 if you have the `opendir' function. */
 #cmakedefine HAVE_OPENDIR ${HAVE_OPENDIR}
 
@@ -417,9 +396,6 @@
 /* Define to 1 if you have the <termios.h> header file. */
 #cmakedefine HAVE_TERMIOS_H ${HAVE_TERMIOS_H}
 
-/* Define if the neat program is available */
-#cmakedefine HAVE_TWOPI ${HAVE_TWOPI}
-
 /* Define to 1 if the system has the type `uint64_t'. */
 #cmakedefine HAVE_UINT64_T ${HAVE_UINT64_T}
 
@@ -438,9 +414,6 @@
 /* Define to 1 if you have the `writev' function. */
 #cmakedefine HAVE_WRITEV ${HAVE_WRITEV}
 
-/* Define if the xdot.py program is available */
-#cmakedefine HAVE_XDOT ${HAVE_XDOT}
-
 /* Define to 1 if you have the <zlib.h> header file. */
 #cmakedefine HAVE_ZLIB_H ${HAVE_ZLIB_H}
 
@@ -567,33 +540,6 @@
 /* Define if this is Win32ish platform */
 #cmakedefine LLVM_ON_WIN32 ${LLVM_ON_WIN32}
 
-/* Define to path to circo program if found or 'echo circo' otherwise */
-#cmakedefine LLVM_PATH_CIRCO "${LLVM_PATH_CIRCO}"
-
-/* Define to path to dot program if found or 'echo dot' otherwise */
-#cmakedefine LLVM_PATH_DOT "${LLVM_PATH_DOT}"
-
-/* Define to path to dotty program if found or 'echo dotty' otherwise */
-#cmakedefine LLVM_PATH_DOTTY "${LLVM_PATH_DOTTY}"
-
-/* Define to path to fdp program if found or 'echo fdp' otherwise */
-#cmakedefine LLVM_PATH_FDP "${LLVM_PATH_FDP}"
-
-/* Define to path to Graphviz program if found or 'echo Graphviz' otherwise */
-#cmakedefine LLVM_PATH_GRAPHVIZ "${LLVM_PATH_GRAPHVIZ}"
-
-/* Define to path to gv program if found or 'echo gv' otherwise */
-#cmakedefine LLVM_PATH_GV "${LLVM_PATH_GV}"
-
-/* Define to path to neato program if found or 'echo neato' otherwise */
-#cmakedefine LLVM_PATH_NEATO "${LLVM_PATH_NEATO}"
-
-/* Define to path to twopi program if found or 'echo twopi' otherwise */
-#cmakedefine LLVM_PATH_TWOPI "${LLVM_PATH_TWOPI}"
-
-/* Define to path to xdot.py program if found or 'echo xdot' otherwise */
-#cmakedefine LLVM_PATH_XDOT "${LLVM_PATH_XDOT}"
-
 /* Installation prefix directory */
 #cmakedefine LLVM_PREFIX "${LLVM_PREFIX}"
 
diff --git a/include/llvm/Config/config.h.in b/include/llvm/Config/config.h.in
index 6b8dbb7c77..1c2e53d81f 100644
--- a/include/llvm/Config/config.h.in
+++ b/include/llvm/Config/config.h.in
@@ -39,9 +39,6 @@
 /* Define to 1 if you have the `ceilf' function. */
 #undef HAVE_CEILF
 
-/* Define if the neat program is available */
-#undef HAVE_CIRCO
-
 /* Define to 1 if you have the <CrashReporterClient.h> header file. */
 #undef HAVE_CRASHREPORTERCLIENT_H
 
@@ -77,12 +74,6 @@
 /* Define if dlopen() is available on this platform. */
 #undef HAVE_DLOPEN
 
-/* Define if the dot program is available */
-#undef HAVE_DOT
-
-/* Define if the dotty program is available */
-#undef HAVE_DOTTY
-
 /* Define to 1 if you have the <errno.h> header file. */
 #undef HAVE_ERRNO_H
 
@@ -98,9 +89,6 @@
 /* Define to 1 if you have the <fcntl.h> header file. */
 #undef HAVE_FCNTL_H
 
-/* Define if the neat program is available */
-#undef HAVE_FDP
-
 /* Define to 1 if you have the <fenv.h> header file. */
 #undef HAVE_FENV_H
 
@@ -143,12 +131,6 @@
 /* Define to 1 if you have the `gettimeofday' function. */
 #undef HAVE_GETTIMEOFDAY
 
-/* Define if the Graphviz program is available */
-#undef HAVE_GRAPHVIZ
-
-/* Define if the gv program is available */
-#undef HAVE_GV
-
 /* Define to 1 if the system has the type `int64_t'. */
 #undef HAVE_INT64_T
 
@@ -259,9 +241,6 @@
 /* Define to 1 if you have the `nearbyintf' function. */
 #undef HAVE_NEARBYINTF
 
-/* Define if the neat program is available */
-#undef HAVE_NEATO
-
 /* Define to 1 if you have the `posix_spawn' function. */
 #undef HAVE_POSIX_SPAWN
 
@@ -402,9 +381,6 @@
 /* Define to 1 if you have the <termios.h> header file. */
 #undef HAVE_TERMIOS_H
 
-/* Define if the neat program is available */
-#undef HAVE_TWOPI
-
 /* Define to 1 if the system has the type `uint64_t'. */
 #undef HAVE_UINT64_T
 
@@ -423,9 +399,6 @@
 /* Define to 1 if you have the `writev' function. */
 #undef HAVE_WRITEV
 
-/* Define if the xdot program is available */
-#undef HAVE_XDOT
-
 /* Define to 1 if you have the <zlib.h> header file. */
 #undef HAVE_ZLIB_H
 
@@ -549,33 +522,6 @@
 /* Define if this is Win32ish platform */
 #undef LLVM_ON_WIN32
 
-/* Define to path to circo program if found or 'echo circo' otherwise */
-#undef LLVM_PATH_CIRCO
-
-/* Define to path to dot program if found or 'echo dot' otherwise */
-#undef LLVM_PATH_DOT
-
-/* Define to path to dotty program if found or 'echo dotty' otherwise */
-#undef LLVM_PATH_DOTTY
-
-/* Define to path to fdp program if found or 'echo fdp' otherwise */
-#undef LLVM_PATH_FDP
-
-/* Define to path to Graphviz program if found or 'echo Graphviz' otherwise */
-#undef LLVM_PATH_GRAPHVIZ
-
-/* Define to path to gv program if found or 'echo gv' otherwise */
-#undef LLVM_PATH_GV
-
-/* Define to path to neato program if found or 'echo neato' otherwise */
-#undef LLVM_PATH_NEATO
-
-/* Define to path to twopi program if found or 'echo twopi' otherwise */
-#undef LLVM_PATH_TWOPI
-
-/* Define to path to xdot program if found or 'echo xdot' otherwise */
-#undef LLVM_PATH_XDOT
-
 /* Installation prefix directory */
 #undef LLVM_PREFIX
 
diff --git a/include/llvm/Config/llvm-config.h.cmake b/include/llvm/Config/llvm-config.h.cmake
index 65116cb469..7217561c27 100644
--- a/include/llvm/Config/llvm-config.h.cmake
+++ b/include/llvm/Config/llvm-config.h.cmake
@@ -79,33 +79,6 @@
 /* Define if this is Win32ish platform */
 #cmakedefine LLVM_ON_WIN32 ${LLVM_ON_WIN32}
 
-/* Define to path to circo program if found or 'echo circo' otherwise */
-#cmakedefine LLVM_PATH_CIRCO "${LLVM_PATH_CIRCO}"
-
-/* Define to path to dot program if found or 'echo dot' otherwise */
-#cmakedefine LLVM_PATH_DOT "${LLVM_PATH_DOT}"
-
-/* Define to path to dotty program if found or 'echo dotty' otherwise */
-#cmakedefine LLVM_PATH_DOTTY "${LLVM_PATH_DOTTY}"
-
-/* Define to path to fdp program if found or 'echo fdp' otherwise */
-#cmakedefine LLVM_PATH_FDP "${LLVM_PATH_FDP}"
-
-/* Define to path to Graphviz program if found or 'echo Graphviz' otherwise */
-#cmakedefine LLVM_PATH_GRAPHVIZ "${LLVM_PATH_GRAPHVIZ}"
-
-/* Define to path to gv program if found or 'echo gv' otherwise */
-#cmakedefine LLVM_PATH_GV "${LLVM_PATH_GV}"
-
-/* Define to path to neato program if found or 'echo neato' otherwise */
-#cmakedefine LLVM_PATH_NEATO "${LLVM_PATH_NEATO}"
-
-/* Define to path to twopi program if found or 'echo twopi' otherwise */
-#cmakedefine LLVM_PATH_TWOPI "${LLVM_PATH_TWOPI}"
-
-/* Define to path to xdot.py program if found or 'echo xdot.py' otherwise */
-#cmakedefine LLVM_PATH_XDOT_PY "${LLVM_PATH_XDOT_PY}"
-
 /* Installation prefix directory */
 #cmakedefine LLVM_PREFIX "${LLVM_PREFIX}"
 
diff --git a/include/llvm/Config/llvm-config.h.in b/include/llvm/Config/llvm-config.h.in
index a4fae5537a..655d7cfea3 100644
--- a/include/llvm/Config/llvm-config.h.in
+++ b/include/llvm/Config/llvm-config.h.in
@@ -79,33 +79,6 @@
 /* Define if this is Win32ish platform */
 #undef LLVM_ON_WIN32
 
-/* Define to path to circo program if found or 'echo circo' otherwise */
-#undef LLVM_PATH_CIRCO
-
-/* Define to path to dot program if found or 'echo dot' otherwise */
-#undef LLVM_PATH_DOT
-
-/* Define to path to dotty program if found or 'echo dotty' otherwise */
-#undef LLVM_PATH_DOTTY
-
-/* Define to path to fdp program if found or 'echo fdp' otherwise */
-#undef LLVM_PATH_FDP
-
-/* Define to path to Graphviz program if found or 'echo Graphviz' otherwise */
-#undef LLVM_PATH_GRAPHVIZ
-
-/* Define to path to gv program if found or 'echo gv' otherwise */
-#undef LLVM_PATH_GV
-
-/* Define to path to neato program if found or 'echo neato' otherwise */
-#undef LLVM_PATH_NEATO
-
-/* Define to path to twopi program if found or 'echo twopi' otherwise */
-#undef LLVM_PATH_TWOPI
-
-/* Define to path to xdot.py program if found or 'echo xdot.py' otherwise */
-#undef LLVM_PATH_XDOT_PY
-
 /* Installation prefix directory */
 #undef LLVM_PREFIX
 
diff --git a/include/llvm/Support/GraphWriter.h b/include/llvm/Support/GraphWriter.h
index 539673a8be..2f02aa7a1c 100644
--- a/include/llvm/Support/GraphWriter.h
+++ b/include/llvm/Support/GraphWriter.h
@@ -50,7 +50,7 @@ namespace GraphProgram {
    };
 }
 
-void DisplayGraph(StringRef Filename, bool wait = true,
+bool DisplayGraph(StringRef Filename, bool wait = true,
                   GraphProgram::Name program = GraphProgram::DOT);
 
 template<typename GraphType>
diff --git a/lib/Support/GraphWriter.cpp b/lib/Support/GraphWriter.cpp
index f5b2943e86..b707a2daa9 100644
--- a/lib/Support/GraphWriter.cpp
+++ b/lib/Support/GraphWriter.cpp
@@ -78,148 +78,158 @@ std::string llvm::createGraphFilename(const Twine &Name, int &FD) {
   return Filename.str();
 }
 
-// Execute the graph viewer. Return true if successful.
-static bool LLVM_ATTRIBUTE_UNUSED
-ExecGraphViewer(StringRef ExecPath, std::vector<const char*> &args,
-                StringRef Filename, bool wait, std::string &ErrMsg) {
+// Execute the graph viewer. Return true if there were errors.
+static bool ExecGraphViewer(StringRef ExecPath, std::vector<const char *> &args,
+                            StringRef Filename, bool wait,
+                            std::string &ErrMsg) {
+  assert(args.back() == nullptr);
   if (wait) {
-    if (sys::ExecuteAndWait(ExecPath, &args[0],nullptr,nullptr,0,0,&ErrMsg)) {
+    if (sys::ExecuteAndWait(ExecPath, args.data(), nullptr, nullptr, 0, 0,
+                            &ErrMsg)) {
       errs() << "Error: " << ErrMsg << "\n";
-      return false;
+      return true;
     }
     sys::fs::remove(Filename);
     errs() << " done. \n";
-  }
-  else {
-    sys::ExecuteNoWait(ExecPath, &args[0],nullptr,nullptr,0,&ErrMsg);
+  } else {
+    sys::ExecuteNoWait(ExecPath, args.data(), nullptr, nullptr, 0, &ErrMsg);
     errs() << "Remember to erase graph file: " << Filename.str() << "\n";
   }
-  return true;
+  return false;
+}
+
+struct GraphSession {
+  std::string LogBuffer;
+  bool TryFindProgram(StringRef Names, std::string &ProgramPath) {
+    raw_string_ostream Log(LogBuffer);
+    SmallVector<StringRef, 8> parts;
+    Names.split(parts, "|");
+    for (auto Name : parts) {
+      ProgramPath = sys::FindProgramByName(Name);
+      if (!ProgramPath.empty())
+        return true;
+      Log << "  Tried '" << Name << "'\n";
+    }
+    return false;
+  }
+};
+
+static const char *getProgramName(GraphProgram::Name program) {
+  switch (program) {
+  case GraphProgram::DOT:
+    return "dot";
+  case GraphProgram::FDP:
+    return "fdp";
+  case GraphProgram::NEATO:
+    return "neato";
+  case GraphProgram::TWOPI:
+    return "twopi";
+  case GraphProgram::CIRCO:
+    return "circo";
+  }
 }
 
-void llvm::DisplayGraph(StringRef FilenameRef, bool wait,
+bool llvm::DisplayGraph(StringRef FilenameRef, bool wait,
                         GraphProgram::Name program) {
   std::string Filename = FilenameRef;
   wait &= !ViewBackground;
   std::string ErrMsg;
-#if HAVE_GRAPHVIZ
-  std::string Graphviz(LLVM_PATH_GRAPHVIZ);
-
-  std::vector<const char*> args;
-  args.push_back(Graphviz.c_str());
-  args.push_back(Filename.c_str());
-  args.push_back(nullptr);
-
-  errs() << "Running 'Graphviz' program... ";
-  if (!ExecGraphViewer(Graphviz, args, Filename, wait, ErrMsg))
-    return;
-
-#elif HAVE_XDOT
-  std::vector<const char*> args;
-  args.push_back(LLVM_PATH_XDOT);
-  args.push_back(Filename.c_str());
-
-  switch (program) {
-  case GraphProgram::DOT:   args.push_back("-f"); args.push_back("dot"); break;
-  case GraphProgram::FDP:   args.push_back("-f"); args.push_back("fdp"); break;
-  case GraphProgram::NEATO: args.push_back("-f"); args.push_back("neato");break;
-  case GraphProgram::TWOPI: args.push_back("-f"); args.push_back("twopi");break;
-  case GraphProgram::CIRCO: args.push_back("-f"); args.push_back("circo");break;
+  std::string ViewerPath;
+  GraphSession S;
+
+  // Graphviz
+  if (S.TryFindProgram("Graphviz", ViewerPath)) {
+    std::vector<const char *> args;
+    args.push_back(ViewerPath.c_str());
+    args.push_back(Filename.c_str());
+    args.push_back(nullptr);
+
+    errs() << "Running 'Graphviz' program... ";
+    return ExecGraphViewer(ViewerPath, args, Filename, wait, ErrMsg);
   }
 
-  args.push_back(0);
+  // xdot
+  if (S.TryFindProgram("xdot|xdot.py", ViewerPath)) {
+    std::vector<const char *> args;
+    args.push_back(ViewerPath.c_str());
+    args.push_back(Filename.c_str());
 
-  errs() << "Running 'xdot.py' program... ";
-  if (!ExecGraphViewer(LLVM_PATH_XDOT, args, Filename, wait, ErrMsg))
-    return;
+    args.push_back("-f");
+    args.push_back(getProgramName(program));
 
-#elif (HAVE_GV && (HAVE_DOT || HAVE_FDP || HAVE_NEATO || \
-                   HAVE_TWOPI || HAVE_CIRCO))
-  std::string PSFilename = Filename + ".ps";
-  std::string prog;
+    args.push_back(nullptr);
 
-  // Set default grapher
-#if HAVE_CIRCO
-  prog = LLVM_PATH_CIRCO;
-#endif
-#if HAVE_TWOPI
-  prog = LLVM_PATH_TWOPI;
-#endif
-#if HAVE_NEATO
-  prog = LLVM_PATH_NEATO;
-#endif
-#if HAVE_FDP
-  prog = LLVM_PATH_FDP;
-#endif
-#if HAVE_DOT
-  prog = LLVM_PATH_DOT;
-#endif
+    errs() << "Running 'xdot.py' program... ";
+    return ExecGraphViewer(ViewerPath, args, Filename, wait, ErrMsg);
+  }
 
-  // Find which program the user wants
-#if HAVE_DOT
-  if (program == GraphProgram::DOT)
-    prog = LLVM_PATH_DOT;
-#endif
-#if (HAVE_FDP)
-  if (program == GraphProgram::FDP)
-    prog = LLVM_PATH_FDP;
-#endif
-#if (HAVE_NEATO)
-  if (program == GraphProgram::NEATO)
-    prog = LLVM_PATH_NEATO;
-#endif
-#if (HAVE_TWOPI)
-  if (program == GraphProgram::TWOPI)
-    prog = LLVM_PATH_TWOPI;
-#endif
-#if (HAVE_CIRCO)
-  if (program == GraphProgram::CIRCO)
-    prog = LLVM_PATH_CIRCO;
+  enum PSViewerKind { PSV_None, PSV_OSXOpen, PSV_Ghostview };
+  PSViewerKind PSViewer = PSV_None;
+#ifdef __APPLE__
+  if (S.TryFindProgram("open", ViewerPath))
+    PSViewer = PSV_OSXOpen;
 #endif
+  if (!PSViewer && S.TryFindProgram("gv", ViewerPath))
+    PSViewer = PSV_Ghostview;
+
+  // PostScript graph generator + PostScript viewer
+  std::string GeneratorPath;
+  if (PSViewer &&
+      (S.TryFindProgram(getProgramName(program), GeneratorPath) ||
+       S.TryFindProgram("circo|twopi|neato|fdp|dot", GeneratorPath))) {
+    std::string PSFilename = Filename + ".ps";
+
+    std::vector<const char *> args;
+    args.push_back(GeneratorPath.c_str());
+    args.push_back("-Tps");
+    args.push_back("-Nfontname=Courier");
+    args.push_back("-Gsize=7.5,10");
+    args.push_back(Filename.c_str());
+    args.push_back("-o");
+    args.push_back(PSFilename.c_str());
+    args.push_back(nullptr);
+
+    errs() << "Running '" << GeneratorPath << "' program... ";
+
+    if (ExecGraphViewer(GeneratorPath, args, Filename, wait, ErrMsg))
+      return true;
+
+    args.clear();
+    args.push_back(ViewerPath.c_str());
+    switch (PSViewer) {
+    case PSV_OSXOpen:
+      args.push_back("-W");
+      args.push_back(PSFilename.c_str());
+      break;
+    case PSV_Ghostview:
+      args.push_back("--spartan");
+      args.push_back(PSFilename.c_str());
+      break;
+    case PSV_None:
+      llvm_unreachable("Invalid viewer");
+    }
+    args.push_back(nullptr);
 
-  std::vector<const char*> args;
-  args.push_back(prog.c_str());
-  args.push_back("-Tps");
-  args.push_back("-Nfontname=Courier");
-  args.push_back("-Gsize=7.5,10");
-  args.push_back(Filename.c_str());
-  args.push_back("-o");
-  args.push_back(PSFilename.c_str());
-  args.push_back(0);
-
-  errs() << "Running '" << prog << "' program... ";
-
-  if (!ExecGraphViewer(prog, args, Filename, wait, ErrMsg))
-    return;
-
-  std::string gv(LLVM_PATH_GV);
-  args.clear();
-  args.push_back(gv.c_str());
-  args.push_back(PSFilename.c_str());
-  args.push_back("--spartan");
-  args.push_back(0);
-
-  ErrMsg.clear();
-  if (!ExecGraphViewer(gv, args, PSFilename, wait, ErrMsg))
-    return;
-
-#elif HAVE_DOTTY
-  std::string dotty(LLVM_PATH_DOTTY);
+    ErrMsg.clear();
+    return ExecGraphViewer(ViewerPath, args, PSFilename, wait, ErrMsg);
+  }
 
-  std::vector<const char*> args;
-  args.push_back(dotty.c_str());
-  args.push_back(Filename.c_str());
-  args.push_back(0);
+  // dotty
+  if (S.TryFindProgram("dotty", ViewerPath)) {
+    std::vector<const char *> args;
+    args.push_back(ViewerPath.c_str());
+    args.push_back(Filename.c_str());
+    args.push_back(nullptr);
 
 // Dotty spawns another app and doesn't wait until it returns
-#if defined (__MINGW32__) || defined (_WINDOWS)
-  wait = false;
-#endif
-  errs() << "Running 'dotty' program... ";
-  if (!ExecGraphViewer(dotty, args, Filename, wait, ErrMsg))
-    return;
-#else
-  (void)Filename;
-  (void)ErrMsg;
+#ifdef LLVM_ON_WIN32
+    wait = false;
 #endif
+    errs() << "Running 'dotty' program... ";
+    return ExecGraphViewer(ViewerPath, args, Filename, wait, ErrMsg);
+  }
+
+  errs() << "Error: Couldn't find a usable graph viewer program:\n";
+  errs() << S.LogBuffer << "\n";
+  return true;
 }