clang-cl: implement custom search for cl.exe in /fallback mode

This solves the problem of fallback onto ourselves if clang-cl
has been renamed to cl.exe and put on the PATH, as happens with
the VS integration.

Differential Revision: http://llvm-reviews.chandlerc.com/D1731

llvm-svn: 191099

1 files changed, 39 insertions, 4 deletions

diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index c2ba2e93afd..4302f1a9cd0 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -22,6 +22,7 @@
 #include "clang/Driver/ToolChain.h"
 #include "clang/Driver/Util.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Option/Arg.h"
@@ -31,6 +32,7 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/Host.h"
+#include "llvm/Support/Path.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/raw_ostream.h"
@@ -6641,6 +6643,40 @@ void visualstudio::Compile::ConstructJob(Compilation &C, const JobAction &JA,
   C.addCommand(GetCommand(C, JA, Output, Inputs, Args, LinkingOutput));
 }
 
+// Try to find FallbackName on PATH that is not identical to ClangProgramPath.
+// If one cannot be found, return FallbackName.
+// We do this special search to prevent clang-cl from falling back onto itself
+// if it's available as cl.exe on the path.
+static std::string FindFallback(const char *FallbackName,
+                                const char *ClangProgramPath) {
+  llvm::Optional<std::string> OptPath = llvm::sys::Process::GetEnv("PATH");
+  if (!OptPath.hasValue())
+    return FallbackName;
+
+#ifdef LLVM_ON_WIN32
+  const StringRef PathSeparators = ";";
+#else
+  const StringRef PathSeparators = ":";
+#endif
+
+  SmallVector<StringRef, 8> PathSegments;
+  llvm::SplitString(OptPath.getValue(), PathSegments, PathSeparators);
+
+  for (size_t i = 0, e = PathSegments.size(); i != e; ++i) {
+    const StringRef &PathSegment = PathSegments[i];
+    if (PathSegment.empty())
+      continue;
+
+    SmallString<128> FilePath(PathSegment);
+    llvm::sys::path::append(FilePath, FallbackName);
+    if (llvm::sys::fs::can_execute(Twine(FilePath)) &&
+        !llvm::sys::fs::equivalent(Twine(FilePath), ClangProgramPath))
+      return FilePath.str();
+  }
+
+  return FallbackName;
+}
+
 Command *visualstudio::Compile::GetCommand(Compilation &C, const JobAction &JA,
                                            const InputInfo &Output,
                                            const InputInfoList &Inputs,
@@ -6693,9 +6729,8 @@ Command *visualstudio::Compile::GetCommand(Compilation &C, const JobAction &JA,
                                       Output.getFilename());
   CmdArgs.push_back(Fo);
 
-  // FIXME: If we've put clang-cl as cl.exe on the path, we have a problem.
-  const char *Exec =
-    Args.MakeArgString(getToolChain().GetProgramPath("cl.exe"));
+  const Driver &D = getToolChain().getDriver();
+  std::string Exec = FindFallback("cl.exe", D.getClangProgramPath());
 
-  return new Command(JA, *this, Exec, CmdArgs);
+  return new Command(JA, *this, Args.MakeArgString(Exec), CmdArgs);
 }