lld/COFF: Simplify getOutputPath() using sys::path functions.

[thakis]

Summary

Also mention "basename" and "dirname" in Path.h since I tried
to find these functions by looking for these strings. It might
help others find them faster if the comments contain these strings.

No behavior change.

[ruiu]

LGTM

lld/COFF/Driver.cpp

107–108

It seems that you can simplify this further to sys::path::stem(path) + (config->dll ? ".dll" : ".exe"), but I'm fine with this too.

[thakis]

lld/COFF/Driver.cpp

107–108

That's even nicer, thanks.

lld/COFF/Driver.cpp

static std::pair<StringRef, StringRef> getOldNewOptions(opt::InputArgList &args,
   std::pair<StringRef, StringRef> ret = s.split(';');
   if (ret.second.empty())
     error(arg->getSpelling() + " expects 'old;new' format, but got " + s);
   return ret;
 }
 
 // Drop directory components and replace extension with ".exe" or ".dll".
 static std::string getOutputPath(StringRef path) {
-  auto p = path.find_last_of("\\/");
-  StringRef s = (p == StringRef::npos) ? path : path.substr(p + 1);
-  const char* e = config->dll ? ".dll" : ".exe";
-  return (s.substr(0, s.rfind('.')) + e).str();
+  SmallString<128> outputPath = sys::path::filename(path);
+  sys::path::replace_extension(outputPath, config->dll ? ".dll" : ".exe");
+  return outputPath.str();
 }
 
 // Returns true if S matches /crtend.?\.o$/.
 static bool isCrtend(StringRef s) {
   if (!s.endswith(".o"))
     return false;
   s = s.drop_back(2);
   if (s.endswith("crtend"))

llvm/include/llvm/Support/Path.h

 reverse_iterator rend(StringRef path);
 
 /// @}
 /// @name Lexical Modifiers
 /// @{
 
 /// Remove the last component from \a path unless it is the root dir.
 ///
+/// Similar to the POSIX "dirname" utility.
+///
 /// @code
 ///   directory/filename.cpp => directory/
 ///   directory/             => directory
 ///   filename.cpp           => <empty>
 ///   /                      => /
 /// @endcode
 ///
 /// @param path A path that is modified to not have a file component.

 ///   /foo.txt    => foo.txt
 ///   .          => .
 ///   ..         => ..
 ///   /          => /
 /// @endcode
 ///
 /// @param path Input path.
 /// @result The filename part of \a path. This is defined as the last component
-///         of \a path.
+///         of \a path. Similar to the POSIX "basename" utility.
 StringRef filename(StringRef path, Style style = Style::native);
 
 /// Get stem.
 ///
 /// If filename contains a dot but not solely one or two dots, result is the
 /// substring of filename ending at (but not including) the last dot. Otherwise
 /// it is filename.
 ///