[llvm] Use early exits and get rid of if-return-else-return pattern; NFC

[kbobyrev]

Summary

https://llvm.org/docs/CodingStandards.html#use-early-exits-and-continue-to-simplify-code

llvm/lib/Support/Path.cpp

if (b != e) {
     bool has_net =
         b->size() > 2 && is_separator((*b)[0], style) && (*b)[1] == (*b)[0];
     bool has_drive = (real_style(style) == Style::windows) && b->endswith(":");
 
     if (has_net || has_drive) {
       if ((++pos != e) && is_separator((*pos)[0], style)) {
         // {C:/,//net/}, so get the first two components.
         return path.substr(0, b->size() + pos->size());
-      } else {
-        // just {C:,//net}, return the first component.
-        return *b;
-      }
-    }
+      }
 
     // POSIX style root directory.
     if (is_separator((*b)[0], style)) {
       return *b;
     }
   }
 
   return StringRef();
void append(SmallVectorImpl<char> &path, const_iterator begin,
   for (; begin != end; ++begin)
     path::append(path, style, *begin);
 }
 
 StringRef parent_path(StringRef path, Style style) {
   size_t end_pos = parent_path_end(path, style);
   if (end_pos == StringRef::npos)
     return StringRef();
-  else
-    return path.substr(0, end_pos);
 }
 
 void remove_filename(SmallVectorImpl<char> &path, Style style) {
   size_t end_pos = parent_path_end(StringRef(path.begin(), path.size()), style);
   if (end_pos != StringRef::npos)
     path.set_size(end_pos);
 }
 

 
 StringRef filename(StringRef path, Style style) { return *rbegin(path, style); }
 
 StringRef stem(StringRef path, Style style) {
   StringRef fname = filename(path, style);
   size_t pos = fname.find_last_of('.');
   if (pos == StringRef::npos)
     return fname;
-  else
-    if ((fname.size() == 1 && fname == ".") ||
-        (fname.size() == 2 && fname == ".."))
-      return fname;
-    else
-      return fname.substr(0, pos);
 }
 
 StringRef extension(StringRef path, Style style) {
   StringRef fname = filename(path, style);
   size_t pos = fname.find_last_of('.');
   if (pos == StringRef::npos)
     return StringRef();
-  else
-    if ((fname.size() == 1 && fname == ".") ||
-        (fname.size() == 2 && fname == ".."))
-      return StringRef();
-    else
-      return fname.substr(pos);
 }
 
 bool is_separator(char value, Style style) {
   if (value == '/')
     return true;
   if (real_style(style) == Style::windows)
     return value == '\\';
   return false;
if (sys::RemoveFileOnSignal(ResultPath)) {
     // Make sure we delete the file when RemoveFileOnSignal fails.
     consumeError(Ret.discard());
     std::error_code EC(errc::operation_not_permitted);
     return errorCodeToError(EC);
   }
 #endif
   return std::move(Ret);
 }
-}
+} // namespace fs
 
-} // end namsspace sys
-} // end namespace llvm
+} // namespace sys
+} // namespace llvm