Delete non-directory valid paths right away

It's unlikely that rename() is faster than unlink() on a regular file
or symlink, so don't bother.

src/libstore/gc.cc

@@ -434,7 +434,12 @@ bool LocalStore::tryToDelete(GCState & state, const Path & path)
 {
     checkInterrupt();
 
-    if (!pathExists(path)) return true;
+    struct stat st;
+    if (lstat(path.c_str(), &st)) {
+        if (errno == ENOENT) return true;
+        throw SysError(format("getting status of %1%") % path);
+    }
+
     if (state.deleted.find(path) != state.deleted.end()) return true;
     if (state.live.find(path) != state.live.end()) return false;
 
@@ -514,21 +519,27 @@ bool LocalStore::tryToDelete(GCState & state, const Path & path)
     /* The path is garbage, so delete it. */
     if (shouldDelete(state.options.action)) {
 
+        /* If it's a valid path that's not a regular file or symlink,
+           invalidate it, rename it, and schedule it for deletion.
+           The renaming is to ensure that later (when we're not
+           holding the global GC lock) we can delete the path without
+           being afraid that the path has become alive again.
+           Otherwise delete it right away. */
         if (isValidPath(path)) {
-            /* If it's a valid path, invalidate it, rename it, and
+            if (S_ISDIR(st.st_mode)) {
-               schedule it for deletion.  The renaming is to ensure
-               that later (when we're not holding the global GC lock)
-               we can delete the path without being afraid that the
-               path has become alive again. */
                 printMsg(lvlInfo, format("invalidating `%1%'") % path);
                 // Estimate the amount freed using the narSize field.
                 state.bytesInvalidated += queryPathInfo(path).narSize;
                 invalidatePathChecked(path);
-            Path tmp = (format("%1%-gc-%2%") % path % getpid()).str();
                 makeMutable(path.c_str());
+                Path tmp = (format("%1%-gc-%2%") % path % getpid()).str();
                 if (rename(path.c_str(), tmp.c_str()))
                     throw SysError(format("unable to rename `%1%' to `%2%'") % path % tmp);
                 state.invalidated.insert(tmp);
+            } else {
+                invalidatePathChecked(path);
+                deleteGarbage(state, path);
+            }
         } else
             deleteGarbage(state, path);