Index: include/llvm/Support/Path.h
===================================================================
--- include/llvm/Support/Path.h
+++ include/llvm/Support/Path.h
@@ -180,6 +180,18 @@
 /// @param path A path that is transformed to native format.
 void native(SmallVectorImpl<char> &path);
 
+/// @brief Convert path to the canonical form in place.
+///
+/// @code
+///   /foo/./net/..//bar/ => /foo/bar
+///   /foo/bar/net/ => /foo/bar/net
+///   /foo/bar/../../net => /net
+/// @endcode
+///
+/// @param Path A path that is transformed to canonical format.
+/// @param Result Holds the result of the transformation.
+void canonical(StringRef path, SmallVectorImpl<char> &Result);
+
 /// @}
 /// @name Lexical Observers
 /// @{
Index: lib/Support/Path.cpp
===================================================================
--- lib/Support/Path.cpp
+++ lib/Support/Path.cpp
@@ -531,6 +531,36 @@
 #endif
 }
 
+void canonical(StringRef Path, SmallVectorImpl<char> &Result) {
+  Result.clear();
+  SmallVector<StringRef, 16> Components;
+
+  // Split the path into the root and relative parts
+  // This is needed to ensure that the root path is just one component,
+  // as the path iterator can represent the root path using more than one
+  // component.
+  auto Root = root_path(Path);
+  auto Relative = Path.substr(Root.size());
+  if (!Root.empty())
+    Components.push_back(Root);
+
+  for(auto I = begin(Relative), End = end(Relative); I != End; ++I) {
+    auto Component = *I;
+    if (Component == ".")
+      continue;
+    else if(Component == ".." && !Components.empty() &&
+            Components.back() != "..") {
+      // Remove the previous component unless it's root
+      if (Components.back() != Root)
+        Components.pop_back();
+      continue;
+    }
+    Components.push_back(Component);
+  }
+  for (const auto &Component : Components)
+    append(Result, Component);
+}
+
 const StringRef filename(StringRef path) {
   return *(--end(path));
 }
Index: unittests/Support/Path.cpp
===================================================================
--- unittests/Support/Path.cpp
+++ unittests/Support/Path.cpp
@@ -144,6 +144,7 @@
     EXPECT_EQ(*(--sys::path::end(filename)), (stem + ext).str());
 
     path::native(*i, temp_store);
+    path::canonical(*i, temp_store);
   }
 }
 
@@ -258,6 +259,32 @@
 #endif
 }
 
+TEST(Support, CanonicalPath) {
+  auto canonical = [] (StringRef Path) -> std::string {
+    SmallString<256> Result;
+    path::canonical(Path, Result);
+    return Result.str();
+  };
+#ifdef LLVM_ON_WIN32
+  EXPECT_EQ(canonical("..\\foo/."), "..\\foo");
+  EXPECT_EQ(canonical("a:/foo\net/.."),"a:\\foo");
+  EXPECT_EQ(canonical("d:\\foo/net\\bar"), "d:\\foo\\net\\bar");
+  EXPECT_EQ(canonical("..\\\\./.."), "..\\..");
+  EXPECT_EQ(canonical("a:\\\\foo\\.\\net/..\\\\bar\\"), "a:\\foo\\bar");
+  EXPECT_EQ(canonical("\\\\net\\dir\\../bar"), "\\\\net\\bar");
+  EXPECT_EQ(canonical("a:/.."), "a:\\");
+#else
+  EXPECT_EQ(canonical("/foo/./net/..//bar/"), "/foo/bar");
+  EXPECT_EQ(canonical("foo/./bar/../../../net"), "../net");
+  EXPECT_EQ(canonical("../foo/."), "../foo");
+  EXPECT_EQ(canonical("..//./.."), "../..");
+  EXPECT_EQ(canonical("/foo/./net/../../net"), "/net");
+  EXPECT_EQ(canonical("/foo/bar/net/"), "/foo/bar/net");
+  EXPECT_EQ(canonical("/foo/../net"), "/net");
+  EXPECT_EQ(canonical("/.."), "/");
+#endif
+}
+
 class FileSystemTest : public testing::Test {
 protected:
   /// Unique temporary directory in which all created filesystem entities must