diff --git a/llvm/include/llvm/Support/Path.h b/llvm/include/llvm/Support/Path.h
--- a/llvm/include/llvm/Support/Path.h
+++ b/llvm/include/llvm/Support/Path.h
@@ -476,6 +476,11 @@
 bool remove_dots(SmallVectorImpl<char> &path, bool remove_dot_dot = false,
                  Style style = Style::native);
 
+/// Attempt to guess path style for a given path string.
+///
+/// @param path Input path.
+llvm::Optional<Style> guess_style(StringRef absolute_path);
+
 } // end namespace path
 } // end namespace sys
 } // end namespace llvm
diff --git a/llvm/lib/Support/Path.cpp b/llvm/lib/Support/Path.cpp
--- a/llvm/lib/Support/Path.cpp
+++ b/llvm/lib/Support/Path.cpp
@@ -763,6 +763,17 @@
   return true;
 }
 
+llvm::Optional<Style> guess_style(StringRef absolute_path) {
+  if (absolute_path.startswith("/"))
+    return Style::posix;
+  if (absolute_path.startswith(R"(\\)"))
+    return Style::windows;
+  if (absolute_path.size() > 3 && llvm::isAlpha(absolute_path[0]) &&
+      absolute_path.substr(1, 2) == R"(:\)")
+    return Style::windows;
+  return llvm::None;
+}
+
 } // end namespace path
 
 namespace fs {
diff --git a/llvm/unittests/Support/Path.cpp b/llvm/unittests/Support/Path.cpp
--- a/llvm/unittests/Support/Path.cpp
+++ b/llvm/unittests/Support/Path.cpp
@@ -1521,6 +1521,17 @@
   EXPECT_EQ(Path, "C:\\old/foo\\bar");
 }
 
+TEST(Support, GuessStyle) {
+  EXPECT_EQ(path::Style::posix, path::guess_style("/foo/bar.txt"));
+  EXPECT_EQ(path::Style::posix, path::guess_style("//net/bar.txt"));
+  EXPECT_EQ(path::Style::windows,
+            path::guess_style(R"(C:\foo.txt)"));
+  EXPECT_EQ(path::Style::windows,
+            path::guess_style(R"(\\net\foo.txt)"));
+  EXPECT_EQ(llvm::None, path::guess_style("foo.txt"));
+  EXPECT_EQ(llvm::None, path::guess_style("foo/bar.txt"));
+}
+
 TEST_F(FileSystemTest, OpenFileForRead) {
   // Create a temp file.
   int FileDescriptor;