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
@@ -27,6 +27,27 @@
 
 enum class Style { windows, posix, native };
 
+/// Check if \p S uses POSIX path rules.
+constexpr bool is_style_posix(Style S) {
+  if (S == Style::posix)
+    return true;
+  if (S != Style::native)
+    return false;
+#if defined(_WIN32)
+  return false;
+#else
+  return true;
+#endif
+}
+
+/// Check if \p S uses Windows path rules.
+constexpr bool is_style_windows(Style S) { return !is_style_posix(S); }
+
+/// Check if \p S uses the same path rules as Style::native.
+constexpr bool is_style_native(Style S) {
+  return is_style_posix(S) == is_style_posix(Style::native);
+}
+
 /// @name Lexical Component Iterator
 /// @{
 
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
@@ -37,11 +37,9 @@
   using llvm::sys::path::Style;
 
   inline Style real_style(Style style) {
-#ifdef _WIN32
-    return (style == Style::posix) ? Style::posix : Style::windows;
-#else
-    return (style == Style::windows) ? Style::windows : Style::posix;
-#endif
+    if (is_style_posix(style))
+      return Style::posix;
+    return Style::windows;
   }
 
   inline const char *separators(Style style) {
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
@@ -69,6 +69,29 @@
   int FD;
 };
 
+TEST(is_style_Style, Works) {
+  using namespace llvm::sys::path;
+  // Check platform-independent results.
+  EXPECT_TRUE(is_style_posix(Style::posix));
+  EXPECT_TRUE(is_style_windows(Style::windows));
+  EXPECT_FALSE(is_style_posix(Style::windows));
+  EXPECT_FALSE(is_style_windows(Style::posix));
+
+  // Check platform-dependent results.
+#if defined(_WIN32)
+  EXPECT_FALSE(is_style_posix(Style::native));
+  EXPECT_TRUE(is_style_windows(Style::native));
+#else
+  EXPECT_TRUE(is_style_posix(Style::native));
+  EXPECT_FALSE(is_style_windows(Style::native));
+#endif
+
+  // Check is_style_native().
+  EXPECT_TRUE(is_style_native(Style::native));
+  EXPECT_EQ(is_style_posix(Style::native), is_style_native(Style::posix));
+  EXPECT_EQ(is_style_windows(Style::native), is_style_native(Style::windows));
+}
+
 TEST(is_separator, Works) {
   EXPECT_TRUE(path::is_separator('/'));
   EXPECT_FALSE(path::is_separator('\0'));
@@ -78,11 +101,8 @@
   EXPECT_TRUE(path::is_separator('\\', path::Style::windows));
   EXPECT_FALSE(path::is_separator('\\', path::Style::posix));
 
-#ifdef _WIN32
-  EXPECT_TRUE(path::is_separator('\\'));
-#else
-  EXPECT_FALSE(path::is_separator('\\'));
-#endif
+  EXPECT_EQ(path::is_style_windows(path::Style::native),
+            path::is_separator('\\'));
 }
 
 TEST(is_absolute_gnu, Works) {
@@ -107,6 +127,10 @@
               std::get<1>(Path));
     EXPECT_EQ(path::is_absolute_gnu(std::get<0>(Path), path::Style::windows),
               std::get<2>(Path));
+
+    constexpr int Native = is_style_posix(path::Style::native) ? 1 : 2;
+    EXPECT_EQ(path::is_absolute_gnu(std::get<0>(Path), path::Style::native),
+              std::get<Native>(Path));
   }
 }