diff --git a/src/gn/binary_target_generator.cc b/src/gn/binary_target_generator.cc
index 485884e..4cac96f 100644
--- a/src/gn/binary_target_generator.cc
+++ b/src/gn/binary_target_generator.cc
@@ -93,7 +93,8 @@
   bool ret = TargetGenerator::FillSources();
   for (std::size_t i = 0; i < target_->sources().size(); ++i) {
     const auto& source = target_->sources()[i];
-    switch (source.type()) {
+    const SourceFile::Type source_type = source.GetType();
+    switch (source_type) {
       case SourceFile::SOURCE_CPP:
       case SourceFile::SOURCE_MODULEMAP:
       case SourceFile::SOURCE_H:
@@ -121,7 +122,7 @@
                     ". " + source.value() + " is not one of the valid types.");
     }
 
-    target_->source_types_used().Set(source.type());
+    target_->source_types_used().Set(source_type);
   }
   return ret;
 }
diff --git a/src/gn/compile_commands_writer.cc b/src/gn/compile_commands_writer.cc
index 74f6990..c0b94d1 100644
--- a/src/gn/compile_commands_writer.cc
+++ b/src/gn/compile_commands_writer.cc
@@ -252,7 +252,7 @@
     for (const auto& source : target->sources()) {
       // If this source is not a C/C++/ObjC/ObjC++ source (not header) file,
       // continue as it does not belong in the compilation database.
-      SourceFile::Type source_type = source.type();
+      const SourceFile::Type source_type = source.GetType();
       if (source_type != SourceFile::SOURCE_CPP &&
           source_type != SourceFile::SOURCE_C &&
           source_type != SourceFile::SOURCE_M &&
diff --git a/src/gn/header_checker.cc b/src/gn/header_checker.cc
index 212f581..32f4d90 100644
--- a/src/gn/header_checker.cc
+++ b/src/gn/header_checker.cc
@@ -154,7 +154,7 @@
 
   for (const auto& file : files) {
     // Only check C-like source files (RC files also have includes).
-    SourceFile::Type type = file.first.type();
+    const SourceFile::Type type = file.first.GetType();
     if (type != SourceFile::SOURCE_CPP && type != SourceFile::SOURCE_H &&
         type != SourceFile::SOURCE_C && type != SourceFile::SOURCE_M &&
         type != SourceFile::SOURCE_MM && type != SourceFile::SOURCE_RC)
diff --git a/src/gn/ninja_binary_target_writer.cc b/src/gn/ninja_binary_target_writer.cc
index b26171a..48f485a 100644
--- a/src/gn/ninja_binary_target_writer.cc
+++ b/src/gn/ninja_binary_target_writer.cc
@@ -228,7 +228,7 @@
     for (const OutputFile& output : outputs) {
       SourceFile output_as_source =
           output.AsSourceFile(source_set->settings()->build_settings());
-      if (output_as_source.type() == SourceFile::SOURCE_O) {
+      if (output_as_source.IsObjectType()) {
         obj_files->push_back(output);
       }
     }
diff --git a/src/gn/ninja_c_binary_target_writer.cc b/src/gn/ninja_c_binary_target_writer.cc
index cd76a16..d9c3ad2 100644
--- a/src/gn/ninja_c_binary_target_writer.cc
+++ b/src/gn/ninja_c_binary_target_writer.cc
@@ -76,9 +76,8 @@
 
 const SourceFile* GetModuleMapFromTargetSources(const Target* target) {
   for (const SourceFile& sf : target->sources()) {
-    if (sf.type() == SourceFile::SOURCE_MODULEMAP) {
+    if (sf.IsModuleMapType())
       return &sf;
-    }
   }
   return nullptr;
 }
@@ -552,13 +551,13 @@
   std::vector<OutputFile> tool_outputs;  // Prevent reallocation in loop.
   std::vector<OutputFile> deps;
   for (const auto& source : target_->sources()) {
-    DCHECK_NE(source.type(), SourceFile::SOURCE_SWIFT);
+    DCHECK_NE(source.GetType(), SourceFile::SOURCE_SWIFT);
 
     // Clear the vector but maintain the max capacity to prevent reallocations.
     deps.resize(0);
     const char* tool_name = Tool::kToolNone;
     if (!target_->GetOutputFilesForSource(source, &tool_name, &tool_outputs)) {
-      if (source.type() == SourceFile::SOURCE_DEF)
+      if (source.IsDefType())
         other_files->push_back(source);
       continue;  // No output for this source.
     }
@@ -606,7 +605,7 @@
 
     // It's theoretically possible for a compiler to produce more than one
     // output, but we'll only link to the first output.
-    if (source.type() != SourceFile::SOURCE_MODULEMAP) {
+    if (!source.IsModuleMapType()) {
       object_files->push_back(tool_outputs[0]);
     }
   }
@@ -644,7 +643,7 @@
       const SourceFile output_as_source =
           output.AsSourceFile(target_->settings()->build_settings());
 
-      if (output_as_source.type() == SourceFile::SOURCE_O) {
+      if (output_as_source.IsObjectType()) {
         object_files->push_back(output);
       }
     }
@@ -654,7 +653,7 @@
       // Avoid re-allocation during loop.
       std::vector<OutputFile> partial_outputs;
       for (const auto& source : target_->sources()) {
-        if (source.type() != SourceFile::SOURCE_SWIFT)
+        if (!source.IsSwiftType())
           continue;
 
         partial_outputs.resize(0);
@@ -665,7 +664,7 @@
           additional_outputs.push_back(output);
           SourceFile output_as_source =
               output.AsSourceFile(target_->settings()->build_settings());
-          if (output_as_source.type() == SourceFile::SOURCE_O) {
+          if (output_as_source.IsObjectType()) {
             object_files->push_back(output);
           }
         }
@@ -745,7 +744,7 @@
   const SourceFile* optional_def_file = nullptr;
   if (!other_files.empty()) {
     for (const SourceFile& src_file : other_files) {
-      if (src_file.type() == SourceFile::SOURCE_DEF) {
+      if (src_file.IsDefType()) {
         optional_def_file = &src_file;
         implicit_deps.push_back(
             OutputFile(settings_->build_settings(), src_file));
diff --git a/src/gn/source_file.cc b/src/gn/source_file.cc
index 52066d7..f9d816a 100644
--- a/src/gn/source_file.cc
+++ b/src/gn/source_file.cc
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <string.h>
+
 #include "gn/source_file.h"
 
 #include "base/logging.h"
@@ -21,40 +23,93 @@
   DCHECK(!EndsWithSlash(s)) << s;
 }
 
+bool EndsWithExtension(std::string_view str, std::string_view ext) {
+  return str.size() > ext.size() && str[str.size() - ext.size() - 1] == '.' &&
+         !::memcmp(str.data() + str.size() - ext.size(), ext.data(),
+                   ext.size());
+}
+
 SourceFile::Type GetSourceFileType(const std::string& file) {
-  std::string_view extension = FindExtension(&file);
-  if (extension == "cc" || extension == "cpp" || extension == "cxx" ||
-      extension == "c++")
-    return SourceFile::SOURCE_CPP;
-  if (extension == "h" || extension == "hpp" || extension == "hxx" ||
-      extension == "hh" || extension == "inc" || extension == "ipp" ||
-      extension == "inl")
-    return SourceFile::SOURCE_H;
-  if (extension == "c")
-    return SourceFile::SOURCE_C;
-  if (extension == "m")
-    return SourceFile::SOURCE_M;
-  if (extension == "mm")
-    return SourceFile::SOURCE_MM;
-  if (extension == "modulemap")
-    return SourceFile::SOURCE_MODULEMAP;
-  if (extension == "rc")
-    return SourceFile::SOURCE_RC;
-  if (extension == "S" || extension == "s" || extension == "asm")
-    return SourceFile::SOURCE_S;
-  if (extension == "o" || extension == "obj")
-    return SourceFile::SOURCE_O;
-  if (extension == "def")
-    return SourceFile::SOURCE_DEF;
-  if (extension == "rs")
-    return SourceFile::SOURCE_RS;
-  if (extension == "go")
-    return SourceFile::SOURCE_GO;
-  if (extension == "swift")
+  size_t size = file.size();
+  const char* str = file.data();
+
+  // First, single-char extensions.
+  if (size > 2 && str[size - 2] == '.') {
+    switch (str[size - 1]) {
+      case 'c':
+        return SourceFile::SOURCE_C;  // .c
+      case 'h':
+        return SourceFile::SOURCE_H;  // .h
+      case 'm':
+        return SourceFile::SOURCE_M;  // .m
+      case 'o':
+        return SourceFile::SOURCE_O;  // .o
+      case 'S':
+      case 's':
+        return SourceFile::SOURCE_S;  // .S and .s
+      default:
+        return SourceFile::SOURCE_UNKNOWN;
+    }
+  }
+
+  // Second, two-char extensions
+  if (size > 3 && str[size - 3] == '.') {
+#define TAG2(c1, c2) ((unsigned)(c1) | ((unsigned)(c2) << 8))
+    switch (TAG2(str[size - 2], str[size - 1])) {
+      case TAG2('c', 'c'):
+        return SourceFile::SOURCE_CPP;  // .cc
+      case TAG2('g', 'o'):
+        return SourceFile::SOURCE_GO;  // .go
+      case TAG2('h', 'h'):
+        return SourceFile::SOURCE_H;   // .hh
+      case TAG2('m', 'm'):
+        return SourceFile::SOURCE_MM;  // .mm
+      case TAG2('r', 'c'):
+        return SourceFile::SOURCE_RC;  // .rc
+      case TAG2('r', 's'):
+        return SourceFile::SOURCE_RS;  // .rs
+      default:
+        return SourceFile::SOURCE_UNKNOWN;
+    }
+#undef TAG2
+  }
+
+  if (size > 4 && str[size - 4] == '.') {
+#define TAG3(c1, c2, c3) \
+  ((unsigned)(c1) | ((unsigned)(c2) << 8) | ((unsigned)(c3) << 16))
+    switch (TAG3(str[size - 3], str[size - 2], str[size - 1])) {
+      case TAG3('c', 'p', 'p'):
+      case TAG3('c', 'x', 'x'):
+      case TAG3('c', '+', '+'):
+        return SourceFile::SOURCE_CPP;
+      case TAG3('h', 'p', 'p'):
+      case TAG3('h', 'x', 'x'):
+      case TAG3('i', 'n', 'c'):
+      case TAG3('i', 'p', 'p'):
+      case TAG3('i', 'n', 'l'):
+        return SourceFile::SOURCE_H;
+      case TAG3('a', 's', 'm'):
+        return SourceFile::SOURCE_S;
+      case TAG3('d', 'e', 'f'):
+        return SourceFile::SOURCE_DEF;
+      case TAG3('o', 'b', 'j'):
+        return SourceFile::SOURCE_O;
+      default:
+        return SourceFile::SOURCE_UNKNOWN;
+    }
+#undef TAG3
+  }
+
+  // Other cases
+  if (EndsWithExtension(file, "swift"))
     return SourceFile::SOURCE_SWIFT;
-  if (extension == "swiftmodule")
+
+  if (EndsWithExtension(file, "swiftmodule"))
     return SourceFile::SOURCE_SWIFTMODULE;
 
+  if (EndsWithExtension(file, "modulemap"))
+    return SourceFile::SOURCE_MODULEMAP;
+
   return SourceFile::SOURCE_UNKNOWN;
 }
 
@@ -73,8 +128,35 @@
 SourceFile::SourceFile(std::string&& value)
     : SourceFile(StringAtom(Normalized(std::move(value)))) {}
 
-SourceFile::SourceFile(StringAtom value) : value_(value) {
-  type_ = GetSourceFileType(value_.str());
+SourceFile::SourceFile(StringAtom value) : value_(value) {}
+
+SourceFile::Type SourceFile::GetType() const {
+  return GetSourceFileType(value_.str());
+}
+
+bool SourceFile::IsDefType() const {
+  std::string_view v = value_.str();
+  return EndsWithExtension(v, "def");
+}
+
+bool SourceFile::IsObjectType() const {
+  std::string_view v = value_.str();
+  return EndsWithExtension(v, "o") || EndsWithExtension(v, "obj");
+}
+
+bool SourceFile::IsModuleMapType() const {
+  std::string_view v = value_.str();
+  return EndsWithExtension(v, "modulemap");
+}
+
+bool SourceFile::IsSwiftType() const {
+  std::string_view v = value_.str();
+  return EndsWithExtension(v, "swift");
+}
+
+bool SourceFile::IsSwiftModuleType() const {
+  std::string_view v = value_.str();
+  return EndsWithExtension(v, "swiftmodule");
 }
 
 std::string SourceFile::GetName() const {
@@ -103,7 +185,6 @@
 
 void SourceFile::SetValue(const std::string& value) {
   value_ = StringAtom(value);
-  type_ = GetSourceFileType(value);
 }
 
 SourceFileTypeSet::SourceFileTypeSet() : empty_(true) {
diff --git a/src/gn/source_file.h b/src/gn/source_file.h
index 5ad8f62..b13a400 100644
--- a/src/gn/source_file.h
+++ b/src/gn/source_file.h
@@ -59,7 +59,14 @@
 
   bool is_null() const { return value_.empty(); }
   const std::string& value() const { return value_.str(); }
-  Type type() const { return type_; }
+  Type GetType() const;
+
+  // Optimized implementation of GetType() == SOURCE_XXX
+  bool IsDefType() const;          // SOURCE_DEF
+  bool IsModuleMapType() const;    // SOURCE_MODULEMAP
+  bool IsObjectType() const;       // SOURCE_O
+  bool IsSwiftType() const;        // SOURCE_SWIFT
+  bool IsSwiftModuleType() const;  // SOURCE_SWIFTMODULE
 
   // Returns everything after the last slash.
   std::string GetName() const;
@@ -121,7 +128,6 @@
   void SetValue(const std::string& value);
 
   StringAtom value_;
-  Type type_ = SOURCE_UNKNOWN;
 };
 
 namespace std {
@@ -129,8 +135,7 @@
 template <>
 struct hash<SourceFile> {
   std::size_t operator()(const SourceFile& v) const {
-    hash<std::string> h;
-    return h(v.value());
+    return SourceFile::PtrHash()(v);
   }
 };
 
diff --git a/src/gn/source_file_unittest.cc b/src/gn/source_file_unittest.cc
index 9d3a123..6c409b1 100644
--- a/src/gn/source_file_unittest.cc
+++ b/src/gn/source_file_unittest.cc
@@ -18,3 +18,45 @@
   EXPECT_TRUE(b_str.empty());  // Should have been swapped in.
   EXPECT_EQ("//bar.cc", b.value());
 }
+
+TEST(SourceFile, GetType) {
+  static const struct {
+    std::string_view path;
+    SourceFile::Type type;
+  } kData[] = {
+      {"", SourceFile::SOURCE_UNKNOWN},
+      {"a.c", SourceFile::SOURCE_C},
+      {"a.cc", SourceFile::SOURCE_CPP},
+      {"a.cpp", SourceFile::SOURCE_CPP},
+      {"a.cxx", SourceFile::SOURCE_CPP},
+      {"a.c++", SourceFile::SOURCE_CPP},
+      {"foo.h", SourceFile::SOURCE_H},
+      {"foo.hh", SourceFile::SOURCE_H},
+      {"foo.hpp", SourceFile::SOURCE_H},
+      {"foo.inc", SourceFile::SOURCE_H},
+      {"foo.inl", SourceFile::SOURCE_H},
+      {"foo.ipp", SourceFile::SOURCE_H},
+      {"foo.m", SourceFile::SOURCE_M},
+      {"foo.mm", SourceFile::SOURCE_MM},
+      {"foo.o", SourceFile::SOURCE_O},
+      {"foo.obj", SourceFile::SOURCE_O},
+      {"foo.S", SourceFile::SOURCE_S},
+      {"foo.s", SourceFile::SOURCE_S},
+      {"foo.asm", SourceFile::SOURCE_S},
+      {"foo.go", SourceFile::SOURCE_GO},
+      {"foo.rc", SourceFile::SOURCE_RC},
+      {"foo.rs", SourceFile::SOURCE_RS},
+      {"foo.def", SourceFile::SOURCE_DEF},
+      {"foo.swift", SourceFile::SOURCE_SWIFT},
+      {"foo.swiftmodule", SourceFile::SOURCE_SWIFTMODULE},
+      {"foo.modulemap", SourceFile::SOURCE_MODULEMAP},
+
+      // A few degenerate cases
+      {"foo.obj/a", SourceFile::SOURCE_UNKNOWN},
+      {"foo.cppp", SourceFile::SOURCE_UNKNOWN},
+      {"cpp", SourceFile::SOURCE_UNKNOWN},
+  };
+  for (const auto& data : kData) {
+    EXPECT_EQ(data.type, SourceFile(data.path).GetType());
+  }
+}
diff --git a/src/gn/swift_values.cc b/src/gn/swift_values.cc
index c15e319..a9677a6 100644
--- a/src/gn/swift_values.cc
+++ b/src/gn/swift_values.cc
@@ -56,7 +56,7 @@
 
   const SourceFile module_output_file_as_source =
       module_output_file.AsSourceFile(target->settings()->build_settings());
-  if (module_output_file_as_source.type() != SourceFile::SOURCE_SWIFTMODULE) {
+  if (!module_output_file_as_source.IsSwiftModuleType()) {
     *err = Err(tool->defined_from(), "Incorrect outputs for tool",
                "The first output of tool " + std::string(tool->name()) +
                    " must be a .swiftmodule file.");
diff --git a/src/gn/target.cc b/src/gn/target.cc
index 66ffc1f..7071357 100644
--- a/src/gn/target.cc
+++ b/src/gn/target.cc
@@ -589,7 +589,7 @@
     // All binary targets do a tool lookup.
     DCHECK(IsBinary());
 
-    SourceFile::Type file_type = source.type();
+    const SourceFile::Type file_type = source.GetType();
     if (file_type == SourceFile::SOURCE_UNKNOWN)
       return false;
     if (file_type == SourceFile::SOURCE_O) {