Support: Avoid std::tie in Support/FileSystem/UniqueID.h, NFC

[dexonsmith]

Summary

Running -fsyntax-only on UniqueID.h is 2x faster with this patch
(which avoids calling std::tie for operator<). Since the transitive
includers of this file will go up as FileEntryRef gets used in more
places, avoid that compile-time hit. This is a follow-up to
23ed570af1cc165afea1b70a533a4a39d6656501 (suggested by Reid Kleckner).

Also drop the <tuple> include from FileSystem.h (which was vestigal
from before UniqueID.h was split out).

[rnk]

lgtm

llvm/include/llvm/Support/FileSystem.h

 #include "llvm/Support/MD5.h"
 #include <cassert>
 #include <cstdint>
 #include <ctime>
 #include <memory>
 #include <stack>
 #include <string>
 #include <system_error>
-#include <tuple>
 #include <vector>
 
 #ifdef HAVE_SYS_STAT_H
 #include <sys/stat.h>
 #endif
 
 namespace llvm {
 namespace sys {

llvm/include/llvm/Support/FileSystem/UniqueID.h

 // reused without bloating the includes.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_SUPPORT_FILESYSTEM_UNIQUEID_H
 #define LLVM_SUPPORT_FILESYSTEM_UNIQUEID_H
 
 #include <cstdint>
-#include <tuple>
 
 namespace llvm {
 namespace sys {
 namespace fs {
 
 class UniqueID {
   uint64_t Device;
   uint64_t File;
 
 public:
   UniqueID() = default;
   UniqueID(uint64_t Device, uint64_t File) : Device(Device), File(File) {}
 
   bool operator==(const UniqueID &Other) const {
     return Device == Other.Device && File == Other.File;
   }
   bool operator!=(const UniqueID &Other) const { return !(*this == Other); }
   bool operator<(const UniqueID &Other) const {
-    return std::tie(Device, File) < std::tie(Other.Device, Other.File);
+    /// Don't use std::tie since it bloats the compile time of this header.
+    if (Device < Other.Device)
+      return true;
+    if (Other.Device < Device)
+      return false;
+    return File < Other.File;
   }
 
   uint64_t getDevice() const { return Device; }
   uint64_t getFile() const { return File; }
 };
 
 } // end namespace fs
 } // end namespace sys
 } // end namespace llvm
 
 #endif // LLVM_SUPPORT_FILESYSTEM_UNIQUEID_H

llvm/unittests/Support/CMakeLists.txt

add_llvm_unittest(SupportTests
   ErrnoTest.cpp
   ErrorOrTest.cpp
   ErrorTest.cpp
   ExtensibleRTTITest.cpp
   FileCollectorTest.cpp
   FileOutputBufferTest.cpp
   FileUtilitiesTest.cpp
   FormatVariadicTest.cpp
+  FSUniqueIDTest.cpp
   GlobPatternTest.cpp
   Host.cpp
   IndexedAccessorTest.cpp
   ItaniumManglingCanonicalizerTest.cpp
   JSONTest.cpp
   KnownBitsTest.cpp
   LEB128Test.cpp
   LineIteratorTest.cpp

llvm/unittests/Support/FSUniqueIDTest.cpp

+//===- llvm/unittest/Support/FSUniqueIDTest.cpp - Test sys::fs::UniqueID --===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/FileSystem/UniqueID.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+using namespace llvm::sys::fs;
+
+namespace {
+
+TEST(FSUniqueIDTest, construct) {
+  EXPECT_EQ(20u, UniqueID(20, 10).getDevice());
+  EXPECT_EQ(10u, UniqueID(20, 10).getFile());
+}
+
+TEST(FSUniqueIDTest, equals) {
+  EXPECT_TRUE(UniqueID(20, 10) == UniqueID(20, 10));
+  EXPECT_FALSE(UniqueID(20, 20) == UniqueID(20, 10));
+  EXPECT_FALSE(UniqueID(10, 10) == UniqueID(20, 10));
+}
+
+TEST(FSUniqueIDTest, less) {
+  EXPECT_FALSE(UniqueID(20, 2) < UniqueID(20, 2));
+  EXPECT_FALSE(UniqueID(20, 3) < UniqueID(20, 2));
+  EXPECT_FALSE(UniqueID(30, 2) < UniqueID(20, 2));
+  EXPECT_FALSE(UniqueID(30, 2) < UniqueID(20, 40));
+  EXPECT_TRUE(UniqueID(20, 2) < UniqueID(20, 3));
+  EXPECT_TRUE(UniqueID(20, 2) < UniqueID(30, 2));
+  EXPECT_TRUE(UniqueID(20, 40) < UniqueID(30, 2));
+}
+
+} // anonymous namespace