From 6d94eeadd28af4d488b5875778a3ebfa0d749b52 Mon Sep 17 00:00:00 2001
From: Jonas Devlieghere <jonas@devlieghere.com>
Date: Wed, 6 Jan 2021 14:37:17 -0800
Subject: [PATCH] [lldb] Ad os_signpost support to lldb_private::Timer

Emit os_signposts when supported from LLDB's timer class. A vast amount
of performance sensitive places in LLDB are already instrumented with
the Timer class.

By emitting signposts we can examine this information in Instruments. I
recommend looking at Daniel's differential for why this is so powerful:
https://reviews.llvm.org/D52954.

Differential revision: https://reviews.llvm.org/D93657
---
 lldb/include/lldb/Utility/Timer.h | 1 +
 lldb/source/Utility/Timer.cpp     | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/lldb/include/lldb/Utility/Timer.h b/lldb/include/lldb/Utility/Timer.h
index 91f9c57c03c1..edc064b23b57 100644
--- a/lldb/include/lldb/Utility/Timer.h
+++ b/lldb/include/lldb/Utility/Timer.h
@@ -25,6 +25,7 @@ public:
   class Category {
   public:
     explicit Category(const char *category_name);
+    llvm::StringRef GetName() { return m_name; }
 
   private:
     friend class Timer;
diff --git a/lldb/source/Utility/Timer.cpp b/lldb/source/Utility/Timer.cpp
index d55c9863117b..7ead51069529 100644
--- a/lldb/source/Utility/Timer.cpp
+++ b/lldb/source/Utility/Timer.cpp
@@ -7,6 +7,8 @@
 //===----------------------------------------------------------------------===//
 #include "lldb/Utility/Timer.h"
 #include "lldb/Utility/Stream.h"
+#include "llvm/Support/ManagedStatic.h"
+#include "llvm/Support/Signposts.h"
 
 #include <algorithm>
 #include <map>
@@ -28,6 +30,9 @@ typedef std::vector<Timer *> TimerStack;
 static std::atomic<Timer::Category *> g_categories;
 } // end of anonymous namespace
 
+/// Allows llvm::Timer to emit signposts when supported.
+static llvm::ManagedStatic<llvm::SignpostEmitter> Signposts;
+
 std::atomic<bool> Timer::g_quiet(true);
 std::atomic<unsigned> Timer::g_display_depth(0);
 static std::mutex &GetFileMutex() {
@@ -54,6 +59,7 @@ void Timer::SetQuiet(bool value) { g_quiet = value; }
 
 Timer::Timer(Timer::Category &category, const char *format, ...)
     : m_category(category), m_total_start(std::chrono::steady_clock::now()) {
+  Signposts->startInterval(this, m_category.GetName());
   TimerStack &stack = GetTimerStackForCurrentThread();
 
   stack.push_back(this);
@@ -80,6 +86,8 @@ Timer::~Timer() {
   auto total_dur = stop_time - m_total_start;
   auto timer_dur = total_dur - m_child_duration;
 
+  Signposts->endInterval(this, m_category.GetName());
+
   TimerStack &stack = GetTimerStackForCurrentThread();
   if (g_quiet && stack.size() <= g_display_depth) {
     std::lock_guard<std::mutex> lock(GetFileMutex());