Index: include/llvm/Support/Timer.h
===================================================================
--- include/llvm/Support/Timer.h
+++ include/llvm/Support/Timer.h
@@ -10,6 +10,7 @@
 #ifndef LLVM_SUPPORT_TIMER_H
 #define LLVM_SUPPORT_TIMER_H
 
+#include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/DataTypes.h"
 #include <cassert>
@@ -194,6 +195,10 @@
 
 public:
   explicit TimerGroup(StringRef Name, StringRef Description);
+
+  explicit TimerGroup(StringRef Name, StringRef Description,
+                      const StringMap<TimeRecord> &Records);
+
   ~TimerGroup();
 
   void setName(StringRef NewName, StringRef NewDescription) {
@@ -207,6 +212,8 @@
   /// This static method prints all timers and clears them all out.
   static void printAll(raw_ostream &OS);
 
+  const char *printJSONValues(raw_ostream &OS, const char *delim);
+
   /// Prints all timers as JSON key/value pairs, and clears them all out.
   static const char *printAllJSONValues(raw_ostream &OS, const char *delim);
 
@@ -223,7 +230,6 @@
   void PrintQueuedTimers(raw_ostream &OS);
   void printJSONValue(raw_ostream &OS, const PrintRecord &R,
                       const char *suffix, double Value);
-  const char *printJSONValues(raw_ostream &OS, const char *delim);
 };
 
 } // end namespace llvm
Index: lib/Support/Timer.cpp
===================================================================
--- lib/Support/Timer.cpp
+++ lib/Support/Timer.cpp
@@ -22,6 +22,8 @@
 #include "llvm/Support/Process.h"
 #include "llvm/Support/YAMLTraits.h"
 #include "llvm/Support/raw_ostream.h"
+#include <limits>
+
 using namespace llvm;
 
 // This ugly hack is brought to you courtesy of constructor/destructor ordering
@@ -234,6 +236,15 @@
   TimerGroupList = this;
 }
 
+TimerGroup::TimerGroup(StringRef Name, StringRef Description,
+                       const StringMap<TimeRecord> &Records)
+    : TimerGroup(Name, Description) {
+  TimersToPrint.reserve(Records.size());
+  for (const auto &P : Records)
+    TimersToPrint.emplace_back(P.getValue(), P.getKey(), P.getKey());
+  assert(TimersToPrint.size() == Records.size() && "Size mismatch");
+}
+
 TimerGroup::~TimerGroup() {
   // If the timer group is destroyed before the timers it owns, accumulate and
   // print the timing data.
@@ -367,13 +378,17 @@
 void TimerGroup::printJSONValue(raw_ostream &OS, const PrintRecord &R,
                                 const char *suffix, double Value) {
   assert(yaml::needsQuotes(Name) == yaml::QuotingType::None &&
-         "TimerGroup name needs no quotes");
+         "TimerGroup name should not need quotes");
   assert(yaml::needsQuotes(R.Name) == yaml::QuotingType::None &&
-         "Timer name needs no quotes");
-  OS << "\t\"time." << Name << '.' << R.Name << suffix << "\": " << Value;
+         "Timer name should not need quotes");
+  constexpr auto max_digits10 = std::numeric_limits<double>::max_digits10;
+  OS << "\t\"time." << Name << '.' << R.Name << suffix
+     << "\": " << format("%.*e", max_digits10 - 1, Value);
 }
 
 const char *TimerGroup::printJSONValues(raw_ostream &OS, const char *delim) {
+  sys::SmartScopedLock<true> L(*TimerLock);
+
   prepareToPrintList();
   for (const PrintRecord &R : TimersToPrint) {
     OS << delim;