From 1487a2ee93918120d2b46a8430d9b19714c93da1 Mon Sep 17 00:00:00 2001
From: "Duncan P. N. Exon Smith" <dexonsmith@apple.com>
Date: Wed, 20 Apr 2016 19:05:59 +0000
Subject: [PATCH] IR: Avoid mallocs in constructor of ModuleSlotTracker

A ModuleSlotTracker can be created without actually being used (e.g.,
r266889 added one to the Verifier).  Create the SlotTracker within it
lazily on the first call to ModuleSlotTracker::getMachine.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@266902 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/IR/ModuleSlotTracker.h |  6 +++++-
 lib/IR/AsmWriter.cpp                | 19 +++++++++++++++----
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/include/llvm/IR/ModuleSlotTracker.h b/include/llvm/IR/ModuleSlotTracker.h
index 49730a66bdf..eb26fba906e 100644
--- a/include/llvm/IR/ModuleSlotTracker.h
+++ b/include/llvm/IR/ModuleSlotTracker.h
@@ -30,6 +30,8 @@ class Value;
 class ModuleSlotTracker {
   /// Storage for a slot tracker.
   std::unique_ptr<SlotTracker> MachineStorage;
+  bool ShouldCreateStorage = false;
+  bool ShouldInitializeAllMetadata = false;
 
   const Module *M = nullptr;
   const Function *F = nullptr;
@@ -53,7 +55,9 @@ public:
   /// Destructor to clean up storage.
   ~ModuleSlotTracker();
 
-  SlotTracker *getMachine() const { return Machine; }
+  /// Lazily creates a slot tracker.
+  SlotTracker *getMachine();
+
   const Module *getModule() const { return M; }
   const Function *getCurrentFunction() const { return F; }
 
diff --git a/lib/IR/AsmWriter.cpp b/lib/IR/AsmWriter.cpp
index 916f90fd598..43165bf65ed 100644
--- a/lib/IR/AsmWriter.cpp
+++ b/lib/IR/AsmWriter.cpp
@@ -697,14 +697,25 @@ ModuleSlotTracker::ModuleSlotTracker(SlotTracker &Machine, const Module *M,
 
 ModuleSlotTracker::ModuleSlotTracker(const Module *M,
                                      bool ShouldInitializeAllMetadata)
-    : MachineStorage(M ? new SlotTracker(M, ShouldInitializeAllMetadata)
-                       : nullptr),
-      M(M), Machine(MachineStorage.get()) {}
+    : ShouldCreateStorage(M),
+      ShouldInitializeAllMetadata(ShouldInitializeAllMetadata), M(M) {}
 
 ModuleSlotTracker::~ModuleSlotTracker() {}
 
+SlotTracker *ModuleSlotTracker::getMachine() {
+  if (!ShouldCreateStorage)
+    return Machine;
+
+  ShouldCreateStorage = false;
+  MachineStorage =
+      llvm::make_unique<SlotTracker>(M, ShouldInitializeAllMetadata);
+  Machine = MachineStorage.get();
+  return Machine;
+}
+
 void ModuleSlotTracker::incorporateFunction(const Function &F) {
-  if (!Machine)
+  // Using getMachine() may lazily create the slot tracker.
+  if (!getMachine())
     return;
 
   // Nothing to do if this is the right function already.