From 58b04b7e2eec3332f1fcbdce679912d323aa29f3 Mon Sep 17 00:00:00 2001
From: Eli Bendersky <eliben@google.com>
Date: Mon, 22 Apr 2013 21:21:08 +0000
Subject: [PATCH] Optimize MachineBasicBlock::getSymbol by caching the symbol.
 Since the symbol name computation is expensive, this helps save about 25% of
 the time spent in this function.

llvm-svn: 180049
---
 llvm/include/llvm/CodeGen/MachineBasicBlock.h |  5 ++++-
 llvm/lib/CodeGen/MachineBasicBlock.cpp        | 18 +++++++++++-------
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/llvm/include/llvm/CodeGen/MachineBasicBlock.h b/llvm/include/llvm/CodeGen/MachineBasicBlock.h
index 492a3ff49f8c..0f2f8746b382 100644
--- a/llvm/include/llvm/CodeGen/MachineBasicBlock.h
+++ b/llvm/include/llvm/CodeGen/MachineBasicBlock.h
@@ -71,7 +71,6 @@ class MachineBasicBlock : public ilist_node<MachineBasicBlock> {
   std::vector<MachineBasicBlock *> Predecessors;
   std::vector<MachineBasicBlock *> Successors;
 
-
   /// Weights - Keep track of the weights to the successors. This vector
   /// has the same order as Successors, or it is empty if we don't use it
   /// (disable optimization).
@@ -96,6 +95,10 @@ class MachineBasicBlock : public ilist_node<MachineBasicBlock> {
   /// target of an indirect branch.
   bool AddressTaken;
 
+  /// \brief since getSymbol is a relatively heavy-weight operation, the symbol
+  /// is only computed once and is cached.
+  mutable MCSymbol *CachedMCSymbol;
+
   // Intrusive list support
   MachineBasicBlock() {}
 
diff --git a/llvm/lib/CodeGen/MachineBasicBlock.cpp b/llvm/lib/CodeGen/MachineBasicBlock.cpp
index 898e165feeab..78e9950e5ef5 100644
--- a/llvm/lib/CodeGen/MachineBasicBlock.cpp
+++ b/llvm/lib/CodeGen/MachineBasicBlock.cpp
@@ -37,7 +37,7 @@ using namespace llvm;
 
 MachineBasicBlock::MachineBasicBlock(MachineFunction &mf, const BasicBlock *bb)
   : BB(bb), Number(-1), xParent(&mf), Alignment(0), IsLandingPad(false),
-    AddressTaken(false) {
+    AddressTaken(false), CachedMCSymbol(NULL) {
   Insts.Parent = this;
 }
 
@@ -48,12 +48,16 @@ MachineBasicBlock::~MachineBasicBlock() {
 /// getSymbol - Return the MCSymbol for this basic block.
 ///
 MCSymbol *MachineBasicBlock::getSymbol() const {
-  const MachineFunction *MF = getParent();
-  MCContext &Ctx = MF->getContext();
-  const char *Prefix = Ctx.getAsmInfo().getPrivateGlobalPrefix();
-  return Ctx.GetOrCreateSymbol(Twine(Prefix) + "BB" +
-                               Twine(MF->getFunctionNumber()) + "_" +
-                               Twine(getNumber()));
+  if (!CachedMCSymbol) {
+    const MachineFunction *MF = getParent();
+    MCContext &Ctx = MF->getContext();
+    const char *Prefix = Ctx.getAsmInfo().getPrivateGlobalPrefix();
+    CachedMCSymbol = Ctx.GetOrCreateSymbol(Twine(Prefix) + "BB" +
+                                           Twine(MF->getFunctionNumber()) +
+                                           "_" + Twine(getNumber()));
+  }
+
+  return CachedMCSymbol;
 }