From 09713794c17061ae36cc696cfc928c5a0c2bdc75 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Mon, 1 Dec 2008 07:29:03 +0000
Subject: [PATCH] pull the predMap densemap out of the inner loop of
 performPRE, so that it isn't reallocated all the time.  This is a tiny
 speedup for GVN: 3.90->3.88s

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60338 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/GVN.cpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index 9189f41c19c..2995b1000a3 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -1225,6 +1225,7 @@ bool GVN::processBlock(DomTreeNode* DTN) {
 bool GVN::performPRE(Function& F) {
   bool changed = false;
   SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
+  DenseMap<BasicBlock*, Value*> predMap;
   for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
        DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
     BasicBlock* CurrentBlock = *DI;
@@ -1252,7 +1253,8 @@ bool GVN::performPRE(Function& F) {
       unsigned numWith = 0;
       unsigned numWithout = 0;
       BasicBlock* PREPred = 0;
-      DenseMap<BasicBlock*, Value*> predMap;
+      predMap.clear();
+
       for (pred_iterator PI = pred_begin(CurrentBlock),
            PE = pred_end(CurrentBlock); PI != PE; ++PI) {
         // We're not interested in PRE where the block is its
@@ -1359,7 +1361,7 @@ bool GVN::performPRE(Function& F) {
       
       Instruction* erase = BI;
       BI++;
-      DEBUG(cerr << "GVN removed: " << *erase);
+      DEBUG(cerr << "GVN PRE removed: " << *erase);
       MD->removeInstruction(erase);
       erase->eraseFromParent();
       changed = true;
-- 
2.34.1