From 0df7ddbd31397356ef2ac0b44a2f188353ceeed9 Mon Sep 17 00:00:00 2001
From: Anand Shukla <ashukla@cs.uiuc.edu>
Date: Fri, 18 Jul 2003 16:08:32 +0000
Subject: [PATCH] A pass to combine multiple backedges that go to same target

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7201 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../ProfilePaths/CombineBranch.cpp            | 227 ++++++++++++++++++
 1 file changed, 227 insertions(+)
 create mode 100644 lib/Transforms/Instrumentation/ProfilePaths/CombineBranch.cpp

diff --git a/lib/Transforms/Instrumentation/ProfilePaths/CombineBranch.cpp b/lib/Transforms/Instrumentation/ProfilePaths/CombineBranch.cpp
new file mode 100644
index 00000000000..f92de7000f8
--- /dev/null
+++ b/lib/Transforms/Instrumentation/ProfilePaths/CombineBranch.cpp
@@ -0,0 +1,227 @@
+//===-- InstLoops.cpp ---------------------------------------- ---*- C++ -*--=//
+// Pass to instrument loops
+//
+// At every backedge, insert a counter for that backedge and a call function
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Reoptimizer/InstLoops.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Constants.h"
+#include "llvm/iMemory.h"
+#include "llvm/GlobalVariable.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/iOther.h"
+#include "llvm/iOperators.h"
+#include "llvm/iTerminators.h"
+#include "llvm/iPHINode.h"
+#include "llvm/Module.h"
+#include "llvm/Function.h"
+#include "llvm/Pass.h"
+
+//this is used to color vertices
+//during DFS
+
+enum Color{
+  WHITE,
+  GREY,
+  BLACK
+};
+
+namespace{
+  struct CombineBranches : public FunctionPass {
+  private:
+    //DominatorSet *DS;
+    void getBackEdgesVisit(BasicBlock *u,
+			   std::map<BasicBlock *, Color > &color,
+			   std::map<BasicBlock *, int > &d, 
+			   int &time,
+			   std::map<BasicBlock *, BasicBlock *> &be);
+    void removeRedundant(std::map<BasicBlock *, BasicBlock *> &be);
+    void getBackEdges(Function &F);
+  public:
+    bool runOnFunction(Function &F);
+  };
+  
+  RegisterOpt<CombineBranches> X("branch-combine", "Multiple backedges going to same target are merged");
+}
+
+// Create a new pass to merge branches
+//
+Pass *createCombineBranchesPass() {
+  return new CombineBranches();
+}
+
+
+//helper function to get back edges: it is called by 
+//the "getBackEdges" function below
+void CombineBranches::getBackEdgesVisit(BasicBlock *u,
+                       std::map<BasicBlock *, Color > &color,
+                       std::map<BasicBlock *, int > &d, 
+                       int &time,
+		       std::map<BasicBlock *, BasicBlock *> &be) {
+  
+  color[u]=GREY;
+  time++;
+  d[u]=time;
+
+  for(BasicBlock::succ_iterator vl = succ_begin(u), 
+	ve = succ_end(u); vl != ve; ++vl){
+    
+    BasicBlock *BB = *vl;
+
+    if(color[BB]!=GREY && color[BB]!=BLACK){
+      getBackEdgesVisit(BB, color, d, time, be);
+    }
+    
+    //now checking for d and f vals
+    else if(color[BB]==GREY){
+      //so v is ancestor of u if time of u > time of v
+      if(d[u] >= d[BB]){
+	//u->BB is a backedge
+	be[u] = BB;
+      }
+    }
+  }
+  color[u]=BLACK;//done with visiting the node and its neighbors
+}
+
+//look at all BEs, and remove all BEs that are dominated by other BE's in the
+//set
+void CombineBranches::removeRedundant(std::map<BasicBlock *, BasicBlock *> &be){
+  std::vector<BasicBlock *> toDelete;
+  std::map<BasicBlock *, int> seenBB;
+  
+  for(std::map<BasicBlock *, BasicBlock *>::iterator MI = be.begin(), 
+	ME = be.end(); MI != ME; ++MI){
+    
+    if(seenBB[MI->second])
+      continue;
+    
+    seenBB[MI->second] = 1;
+
+    std::vector<BasicBlock *> sameTarget;
+    sameTarget.clear();
+    
+    for(std::map<BasicBlock *, BasicBlock *>::iterator MMI = be.begin(), 
+	  MME = be.end(); MMI != MME; ++MMI){
+      
+      if(MMI->first == MI->first)
+	continue;
+      
+      if(MMI->second == MI->second)
+	sameTarget.push_back(MMI->first);
+      
+    }
+    
+    //so more than one branch to same target
+    if(sameTarget.size()){
+
+      sameTarget.push_back(MI->first);
+
+      BasicBlock *newBB = new BasicBlock("newCommon", MI->first->getParent());
+      BranchInst *newBranch = new BranchInst(MI->second);
+
+      newBB->getInstList().push_back(newBranch);
+
+      std::map<PHINode *, std::vector<unsigned int> > phiMap;
+
+      
+      for(std::vector<BasicBlock *>::iterator VBI = sameTarget.begin(),
+	    VBE = sameTarget.end(); VBI != VBE; ++VBI){
+
+	//std::cerr<<(*VBI)->getName()<<"\n";
+
+	BranchInst *ti = cast<BranchInst>((*VBI)->getTerminator());
+	unsigned char index = 1;
+	if(ti->getSuccessor(0) == MI->second){
+	  index = 0;
+	}
+
+	ti->setSuccessor(index, newBB);
+
+	for(BasicBlock::iterator BB2Inst = MI->second->begin(), 
+	      BBend = MI->second->end(); BB2Inst != BBend; ++BB2Inst){
+	  
+	  if (PHINode *phiInst = dyn_cast<PHINode>(BB2Inst)){
+	    int bbIndex;
+	    bbIndex = phiInst->getBasicBlockIndex(*VBI);
+	    if(bbIndex>=0){
+	      phiMap[phiInst].push_back(bbIndex);
+	      //phiInst->setIncomingBlock(bbIndex, newBB); 
+	    }
+	  }
+	}
+      }
+
+      for(std::map<PHINode *, std::vector<unsigned int> >::iterator
+	    PI = phiMap.begin(), PE = phiMap.end(); PI != PE; ++PI){
+	
+	PHINode *phiNode = new PHINode(PI->first->getType(), "phi", newBranch);
+	for(std::vector<unsigned int>::iterator II = PI->second.begin(),
+	      IE = PI->second.end(); II != IE; ++II){
+	  phiNode->addIncoming(PI->first->getIncomingValue(*II),
+			       PI->first->getIncomingBlock(*II));
+	}
+
+	std::vector<BasicBlock *> tempBB;
+	for(std::vector<unsigned int>::iterator II = PI->second.begin(),
+	      IE = PI->second.end(); II != IE; ++II){
+	  tempBB.push_back(PI->first->getIncomingBlock(*II));
+	}
+
+	for(std::vector<BasicBlock *>::iterator II = tempBB.begin(),
+	      IE = tempBB.end(); II != IE; ++II){
+	  PI->first->removeIncomingValue(*II);
+	}
+
+	PI->first->addIncoming(phiNode, newBB);
+      }
+      //std::cerr<<"%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%\n";
+      //std::cerr<<MI->second;
+      //std::cerr<<"-----------------------------------\n";
+      //std::cerr<<newBB;
+      //std::cerr<<"END%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%\n";
+      
+    }
+  }
+}
+
+//getting the backedges in a graph
+//Its a variation of DFS to get the backedges in the graph
+//We get back edges by associating a time
+//and a color with each vertex.
+//The time of a vertex is the time when it was first visited
+//The color of a vertex is initially WHITE,
+//Changes to GREY when it is first visited,
+//and changes to BLACK when ALL its neighbors
+//have been visited
+//So we have a back edge when we meet a successor of
+//a node with smaller time, and GREY color
+void CombineBranches::getBackEdges(Function &F){
+  std::map<BasicBlock *, Color > color;
+  std::map<BasicBlock *, int> d;
+  std::map<BasicBlock *, BasicBlock *> be;
+  int time=0;
+  getBackEdgesVisit(F.begin(), color, d, time, be);
+
+  removeRedundant(be);
+}
+
+//Per function pass for inserting counters and call function
+bool CombineBranches::runOnFunction(Function &F){
+  
+  if(F.isExternal()) {
+    return false;
+  }
+
+  //if(F.getName() == "main"){
+   // F.setName("llvm_gprof_main");
+  //}
+  
+  //std::cerr<<F;
+  //std::cerr<<"///////////////////////////////////////////////\n";
+  getBackEdges(F);
+  
+  return true;
+}