[llvm-commits] CVS: llvm/lib/Transforms/Scalar/GVNPRE.cpp

Owen Anderson resistor at mac.com
Tue May 29 16:54:17 CDT 2007



Changes in directory llvm/lib/Transforms/Scalar:

GVNPRE.cpp added (r1.1)
---
Log message:

Very first part of a GVN-PRE implementation.  It currently performs a bunch of analysis, and nothing more.  It is also quite slow for the moment.  However,
it should give a sense of what's going on.


---
Diffs of the changes:  (+459 -0)

 GVNPRE.cpp |  459 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 459 insertions(+)


Index: llvm/lib/Transforms/Scalar/GVNPRE.cpp
diff -c /dev/null llvm/lib/Transforms/Scalar/GVNPRE.cpp:1.1
*** /dev/null	Tue May 29 16:54:00 2007
--- llvm/lib/Transforms/Scalar/GVNPRE.cpp	Tue May 29 16:53:49 2007
***************
*** 0 ****
--- 1,459 ----
+ //===- GVNPRE.cpp - Eliminate redundant values and expressions ------------===//
+ //
+ //                     The LLVM Compiler Infrastructure
+ //
+ // This file was developed by the Owen Anderson and is distributed under
+ // the University of Illinois Open Source License. See LICENSE.TXT for details.
+ //
+ //===----------------------------------------------------------------------===//
+ //
+ // This pass performs a hybrid of global value numbering and partial redundancy
+ // elimination, known as GVN-PRE.  It performs partial redundancy elimination on
+ // values, rather than lexical expressions, allowing a more comprehensive view 
+ // the optimization.  It replaces redundant values with uses of earlier 
+ // occurences of the same value.  While this is beneficial in that it eliminates
+ // unneeded computation, it also increases register pressure by creating large
+ // live ranges, and should be used with caution on platforms that a very 
+ // sensitive to register pressure.
+ //
+ //===----------------------------------------------------------------------===//
+ 
+ #define DEBUG_TYPE "gvnpre"
+ #include "llvm/Value.h"
+ #include "llvm/Transforms/Scalar.h"
+ #include "llvm/Instructions.h"
+ #include "llvm/Function.h"
+ #include "llvm/Analysis/Dominators.h"
+ #include "llvm/Analysis/PostDominators.h"
+ #include "llvm/ADT/DepthFirstIterator.h"
+ #include "llvm/ADT/Statistic.h"
+ #include "llvm/Support/Compiler.h"
+ #include <algorithm>
+ #include <map>
+ #include <set>
+ #include <cstdio>
+ using namespace llvm;
+ 
+ namespace {
+ 
+   class VISIBILITY_HIDDEN GVNPRE : public FunctionPass {
+     bool runOnFunction(Function &F);
+   public:
+     static char ID; // Pass identification, replacement for typeid
+     GVNPRE() : FunctionPass((intptr_t)&ID) { nextValueNumber = 0; }
+ 
+   private:
+     uint32_t nextValueNumber;
+   
+     struct Expression {
+       char opcode;
+       Value* value;
+       uint32_t lhs;
+       uint32_t rhs;
+       
+       bool operator<(const Expression& other) const {
+         if (opcode < other.opcode)
+           return true;
+         else if (other.opcode < opcode)
+           return false;
+         
+         if (opcode == 0) {
+           if (value < other.value)
+             return true;
+           else
+             return false;
+         } else {
+           if (lhs < other.lhs)
+             return true;
+           else if (other.lhs < lhs)
+             return true;
+           else if (rhs < other.rhs)
+             return true;
+           else
+             return false;
+         }
+       }
+       
+       bool operator==(const Expression& other) const {
+         if (opcode != other.opcode)
+           return false;
+         
+         if (value != other.value)
+           return false;
+         
+         if (lhs != other.lhs)
+           return false;
+           
+         if (rhs != other.rhs)
+           return false;
+         
+         return true;
+       }
+     };
+   
+     typedef std::map<Expression, uint32_t> ValueTable;
+   
+     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+       AU.setPreservesCFG();
+       AU.addRequired<DominatorTree>();
+       AU.addRequired<PostDominatorTree>();
+     }
+   
+     // Helper fuctions
+     // FIXME: eliminate or document these better
+     void dump(ValueTable& VN, std::set<Expression>& s);
+     void clean(ValueTable VN, std::set<Expression>& set);
+     Expression add(ValueTable& VN, std::set<Expression>& MS, Instruction* V);
+     ValueTable::iterator lookup(ValueTable& VN, Value* V);
+     Expression buildExpression(ValueTable& VN, Value* V);
+     std::set<Expression>::iterator find_leader(ValueTable VN, 
+                                                std::set<Expression>& vals,
+                                                uint32_t v);
+     void phi_translate(ValueTable& VN, 
+                        std::set<Expression>& anticIn, BasicBlock* B,
+                        std::set<Expression>& out);
+     
+     // For a given block, calculate the generated expressions, temporaries,
+     // and the AVAIL_OUT set
+     void CalculateAvailOut(ValueTable& VN, std::set<Expression>& MS,
+                        DominatorTree::Node* DI,
+                        std::set<Expression>& currExps,
+                        std::set<PHINode*>& currPhis,
+                        std::set<Expression>& currTemps,
+                        std::set<Expression>& currAvail,
+                        std::map<BasicBlock*, std::set<Expression> > availOut);
+   
+   };
+   
+   char GVNPRE::ID = 0;
+   
+ }
+ 
+ FunctionPass *llvm::createGVNPREPass() { return new GVNPRE(); }
+ 
+ RegisterPass<GVNPRE> X("gvnpre",
+                        "Global Value Numbering/Partial Redundancy Elimination");
+ 
+ // Given a Value, build an Expression to represent it
+ GVNPRE::Expression GVNPRE::buildExpression(ValueTable& VN, Value* V) {
+   if (Instruction* I = dyn_cast<Instruction>(V)) {
+     Expression e;
+     
+     switch (I->getOpcode()) {
+     case 7:
+       e.opcode = 1; // ADD
+       break;
+     case 8:
+       e.opcode = 2; // SUB
+       break;
+     case 9:
+       e.opcode = 3; // MUL
+       break;
+     case 10:
+       e.opcode = 4; // UDIV
+       break;
+     case 11:
+       e.opcode = 5; // SDIV
+       break;
+     case 12:
+       e.opcode = 6; // FDIV
+       break;
+     case 13:
+       e.opcode = 7; // UREM
+       break;
+     case 14:
+       e.opcode = 8; // SREM
+       break;
+     case 15:
+       e.opcode = 9; // FREM
+       break;
+     default:
+      e.opcode = 0; // OPAQUE
+      e.lhs = 0;
+      e.rhs = 0;
+      e.value = V;
+      return e;
+     }
+     
+     e.value = 0;
+     
+     ValueTable::iterator lhs = lookup(VN, I->getOperand(0));
+     if (lhs == VN.end()) {
+       Expression lhsExp = buildExpression(VN, I->getOperand(0));
+       VN.insert(std::make_pair(lhsExp, nextValueNumber));
+       e.lhs = nextValueNumber;
+       nextValueNumber++;
+     } else
+       e.lhs = lhs->second;
+     ValueTable::iterator rhs = lookup(VN, I->getOperand(1));
+     if (rhs == VN.end()) {
+       Expression rhsExp = buildExpression(VN, I->getOperand(1));
+       VN.insert(std::make_pair(rhsExp, nextValueNumber));
+       e.rhs = nextValueNumber;
+       nextValueNumber++;
+     } else
+       e.rhs = rhs->second;
+   
+     return e;
+   } else {
+     Expression e;
+     e.opcode = 0;
+     e.value = V;
+     e.lhs = 0;
+     e.rhs = 0;
+     
+     return e;
+   }
+ }
+ 
+ GVNPRE::Expression GVNPRE::add(ValueTable& VN, std::set<Expression>& MS,
+                                Instruction* V) {
+   Expression e = buildExpression(VN, V);
+   if (VN.insert(std::make_pair(e, nextValueNumber)).second)
+     nextValueNumber++;
+   if (e.opcode != 0 || (e.opcode == 0 && isa<PHINode>(e.value)))
+     MS.insert(e);
+   return e;
+ }
+ 
+ GVNPRE::ValueTable::iterator GVNPRE::lookup(ValueTable& VN, Value* V) {
+   Expression e = buildExpression(VN, V);
+   return VN.find(e);
+ }
+ 
+ std::set<GVNPRE::Expression>::iterator GVNPRE::find_leader(GVNPRE::ValueTable VN,
+                            std::set<GVNPRE::Expression>& vals,
+                            uint32_t v) {
+   for (std::set<Expression>::iterator I = vals.begin(), E = vals.end();
+        I != E; ++I)
+     if (VN[*I] == v)
+       return I;
+   
+   return vals.end();
+ }
+ 
+ void GVNPRE::phi_translate(GVNPRE::ValueTable& VN, 
+                            std::set<GVNPRE::Expression>& anticIn, BasicBlock* B,
+                            std::set<GVNPRE::Expression>& out) {
+   BasicBlock* succ = B->getTerminator()->getSuccessor(0);
+   
+   for (std::set<Expression>::iterator I = anticIn.begin(), E = anticIn.end();
+        I != E; ++I) {
+     if (I->opcode == 0) {
+       Value *v = I->value;
+       if (PHINode* p = dyn_cast<PHINode>(v))
+         if (p->getParent() == succ) {
+           out.insert(buildExpression(VN, p->getIncomingValueForBlock(B)));
+           continue;
+         }
+     }
+     //out.insert(*I);
+   }
+ }
+ 
+ // Remove all expressions whose operands are not themselves in the set
+ void GVNPRE::clean(GVNPRE::ValueTable VN, std::set<GVNPRE::Expression>& set) {
+   unsigned size = set.size();
+   unsigned old = 0;
+   
+   while (size != old) {
+     old = size;
+   
+     std::vector<Expression> worklist(set.begin(), set.end());
+     while (!worklist.empty()) {
+       Expression e = worklist.back();
+       worklist.pop_back();
+     
+       if (e.opcode == 0) // OPAQUE
+         continue;
+       
+       bool lhsValid = false;
+       for (std::set<Expression>::iterator I = set.begin(), E = set.end();
+            I != E; ++I)
+         if (VN[*I] == e.lhs);
+           lhsValid = true;
+           
+       bool rhsValid = false;
+       for (std::set<Expression>::iterator I = set.begin(), E = set.end();
+            I != E; ++I)
+         if (VN[*I] == e.rhs);
+           rhsValid = true;
+       
+       if (!lhsValid || !rhsValid)
+         set.erase(e);
+     }
+     
+     size = set.size();
+   }
+ }
+ 
+ void GVNPRE::dump(GVNPRE::ValueTable& VN, std::set<GVNPRE::Expression>& s) {
+   printf("{ ");
+   for (std::set<Expression>::iterator I = s.begin(), E = s.end(); I != E; ++I) {
+     printf("(%d, %s, value.%d, value.%d) ", I->opcode, I->value == 0 ? "0" : I->value->getName().c_str(), I->lhs, I->rhs);
+   }
+   printf("}\n\n");
+ }
+ 
+ void GVNPRE::CalculateAvailOut(GVNPRE::ValueTable& VN, std::set<Expression>& MS,
+                        DominatorTree::Node* DI,
+                        std::set<Expression>& currExps,
+                        std::set<PHINode*>& currPhis,
+                        std::set<Expression>& currTemps,
+                        std::set<Expression>& currAvail,
+                        std::map<BasicBlock*, std::set<Expression> > availOut) {
+   
+   BasicBlock* BB = DI->getBlock();
+   
+   // A block inherits AVAIL_OUT from its dominator
+   if (DI->getIDom() != 0)
+   currAvail.insert(availOut[DI->getIDom()->getBlock()].begin(),
+                    availOut[DI->getIDom()->getBlock()].end());
+     
+     
+  for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
+       BI != BE; ++BI) {
+        
+     // Handle PHI nodes...
+     if (PHINode* p = dyn_cast<PHINode>(BI)) {
+       add(VN, MS, p);
+       currPhis.insert(p);
+     
+     // Handle binary ops...
+     } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(BI)) {
+       Expression leftValue = buildExpression(VN, BO->getOperand(0));
+       Expression rightValue = buildExpression(VN, BO->getOperand(1));
+       
+       Expression e = add(VN, MS, BO);
+       
+       currExps.insert(leftValue);
+       currExps.insert(rightValue);
+       currExps.insert(e);
+       
+       currTemps.insert(e);
+         
+     // Handle unsupported ops
+     } else {
+       Expression e = add(VN, MS, BI);
+       currTemps.insert(e);
+     }
+       
+     currAvail.insert(buildExpression(VN, BI));
+   }
+ }
+ 
+ bool GVNPRE::runOnFunction(Function &F) {
+   ValueTable VN;
+   std::set<Expression> maximalSet;
+ 
+   std::map<BasicBlock*, std::set<Expression> > generatedExpressions;
+   std::map<BasicBlock*, std::set<PHINode*> > generatedPhis;
+   std::map<BasicBlock*, std::set<Expression> > generatedTemporaries;
+   std::map<BasicBlock*, std::set<Expression> > availableOut;
+   std::map<BasicBlock*, std::set<Expression> > anticipatedIn;
+   
+   DominatorTree &DT = getAnalysis<DominatorTree>();   
+   
+   // First Phase of BuildSets - calculate AVAIL_OUT
+   
+   // Top-down walk of the dominator tree
+   for (df_iterator<DominatorTree::Node*> DI = df_begin(DT.getRootNode()),
+          E = df_end(DT.getRootNode()); DI != E; ++DI) {
+     
+     // Get the sets to update for this block
+     std::set<Expression>& currExps = generatedExpressions[DI->getBlock()];
+     std::set<PHINode*>& currPhis = generatedPhis[DI->getBlock()];
+     std::set<Expression>& currTemps = generatedTemporaries[DI->getBlock()];
+     std::set<Expression>& currAvail = availableOut[DI->getBlock()];     
+     
+     CalculateAvailOut(VN, maximalSet, *DI, currExps, currPhis,
+                       currTemps, currAvail, availableOut);
+   }
+   
+   PostDominatorTree &PDT = getAnalysis<PostDominatorTree>();
+   
+   // Second Phase of BuildSets - calculate ANTIC_IN
+   
+   bool changed = true;
+   unsigned iterations = 0;
+   while (changed) {
+     changed = false;
+     std::set<Expression> anticOut;
+     
+     // Top-down walk of the postdominator tree
+     for (df_iterator<PostDominatorTree::Node*> PDI = 
+          df_begin(PDT.getRootNode()), E = df_end(DT.getRootNode());
+          PDI != E; ++PDI) {
+       BasicBlock* BB = PDI->getBlock();
+       
+       std::set<Expression>& anticIn = anticipatedIn[BB];
+       std::set<Expression> old (anticIn.begin(), anticIn.end());
+       
+       if (BB->getTerminator()->getNumSuccessors() == 1) {
+          phi_translate(VN, anticIn, BB, anticOut);
+       } else if (BB->getTerminator()->getNumSuccessors() > 1) {
+         for (unsigned i = 0; i < BB->getTerminator()->getNumSuccessors(); ++i) {
+           BasicBlock* currSucc = BB->getTerminator()->getSuccessor(i);
+           std::set<Expression> temp;
+           if (i == 0)
+             temp.insert(maximalSet.begin(), maximalSet.end());
+           else
+             temp.insert(anticIn.begin(), anticIn.end());
+        
+           anticIn.clear();
+           std::insert_iterator<std::set<Expression> >  ai_ins(anticIn,
+                                                        anticIn.begin());
+                                                        
+           std::set_difference(anticipatedIn[currSucc].begin(),
+                               anticipatedIn[currSucc].end(),
+                               temp.begin(),
+                               temp.end(),
+                               ai_ins);
+         }
+       }
+       
+       std::set<Expression> S;
+       std::insert_iterator<std::set<Expression> >  s_ins(S, S.begin());
+       std::set_union(anticOut.begin(), anticOut.end(),
+                      generatedExpressions[BB].begin(),
+                      generatedExpressions[BB].end(),
+                      s_ins);
+       
+       anticIn.clear();
+       std::insert_iterator<std::set<Expression> >  antic_ins(anticIn, 
+                                                              anticIn.begin());
+       std::set_difference(S.begin(), S.end(),
+                           generatedTemporaries[BB].begin(),
+                           generatedTemporaries[BB].end(),
+                           antic_ins);
+       
+       clean(VN, anticIn);
+       
+       
+       
+       if (old != anticIn)
+         changed = true;
+       
+       anticOut.clear();
+     }
+     iterations++;
+   }
+   
+   /* printf("Iterations: %d\n", iterations);
+   
+   for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
+     printf("Name: ");
+     printf(I->getName().c_str());
+     printf("\nTMP_GEN: ");
+     dump(VN, generatedTemporaries[I]);
+     printf("\nEXP_GEN: ");
+     dump(VN, generatedExpressions[I]);
+     //printf("\nANTIC_OUT: ");
+     //dump(VN, anticipatedOut[I]);
+     printf("\nANTIC_IN: \n");
+     dump(VN, anticipatedIn[I]);
+     printf("\n");
+   } */
+   
+   return false;
+ }






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