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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. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37343 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson
parent
62ccdbf0b3
commit
ea12a06a81
459
lib/Transforms/Scalar/GVNPRE.cpp
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459
lib/Transforms/Scalar/GVNPRE.cpp
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@ -0,0 +1,459 @@
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//===- GVNPRE.cpp - Eliminate redundant values and expressions ------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the Owen Anderson and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass performs a hybrid of global value numbering and partial redundancy
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// elimination, known as GVN-PRE. It performs partial redundancy elimination on
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// values, rather than lexical expressions, allowing a more comprehensive view
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// the optimization. It replaces redundant values with uses of earlier
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// occurences of the same value. While this is beneficial in that it eliminates
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// unneeded computation, it also increases register pressure by creating large
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// live ranges, and should be used with caution on platforms that a very
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// sensitive to register pressure.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "gvnpre"
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#include "llvm/Value.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Instructions.h"
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#include "llvm/Function.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/PostDominators.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Support/Compiler.h"
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#include <algorithm>
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#include <map>
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#include <set>
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#include <cstdio>
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using namespace llvm;
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namespace {
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class VISIBILITY_HIDDEN GVNPRE : public FunctionPass {
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bool runOnFunction(Function &F);
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public:
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static char ID; // Pass identification, replacement for typeid
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GVNPRE() : FunctionPass((intptr_t)&ID) { nextValueNumber = 0; }
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private:
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uint32_t nextValueNumber;
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struct Expression {
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char opcode;
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Value* value;
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uint32_t lhs;
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uint32_t rhs;
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bool operator<(const Expression& other) const {
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if (opcode < other.opcode)
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return true;
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else if (other.opcode < opcode)
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return false;
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if (opcode == 0) {
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if (value < other.value)
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return true;
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else
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return false;
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} else {
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if (lhs < other.lhs)
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return true;
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else if (other.lhs < lhs)
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return true;
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else if (rhs < other.rhs)
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return true;
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else
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return false;
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}
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}
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bool operator==(const Expression& other) const {
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if (opcode != other.opcode)
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return false;
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if (value != other.value)
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return false;
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if (lhs != other.lhs)
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return false;
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if (rhs != other.rhs)
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return false;
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return true;
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}
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};
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typedef std::map<Expression, uint32_t> ValueTable;
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesCFG();
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AU.addRequired<DominatorTree>();
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AU.addRequired<PostDominatorTree>();
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}
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// Helper fuctions
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// FIXME: eliminate or document these better
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void dump(ValueTable& VN, std::set<Expression>& s);
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void clean(ValueTable VN, std::set<Expression>& set);
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Expression add(ValueTable& VN, std::set<Expression>& MS, Instruction* V);
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ValueTable::iterator lookup(ValueTable& VN, Value* V);
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Expression buildExpression(ValueTable& VN, Value* V);
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std::set<Expression>::iterator find_leader(ValueTable VN,
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std::set<Expression>& vals,
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uint32_t v);
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void phi_translate(ValueTable& VN,
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std::set<Expression>& anticIn, BasicBlock* B,
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std::set<Expression>& out);
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// For a given block, calculate the generated expressions, temporaries,
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// and the AVAIL_OUT set
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void CalculateAvailOut(ValueTable& VN, std::set<Expression>& MS,
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DominatorTree::Node* DI,
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std::set<Expression>& currExps,
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std::set<PHINode*>& currPhis,
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std::set<Expression>& currTemps,
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std::set<Expression>& currAvail,
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std::map<BasicBlock*, std::set<Expression> > availOut);
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};
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char GVNPRE::ID = 0;
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}
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FunctionPass *llvm::createGVNPREPass() { return new GVNPRE(); }
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RegisterPass<GVNPRE> X("gvnpre",
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"Global Value Numbering/Partial Redundancy Elimination");
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// Given a Value, build an Expression to represent it
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GVNPRE::Expression GVNPRE::buildExpression(ValueTable& VN, Value* V) {
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if (Instruction* I = dyn_cast<Instruction>(V)) {
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Expression e;
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switch (I->getOpcode()) {
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case 7:
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e.opcode = 1; // ADD
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break;
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case 8:
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e.opcode = 2; // SUB
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break;
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case 9:
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e.opcode = 3; // MUL
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break;
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case 10:
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e.opcode = 4; // UDIV
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break;
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case 11:
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e.opcode = 5; // SDIV
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break;
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case 12:
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e.opcode = 6; // FDIV
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break;
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case 13:
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e.opcode = 7; // UREM
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break;
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case 14:
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e.opcode = 8; // SREM
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break;
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case 15:
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e.opcode = 9; // FREM
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break;
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default:
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e.opcode = 0; // OPAQUE
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e.lhs = 0;
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e.rhs = 0;
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e.value = V;
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return e;
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}
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e.value = 0;
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ValueTable::iterator lhs = lookup(VN, I->getOperand(0));
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if (lhs == VN.end()) {
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Expression lhsExp = buildExpression(VN, I->getOperand(0));
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VN.insert(std::make_pair(lhsExp, nextValueNumber));
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e.lhs = nextValueNumber;
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nextValueNumber++;
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} else
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e.lhs = lhs->second;
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ValueTable::iterator rhs = lookup(VN, I->getOperand(1));
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if (rhs == VN.end()) {
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Expression rhsExp = buildExpression(VN, I->getOperand(1));
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VN.insert(std::make_pair(rhsExp, nextValueNumber));
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e.rhs = nextValueNumber;
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nextValueNumber++;
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} else
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e.rhs = rhs->second;
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return e;
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} else {
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Expression e;
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e.opcode = 0;
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e.value = V;
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e.lhs = 0;
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e.rhs = 0;
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return e;
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}
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}
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GVNPRE::Expression GVNPRE::add(ValueTable& VN, std::set<Expression>& MS,
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Instruction* V) {
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Expression e = buildExpression(VN, V);
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if (VN.insert(std::make_pair(e, nextValueNumber)).second)
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nextValueNumber++;
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if (e.opcode != 0 || (e.opcode == 0 && isa<PHINode>(e.value)))
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MS.insert(e);
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return e;
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}
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GVNPRE::ValueTable::iterator GVNPRE::lookup(ValueTable& VN, Value* V) {
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Expression e = buildExpression(VN, V);
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return VN.find(e);
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}
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std::set<GVNPRE::Expression>::iterator GVNPRE::find_leader(GVNPRE::ValueTable VN,
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std::set<GVNPRE::Expression>& vals,
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uint32_t v) {
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for (std::set<Expression>::iterator I = vals.begin(), E = vals.end();
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I != E; ++I)
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if (VN[*I] == v)
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return I;
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return vals.end();
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}
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void GVNPRE::phi_translate(GVNPRE::ValueTable& VN,
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std::set<GVNPRE::Expression>& anticIn, BasicBlock* B,
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std::set<GVNPRE::Expression>& out) {
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BasicBlock* succ = B->getTerminator()->getSuccessor(0);
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for (std::set<Expression>::iterator I = anticIn.begin(), E = anticIn.end();
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I != E; ++I) {
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if (I->opcode == 0) {
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Value *v = I->value;
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if (PHINode* p = dyn_cast<PHINode>(v))
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if (p->getParent() == succ) {
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out.insert(buildExpression(VN, p->getIncomingValueForBlock(B)));
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continue;
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}
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}
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//out.insert(*I);
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}
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}
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// Remove all expressions whose operands are not themselves in the set
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void GVNPRE::clean(GVNPRE::ValueTable VN, std::set<GVNPRE::Expression>& set) {
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unsigned size = set.size();
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unsigned old = 0;
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while (size != old) {
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old = size;
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std::vector<Expression> worklist(set.begin(), set.end());
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while (!worklist.empty()) {
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Expression e = worklist.back();
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worklist.pop_back();
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if (e.opcode == 0) // OPAQUE
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continue;
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bool lhsValid = false;
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for (std::set<Expression>::iterator I = set.begin(), E = set.end();
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I != E; ++I)
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if (VN[*I] == e.lhs);
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lhsValid = true;
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bool rhsValid = false;
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for (std::set<Expression>::iterator I = set.begin(), E = set.end();
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I != E; ++I)
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if (VN[*I] == e.rhs);
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rhsValid = true;
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if (!lhsValid || !rhsValid)
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set.erase(e);
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}
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size = set.size();
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}
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}
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void GVNPRE::dump(GVNPRE::ValueTable& VN, std::set<GVNPRE::Expression>& s) {
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printf("{ ");
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for (std::set<Expression>::iterator I = s.begin(), E = s.end(); I != E; ++I) {
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printf("(%d, %s, value.%d, value.%d) ", I->opcode, I->value == 0 ? "0" : I->value->getName().c_str(), I->lhs, I->rhs);
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}
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printf("}\n\n");
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}
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void GVNPRE::CalculateAvailOut(GVNPRE::ValueTable& VN, std::set<Expression>& MS,
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DominatorTree::Node* DI,
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std::set<Expression>& currExps,
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std::set<PHINode*>& currPhis,
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std::set<Expression>& currTemps,
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std::set<Expression>& currAvail,
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std::map<BasicBlock*, std::set<Expression> > availOut) {
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BasicBlock* BB = DI->getBlock();
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// A block inherits AVAIL_OUT from its dominator
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if (DI->getIDom() != 0)
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currAvail.insert(availOut[DI->getIDom()->getBlock()].begin(),
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availOut[DI->getIDom()->getBlock()].end());
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for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
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BI != BE; ++BI) {
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// Handle PHI nodes...
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if (PHINode* p = dyn_cast<PHINode>(BI)) {
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add(VN, MS, p);
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currPhis.insert(p);
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// Handle binary ops...
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} else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(BI)) {
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Expression leftValue = buildExpression(VN, BO->getOperand(0));
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Expression rightValue = buildExpression(VN, BO->getOperand(1));
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Expression e = add(VN, MS, BO);
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currExps.insert(leftValue);
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currExps.insert(rightValue);
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currExps.insert(e);
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currTemps.insert(e);
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// Handle unsupported ops
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} else {
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Expression e = add(VN, MS, BI);
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currTemps.insert(e);
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}
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currAvail.insert(buildExpression(VN, BI));
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}
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}
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bool GVNPRE::runOnFunction(Function &F) {
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ValueTable VN;
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std::set<Expression> maximalSet;
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std::map<BasicBlock*, std::set<Expression> > generatedExpressions;
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std::map<BasicBlock*, std::set<PHINode*> > generatedPhis;
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std::map<BasicBlock*, std::set<Expression> > generatedTemporaries;
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std::map<BasicBlock*, std::set<Expression> > availableOut;
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std::map<BasicBlock*, std::set<Expression> > anticipatedIn;
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DominatorTree &DT = getAnalysis<DominatorTree>();
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// First Phase of BuildSets - calculate AVAIL_OUT
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// Top-down walk of the dominator tree
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for (df_iterator<DominatorTree::Node*> DI = df_begin(DT.getRootNode()),
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E = df_end(DT.getRootNode()); DI != E; ++DI) {
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// Get the sets to update for this block
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std::set<Expression>& currExps = generatedExpressions[DI->getBlock()];
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std::set<PHINode*>& currPhis = generatedPhis[DI->getBlock()];
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std::set<Expression>& currTemps = generatedTemporaries[DI->getBlock()];
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std::set<Expression>& currAvail = availableOut[DI->getBlock()];
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CalculateAvailOut(VN, maximalSet, *DI, currExps, currPhis,
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currTemps, currAvail, availableOut);
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}
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PostDominatorTree &PDT = getAnalysis<PostDominatorTree>();
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// Second Phase of BuildSets - calculate ANTIC_IN
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bool changed = true;
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unsigned iterations = 0;
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while (changed) {
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changed = false;
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std::set<Expression> anticOut;
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// Top-down walk of the postdominator tree
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for (df_iterator<PostDominatorTree::Node*> PDI =
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df_begin(PDT.getRootNode()), E = df_end(DT.getRootNode());
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PDI != E; ++PDI) {
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BasicBlock* BB = PDI->getBlock();
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std::set<Expression>& anticIn = anticipatedIn[BB];
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std::set<Expression> old (anticIn.begin(), anticIn.end());
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if (BB->getTerminator()->getNumSuccessors() == 1) {
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phi_translate(VN, anticIn, BB, anticOut);
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} else if (BB->getTerminator()->getNumSuccessors() > 1) {
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for (unsigned i = 0; i < BB->getTerminator()->getNumSuccessors(); ++i) {
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BasicBlock* currSucc = BB->getTerminator()->getSuccessor(i);
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std::set<Expression> temp;
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if (i == 0)
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temp.insert(maximalSet.begin(), maximalSet.end());
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else
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temp.insert(anticIn.begin(), anticIn.end());
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anticIn.clear();
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std::insert_iterator<std::set<Expression> > ai_ins(anticIn,
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anticIn.begin());
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std::set_difference(anticipatedIn[currSucc].begin(),
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anticipatedIn[currSucc].end(),
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temp.begin(),
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temp.end(),
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ai_ins);
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}
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}
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std::set<Expression> S;
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std::insert_iterator<std::set<Expression> > s_ins(S, S.begin());
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std::set_union(anticOut.begin(), anticOut.end(),
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generatedExpressions[BB].begin(),
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generatedExpressions[BB].end(),
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s_ins);
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anticIn.clear();
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std::insert_iterator<std::set<Expression> > antic_ins(anticIn,
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anticIn.begin());
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std::set_difference(S.begin(), S.end(),
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generatedTemporaries[BB].begin(),
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generatedTemporaries[BB].end(),
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antic_ins);
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clean(VN, anticIn);
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if (old != anticIn)
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changed = true;
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anticOut.clear();
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}
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iterations++;
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}
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/* printf("Iterations: %d\n", iterations);
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for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
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printf("Name: ");
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printf(I->getName().c_str());
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printf("\nTMP_GEN: ");
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dump(VN, generatedTemporaries[I]);
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printf("\nEXP_GEN: ");
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dump(VN, generatedExpressions[I]);
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//printf("\nANTIC_OUT: ");
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//dump(VN, anticipatedOut[I]);
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printf("\nANTIC_IN: \n");
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dump(VN, anticipatedIn[I]);
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printf("\n");
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} */
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return false;
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}
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