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llvm-mirror/lib/Transforms/Scalar/CorrelatedExprs.cpp
Chris Lattner 8f8a1ed82e remove dead code 
llvm-svn: 31398
2006-11-03 01:34:58 +00:00

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//===- CorrelatedExprs.cpp - Pass to detect and eliminated c.e.'s ---------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Correlated Expression Elimination propagates information from conditional
// branches to blocks dominated by destinations of the branch. It propagates
// information from the condition check itself into the body of the branch,
// allowing transformations like these for example:
//
// if (i == 7)
// ... 4*i; // constant propagation
//
// M = i+1; N = j+1;
// if (i == j)
// X = M-N; // = M-M == 0;
//
// This is called Correlated Expression Elimination because we eliminate or
// simplify expressions that are correlated with the direction of a branch. In
// this way we use static information to give us some information about the
// dynamic value of a variable.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/Pass.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
#include "llvm/Type.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Support/ConstantRange.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/Statistic.h"
#include <algorithm>
#include <iostream>
using namespace llvm;
namespace {
Statistic<> NumSetCCRemoved("cee", "Number of setcc instruction eliminated");
Statistic<> NumOperandsCann("cee", "Number of operands canonicalized");
Statistic<> BranchRevectors("cee", "Number of branches revectored");
class ValueInfo;
class Relation {
Value *Val; // Relation to what value?
Instruction::BinaryOps Rel; // SetCC relation, or Add if no information
public:
Relation(Value *V) : Val(V), Rel(Instruction::Add) {}
bool operator<(const Relation &R) const { return Val < R.Val; }
Value *getValue() const { return Val; }
Instruction::BinaryOps getRelation() const { return Rel; }
// contradicts - Return true if the relationship specified by the operand
// contradicts already known information.
//
bool contradicts(Instruction::BinaryOps Rel, const ValueInfo &VI) const;
// incorporate - Incorporate information in the argument into this relation
// entry. This assumes that the information doesn't contradict itself. If
// any new information is gained, true is returned, otherwise false is
// returned to indicate that nothing was updated.
//
bool incorporate(Instruction::BinaryOps Rel, ValueInfo &VI);
// KnownResult - Whether or not this condition determines the result of a
// setcc in the program. False & True are intentionally 0 & 1 so we can
// convert to bool by casting after checking for unknown.
//
enum KnownResult { KnownFalse = 0, KnownTrue = 1, Unknown = 2 };
// getImpliedResult - If this relationship between two values implies that
// the specified relationship is true or false, return that. If we cannot
// determine the result required, return Unknown.
//
KnownResult getImpliedResult(Instruction::BinaryOps Rel) const;
// print - Output this relation to the specified stream
void print(std::ostream &OS) const;
void dump() const;
};
// ValueInfo - One instance of this record exists for every value with
// relationships between other values. It keeps track of all of the
// relationships to other values in the program (specified with Relation) that
// are known to be valid in a region.
//
class ValueInfo {
// RelationShips - this value is know to have the specified relationships to
// other values. There can only be one entry per value, and this list is
// kept sorted by the Val field.
std::vector<Relation> Relationships;
// If information about this value is known or propagated from constant
// expressions, this range contains the possible values this value may hold.
ConstantRange Bounds;
// If we find that this value is equal to another value that has a lower
// rank, this value is used as it's replacement.
//
Value *Replacement;
public:
ValueInfo(const Type *Ty)
: Bounds(Ty->isIntegral() ? Ty : Type::IntTy), Replacement(0) {}
// getBounds() - Return the constant bounds of the value...
const ConstantRange &getBounds() const { return Bounds; }
ConstantRange &getBounds() { return Bounds; }
const std::vector<Relation> &getRelationships() { return Relationships; }
// getReplacement - Return the value this value is to be replaced with if it
// exists, otherwise return null.
//
Value *getReplacement() const { return Replacement; }
// setReplacement - Used by the replacement calculation pass to figure out
// what to replace this value with, if anything.
//
void setReplacement(Value *Repl) { Replacement = Repl; }
// getRelation - return the relationship entry for the specified value.
// This can invalidate references to other Relations, so use it carefully.
//
Relation &getRelation(Value *V) {
// Binary search for V's entry...
std::vector<Relation>::iterator I =
std::lower_bound(Relationships.begin(), Relationships.end(),
Relation(V));
// If we found the entry, return it...
if (I != Relationships.end() && I->getValue() == V)
return *I;
// Insert and return the new relationship...
return *Relationships.insert(I, V);
}
const Relation *requestRelation(Value *V) const {
// Binary search for V's entry...
std::vector<Relation>::const_iterator I =
std::lower_bound(Relationships.begin(), Relationships.end(),
Relation(V));
if (I != Relationships.end() && I->getValue() == V)
return &*I;
return 0;
}
// print - Output information about this value relation...
void print(std::ostream &OS, Value *V) const;
void dump() const;
};
// RegionInfo - Keeps track of all of the value relationships for a region. A
// region is the are dominated by a basic block. RegionInfo's keep track of
// the RegionInfo for their dominator, because anything known in a dominator
// is known to be true in a dominated block as well.
//
class RegionInfo {
BasicBlock *BB;
// ValueMap - Tracks the ValueInformation known for this region
typedef std::map<Value*, ValueInfo> ValueMapTy;
ValueMapTy ValueMap;
public:
RegionInfo(BasicBlock *bb) : BB(bb) {}
// getEntryBlock - Return the block that dominates all of the members of
// this region.
BasicBlock *getEntryBlock() const { return BB; }
// empty - return true if this region has no information known about it.
bool empty() const { return ValueMap.empty(); }
const RegionInfo &operator=(const RegionInfo &RI) {
ValueMap = RI.ValueMap;
return *this;
}
// print - Output information about this region...
void print(std::ostream &OS) const;
void dump() const;
// Allow external access.
typedef ValueMapTy::iterator iterator;
iterator begin() { return ValueMap.begin(); }
iterator end() { return ValueMap.end(); }
ValueInfo &getValueInfo(Value *V) {
ValueMapTy::iterator I = ValueMap.lower_bound(V);
if (I != ValueMap.end() && I->first == V) return I->second;
return ValueMap.insert(I, std::make_pair(V, V->getType()))->second;
}
const ValueInfo *requestValueInfo(Value *V) const {
ValueMapTy::const_iterator I = ValueMap.find(V);
if (I != ValueMap.end()) return &I->second;
return 0;
}
/// removeValueInfo - Remove anything known about V from our records. This
/// works whether or not we know anything about V.
///
void removeValueInfo(Value *V) {
ValueMap.erase(V);
}
};
/// CEE - Correlated Expression Elimination
class CEE : public FunctionPass {
std::map<Value*, unsigned> RankMap;
std::map<BasicBlock*, RegionInfo> RegionInfoMap;
ETForest *EF;
DominatorTree *DT;
public:
virtual bool runOnFunction(Function &F);
// We don't modify the program, so we preserve all analyses
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<ETForest>();
AU.addRequired<DominatorTree>();
AU.addRequiredID(BreakCriticalEdgesID);
};
// print - Implement the standard print form to print out analysis
// information.
virtual void print(std::ostream &O, const Module *M) const;
private:
RegionInfo &getRegionInfo(BasicBlock *BB) {
std::map<BasicBlock*, RegionInfo>::iterator I
= RegionInfoMap.lower_bound(BB);
if (I != RegionInfoMap.end() && I->first == BB) return I->second;
return RegionInfoMap.insert(I, std::make_pair(BB, BB))->second;
}
void BuildRankMap(Function &F);
unsigned getRank(Value *V) const {
if (isa<Constant>(V)) return 0;
std::map<Value*, unsigned>::const_iterator I = RankMap.find(V);
if (I != RankMap.end()) return I->second;
return 0; // Must be some other global thing
}
bool TransformRegion(BasicBlock *BB, std::set<BasicBlock*> &VisitedBlocks);
bool ForwardCorrelatedEdgeDestination(TerminatorInst *TI, unsigned SuccNo,
RegionInfo &RI);
void ForwardSuccessorTo(TerminatorInst *TI, unsigned Succ, BasicBlock *D,
RegionInfo &RI);
void ReplaceUsesOfValueInRegion(Value *Orig, Value *New,
BasicBlock *RegionDominator);
void CalculateRegionExitBlocks(BasicBlock *BB, BasicBlock *OldSucc,
std::vector<BasicBlock*> &RegionExitBlocks);
void InsertRegionExitMerges(PHINode *NewPHI, Instruction *OldVal,
const std::vector<BasicBlock*> &RegionExitBlocks);
void PropagateBranchInfo(BranchInst *BI);
void PropagateSwitchInfo(SwitchInst *SI);
void PropagateEquality(Value *Op0, Value *Op1, RegionInfo &RI);
void PropagateRelation(Instruction::BinaryOps Opcode, Value *Op0,
Value *Op1, RegionInfo &RI);
void UpdateUsersOfValue(Value *V, RegionInfo &RI);
void IncorporateInstruction(Instruction *Inst, RegionInfo &RI);
void ComputeReplacements(RegionInfo &RI);
// getSetCCResult - Given a setcc instruction, determine if the result is
// determined by facts we already know about the region under analysis.
// Return KnownTrue, KnownFalse, or Unknown based on what we can determine.
//
Relation::KnownResult getSetCCResult(SetCondInst *SC, const RegionInfo &RI);
bool SimplifyBasicBlock(BasicBlock &BB, const RegionInfo &RI);
bool SimplifyInstruction(Instruction *Inst, const RegionInfo &RI);
};
RegisterPass<CEE> X("cee", "Correlated Expression Elimination");
}
FunctionPass *llvm::createCorrelatedExpressionEliminationPass() {
return new CEE();
}
bool CEE::runOnFunction(Function &F) {
// Build a rank map for the function...
BuildRankMap(F);
// Traverse the dominator tree, computing information for each node in the
// tree. Note that our traversal will not even touch unreachable basic
// blocks.
EF = &getAnalysis<ETForest>();
DT = &getAnalysis<DominatorTree>();
std::set<BasicBlock*> VisitedBlocks;
bool Changed = TransformRegion(&F.getEntryBlock(), VisitedBlocks);
RegionInfoMap.clear();
RankMap.clear();
return Changed;
}
// TransformRegion - Transform the region starting with BB according to the
// calculated region information for the block. Transforming the region
// involves analyzing any information this block provides to successors,
// propagating the information to successors, and finally transforming
// successors.
//
// This method processes the function in depth first order, which guarantees
// that we process the immediate dominator of a block before the block itself.
// Because we are passing information from immediate dominators down to
// dominatees, we obviously have to process the information source before the
// information consumer.
//
bool CEE::TransformRegion(BasicBlock *BB, std::set<BasicBlock*> &VisitedBlocks){
// Prevent infinite recursion...
if (VisitedBlocks.count(BB)) return false;
VisitedBlocks.insert(BB);
// Get the computed region information for this block...
RegionInfo &RI = getRegionInfo(BB);
// Compute the replacement information for this block...
ComputeReplacements(RI);
// If debugging, print computed region information...
DEBUG(RI.print(std::cerr));
// Simplify the contents of this block...
bool Changed = SimplifyBasicBlock(*BB, RI);
// Get the terminator of this basic block...
TerminatorInst *TI = BB->getTerminator();
// Loop over all of the blocks that this block is the immediate dominator for.
// Because all information known in this region is also known in all of the
// blocks that are dominated by this one, we can safely propagate the
// information down now.
//
DominatorTree::Node *BBN = (*DT)[BB];
if (!RI.empty()) // Time opt: only propagate if we can change something
for (unsigned i = 0, e = BBN->getChildren().size(); i != e; ++i) {
BasicBlock *Dominated = BBN->getChildren()[i]->getBlock();
assert(RegionInfoMap.find(Dominated) == RegionInfoMap.end() &&
"RegionInfo should be calculated in dominanace order!");
getRegionInfo(Dominated) = RI;
}
// Now that all of our successors have information if they deserve it,
// propagate any information our terminator instruction finds to our
// successors.
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
if (BI->isConditional())
PropagateBranchInfo(BI);
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
PropagateSwitchInfo(SI);
}
// If this is a branch to a block outside our region that simply performs
// another conditional branch, one whose outcome is known inside of this
// region, then vector this outgoing edge directly to the known destination.
//
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
while (ForwardCorrelatedEdgeDestination(TI, i, RI)) {
++BranchRevectors;
Changed = true;
}
// Now that all of our successors have information, recursively process them.
for (unsigned i = 0, e = BBN->getChildren().size(); i != e; ++i)
Changed |= TransformRegion(BBN->getChildren()[i]->getBlock(),VisitedBlocks);
return Changed;
}
// isBlockSimpleEnoughForCheck to see if the block is simple enough for us to
// revector the conditional branch in the bottom of the block, do so now.
//
static bool isBlockSimpleEnough(BasicBlock *BB) {
assert(isa<BranchInst>(BB->getTerminator()));
BranchInst *BI = cast<BranchInst>(BB->getTerminator());
assert(BI->isConditional());
// Check the common case first: empty block, or block with just a setcc.
if (BB->size() == 1 ||
(BB->size() == 2 && &BB->front() == BI->getCondition() &&
BI->getCondition()->hasOneUse()))
return true;
// Check the more complex case now...
BasicBlock::iterator I = BB->begin();
// FIXME: This should be reenabled once the regression with SIM is fixed!
#if 0
// PHI Nodes are ok, just skip over them...
while (isa<PHINode>(*I)) ++I;
#endif
// Accept the setcc instruction...
if (&*I == BI->getCondition())
++I;
// Nothing else is acceptable here yet. We must not revector... unless we are
// at the terminator instruction.
if (&*I == BI)
return true;
return false;
}
bool CEE::ForwardCorrelatedEdgeDestination(TerminatorInst *TI, unsigned SuccNo,
RegionInfo &RI) {
// If this successor is a simple block not in the current region, which
// contains only a conditional branch, we decide if the outcome of the branch
// can be determined from information inside of the region. Instead of going
// to this block, we can instead go to the destination we know is the right
// target.
//
// Check to see if we dominate the block. If so, this block will get the
// condition turned to a constant anyway.
//
//if (EF->dominates(RI.getEntryBlock(), BB))
// return 0;
BasicBlock *BB = TI->getParent();
// Get the destination block of this edge...
BasicBlock *OldSucc = TI->getSuccessor(SuccNo);
// Make sure that the block ends with a conditional branch and is simple
// enough for use to be able to revector over.
BranchInst *BI = dyn_cast<BranchInst>(OldSucc->getTerminator());
if (BI == 0 || !BI->isConditional() || !isBlockSimpleEnough(OldSucc))
return false;
// We can only forward the branch over the block if the block ends with a
// setcc we can determine the outcome for.
//
// FIXME: we can make this more generic. Code below already handles more
// generic case.
SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition());
if (SCI == 0) return false;
// Make a new RegionInfo structure so that we can simulate the effect of the
// PHI nodes in the block we are skipping over...
//
RegionInfo NewRI(RI);
// Remove value information for all of the values we are simulating... to make
// sure we don't have any stale information.
for (BasicBlock::iterator I = OldSucc->begin(), E = OldSucc->end(); I!=E; ++I)
if (I->getType() != Type::VoidTy)
NewRI.removeValueInfo(I);
// Put the newly discovered information into the RegionInfo...
for (BasicBlock::iterator I = OldSucc->begin(), E = OldSucc->end(); I!=E; ++I)
if (PHINode *PN = dyn_cast<PHINode>(I)) {
int OpNum = PN->getBasicBlockIndex(BB);
assert(OpNum != -1 && "PHI doesn't have incoming edge for predecessor!?");
PropagateEquality(PN, PN->getIncomingValue(OpNum), NewRI);
} else if (SetCondInst *SCI = dyn_cast<SetCondInst>(I)) {
Relation::KnownResult Res = getSetCCResult(SCI, NewRI);
if (Res == Relation::Unknown) return false;
PropagateEquality(SCI, ConstantBool::get(Res), NewRI);
} else {
assert(isa<BranchInst>(*I) && "Unexpected instruction type!");
}
// Compute the facts implied by what we have discovered...
ComputeReplacements(NewRI);
ValueInfo &PredicateVI = NewRI.getValueInfo(BI->getCondition());
if (PredicateVI.getReplacement() &&
isa<Constant>(PredicateVI.getReplacement()) &&
!isa<GlobalValue>(PredicateVI.getReplacement())) {
ConstantBool *CB = cast<ConstantBool>(PredicateVI.getReplacement());
// Forward to the successor that corresponds to the branch we will take.
ForwardSuccessorTo(TI, SuccNo, BI->getSuccessor(!CB->getValue()), NewRI);
return true;
}
return false;
}
static Value *getReplacementOrValue(Value *V, RegionInfo &RI) {
if (const ValueInfo *VI = RI.requestValueInfo(V))
if (Value *Repl = VI->getReplacement())
return Repl;
return V;
}
/// ForwardSuccessorTo - We have found that we can forward successor # 'SuccNo'
/// of Terminator 'TI' to the 'Dest' BasicBlock. This method performs the
/// mechanics of updating SSA information and revectoring the branch.
///
void CEE::ForwardSuccessorTo(TerminatorInst *TI, unsigned SuccNo,
BasicBlock *Dest, RegionInfo &RI) {
// If there are any PHI nodes in the Dest BB, we must duplicate the entry
// in the PHI node for the old successor to now include an entry from the
// current basic block.
//
BasicBlock *OldSucc = TI->getSuccessor(SuccNo);
BasicBlock *BB = TI->getParent();
DEBUG(std::cerr << "Forwarding branch in basic block %" << BB->getName()
<< " from block %" << OldSucc->getName() << " to block %"
<< Dest->getName() << "\n");
DEBUG(std::cerr << "Before forwarding: " << *BB->getParent());
// Because we know that there cannot be critical edges in the flow graph, and
// that OldSucc has multiple outgoing edges, this means that Dest cannot have
// multiple incoming edges.
//
#ifndef NDEBUG
pred_iterator DPI = pred_begin(Dest); ++DPI;
assert(DPI == pred_end(Dest) && "Critical edge found!!");
#endif
// Loop over any PHI nodes in the destination, eliminating them, because they
// may only have one input.
//
while (PHINode *PN = dyn_cast<PHINode>(&Dest->front())) {
assert(PN->getNumIncomingValues() == 1 && "Crit edge found!");
// Eliminate the PHI node
PN->replaceAllUsesWith(PN->getIncomingValue(0));
Dest->getInstList().erase(PN);
}
// If there are values defined in the "OldSucc" basic block, we need to insert
// PHI nodes in the regions we are dealing with to emulate them. This can
// insert dead phi nodes, but it is more trouble to see if they are used than
// to just blindly insert them.
//
if (EF->dominates(OldSucc, Dest)) {
// RegionExitBlocks - Find all of the blocks that are not dominated by Dest,
// but have predecessors that are. Additionally, prune down the set to only
// include blocks that are dominated by OldSucc as well.
//
std::vector<BasicBlock*> RegionExitBlocks;
CalculateRegionExitBlocks(Dest, OldSucc, RegionExitBlocks);
for (BasicBlock::iterator I = OldSucc->begin(), E = OldSucc->end();
I != E; ++I)
if (I->getType() != Type::VoidTy) {
// Create and insert the PHI node into the top of Dest.
PHINode *NewPN = new PHINode(I->getType(), I->getName()+".fw_merge",
Dest->begin());
// There is definitely an edge from OldSucc... add the edge now
NewPN->addIncoming(I, OldSucc);
// There is also an edge from BB now, add the edge with the calculated
// value from the RI.
NewPN->addIncoming(getReplacementOrValue(I, RI), BB);
// Make everything in the Dest region use the new PHI node now...
ReplaceUsesOfValueInRegion(I, NewPN, Dest);
// Make sure that exits out of the region dominated by NewPN get PHI
// nodes that merge the values as appropriate.
InsertRegionExitMerges(NewPN, I, RegionExitBlocks);
}
}
// If there were PHI nodes in OldSucc, we need to remove the entry for this
// edge from the PHI node, and we need to replace any references to the PHI
// node with a new value.
//
for (BasicBlock::iterator I = OldSucc->begin(); isa<PHINode>(I); ) {
PHINode *PN = cast<PHINode>(I);
// Get the value flowing across the old edge and remove the PHI node entry
// for this edge: we are about to remove the edge! Don't remove the PHI
// node yet though if this is the last edge into it.
Value *EdgeValue = PN->removeIncomingValue(BB, false);
// Make sure that anything that used to use PN now refers to EdgeValue
ReplaceUsesOfValueInRegion(PN, EdgeValue, Dest);
// If there is only one value left coming into the PHI node, replace the PHI
// node itself with the one incoming value left.
//
if (PN->getNumIncomingValues() == 1) {
assert(PN->getNumIncomingValues() == 1);
PN->replaceAllUsesWith(PN->getIncomingValue(0));
PN->getParent()->getInstList().erase(PN);
I = OldSucc->begin();
} else if (PN->getNumIncomingValues() == 0) { // Nuke the PHI
// If we removed the last incoming value to this PHI, nuke the PHI node
// now.
PN->replaceAllUsesWith(Constant::getNullValue(PN->getType()));
PN->getParent()->getInstList().erase(PN);
I = OldSucc->begin();
} else {
++I; // Otherwise, move on to the next PHI node
}
}
// Actually revector the branch now...
TI->setSuccessor(SuccNo, Dest);
// If we just introduced a critical edge in the flow graph, make sure to break
// it right away...
SplitCriticalEdge(TI, SuccNo, this);
// Make sure that we don't introduce critical edges from oldsucc now!
for (unsigned i = 0, e = OldSucc->getTerminator()->getNumSuccessors();
i != e; ++i)
SplitCriticalEdge(OldSucc->getTerminator(), i, this);
// Since we invalidated the CFG, recalculate the dominator set so that it is
// useful for later processing!
// FIXME: This is much worse than it really should be!
//EF->recalculate();
DEBUG(std::cerr << "After forwarding: " << *BB->getParent());
}
/// ReplaceUsesOfValueInRegion - This method replaces all uses of Orig with uses
/// of New. It only affects instructions that are defined in basic blocks that
/// are dominated by Head.
///
void CEE::ReplaceUsesOfValueInRegion(Value *Orig, Value *New,
BasicBlock *RegionDominator) {
assert(Orig != New && "Cannot replace value with itself");
std::vector<Instruction*> InstsToChange;
std::vector<PHINode*> PHIsToChange;
InstsToChange.reserve(Orig->getNumUses());
// Loop over instructions adding them to InstsToChange vector, this allows us
// an easy way to avoid invalidating the use_iterator at a bad time.
for (Value::use_iterator I = Orig->use_begin(), E = Orig->use_end();
I != E; ++I)
if (Instruction *User = dyn_cast<Instruction>(*I))
if (EF->dominates(RegionDominator, User->getParent()))
InstsToChange.push_back(User);
else if (PHINode *PN = dyn_cast<PHINode>(User)) {
PHIsToChange.push_back(PN);
}
// PHIsToChange contains PHI nodes that use Orig that do not live in blocks
// dominated by orig. If the block the value flows in from is dominated by
// RegionDominator, then we rewrite the PHI
for (unsigned i = 0, e = PHIsToChange.size(); i != e; ++i) {
PHINode *PN = PHIsToChange[i];
for (unsigned j = 0, e = PN->getNumIncomingValues(); j != e; ++j)
if (PN->getIncomingValue(j) == Orig &&
EF->dominates(RegionDominator, PN->getIncomingBlock(j)))
PN->setIncomingValue(j, New);
}
// Loop over the InstsToChange list, replacing all uses of Orig with uses of
// New. This list contains all of the instructions in our region that use
// Orig.
for (unsigned i = 0, e = InstsToChange.size(); i != e; ++i)
if (PHINode *PN = dyn_cast<PHINode>(InstsToChange[i])) {
// PHINodes must be handled carefully. If the PHI node itself is in the
// region, we have to make sure to only do the replacement for incoming
// values that correspond to basic blocks in the region.
for (unsigned j = 0, e = PN->getNumIncomingValues(); j != e; ++j)
if (PN->getIncomingValue(j) == Orig &&
EF->dominates(RegionDominator, PN->getIncomingBlock(j)))
PN->setIncomingValue(j, New);
} else {
InstsToChange[i]->replaceUsesOfWith(Orig, New);
}
}
static void CalcRegionExitBlocks(BasicBlock *Header, BasicBlock *BB,
std::set<BasicBlock*> &Visited,
ETForest &EF,
std::vector<BasicBlock*> &RegionExitBlocks) {
if (Visited.count(BB)) return;
Visited.insert(BB);
if (EF.dominates(Header, BB)) { // Block in the region, recursively traverse
for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
CalcRegionExitBlocks(Header, *I, Visited, EF, RegionExitBlocks);
} else {
// Header does not dominate this block, but we have a predecessor that does
// dominate us. Add ourself to the list.
RegionExitBlocks.push_back(BB);
}
}
/// CalculateRegionExitBlocks - Find all of the blocks that are not dominated by
/// BB, but have predecessors that are. Additionally, prune down the set to
/// only include blocks that are dominated by OldSucc as well.
///
void CEE::CalculateRegionExitBlocks(BasicBlock *BB, BasicBlock *OldSucc,
std::vector<BasicBlock*> &RegionExitBlocks){
std::set<BasicBlock*> Visited; // Don't infinite loop
// Recursively calculate blocks we are interested in...
CalcRegionExitBlocks(BB, BB, Visited, *EF, RegionExitBlocks);
// Filter out blocks that are not dominated by OldSucc...
for (unsigned i = 0; i != RegionExitBlocks.size(); ) {
if (EF->dominates(OldSucc, RegionExitBlocks[i]))
++i; // Block is ok, keep it.
else {
// Move to end of list...
std::swap(RegionExitBlocks[i], RegionExitBlocks.back());
RegionExitBlocks.pop_back(); // Nuke the end
}
}
}
void CEE::InsertRegionExitMerges(PHINode *BBVal, Instruction *OldVal,
const std::vector<BasicBlock*> &RegionExitBlocks) {
assert(BBVal->getType() == OldVal->getType() && "Should be derived values!");
BasicBlock *BB = BBVal->getParent();
// Loop over all of the blocks we have to place PHIs in, doing it.
for (unsigned i = 0, e = RegionExitBlocks.size(); i != e; ++i) {
BasicBlock *FBlock = RegionExitBlocks[i]; // Block on the frontier
// Create the new PHI node
PHINode *NewPN = new PHINode(BBVal->getType(),
OldVal->getName()+".fw_frontier",
FBlock->begin());
// Add an incoming value for every predecessor of the block...
for (pred_iterator PI = pred_begin(FBlock), PE = pred_end(FBlock);
PI != PE; ++PI) {
// If the incoming edge is from the region dominated by BB, use BBVal,
// otherwise use OldVal.
NewPN->addIncoming(EF->dominates(BB, *PI) ? BBVal : OldVal, *PI);
}
// Now make everyone dominated by this block use this new value!
ReplaceUsesOfValueInRegion(OldVal, NewPN, FBlock);
}
}
// BuildRankMap - This method builds the rank map data structure which gives
// each instruction/value in the function a value based on how early it appears
// in the function. We give constants and globals rank 0, arguments are
// numbered starting at one, and instructions are numbered in reverse post-order
// from where the arguments leave off. This gives instructions in loops higher
// values than instructions not in loops.
//
void CEE::BuildRankMap(Function &F) {
unsigned Rank = 1; // Skip rank zero.
// Number the arguments...
for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
RankMap[I] = Rank++;
// Number the instructions in reverse post order...
ReversePostOrderTraversal<Function*> RPOT(&F);
for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
E = RPOT.end(); I != E; ++I)
for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
BBI != E; ++BBI)
if (BBI->getType() != Type::VoidTy)
RankMap[BBI] = Rank++;
}
// PropagateBranchInfo - When this method is invoked, we need to propagate
// information derived from the branch condition into the true and false
// branches of BI. Since we know that there aren't any critical edges in the
// flow graph, this can proceed unconditionally.
//
void CEE::PropagateBranchInfo(BranchInst *BI) {
assert(BI->isConditional() && "Must be a conditional branch!");
// Propagate information into the true block...
//
PropagateEquality(BI->getCondition(), ConstantBool::getTrue(),
getRegionInfo(BI->getSuccessor(0)));
// Propagate information into the false block...
//
PropagateEquality(BI->getCondition(), ConstantBool::getFalse(),
getRegionInfo(BI->getSuccessor(1)));
}
// PropagateSwitchInfo - We need to propagate the value tested by the
// switch statement through each case block.
//
void CEE::PropagateSwitchInfo(SwitchInst *SI) {
// Propagate information down each of our non-default case labels. We
// don't yet propagate information down the default label, because a
// potentially large number of inequality constraints provide less
// benefit per unit work than a single equality constraint.
//
Value *cond = SI->getCondition();
for (unsigned i = 1; i < SI->getNumSuccessors(); ++i)
PropagateEquality(cond, SI->getSuccessorValue(i),
getRegionInfo(SI->getSuccessor(i)));
}
// PropagateEquality - If we discover that two values are equal to each other in
// a specified region, propagate this knowledge recursively.
//
void CEE::PropagateEquality(Value *Op0, Value *Op1, RegionInfo &RI) {
if (Op0 == Op1) return; // Gee whiz. Are these really equal each other?
if (isa<Constant>(Op0)) // Make sure the constant is always Op1
std::swap(Op0, Op1);
// Make sure we don't already know these are equal, to avoid infinite loops...
ValueInfo &VI = RI.getValueInfo(Op0);
// Get information about the known relationship between Op0 & Op1
Relation &KnownRelation = VI.getRelation(Op1);
// If we already know they're equal, don't reprocess...
if (KnownRelation.getRelation() == Instruction::SetEQ)
return;
// If this is boolean, check to see if one of the operands is a constant. If
// it's a constant, then see if the other one is one of a setcc instruction,
// an AND, OR, or XOR instruction.
//
if (ConstantBool *CB = dyn_cast<ConstantBool>(Op1)) {
if (Instruction *Inst = dyn_cast<Instruction>(Op0)) {
// If we know that this instruction is an AND instruction, and the result
// is true, this means that both operands to the OR are known to be true
// as well.
//
if (CB->getValue() && Inst->getOpcode() == Instruction::And) {
PropagateEquality(Inst->getOperand(0), CB, RI);
PropagateEquality(Inst->getOperand(1), CB, RI);
}
// If we know that this instruction is an OR instruction, and the result
// is false, this means that both operands to the OR are know to be false
// as well.
//
if (!CB->getValue() && Inst->getOpcode() == Instruction::Or) {
PropagateEquality(Inst->getOperand(0), CB, RI);
PropagateEquality(Inst->getOperand(1), CB, RI);
}
// If we know that this instruction is a NOT instruction, we know that the
// operand is known to be the inverse of whatever the current value is.
//
if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Inst))
if (BinaryOperator::isNot(BOp))
PropagateEquality(BinaryOperator::getNotArgument(BOp),
ConstantBool::get(!CB->getValue()), RI);
// If we know the value of a SetCC instruction, propagate the information
// about the relation into this region as well.
//
if (SetCondInst *SCI = dyn_cast<SetCondInst>(Inst)) {
if (CB->getValue()) { // If we know the condition is true...
// Propagate info about the LHS to the RHS & RHS to LHS
PropagateRelation(SCI->getOpcode(), SCI->getOperand(0),
SCI->getOperand(1), RI);
PropagateRelation(SCI->getSwappedCondition(),
SCI->getOperand(1), SCI->getOperand(0), RI);
} else { // If we know the condition is false...
// We know the opposite of the condition is true...
Instruction::BinaryOps C = SCI->getInverseCondition();
PropagateRelation(C, SCI->getOperand(0), SCI->getOperand(1), RI);
PropagateRelation(SetCondInst::getSwappedCondition(C),
SCI->getOperand(1), SCI->getOperand(0), RI);
}
}
}
}
// Propagate information about Op0 to Op1 & visa versa
PropagateRelation(Instruction::SetEQ, Op0, Op1, RI);
PropagateRelation(Instruction::SetEQ, Op1, Op0, RI);
}
// PropagateRelation - We know that the specified relation is true in all of the
// blocks in the specified region. Propagate the information about Op0 and
// anything derived from it into this region.
//
void CEE::PropagateRelation(Instruction::BinaryOps Opcode, Value *Op0,
Value *Op1, RegionInfo &RI) {
assert(Op0->getType() == Op1->getType() && "Equal types expected!");
// Constants are already pretty well understood. We will apply information
// about the constant to Op1 in another call to PropagateRelation.
//
if (isa<Constant>(Op0)) return;
// Get the region information for this block to update...
ValueInfo &VI = RI.getValueInfo(Op0);
// Get information about the known relationship between Op0 & Op1
Relation &Op1R = VI.getRelation(Op1);
// Quick bailout for common case if we are reprocessing an instruction...
if (Op1R.getRelation() == Opcode)
return;
// If we already have information that contradicts the current information we
// are propagating, ignore this info. Something bad must have happened!
//
if (Op1R.contradicts(Opcode, VI)) {
Op1R.contradicts(Opcode, VI);
std::cerr << "Contradiction found for opcode: "
<< Instruction::getOpcodeName(Opcode) << "\n";
Op1R.print(std::cerr);
return;
}
// If the information propagated is new, then we want process the uses of this
// instruction to propagate the information down to them.
//
if (Op1R.incorporate(Opcode, VI))
UpdateUsersOfValue(Op0, RI);
}
// UpdateUsersOfValue - The information about V in this region has been updated.
// Propagate this to all consumers of the value.
//
void CEE::UpdateUsersOfValue(Value *V, RegionInfo &RI) {
for (Value::use_iterator I = V->use_begin(), E = V->use_end();
I != E; ++I)
if (Instruction *Inst = dyn_cast<Instruction>(*I)) {
// If this is an instruction using a value that we know something about,
// try to propagate information to the value produced by the
// instruction. We can only do this if it is an instruction we can
// propagate information for (a setcc for example), and we only WANT to
// do this if the instruction dominates this region.
//
// If the instruction doesn't dominate this region, then it cannot be
// used in this region and we don't care about it. If the instruction
// is IN this region, then we will simplify the instruction before we
// get to uses of it anyway, so there is no reason to bother with it
// here. This check is also effectively checking to make sure that Inst
// is in the same function as our region (in case V is a global f.e.).
//
if (EF->properlyDominates(Inst->getParent(), RI.getEntryBlock()))
IncorporateInstruction(Inst, RI);
}
}
// IncorporateInstruction - We just updated the information about one of the
// operands to the specified instruction. Update the information about the
// value produced by this instruction
//
void CEE::IncorporateInstruction(Instruction *Inst, RegionInfo &RI) {
if (SetCondInst *SCI = dyn_cast<SetCondInst>(Inst)) {
// See if we can figure out a result for this instruction...
Relation::KnownResult Result = getSetCCResult(SCI, RI);
if (Result != Relation::Unknown) {
PropagateEquality(SCI, ConstantBool::get(Result != 0), RI);
}
}
}
// ComputeReplacements - Some values are known to be equal to other values in a
// region. For example if there is a comparison of equality between a variable
// X and a constant C, we can replace all uses of X with C in the region we are
// interested in. We generalize this replacement to replace variables with
// other variables if they are equal and there is a variable with lower rank
// than the current one. This offers a canonicalizing property that exposes
// more redundancies for later transformations to take advantage of.
//
void CEE::ComputeReplacements(RegionInfo &RI) {
// Loop over all of the values in the region info map...
for (RegionInfo::iterator I = RI.begin(), E = RI.end(); I != E; ++I) {
ValueInfo &VI = I->second;
// If we know that this value is a particular constant, set Replacement to
// the constant...
Value *Replacement = VI.getBounds().getSingleElement();
// If this value is not known to be some constant, figure out the lowest
// rank value that it is known to be equal to (if anything).
//
if (Replacement == 0) {
// Find out if there are any equality relationships with values of lower
// rank than VI itself...
unsigned MinRank = getRank(I->first);
// Loop over the relationships known about Op0.
const std::vector<Relation> &Relationships = VI.getRelationships();
for (unsigned i = 0, e = Relationships.size(); i != e; ++i)
if (Relationships[i].getRelation() == Instruction::SetEQ) {
unsigned R = getRank(Relationships[i].getValue());
if (R < MinRank) {
MinRank = R;
Replacement = Relationships[i].getValue();
}
}
}
// If we found something to replace this value with, keep track of it.
if (Replacement)
VI.setReplacement(Replacement);
}
}
// SimplifyBasicBlock - Given information about values in region RI, simplify
// the instructions in the specified basic block.
//
bool CEE::SimplifyBasicBlock(BasicBlock &BB, const RegionInfo &RI) {
bool Changed = false;
for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ) {
Instruction *Inst = I++;
// Convert instruction arguments to canonical forms...
Changed |= SimplifyInstruction(Inst, RI);
if (SetCondInst *SCI = dyn_cast<SetCondInst>(Inst)) {
// Try to simplify a setcc instruction based on inherited information
Relation::KnownResult Result = getSetCCResult(SCI, RI);
if (Result != Relation::Unknown) {
DEBUG(std::cerr << "Replacing setcc with " << Result
<< " constant: " << *SCI);
SCI->replaceAllUsesWith(ConstantBool::get((bool)Result));
// The instruction is now dead, remove it from the program.
SCI->getParent()->getInstList().erase(SCI);
++NumSetCCRemoved;
Changed = true;
}
}
}
return Changed;
}
// SimplifyInstruction - Inspect the operands of the instruction, converting
// them to their canonical form if possible. This takes care of, for example,
// replacing a value 'X' with a constant 'C' if the instruction in question is
// dominated by a true seteq 'X', 'C'.
//
bool CEE::SimplifyInstruction(Instruction *I, const RegionInfo &RI) {
bool Changed = false;
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
if (const ValueInfo *VI = RI.requestValueInfo(I->getOperand(i)))
if (Value *Repl = VI->getReplacement()) {
// If we know if a replacement with lower rank than Op0, make the
// replacement now.
DEBUG(std::cerr << "In Inst: " << *I << " Replacing operand #" << i
<< " with " << *Repl << "\n");
I->setOperand(i, Repl);
Changed = true;
++NumOperandsCann;
}
return Changed;
}
// getSetCCResult - Try to simplify a setcc instruction based on information
// inherited from a dominating setcc instruction. V is one of the operands to
// the setcc instruction, and VI is the set of information known about it. We
// take two cases into consideration here. If the comparison is against a
// constant value, we can use the constant range to see if the comparison is
// possible to succeed. If it is not a comparison against a constant, we check
// to see if there is a known relationship between the two values. If so, we
// may be able to eliminate the check.
//
Relation::KnownResult CEE::getSetCCResult(SetCondInst *SCI,
const RegionInfo &RI) {
Value *Op0 = SCI->getOperand(0), *Op1 = SCI->getOperand(1);
Instruction::BinaryOps Opcode = SCI->getOpcode();
if (isa<Constant>(Op0)) {
if (isa<Constant>(Op1)) {
if (Constant *Result = ConstantFoldInstruction(SCI)) {
// Wow, this is easy, directly eliminate the SetCondInst.
DEBUG(std::cerr << "Replacing setcc with constant fold: " << *SCI);
return cast<ConstantBool>(Result)->getValue()
? Relation::KnownTrue : Relation::KnownFalse;
}
} else {
// We want to swap this instruction so that operand #0 is the constant.
std::swap(Op0, Op1);
Opcode = SCI->getSwappedCondition();
}
}
// Try to figure out what the result of this comparison will be...
Relation::KnownResult Result = Relation::Unknown;
// We have to know something about the relationship to prove anything...
if (const ValueInfo *Op0VI = RI.requestValueInfo(Op0)) {
// At this point, we know that if we have a constant argument that it is in
// Op1. Check to see if we know anything about comparing value with a
// constant, and if we can use this info to fold the setcc.
//
if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(Op1)) {
// Check to see if we already know the result of this comparison...
ConstantRange R = ConstantRange(Opcode, C);
ConstantRange Int = R.intersectWith(Op0VI->getBounds());
// If the intersection of the two ranges is empty, then the condition
// could never be true!
//
if (Int.isEmptySet()) {
Result = Relation::KnownFalse;
// Otherwise, if VI.getBounds() (the possible values) is a subset of R
// (the allowed values) then we know that the condition must always be
// true!
//
} else if (Int == Op0VI->getBounds()) {
Result = Relation::KnownTrue;
}
} else {
// If we are here, we know that the second argument is not a constant
// integral. See if we know anything about Op0 & Op1 that allows us to
// fold this anyway.
//
// Do we have value information about Op0 and a relation to Op1?
if (const Relation *Op2R = Op0VI->requestRelation(Op1))
Result = Op2R->getImpliedResult(Opcode);
}
}
return Result;
}
//===----------------------------------------------------------------------===//
// Relation Implementation
//===----------------------------------------------------------------------===//
// contradicts - Return true if the relationship specified by the operand
// contradicts already known information.
//
bool Relation::contradicts(Instruction::BinaryOps Op,
const ValueInfo &VI) const {
assert (Op != Instruction::Add && "Invalid relation argument!");
// If this is a relationship with a constant, make sure that this relationship
// does not contradict properties known about the bounds of the constant.
//
if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(Val))
if (ConstantRange(Op, C).intersectWith(VI.getBounds()).isEmptySet())
return true;
switch (Rel) {
default: assert(0 && "Unknown Relationship code!");
case Instruction::Add: return false; // Nothing known, nothing contradicts
case Instruction::SetEQ:
return Op == Instruction::SetLT || Op == Instruction::SetGT ||
Op == Instruction::SetNE;
case Instruction::SetNE: return Op == Instruction::SetEQ;
case Instruction::SetLE: return Op == Instruction::SetGT;
case Instruction::SetGE: return Op == Instruction::SetLT;
case Instruction::SetLT:
return Op == Instruction::SetEQ || Op == Instruction::SetGT ||
Op == Instruction::SetGE;
case Instruction::SetGT:
return Op == Instruction::SetEQ || Op == Instruction::SetLT ||
Op == Instruction::SetLE;
}
}
// incorporate - Incorporate information in the argument into this relation
// entry. This assumes that the information doesn't contradict itself. If any
// new information is gained, true is returned, otherwise false is returned to
// indicate that nothing was updated.
//
bool Relation::incorporate(Instruction::BinaryOps Op, ValueInfo &VI) {
assert(!contradicts(Op, VI) &&
"Cannot incorporate contradictory information!");
// If this is a relationship with a constant, make sure that we update the
// range that is possible for the value to have...
//
if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(Val))
VI.getBounds() = ConstantRange(Op, C).intersectWith(VI.getBounds());
switch (Rel) {
default: assert(0 && "Unknown prior value!");
case Instruction::Add: Rel = Op; return true;
case Instruction::SetEQ: return false; // Nothing is more precise
case Instruction::SetNE: return false; // Nothing is more precise
case Instruction::SetLT: return false; // Nothing is more precise
case Instruction::SetGT: return false; // Nothing is more precise
case Instruction::SetLE:
if (Op == Instruction::SetEQ || Op == Instruction::SetLT) {
Rel = Op;
return true;
} else if (Op == Instruction::SetNE) {
Rel = Instruction::SetLT;
return true;
}
return false;
case Instruction::SetGE: return Op == Instruction::SetLT;
if (Op == Instruction::SetEQ || Op == Instruction::SetGT) {
Rel = Op;
return true;
} else if (Op == Instruction::SetNE) {
Rel = Instruction::SetGT;
return true;
}
return false;
}
}
// getImpliedResult - If this relationship between two values implies that
// the specified relationship is true or false, return that. If we cannot
// determine the result required, return Unknown.
//
Relation::KnownResult
Relation::getImpliedResult(Instruction::BinaryOps Op) const {
if (Rel == Op) return KnownTrue;
if (Rel == SetCondInst::getInverseCondition(Op)) return KnownFalse;
switch (Rel) {
default: assert(0 && "Unknown prior value!");
case Instruction::SetEQ:
if (Op == Instruction::SetLE || Op == Instruction::SetGE) return KnownTrue;
if (Op == Instruction::SetLT || Op == Instruction::SetGT) return KnownFalse;
break;
case Instruction::SetLT:
if (Op == Instruction::SetNE || Op == Instruction::SetLE) return KnownTrue;
if (Op == Instruction::SetEQ) return KnownFalse;
break;
case Instruction::SetGT:
if (Op == Instruction::SetNE || Op == Instruction::SetGE) return KnownTrue;
if (Op == Instruction::SetEQ) return KnownFalse;
break;
case Instruction::SetNE:
case Instruction::SetLE:
case Instruction::SetGE:
case Instruction::Add:
break;
}
return Unknown;
}
//===----------------------------------------------------------------------===//
// Printing Support...
//===----------------------------------------------------------------------===//
// print - Implement the standard print form to print out analysis information.
void CEE::print(std::ostream &O, const Module *M) const {
O << "\nPrinting Correlated Expression Info:\n";
for (std::map<BasicBlock*, RegionInfo>::const_iterator I =
RegionInfoMap.begin(), E = RegionInfoMap.end(); I != E; ++I)
I->second.print(O);
}
// print - Output information about this region...
void RegionInfo::print(std::ostream &OS) const {
if (ValueMap.empty()) return;
OS << " RegionInfo for basic block: " << BB->getName() << "\n";
for (std::map<Value*, ValueInfo>::const_iterator
I = ValueMap.begin(), E = ValueMap.end(); I != E; ++I)
I->second.print(OS, I->first);
OS << "\n";
}
// print - Output information about this value relation...
void ValueInfo::print(std::ostream &OS, Value *V) const {
if (Relationships.empty()) return;
if (V) {
OS << " ValueInfo for: ";
WriteAsOperand(OS, V);
}
OS << "\n Bounds = " << Bounds << "\n";
if (Replacement) {
OS << " Replacement = ";
WriteAsOperand(OS, Replacement);
OS << "\n";
}
for (unsigned i = 0, e = Relationships.size(); i != e; ++i)
Relationships[i].print(OS);
}
// print - Output this relation to the specified stream
void Relation::print(std::ostream &OS) const {
OS << " is ";
switch (Rel) {
default: OS << "*UNKNOWN*"; break;
case Instruction::SetEQ: OS << "== "; break;
case Instruction::SetNE: OS << "!= "; break;
case Instruction::SetLT: OS << "< "; break;
case Instruction::SetGT: OS << "> "; break;
case Instruction::SetLE: OS << "<= "; break;
case Instruction::SetGE: OS << ">= "; break;
}
WriteAsOperand(OS, Val);
OS << "\n";
}
// Don't inline these methods or else we won't be able to call them from GDB!
void Relation::dump() const { print(std::cerr); }
void ValueInfo::dump() const { print(std::cerr, 0); }
void RegionInfo::dump() const { print(std::cerr); }
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