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llvm-project/llvm/lib/Transforms/Scalar/CorrelatedExprs.cpp

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//===- CorrelatedExprs.cpp - Pass to detect and eliminated c.e.'s ---------===//
//
// Correlated Expression Elimination propogates information from conditional
// branches to blocks dominated by destinations of the branch. It propogates
// information from the condition check itself into the body of the branch,
// allowing transformations like these for example:
//
// if (i == 7)
// ... 4*i; // constant propogation
//
// 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/Pass.h"
#include "llvm/Function.h"
#include "llvm/iTerminators.h"
#include "llvm/iPHINode.h"
#include "llvm/iOperators.h"
#include "llvm/ConstantHandling.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/ConstantRange.h"
#include "llvm/Support/CFG.h"
#include "Support/PostOrderIterator.h"
#include "Support/StatisticReporter.h"
#include <algorithm>
namespace {
Statistic<>NumSetCCRemoved("cee\t\t- Number of setcc instruction eliminated");
Statistic<>NumOperandsCann("cee\t\t- Number of operands cannonicalized");
Statistic<>BranchRevectors("cee\t\t- 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 propogated 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 Relation's, 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(), 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(), 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; }
const RegionInfo &operator=(const RegionInfo &RI) {
ValueMap = RI.ValueMap;
return *this;
}
// print - Output information about this region...
void print(std::ostream &OS) 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;
}
};
/// CEE - Correlated Expression Elimination
class CEE : public FunctionPass {
std::map<Value*, unsigned> RankMap;
std::map<BasicBlock*, RegionInfo> RegionInfoMap;
DominatorSet *DS;
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<DominatorSet>();
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) || isa<GlobalValue>(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);
BasicBlock *isCorrelatedBranchBlock(BasicBlock *BB, RegionInfo &RI);
void PropogateBranchInfo(BranchInst *BI);
void PropogateEquality(Value *Op0, Value *Op1, RegionInfo &RI);
void PropogateRelation(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);
};
RegisterOpt<CEE> X("cee", "Correlated Expression Elimination");
}
Pass *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.
DS = &getAnalysis<DominatorSet>();
DT = &getAnalysis<DominatorTree>();
std::set<BasicBlock*> VisitedBlocks;
bool Changed = TransformRegion(&F.getEntryNode(), 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,
// propogating 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 propogate the
// information down now.
//
DominatorTree::Node *BBN = (*DT)[BB];
for (unsigned i = 0, e = BBN->getChildren().size(); i != e; ++i) {
BasicBlock *Dominated = BBN->getChildren()[i]->getNode();
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,
// propogate any information our terminator instruction finds to our
// successors.
if (BranchInst *BI = dyn_cast<BranchInst>(TI))
if (BI->isConditional())
PropogateBranchInfo(BI);
// 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 (BasicBlock *Dest = isCorrelatedBranchBlock(TI->getSuccessor(i), 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(i);
// Loop over all of the PHI nodes...
for (BasicBlock::iterator I = Dest->begin();
PHINode *PN = dyn_cast<PHINode>(&*I); ++I) {
// Find the entry in the PHI node for OldSucc, create a duplicate entry
// for BB now.
int BlockIndex = PN->getBasicBlockIndex(OldSucc);
assert(BlockIndex != -1 && "Block should have entry in PHI!");
PN->addIncoming(PN->getIncomingValue(BlockIndex), BB);
}
// Actually revector the branch now...
TI->setSuccessor(i, Dest);
++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]->getNode(), VisitedBlocks);
return Changed;
}
// If this block is a simple block not in the current region, which contains
// only a conditional branch, we determine 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.
//
BasicBlock *CEE::isCorrelatedBranchBlock(BasicBlock *BB, RegionInfo &RI) {
// Check to see if we dominate the block. If so, this block will get the
// condition turned to a constant anyway.
//
//if (DS->dominates(RI.getEntryBlock(), BB))
// return 0;
// Check to see if this is a conditional branch...
if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
if (BI->isConditional()) {
// Make sure that the block is either empty, or only contains a setcc.
if (BB->size() == 1 ||
(BB->size() == 2 && &BB->front() == BI->getCondition() &&
BI->getCondition()->use_size() == 1))
if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition())) {
Relation::KnownResult Result = getSetCCResult(SCI, RI);
if (Result == Relation::KnownTrue)
return BI->getSuccessor(0);
else if (Result == Relation::KnownFalse)
return BI->getSuccessor(1);
}
}
return 0;
}
// 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::aiterator I = F.abegin(), E = F.aend(); 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++;
}
// PropogateBranchInfo - When this method is invoked, we need to propogate
// 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::PropogateBranchInfo(BranchInst *BI) {
assert(BI->isConditional() && "Must be a conditional branch!");
BasicBlock *BB = BI->getParent();
BasicBlock *TrueBB = BI->getSuccessor(0);
BasicBlock *FalseBB = BI->getSuccessor(1);
// Propogate information into the true block...
//
PropogateEquality(BI->getCondition(), ConstantBool::True,
getRegionInfo(TrueBB));
// Propogate information into the false block...
//
PropogateEquality(BI->getCondition(), ConstantBool::False,
getRegionInfo(FalseBB));
}
// PropogateEquality - If we discover that two values are equal to each other in
// a specified region, propogate this knowledge recursively.
//
void CEE::PropogateEquality(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) {
PropogateEquality(Inst->getOperand(0), CB, RI);
PropogateEquality(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) {
PropogateEquality(Inst->getOperand(0), CB, RI);
PropogateEquality(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))
PropogateEquality(BinaryOperator::getNotArgument(BOp),
ConstantBool::get(!CB->getValue()), RI);
// If we know the value of a SetCC instruction, propogate 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...
// Propogate info about the LHS to the RHS & RHS to LHS
PropogateRelation(SCI->getOpcode(), SCI->getOperand(0),
SCI->getOperand(1), RI);
PropogateRelation(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();
PropogateRelation(C, SCI->getOperand(0), SCI->getOperand(1), RI);
PropogateRelation(SetCondInst::getSwappedCondition(C),
SCI->getOperand(1), SCI->getOperand(0), RI);
}
}
}
}
// Propogate information about Op0 to Op1 & visa versa
PropogateRelation(Instruction::SetEQ, Op0, Op1, RI);
PropogateRelation(Instruction::SetEQ, Op1, Op0, RI);
}
// PropogateRelation - We know that the specified relation is true in all of the
// blocks in the specified region. Propogate the information about Op0 and
// anything derived from it into this region.
//
void CEE::PropogateRelation(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 PropogateRelation.
//
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 propogating, 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 propogted is new, then we want process the uses of this
// instruction to propogate the information down to them.
//
if (Op1R.incorporate(Opcode, VI))
UpdateUsersOfValue(Op0, RI);
}
// UpdateUsersOfValue - The information about V in this region has been updated.
// Propogate 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 propogate information to the value produced by the
// instruction. We can only do this if it is an instruction we can
// propogate 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 (DS->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) {
PropogateEquality(SCI, Result ? ConstantBool::True : ConstantBool::False,
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 cannonicalizing 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 cannonical 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;
}
// SimplifySetCC - 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
//===----------------------------------------------------------------------===//
// CheckCondition - Return true if the specified condition is false. Bound may
// be null.
static bool CheckCondition(Constant *Bound, Constant *C,
Instruction::BinaryOps BO) {
assert(C != 0 && "C is not specified!");
if (Bound == 0) return false;
ConstantBool *Val;
switch (BO) {
default: assert(0 && "Unknown Condition code!");
case Instruction::SetEQ: Val = *Bound == *C; break;
case Instruction::SetNE: Val = *Bound != *C; break;
case Instruction::SetLT: Val = *Bound < *C; break;
case Instruction::SetGT: Val = *Bound > *C; break;
case Instruction::SetLE: Val = *Bound <= *C; break;
case Instruction::SetGE: Val = *Bound >= *C; break;
}
// ConstantHandling code may not succeed in the comparison...
if (Val == 0) return false;
return !Val->getValue(); // Return true if the condition is false...
}
// 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";
}
void Relation::dump() const { print(std::cerr); }
void ValueInfo::dump() const { print(std::cerr, 0); }
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