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Initial checkin of Correlated Expression Elimination Pass
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@3599 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
parent
4dd7d3e34d
commit
b0dbd7fc5a
974
lib/Transforms/Scalar/CorrelatedExprs.cpp
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974
lib/Transforms/Scalar/CorrelatedExprs.cpp
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//===- CorrelatedExprs.cpp - Pass to detect and eliminated c.e.'s ---------===//
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//
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// Correlated Expression Elimination propogates information from conditional
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// branches to blocks dominated by destinations of the branch. It propogates
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// information from the condition check itself into the body of the branch,
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// allowing transformations like these for example:
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//
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// if (i == 7)
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// ... 4*i; // constant propogation
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//
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// M = i+1; N = j+1;
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// if (i == j)
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// X = M-N; // = M-M == 0;
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//
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// This is called Correlated Expression Elimination because we eliminate or
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// simplify expressions that are correlated with the direction of a branch. In
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// this way we use static information to give us some information about the
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// dynamic value of a variable.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Pass.h"
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#include "llvm/Function.h"
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#include "llvm/iTerminators.h"
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#include "llvm/iOperators.h"
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#include "llvm/ConstantHandling.h"
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#include "llvm/Assembly/Writer.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Support/ConstantRange.h"
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#include "llvm/Support/CFG.h"
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#include "Support/PostOrderIterator.h"
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#include "Support/StatisticReporter.h"
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#include <algorithm>
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namespace {
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Statistic<>NumSetCCRemoved("cee\t\t- Number of setcc instruction eliminated");
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Statistic<>NumOperandsCann("cee\t\t- Number of operands cannonicalized");
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Statistic<>BranchRevectors("cee\t\t- Number of branches revectored");
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class ValueInfo;
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class Relation {
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Value *Val; // Relation to what value?
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Instruction::BinaryOps Rel; // SetCC relation, or Add if no information
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public:
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Relation(Value *V) : Val(V), Rel(Instruction::Add) {}
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bool operator<(const Relation &R) const { return Val < R.Val; }
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Value *getValue() const { return Val; }
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Instruction::BinaryOps getRelation() const { return Rel; }
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// contradicts - Return true if the relationship specified by the operand
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// contradicts already known information.
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//
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bool contradicts(Instruction::BinaryOps Rel, const ValueInfo &VI) const;
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// incorporate - Incorporate information in the argument into this relation
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// entry. This assumes that the information doesn't contradict itself. If
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// any new information is gained, true is returned, otherwise false is
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// returned to indicate that nothing was updated.
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//
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bool incorporate(Instruction::BinaryOps Rel, ValueInfo &VI);
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// KnownResult - Whether or not this condition determines the result of a
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// setcc in the program. False & True are intentionally 0 & 1 so we can
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// convert to bool by casting after checking for unknown.
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//
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enum KnownResult { KnownFalse = 0, KnownTrue = 1, Unknown = 2 };
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// getImpliedResult - If this relationship between two values implies that
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// the specified relationship is true or false, return that. If we cannot
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// determine the result required, return Unknown.
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//
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KnownResult getImpliedResult(Instruction::BinaryOps Rel) const;
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// print - Output this relation to the specified stream
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void print(std::ostream &OS) const;
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void dump() const;
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};
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// ValueInfo - One instance of this record exists for every value with
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// relationships between other values. It keeps track of all of the
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// relationships to other values in the program (specified with Relation) that
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// are known to be valid in a region.
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//
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class ValueInfo {
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// RelationShips - this value is know to have the specified relationships to
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// other values. There can only be one entry per value, and this list is
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// kept sorted by the Val field.
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std::vector<Relation> Relationships;
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// If information about this value is known or propogated from constant
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// expressions, this range contains the possible values this value may hold.
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ConstantRange Bounds;
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// If we find that this value is equal to another value that has a lower
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// rank, this value is used as it's replacement.
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//
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Value *Replacement;
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public:
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ValueInfo(const Type *Ty)
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: Bounds(Ty->isIntegral() ? Ty : Type::IntTy), Replacement(0) {}
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// getBounds() - Return the constant bounds of the value...
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const ConstantRange &getBounds() const { return Bounds; }
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ConstantRange &getBounds() { return Bounds; }
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const std::vector<Relation> &getRelationships() { return Relationships; }
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// getReplacement - Return the value this value is to be replaced with if it
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// exists, otherwise return null.
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//
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Value *getReplacement() const { return Replacement; }
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// setReplacement - Used by the replacement calculation pass to figure out
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// what to replace this value with, if anything.
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//
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void setReplacement(Value *Repl) { Replacement = Repl; }
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// getRelation - return the relationship entry for the specified value.
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// This can invalidate references to other Relation's, so use it carefully.
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//
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Relation &getRelation(Value *V) {
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// Binary search for V's entry...
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std::vector<Relation>::iterator I =
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std::lower_bound(Relationships.begin(), Relationships.end(), V);
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// If we found the entry, return it...
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if (I != Relationships.end() && I->getValue() == V)
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return *I;
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// Insert and return the new relationship...
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return *Relationships.insert(I, V);
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}
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const Relation *requestRelation(Value *V) const {
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// Binary search for V's entry...
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std::vector<Relation>::const_iterator I =
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std::lower_bound(Relationships.begin(), Relationships.end(), V);
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if (I != Relationships.end() && I->getValue() == V)
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return &*I;
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return 0;
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}
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// print - Output information about this value relation...
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void print(std::ostream &OS, Value *V) const;
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void dump() const;
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};
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// RegionInfo - Keeps track of all of the value relationships for a region. A
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// region is the are dominated by a basic block. RegionInfo's keep track of
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// the RegionInfo for their dominator, because anything known in a dominator
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// is known to be true in a dominated block as well.
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//
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class RegionInfo {
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BasicBlock *BB;
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// ValueMap - Tracks the ValueInformation known for this region
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typedef std::map<Value*, ValueInfo> ValueMapTy;
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ValueMapTy ValueMap;
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public:
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RegionInfo(BasicBlock *bb) : BB(bb) {}
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// getEntryBlock - Return the block that dominates all of the members of
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// this region.
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BasicBlock *getEntryBlock() const { return BB; }
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const RegionInfo &operator=(const RegionInfo &RI) {
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ValueMap = RI.ValueMap;
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return *this;
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}
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// print - Output information about this region...
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void print(std::ostream &OS) const;
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// Allow external access.
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typedef ValueMapTy::iterator iterator;
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iterator begin() { return ValueMap.begin(); }
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iterator end() { return ValueMap.end(); }
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ValueInfo &getValueInfo(Value *V) {
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ValueMapTy::iterator I = ValueMap.lower_bound(V);
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if (I != ValueMap.end() && I->first == V) return I->second;
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return ValueMap.insert(I, std::make_pair(V, V->getType()))->second;
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}
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const ValueInfo *requestValueInfo(Value *V) const {
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ValueMapTy::const_iterator I = ValueMap.find(V);
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if (I != ValueMap.end()) return &I->second;
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return 0;
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}
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};
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/// CEE - Correlated Expression Elimination
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class CEE : public FunctionPass {
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std::map<Value*, unsigned> RankMap;
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std::map<BasicBlock*, RegionInfo> RegionInfoMap;
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DominatorSet *DS;
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DominatorTree *DT;
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public:
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virtual bool runOnFunction(Function &F);
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// We don't modify the program, so we preserve all analyses
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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//AU.preservesCFG();
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AU.addRequired<DominatorSet>();
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AU.addRequired<DominatorTree>();
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};
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// print - Implement the standard print form to print out analysis
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// information.
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virtual void print(std::ostream &O, const Module *M) const;
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virtual void releaseMemory() {
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RegionInfoMap.clear();
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RankMap.clear();
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}
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private:
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RegionInfo &getRegionInfo(BasicBlock *BB) {
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std::map<BasicBlock*, RegionInfo>::iterator I
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= RegionInfoMap.lower_bound(BB);
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if (I != RegionInfoMap.end() && I->first == BB) return I->second;
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return RegionInfoMap.insert(I, std::make_pair(BB, BB))->second;
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}
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void BuildRankMap(Function &F);
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unsigned getRank(Value *V) const {
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if (isa<Constant>(V) || isa<GlobalValue>(V)) return 0;
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std::map<Value*, unsigned>::const_iterator I = RankMap.find(V);
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if (I != RankMap.end()) return I->second;
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return 0; // Must be some other global thing
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}
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bool TransformRegion(BasicBlock *BB, std::set<BasicBlock*> &VisitedBlocks);
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BasicBlock *isCorrelatedBranchBlock(BasicBlock *BB, RegionInfo &RI);
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void PropogateBranchInfo(BranchInst *BI);
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void PropogateEquality(Value *Op0, Value *Op1, RegionInfo &RI);
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void PropogateRelation(Instruction::BinaryOps Opcode, Value *Op0,
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Value *Op1, RegionInfo &RI);
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void UpdateUsersOfValue(Value *V, RegionInfo &RI);
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void IncorporateInstruction(Instruction *Inst, RegionInfo &RI);
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void ComputeReplacements(RegionInfo &RI);
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// getSetCCResult - Given a setcc instruction, determine if the result is
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// determined by facts we already know about the region under analysis.
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// Return KnownTrue, KnownFalse, or Unknown based on what we can determine.
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//
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Relation::KnownResult getSetCCResult(SetCondInst *SC, const RegionInfo &RI);
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bool SimplifyBasicBlock(BasicBlock &BB, const RegionInfo &RI);
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bool SimplifyInstruction(Instruction *Inst, const RegionInfo &RI);
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};
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RegisterOpt<CEE> X("cee", "Correlated Expression Elimination");
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}
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Pass *createCorrelatedExpressionEliminationPass() { return new CEE(); }
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bool CEE::runOnFunction(Function &F) {
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// Build a rank map for the function...
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BuildRankMap(F);
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// Traverse the dominator tree, computing information for each node in the
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// tree. Note that our traversal will not even touch unreachable basic
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// blocks.
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DS = &getAnalysis<DominatorSet>();
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DT = &getAnalysis<DominatorTree>();
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std::set<BasicBlock*> VisitedBlocks;
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return TransformRegion(&F.getEntryNode(), VisitedBlocks);
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}
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// TransformRegion - Transform the region starting with BB according to the
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// calculated region information for the block. Transforming the region
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// involves analyzing any information this block provides to successors,
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// propogating the information to successors, and finally transforming
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// successors.
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//
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// This method processes the function in depth first order, which guarantees
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// that we process the immediate dominator of a block before the block itself.
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// Because we are passing information from immediate dominators down to
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// dominatees, we obviously have to process the information source before the
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// information consumer.
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//
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bool CEE::TransformRegion(BasicBlock *BB, std::set<BasicBlock*> &VisitedBlocks){
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// Prevent infinite recursion...
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if (VisitedBlocks.count(BB)) return false;
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VisitedBlocks.insert(BB);
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// Get the computed region information for this block...
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RegionInfo &RI = getRegionInfo(BB);
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// Compute the replacement information for this block...
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ComputeReplacements(RI);
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// If debugging, print computed region information...
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DEBUG(RI.print(std::cerr));
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// Simplify the contents of this block...
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bool Changed = SimplifyBasicBlock(*BB, RI);
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// Get the terminator of this basic block...
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TerminatorInst *TI = BB->getTerminator();
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// If this is a conditional branch, make sure that there is a branch target
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// for each successor that can hold any information gleaned from the branch,
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// by breaking any critical edges that may be laying about.
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//
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if (TI->getNumSuccessors() > 1) {
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// If any of the successors has multiple incoming branches, add a new dummy
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// destination branch that only contains an unconditional branch to the real
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// target.
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for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
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BasicBlock *Succ = TI->getSuccessor(i);
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// If there is more than one predecessor of the destination block, break
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// this critical edge by inserting a new block. This updates dominatorset
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// and dominatortree information.
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//
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if (isCriticalEdge(TI, i))
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SplitCriticalEdge(TI, i, this);
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}
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}
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// Loop over all of the blocks that this block is the immediate dominator for.
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// Because all information known in this region is also known in all of the
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// blocks that are dominated by this one, we can safely propogate the
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// information down now.
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//
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DominatorTree::Node *BBN = (*DT)[BB];
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for (unsigned i = 0, e = BBN->getChildren().size(); i != e; ++i) {
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BasicBlock *Dominated = BBN->getChildren()[i]->getNode();
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assert(RegionInfoMap.find(Dominated) == RegionInfoMap.end() &&
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"RegionInfo should be calculated in dominanace order!");
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getRegionInfo(Dominated) = RI;
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}
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// Now that all of our successors have information if they deserve it,
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// propogate any information our terminator instruction finds to our
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// successors.
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if (BranchInst *BI = dyn_cast<BranchInst>(TI))
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if (BI->isConditional())
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PropogateBranchInfo(BI);
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// If this is a branch to a block outside our region that simply performs
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// another conditional branch, one whose outcome is known inside of this
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// region, then vector this outgoing edge directly to the known destination.
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//
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for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
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while (BasicBlock *Dest = isCorrelatedBranchBlock(TI->getSuccessor(i), RI)){
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TI->setSuccessor(i, Dest);
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++BranchRevectors;
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}
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}
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// Now that all of our successors have information, recursively process them.
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for (unsigned i = 0, e = BBN->getChildren().size(); i != e; ++i)
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Changed |= TransformRegion(BBN->getChildren()[i]->getNode(), VisitedBlocks);
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// for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
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//Changed |= TransformRegion(TI->getSuccessor(i), VisitedBlocks);
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return Changed;
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}
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// If this block is a simple block not in the current region, which contains
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// only a conditional branch, we determine if the outcome of the branch can be
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// determined from information inside of the region. Instead of going to this
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// block, we can instead go to the destination we know is the right target.
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//
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BasicBlock *CEE::isCorrelatedBranchBlock(BasicBlock *BB, RegionInfo &RI) {
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// Check to see if we dominate the block. If so, this block will get the
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// condition turned to a constant anyway.
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//
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//if (DS->dominates(RI.getEntryBlock(), BB))
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// return 0;
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// Check to see if this is a conditional branch...
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if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
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if (BI->isConditional()) {
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// Make sure that the block is either empty, or only contains a setcc.
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if (BB->size() == 1 ||
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(BB->size() == 2 && &BB->front() == BI->getCondition() &&
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BI->getCondition()->use_size() == 1))
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if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition())) {
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Relation::KnownResult Result = getSetCCResult(SCI, RI);
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if (Result == Relation::KnownTrue)
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return BI->getSuccessor(0);
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else if (Result == Relation::KnownFalse)
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return BI->getSuccessor(1);
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}
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}
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return 0;
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}
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// BuildRankMap - This method builds the rank map data structure which gives
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// each instruction/value in the function a value based on how early it appears
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// in the function. We give constants and globals rank 0, arguments are
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// numbered starting at one, and instructions are numbered in reverse post-order
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// from where the arguments leave off. This gives instructions in loops higher
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// values than instructions not in loops.
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//
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void CEE::BuildRankMap(Function &F) {
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unsigned Rank = 1; // Skip rank zero.
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// Number the arguments...
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for (Function::aiterator I = F.abegin(), E = F.aend(); I != E; ++I)
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RankMap[I] = Rank++;
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// Number the instructions in reverse post order...
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ReversePostOrderTraversal<Function*> RPOT(&F);
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for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
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E = RPOT.end(); I != E; ++I)
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for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
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BBI != E; ++BBI)
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if (BBI->getType() != Type::VoidTy)
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RankMap[BBI] = Rank++;
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}
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// PropogateBranchInfo - When this method is invoked, we need to propogate
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// information derived from the branch condition into the true and false
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// branches of BI. Since we know that there aren't any critical edges in the
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// flow graph, this can proceed unconditionally.
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//
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void CEE::PropogateBranchInfo(BranchInst *BI) {
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assert(BI->isConditional() && "Must be a conditional branch!");
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BasicBlock *BB = BI->getParent();
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BasicBlock *TrueBB = BI->getSuccessor(0);
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BasicBlock *FalseBB = BI->getSuccessor(1);
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// Propogate information into the true block...
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//
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PropogateEquality(BI->getCondition(), ConstantBool::True,
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getRegionInfo(TrueBB));
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// Propogate information into the false block...
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//
|
||||
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); }
|
||||
Loading…
Reference in New Issue
Block a user