-//===- SCCP.cpp - Sparse Conditional Constant Propogation -----------------===//
+//===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
//
-// This file implements sparse conditional constant propogation and merging:
+// The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements sparse conditional constant propagation and merging:
//
// Specifically, this:
// * Assumes values are constant unless proven otherwise
// * Assumes BasicBlocks are dead unless proven otherwise
// * Proves values to be constant, and replaces them with constants
-// . Proves conditional branches constant, and unconditionalizes them
-// * Folds multiple identical constants in the constant pool together
+// * Proves conditional branches to be unconditional
//
// Notice that:
// * This pass has a habit of making definitions be dead. It is a good idea
//
//===----------------------------------------------------------------------===//
-#include "llvm/Transforms/Scalar/ConstantProp.h"
-#include "llvm/ConstantHandling.h"
-#include "llvm/Function.h"
-#include "llvm/BasicBlock.h"
-#include "llvm/ConstantVals.h"
-#include "llvm/iPHINode.h"
-#include "llvm/iMemory.h"
-#include "llvm/iTerminators.h"
-#include "llvm/iOther.h"
+#define DEBUG_TYPE "sccp"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/IPO.h"
+#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Instructions.h"
#include "llvm/Pass.h"
-#include "Support/STLExtras.h"
+#include "llvm/Support/InstVisitor.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Support/CallSite.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/ADT/hash_map"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/STLExtras.h"
#include <algorithm>
-#include <map>
#include <set>
-#include <iostream>
-using std::cerr;
+using namespace llvm;
-// InstVal class - This class represents the different lattice values that an
-// instruction may occupy. It is a simple class with value semantics. The
-// potential constant value that is pointed to is owned by the constant pool
-// for the method being optimized.
+// LatticeVal class - This class represents the different lattice values that an
+// instruction may occupy. It is a simple class with value semantics.
//
-class InstVal {
- enum {
+namespace {
+
+class LatticeVal {
+ enum {
undefined, // This instruction has no known value
constant, // This instruction has a constant value
- // Range, // This instruction is known to fall within a range
overdefined // This instruction has an unknown value
} LatticeValue; // The current lattice position
Constant *ConstantVal; // If Constant value, the current value
public:
- inline InstVal() : LatticeValue(undefined), ConstantVal(0) {}
+ inline LatticeVal() : LatticeValue(undefined), ConstantVal(0) {}
// markOverdefined - Return true if this is a new status to be in...
inline bool markOverdefined() {
inline bool isConstant() const { return LatticeValue == constant; }
inline bool isOverdefined() const { return LatticeValue == overdefined; }
- inline Constant *getConstant() const { return ConstantVal; }
+ inline Constant *getConstant() const {
+ assert(isConstant() && "Cannot get the constant of a non-constant!");
+ return ConstantVal;
+ }
};
+} // end anonymous namespace
//===----------------------------------------------------------------------===//
-// SCCP Class
-//
-// This class does all of the work of Sparse Conditional Constant Propogation.
-// It's public interface consists of a constructor and a doSCCP() method.
//
-class SCCP {
- Function *M; // The function that we are working on
-
+/// SCCPSolver - This class is a general purpose solver for Sparse Conditional
+/// Constant Propagation.
+///
+class SCCPSolver : public InstVisitor<SCCPSolver> {
std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
- std::map<Value*, InstVal> ValueState; // The state each value is in...
+ hash_map<Value*, LatticeVal> ValueState; // The state each value is in...
+
+ /// GlobalValue - If we are tracking any values for the contents of a global
+ /// variable, we keep a mapping from the constant accessor to the element of
+ /// the global, to the currently known value. If the value becomes
+ /// overdefined, it's entry is simply removed from this map.
+ hash_map<GlobalVariable*, LatticeVal> TrackedGlobals;
+
+ /// TrackedFunctionRetVals - If we are tracking arguments into and the return
+ /// value out of a function, it will have an entry in this map, indicating
+ /// what the known return value for the function is.
+ hash_map<Function*, LatticeVal> TrackedFunctionRetVals;
+
+ // The reason for two worklists is that overdefined is the lowest state
+ // on the lattice, and moving things to overdefined as fast as possible
+ // makes SCCP converge much faster.
+ // By having a separate worklist, we accomplish this because everything
+ // possibly overdefined will become overdefined at the soonest possible
+ // point.
+ std::vector<Value*> OverdefinedInstWorkList;
+ std::vector<Value*> InstWorkList;
+
- std::vector<Instruction*> InstWorkList;// The instruction work list
std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
- //===--------------------------------------------------------------------===//
- // The public interface for this class
- //
+ /// UsersOfOverdefinedPHIs - Keep track of any users of PHI nodes that are not
+ /// overdefined, despite the fact that the PHI node is overdefined.
+ std::multimap<PHINode*, Instruction*> UsersOfOverdefinedPHIs;
+
+ /// KnownFeasibleEdges - Entries in this set are edges which have already had
+ /// PHI nodes retriggered.
+ typedef std::pair<BasicBlock*,BasicBlock*> Edge;
+ std::set<Edge> KnownFeasibleEdges;
public:
- // SCCP Ctor - Save the method to operate on...
- inline SCCP(Function *f) : M(f) {}
+ /// MarkBlockExecutable - This method can be used by clients to mark all of
+ /// the blocks that are known to be intrinsically live in the processed unit.
+ void MarkBlockExecutable(BasicBlock *BB) {
+ DEBUG(std::cerr << "Marking Block Executable: " << BB->getName() << "\n");
+ BBExecutable.insert(BB); // Basic block is executable!
+ BBWorkList.push_back(BB); // Add the block to the work list!
+ }
- // doSCCP() - Run the Sparse Conditional Constant Propogation algorithm, and
- // return true if the method was modified.
- bool doSCCP();
+ /// TrackValueOfGlobalVariable - Clients can use this method to
+ /// inform the SCCPSolver that it should track loads and stores to the
+ /// specified global variable if it can. This is only legal to call if
+ /// performing Interprocedural SCCP.
+ void TrackValueOfGlobalVariable(GlobalVariable *GV) {
+ const Type *ElTy = GV->getType()->getElementType();
+ if (ElTy->isFirstClassType()) {
+ LatticeVal &IV = TrackedGlobals[GV];
+ if (!isa<UndefValue>(GV->getInitializer()))
+ IV.markConstant(GV->getInitializer());
+ }
+ }
- //===--------------------------------------------------------------------===//
- // The implementation of this class
- //
-private:
+ /// AddTrackedFunction - If the SCCP solver is supposed to track calls into
+ /// and out of the specified function (which cannot have its address taken),
+ /// this method must be called.
+ void AddTrackedFunction(Function *F) {
+ assert(F->hasInternalLinkage() && "Can only track internal functions!");
+ // Add an entry, F -> undef.
+ TrackedFunctionRetVals[F];
+ }
+
+ /// Solve - Solve for constants and executable blocks.
+ ///
+ void Solve();
+
+ /// ResolveBranchesIn - While solving the dataflow for a function, we assume
+ /// that branches on undef values cannot reach any of their successors.
+ /// However, this is not a safe assumption. After we solve dataflow, this
+ /// method should be use to handle this. If this returns true, the solver
+ /// should be rerun.
+ bool ResolveBranchesIn(Function &F);
+
+ /// getExecutableBlocks - Once we have solved for constants, return the set of
+ /// blocks that is known to be executable.
+ std::set<BasicBlock*> &getExecutableBlocks() {
+ return BBExecutable;
+ }
+
+ /// getValueMapping - Once we have solved for constants, return the mapping of
+ /// LLVM values to LatticeVals.
+ hash_map<Value*, LatticeVal> &getValueMapping() {
+ return ValueState;
+ }
+
+ /// getTrackedFunctionRetVals - Get the inferred return value map.
+ ///
+ const hash_map<Function*, LatticeVal> &getTrackedFunctionRetVals() {
+ return TrackedFunctionRetVals;
+ }
- // markValueOverdefined - Make a value be marked as "constant". If the value
- // is not already a constant, add it to the instruction work list so that
+ /// getTrackedGlobals - Get and return the set of inferred initializers for
+ /// global variables.
+ const hash_map<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
+ return TrackedGlobals;
+ }
+
+
+private:
+ // markConstant - Make a value be marked as "constant". If the value
+ // is not already a constant, add it to the instruction work list so that
// the users of the instruction are updated later.
//
- inline bool markConstant(Instruction *I, Constant *V) {
- //cerr << "markConstant: " << V << " = " << I;
- if (ValueState[I].markConstant(V)) {
- InstWorkList.push_back(I);
- return true;
+ inline void markConstant(LatticeVal &IV, Value *V, Constant *C) {
+ if (IV.markConstant(C)) {
+ DEBUG(std::cerr << "markConstant: " << *C << ": " << *V);
+ InstWorkList.push_back(V);
}
- return false;
+ }
+ inline void markConstant(Value *V, Constant *C) {
+ markConstant(ValueState[V], V, C);
}
- // markValueOverdefined - Make a value be marked as "overdefined". If the
- // value is not already overdefined, add it to the instruction work list so
- // that the users of the instruction are updated later.
- //
- inline bool markOverdefined(Value *V) {
- if (ValueState[V].markOverdefined()) {
- if (Instruction *I = dyn_cast<Instruction>(V)) {
- //cerr << "markOverdefined: " << V;
- InstWorkList.push_back(I); // Only instructions go on the work list
- }
- return true;
+ // markOverdefined - Make a value be marked as "overdefined". If the
+ // value is not already overdefined, add it to the overdefined instruction
+ // work list so that the users of the instruction are updated later.
+
+ inline void markOverdefined(LatticeVal &IV, Value *V) {
+ if (IV.markOverdefined()) {
+ DEBUG(std::cerr << "markOverdefined: ";
+ if (Function *F = dyn_cast<Function>(V))
+ std::cerr << "Function '" << F->getName() << "'\n";
+ else
+ std::cerr << *V);
+ // Only instructions go on the work list
+ OverdefinedInstWorkList.push_back(V);
}
- return false;
+ }
+ inline void markOverdefined(Value *V) {
+ markOverdefined(ValueState[V], V);
+ }
+
+ inline void mergeInValue(LatticeVal &IV, Value *V, LatticeVal &MergeWithV) {
+ if (IV.isOverdefined() || MergeWithV.isUndefined())
+ return; // Noop.
+ if (MergeWithV.isOverdefined())
+ markOverdefined(IV, V);
+ else if (IV.isUndefined())
+ markConstant(IV, V, MergeWithV.getConstant());
+ else if (IV.getConstant() != MergeWithV.getConstant())
+ markOverdefined(IV, V);
}
- // getValueState - Return the InstVal object that corresponds to the value.
- // This function is neccesary because not all values should start out in the
+ // getValueState - Return the LatticeVal object that corresponds to the value.
+ // This function is necessary because not all values should start out in the
// underdefined state... Argument's should be overdefined, and
// constants should be marked as constants. If a value is not known to be an
// Instruction object, then use this accessor to get its value from the map.
//
- inline InstVal &getValueState(Value *V) {
- std::map<Value*, InstVal>::iterator I = ValueState.find(V);
+ inline LatticeVal &getValueState(Value *V) {
+ hash_map<Value*, LatticeVal>::iterator I = ValueState.find(V);
if (I != ValueState.end()) return I->second; // Common case, in the map
-
- if (Constant *CPV = dyn_cast<Constant>(V)) { // Constants are constant
- ValueState[CPV].markConstant(CPV);
- } else if (isa<Argument>(V)) { // Arguments are overdefined
- ValueState[V].markOverdefined();
- }
+
+ if (Constant *CPV = dyn_cast<Constant>(V)) {
+ if (isa<UndefValue>(V)) {
+ // Nothing to do, remain undefined.
+ } else {
+ ValueState[CPV].markConstant(CPV); // Constants are constant
+ }
+ }
// All others are underdefined by default...
return ValueState[V];
}
- // markExecutable - Mark a basic block as executable, adding it to the BB
+ // markEdgeExecutable - Mark a basic block as executable, adding it to the BB
// work list if it is not already executable...
- //
- void markExecutable(BasicBlock *BB) {
- if (BBExecutable.count(BB)) return;
- //cerr << "Marking BB Executable: " << BB;
- BBExecutable.insert(BB); // Basic block is executable!
- BBWorkList.push_back(BB); // Add the block to the work list!
+ //
+ void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
+ if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
+ return; // This edge is already known to be executable!
+
+ if (BBExecutable.count(Dest)) {
+ DEBUG(std::cerr << "Marking Edge Executable: " << Source->getName()
+ << " -> " << Dest->getName() << "\n");
+
+ // The destination is already executable, but we just made an edge
+ // feasible that wasn't before. Revisit the PHI nodes in the block
+ // because they have potentially new operands.
+ for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
+ visitPHINode(*cast<PHINode>(I));
+
+ } else {
+ MarkBlockExecutable(Dest);
+ }
}
+ // getFeasibleSuccessors - Return a vector of booleans to indicate which
+ // successors are reachable from a given terminator instruction.
+ //
+ void getFeasibleSuccessors(TerminatorInst &TI, std::vector<bool> &Succs);
- // UpdateInstruction - Something changed in this instruction... Either an
- // operand made a transition, or the instruction is newly executable. Change
- // the value type of I to reflect these changes if appropriate.
+ // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
+ // block to the 'To' basic block is currently feasible...
//
- void UpdateInstruction(Instruction *I);
+ bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
// OperandChangedState - This method is invoked on all of the users of an
// instruction that was just changed state somehow.... Based on this
// information, we need to update the specified user of this instruction.
//
- void OperandChangedState(User *U);
-};
-
+ void OperandChangedState(User *U) {
+ // Only instructions use other variable values!
+ Instruction &I = cast<Instruction>(*U);
+ if (BBExecutable.count(I.getParent())) // Inst is executable?
+ visit(I);
+ }
-//===----------------------------------------------------------------------===//
-// SCCP Class Implementation
+private:
+ friend class InstVisitor<SCCPSolver>;
+ // visit implementations - Something changed in this instruction... Either an
+ // operand made a transition, or the instruction is newly executable. Change
+ // the value type of I to reflect these changes if appropriate.
+ //
+ void visitPHINode(PHINode &I);
+
+ // Terminators
+ void visitReturnInst(ReturnInst &I);
+ void visitTerminatorInst(TerminatorInst &TI);
+
+ void visitCastInst(CastInst &I);
+ void visitSelectInst(SelectInst &I);
+ void visitBinaryOperator(Instruction &I);
+ void visitShiftInst(ShiftInst &I) { visitBinaryOperator(I); }
+
+ // Instructions that cannot be folded away...
+ void visitStoreInst (Instruction &I);
+ void visitLoadInst (LoadInst &I);
+ void visitGetElementPtrInst(GetElementPtrInst &I);
+ void visitCallInst (CallInst &I) { visitCallSite(CallSite::get(&I)); }
+ void visitInvokeInst (InvokeInst &II) {
+ visitCallSite(CallSite::get(&II));
+ visitTerminatorInst(II);
+ }
+ void visitCallSite (CallSite CS);
+ void visitUnwindInst (TerminatorInst &I) { /*returns void*/ }
+ void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
+ void visitAllocationInst(Instruction &I) { markOverdefined(&I); }
+ void visitVANextInst (Instruction &I) { markOverdefined(&I); }
+ void visitVAArgInst (Instruction &I) { markOverdefined(&I); }
+ void visitFreeInst (Instruction &I) { /*returns void*/ }
+
+ void visitInstruction(Instruction &I) {
+ // If a new instruction is added to LLVM that we don't handle...
+ std::cerr << "SCCP: Don't know how to handle: " << I;
+ markOverdefined(&I); // Just in case
+ }
+};
-// doSCCP() - Run the Sparse Conditional Constant Propogation algorithm, and
-// return true if the method was modified.
+// getFeasibleSuccessors - Return a vector of booleans to indicate which
+// successors are reachable from a given terminator instruction.
//
-bool SCCP::doSCCP() {
- // Mark the first block of the method as being executable...
- markExecutable(M->front());
-
- // Process the work lists until their are empty!
- while (!BBWorkList.empty() || !InstWorkList.empty()) {
- // Process the instruction work list...
- while (!InstWorkList.empty()) {
- Instruction *I = InstWorkList.back();
- InstWorkList.pop_back();
-
- //cerr << "\nPopped off I-WL: " << I;
-
-
- // "I" got into the work list because it either made the transition from
- // bottom to constant, or to Overdefined.
- //
- // Update all of the users of this instruction's value...
- //
- for_each(I->use_begin(), I->use_end(),
- bind_obj(this, &SCCP::OperandChangedState));
+void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
+ std::vector<bool> &Succs) {
+ Succs.resize(TI.getNumSuccessors());
+ if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
+ if (BI->isUnconditional()) {
+ Succs[0] = true;
+ } else {
+ LatticeVal &BCValue = getValueState(BI->getCondition());
+ if (BCValue.isOverdefined() ||
+ (BCValue.isConstant() && !isa<ConstantBool>(BCValue.getConstant()))) {
+ // Overdefined condition variables, and branches on unfoldable constant
+ // conditions, mean the branch could go either way.
+ Succs[0] = Succs[1] = true;
+ } else if (BCValue.isConstant()) {
+ // Constant condition variables mean the branch can only go a single way
+ Succs[BCValue.getConstant() == ConstantBool::False] = true;
+ }
}
+ } else if (InvokeInst *II = dyn_cast<InvokeInst>(&TI)) {
+ // Invoke instructions successors are always executable.
+ Succs[0] = Succs[1] = true;
+ } else if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
+ LatticeVal &SCValue = getValueState(SI->getCondition());
+ if (SCValue.isOverdefined() || // Overdefined condition?
+ (SCValue.isConstant() && !isa<ConstantInt>(SCValue.getConstant()))) {
+ // All destinations are executable!
+ Succs.assign(TI.getNumSuccessors(), true);
+ } else if (SCValue.isConstant()) {
+ Constant *CPV = SCValue.getConstant();
+ // Make sure to skip the "default value" which isn't a value
+ for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i) {
+ if (SI->getSuccessorValue(i) == CPV) {// Found the right branch...
+ Succs[i] = true;
+ return;
+ }
+ }
- // Process the basic block work list...
- while (!BBWorkList.empty()) {
- BasicBlock *BB = BBWorkList.back();
- BBWorkList.pop_back();
-
- //cerr << "\nPopped off BBWL: " << BB;
-
- // If this block only has a single successor, mark it as executable as
- // well... if not, terminate the do loop.
- //
- if (BB->getTerminator()->getNumSuccessors() == 1)
- markExecutable(BB->getTerminator()->getSuccessor(0));
-
- // Loop over all of the instructions and notify them that they are newly
- // executable...
- for_each(BB->begin(), BB->end(),
- bind_obj(this, &SCCP::UpdateInstruction));
+ // Constant value not equal to any of the branches... must execute
+ // default branch then...
+ Succs[0] = true;
}
+ } else {
+ std::cerr << "SCCP: Don't know how to handle: " << TI;
+ Succs.assign(TI.getNumSuccessors(), true);
}
+}
-#if 0
- for (Function::iterator BBI = M->begin(), BBEnd = M->end();
- BBI != BBEnd; ++BBI)
- if (!BBExecutable.count(*BBI))
- cerr << "BasicBlock Dead:" << *BBI;
-#endif
-
-
- // Iterate over all of the instructions in a method, replacing them with
- // constants if we have found them to be of constant values.
- //
- bool MadeChanges = false;
- for (Function::iterator MI = M->begin(), ME = M->end(); MI != ME; ++MI) {
- BasicBlock *BB = *MI;
- for (BasicBlock::iterator BI = BB->begin(); BI != BB->end();) {
- Instruction *Inst = *BI;
- InstVal &IV = ValueState[Inst];
- if (IV.isConstant()) {
- Constant *Const = IV.getConstant();
- // cerr << "Constant: " << Inst << " is: " << Const;
-
- // Replaces all of the uses of a variable with uses of the constant.
- Inst->replaceAllUsesWith(Const);
-
- // Remove the operator from the list of definitions...
- BB->getInstList().remove(BI);
- // The new constant inherits the old name of the operator...
- if (Inst->hasName() && !Const->hasName())
- Const->setName(Inst->getName(), M->getSymbolTableSure());
+// isEdgeFeasible - Return true if the control flow edge from the 'From' basic
+// block to the 'To' basic block is currently feasible...
+//
+bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
+ assert(BBExecutable.count(To) && "Dest should always be alive!");
- // Delete the operator now...
- delete Inst;
+ // Make sure the source basic block is executable!!
+ if (!BBExecutable.count(From)) return false;
- // Hey, we just changed something!
- MadeChanges = true;
- } else if (TerminatorInst *TI = dyn_cast<TerminatorInst>(Inst)) {
- MadeChanges |= ConstantFoldTerminator(BB, BI, TI);
+ // Check to make sure this edge itself is actually feasible now...
+ TerminatorInst *TI = From->getTerminator();
+ if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
+ if (BI->isUnconditional())
+ return true;
+ else {
+ LatticeVal &BCValue = getValueState(BI->getCondition());
+ if (BCValue.isOverdefined()) {
+ // Overdefined condition variables mean the branch could go either way.
+ return true;
+ } else if (BCValue.isConstant()) {
+ // Not branching on an evaluatable constant?
+ if (!isa<ConstantBool>(BCValue.getConstant())) return true;
+
+ // Constant condition variables mean the branch can only go a single way
+ return BI->getSuccessor(BCValue.getConstant() ==
+ ConstantBool::False) == To;
}
+ return false;
+ }
+ } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
+ // Invoke instructions successors are always executable.
+ return true;
+ } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
+ LatticeVal &SCValue = getValueState(SI->getCondition());
+ if (SCValue.isOverdefined()) { // Overdefined condition?
+ // All destinations are executable!
+ return true;
+ } else if (SCValue.isConstant()) {
+ Constant *CPV = SCValue.getConstant();
+ if (!isa<ConstantInt>(CPV))
+ return true; // not a foldable constant?
+
+ // Make sure to skip the "default value" which isn't a value
+ for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i)
+ if (SI->getSuccessorValue(i) == CPV) // Found the taken branch...
+ return SI->getSuccessor(i) == To;
- ++BI;
+ // Constant value not equal to any of the branches... must execute
+ // default branch then...
+ return SI->getDefaultDest() == To;
}
+ return false;
+ } else {
+ std::cerr << "Unknown terminator instruction: " << *TI;
+ abort();
}
-
- // Merge identical constants last: this is important because we may have just
- // introduced constants that already exist, and we don't want to pollute later
- // stages with extraneous constants.
- //
- return MadeChanges;
}
-
-// UpdateInstruction - Something changed in this instruction... Either an
+// visit Implementations - Something changed in this instruction... Either an
// operand made a transition, or the instruction is newly executable. Change
// the value type of I to reflect these changes if appropriate. This method
// makes sure to do the following actions:
// 7. If a conditional branch has a value that is overdefined, make all
// successors executable.
//
-void SCCP::UpdateInstruction(Instruction *I) {
- InstVal &IValue = ValueState[I];
- if (IValue.isOverdefined())
- return; // If already overdefined, we aren't going to effect anything
-
- switch (I->getOpcode()) {
- //===-----------------------------------------------------------------===//
- // Handle PHI nodes...
- //
- case Instruction::PHINode: {
- PHINode *PN = cast<PHINode>(I);
- unsigned NumValues = PN->getNumIncomingValues(), i;
- InstVal *OperandIV = 0;
-
- // Look at all of the executable operands of the PHI node. If any of them
- // are overdefined, the PHI becomes overdefined as well. If they are all
- // constant, and they agree with each other, the PHI becomes the identical
- // constant. If they are constant and don't agree, the PHI is overdefined.
- // If there are no executable operands, the PHI remains undefined.
- //
- for (i = 0; i < NumValues; ++i) {
- if (BBExecutable.count(PN->getIncomingBlock(i))) {
- InstVal &IV = getValueState(PN->getIncomingValue(i));
- if (IV.isUndefined()) continue; // Doesn't influence PHI node.
- if (IV.isOverdefined()) { // PHI node becomes overdefined!
- markOverdefined(PN);
- return;
+void SCCPSolver::visitPHINode(PHINode &PN) {
+ LatticeVal &PNIV = getValueState(&PN);
+ if (PNIV.isOverdefined()) {
+ // There may be instructions using this PHI node that are not overdefined
+ // themselves. If so, make sure that they know that the PHI node operand
+ // changed.
+ std::multimap<PHINode*, Instruction*>::iterator I, E;
+ tie(I, E) = UsersOfOverdefinedPHIs.equal_range(&PN);
+ if (I != E) {
+ std::vector<Instruction*> Users;
+ Users.reserve(std::distance(I, E));
+ for (; I != E; ++I) Users.push_back(I->second);
+ while (!Users.empty()) {
+ visit(Users.back());
+ Users.pop_back();
+ }
+ }
+ return; // Quick exit
+ }
+
+ // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
+ // and slow us down a lot. Just mark them overdefined.
+ if (PN.getNumIncomingValues() > 64) {
+ markOverdefined(PNIV, &PN);
+ return;
+ }
+
+ // Look at all of the executable operands of the PHI node. If any of them
+ // are overdefined, the PHI becomes overdefined as well. If they are all
+ // constant, and they agree with each other, the PHI becomes the identical
+ // constant. If they are constant and don't agree, the PHI is overdefined.
+ // If there are no executable operands, the PHI remains undefined.
+ //
+ Constant *OperandVal = 0;
+ for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
+ LatticeVal &IV = getValueState(PN.getIncomingValue(i));
+ if (IV.isUndefined()) continue; // Doesn't influence PHI node.
+
+ if (isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent())) {
+ if (IV.isOverdefined()) { // PHI node becomes overdefined!
+ markOverdefined(PNIV, &PN);
+ return;
+ }
+
+ if (OperandVal == 0) { // Grab the first value...
+ OperandVal = IV.getConstant();
+ } else { // Another value is being merged in!
+ // There is already a reachable operand. If we conflict with it,
+ // then the PHI node becomes overdefined. If we agree with it, we
+ // can continue on.
+
+ // Check to see if there are two different constants merging...
+ if (IV.getConstant() != OperandVal) {
+ // Yes there is. This means the PHI node is not constant.
+ // You must be overdefined poor PHI.
+ //
+ markOverdefined(PNIV, &PN); // The PHI node now becomes overdefined
+ return; // I'm done analyzing you
}
+ }
+ }
+ }
- if (OperandIV == 0) { // Grab the first value...
- OperandIV = &IV;
- } else { // Another value is being merged in!
- // There is already a reachable operand. If we conflict with it,
- // then the PHI node becomes overdefined. If we agree with it, we
- // can continue on.
-
- // Check to see if there are two different constants merging...
- if (IV.getConstant() != OperandIV->getConstant()) {
- // Yes there is. This means the PHI node is not constant.
- // You must be overdefined poor PHI.
- //
- markOverdefined(I); // The PHI node now becomes overdefined
- return; // I'm done analyzing you
+ // If we exited the loop, this means that the PHI node only has constant
+ // arguments that agree with each other(and OperandVal is the constant) or
+ // OperandVal is null because there are no defined incoming arguments. If
+ // this is the case, the PHI remains undefined.
+ //
+ if (OperandVal)
+ markConstant(PNIV, &PN, OperandVal); // Acquire operand value
+}
+
+void SCCPSolver::visitReturnInst(ReturnInst &I) {
+ if (I.getNumOperands() == 0) return; // Ret void
+
+ // If we are tracking the return value of this function, merge it in.
+ Function *F = I.getParent()->getParent();
+ if (F->hasInternalLinkage() && !TrackedFunctionRetVals.empty()) {
+ hash_map<Function*, LatticeVal>::iterator TFRVI =
+ TrackedFunctionRetVals.find(F);
+ if (TFRVI != TrackedFunctionRetVals.end() &&
+ !TFRVI->second.isOverdefined()) {
+ LatticeVal &IV = getValueState(I.getOperand(0));
+ mergeInValue(TFRVI->second, F, IV);
+ }
+ }
+}
+
+
+void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
+ std::vector<bool> SuccFeasible;
+ getFeasibleSuccessors(TI, SuccFeasible);
+
+ BasicBlock *BB = TI.getParent();
+
+ // Mark all feasible successors executable...
+ for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
+ if (SuccFeasible[i])
+ markEdgeExecutable(BB, TI.getSuccessor(i));
+}
+
+void SCCPSolver::visitCastInst(CastInst &I) {
+ Value *V = I.getOperand(0);
+ LatticeVal &VState = getValueState(V);
+ if (VState.isOverdefined()) // Inherit overdefinedness of operand
+ markOverdefined(&I);
+ else if (VState.isConstant()) // Propagate constant value
+ markConstant(&I, ConstantExpr::getCast(VState.getConstant(), I.getType()));
+}
+
+void SCCPSolver::visitSelectInst(SelectInst &I) {
+ LatticeVal &CondValue = getValueState(I.getCondition());
+ if (CondValue.isOverdefined())
+ markOverdefined(&I);
+ else if (CondValue.isConstant()) {
+ if (CondValue.getConstant() == ConstantBool::True) {
+ LatticeVal &Val = getValueState(I.getTrueValue());
+ if (Val.isOverdefined())
+ markOverdefined(&I);
+ else if (Val.isConstant())
+ markConstant(&I, Val.getConstant());
+ } else if (CondValue.getConstant() == ConstantBool::False) {
+ LatticeVal &Val = getValueState(I.getFalseValue());
+ if (Val.isOverdefined())
+ markOverdefined(&I);
+ else if (Val.isConstant())
+ markConstant(&I, Val.getConstant());
+ } else
+ markOverdefined(&I);
+ }
+}
+
+// Handle BinaryOperators and Shift Instructions...
+void SCCPSolver::visitBinaryOperator(Instruction &I) {
+ LatticeVal &IV = ValueState[&I];
+ if (IV.isOverdefined()) return;
+
+ LatticeVal &V1State = getValueState(I.getOperand(0));
+ LatticeVal &V2State = getValueState(I.getOperand(1));
+
+ if (V1State.isOverdefined() || V2State.isOverdefined()) {
+ // If this is an AND or OR with 0 or -1, it doesn't matter that the other
+ // operand is overdefined.
+ if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
+ LatticeVal *NonOverdefVal = 0;
+ if (!V1State.isOverdefined()) {
+ NonOverdefVal = &V1State;
+ } else if (!V2State.isOverdefined()) {
+ NonOverdefVal = &V2State;
+ }
+
+ if (NonOverdefVal) {
+ if (NonOverdefVal->isUndefined()) {
+ // Could annihilate value.
+ if (I.getOpcode() == Instruction::And)
+ markConstant(IV, &I, Constant::getNullValue(I.getType()));
+ else
+ markConstant(IV, &I, ConstantInt::getAllOnesValue(I.getType()));
+ return;
+ } else {
+ if (I.getOpcode() == Instruction::And) {
+ if (NonOverdefVal->getConstant()->isNullValue()) {
+ markConstant(IV, &I, NonOverdefVal->getConstant());
+ return; // X or 0 = -1
+ }
+ } else {
+ if (ConstantIntegral *CI =
+ dyn_cast<ConstantIntegral>(NonOverdefVal->getConstant()))
+ if (CI->isAllOnesValue()) {
+ markConstant(IV, &I, NonOverdefVal->getConstant());
+ return; // X or -1 = -1
+ }
}
}
}
}
- // If we exited the loop, this means that the PHI node only has constant
- // arguments that agree with each other(and OperandIV is a pointer to one
- // of their InstVal's) or OperandIV is null because there are no defined
- // incoming arguments. If this is the case, the PHI remains undefined.
- //
- if (OperandIV) {
- assert(OperandIV->isConstant() && "Should only be here for constants!");
- markConstant(I, OperandIV->getConstant()); // Aquire operand value
+
+ // If both operands are PHI nodes, it is possible that this instruction has
+ // a constant value, despite the fact that the PHI node doesn't. Check for
+ // this condition now.
+ if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
+ if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
+ if (PN1->getParent() == PN2->getParent()) {
+ // Since the two PHI nodes are in the same basic block, they must have
+ // entries for the same predecessors. Walk the predecessor list, and
+ // if all of the incoming values are constants, and the result of
+ // evaluating this expression with all incoming value pairs is the
+ // same, then this expression is a constant even though the PHI node
+ // is not a constant!
+ LatticeVal Result;
+ for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
+ LatticeVal &In1 = getValueState(PN1->getIncomingValue(i));
+ BasicBlock *InBlock = PN1->getIncomingBlock(i);
+ LatticeVal &In2 =
+ getValueState(PN2->getIncomingValueForBlock(InBlock));
+
+ if (In1.isOverdefined() || In2.isOverdefined()) {
+ Result.markOverdefined();
+ break; // Cannot fold this operation over the PHI nodes!
+ } else if (In1.isConstant() && In2.isConstant()) {
+ Constant *V = ConstantExpr::get(I.getOpcode(), In1.getConstant(),
+ In2.getConstant());
+ if (Result.isUndefined())
+ Result.markConstant(V);
+ else if (Result.isConstant() && Result.getConstant() != V) {
+ Result.markOverdefined();
+ break;
+ }
+ }
+ }
+
+ // If we found a constant value here, then we know the instruction is
+ // constant despite the fact that the PHI nodes are overdefined.
+ if (Result.isConstant()) {
+ markConstant(IV, &I, Result.getConstant());
+ // Remember that this instruction is virtually using the PHI node
+ // operands.
+ UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
+ UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
+ return;
+ } else if (Result.isUndefined()) {
+ return;
+ }
+
+ // Okay, this really is overdefined now. Since we might have
+ // speculatively thought that this was not overdefined before, and
+ // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
+ // make sure to clean out any entries that we put there, for
+ // efficiency.
+ std::multimap<PHINode*, Instruction*>::iterator It, E;
+ tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
+ while (It != E) {
+ if (It->second == &I) {
+ UsersOfOverdefinedPHIs.erase(It++);
+ } else
+ ++It;
+ }
+ tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
+ while (It != E) {
+ if (It->second == &I) {
+ UsersOfOverdefinedPHIs.erase(It++);
+ } else
+ ++It;
+ }
+ }
+
+ markOverdefined(IV, &I);
+ } else if (V1State.isConstant() && V2State.isConstant()) {
+ markConstant(IV, &I, ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
+ V2State.getConstant()));
+ }
+}
+
+// Handle getelementptr instructions... if all operands are constants then we
+// can turn this into a getelementptr ConstantExpr.
+//
+void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
+ LatticeVal &IV = ValueState[&I];
+ if (IV.isOverdefined()) return;
+
+ std::vector<Constant*> Operands;
+ Operands.reserve(I.getNumOperands());
+
+ for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
+ LatticeVal &State = getValueState(I.getOperand(i));
+ if (State.isUndefined())
+ return; // Operands are not resolved yet...
+ else if (State.isOverdefined()) {
+ markOverdefined(IV, &I);
+ return;
}
- return;
+ assert(State.isConstant() && "Unknown state!");
+ Operands.push_back(State.getConstant());
}
- //===-----------------------------------------------------------------===//
- // Handle instructions that unconditionally provide overdefined values...
- //
- case Instruction::Malloc:
- case Instruction::Free:
- case Instruction::Alloca:
- case Instruction::Load:
- case Instruction::Store:
- // TODO: getfield
- case Instruction::Call:
- case Instruction::Invoke:
- markOverdefined(I); // Memory and call's are all overdefined
+ Constant *Ptr = Operands[0];
+ Operands.erase(Operands.begin()); // Erase the pointer from idx list...
+
+ markConstant(IV, &I, ConstantExpr::getGetElementPtr(Ptr, Operands));
+}
+
+/// GetGEPGlobalInitializer - Given a constant and a getelementptr constantexpr,
+/// return the constant value being addressed by the constant expression, or
+/// null if something is funny.
+///
+static Constant *GetGEPGlobalInitializer(Constant *C, ConstantExpr *CE) {
+ if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType()))
+ return 0; // Do not allow stepping over the value!
+
+ // Loop over all of the operands, tracking down which value we are
+ // addressing...
+ for (unsigned i = 2, e = CE->getNumOperands(); i != e; ++i)
+ if (ConstantUInt *CU = dyn_cast<ConstantUInt>(CE->getOperand(i))) {
+ ConstantStruct *CS = dyn_cast<ConstantStruct>(C);
+ if (CS == 0) return 0;
+ if (CU->getValue() >= CS->getNumOperands()) return 0;
+ C = CS->getOperand((unsigned)CU->getValue());
+ } else if (ConstantSInt *CS = dyn_cast<ConstantSInt>(CE->getOperand(i))) {
+ ConstantArray *CA = dyn_cast<ConstantArray>(C);
+ if (CA == 0) return 0;
+ if ((uint64_t)CS->getValue() >= CA->getNumOperands()) return 0;
+ C = CA->getOperand((unsigned)CS->getValue());
+ } else
+ return 0;
+ return C;
+}
+
+void SCCPSolver::visitStoreInst(Instruction &SI) {
+ if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
return;
+ GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
+ hash_map<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
+ if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
- //===-----------------------------------------------------------------===//
- // Handle Terminator instructions...
- //
- case Instruction::Ret: return; // Function return doesn't affect anything
- case Instruction::Br: { // Handle conditional branches...
- BranchInst *BI = cast<BranchInst>(I);
- if (BI->isUnconditional())
- return; // Unconditional branches are already handled!
-
- InstVal &BCValue = getValueState(BI->getCondition());
- if (BCValue.isOverdefined()) {
- // Overdefined condition variables mean the branch could go either way.
- markExecutable(BI->getSuccessor(0));
- markExecutable(BI->getSuccessor(1));
- } else if (BCValue.isConstant()) {
- // Constant condition variables mean the branch can only go a single way.
- ConstantBool *CPB = cast<ConstantBool>(BCValue.getConstant());
- if (CPB->getValue()) // If the branch condition is TRUE...
- markExecutable(BI->getSuccessor(0));
- else // Else if the br cond is FALSE...
- markExecutable(BI->getSuccessor(1));
+ // Get the value we are storing into the global.
+ LatticeVal &PtrVal = getValueState(SI.getOperand(0));
+
+ mergeInValue(I->second, GV, PtrVal);
+ if (I->second.isOverdefined())
+ TrackedGlobals.erase(I); // No need to keep tracking this!
+}
+
+
+// Handle load instructions. If the operand is a constant pointer to a constant
+// global, we can replace the load with the loaded constant value!
+void SCCPSolver::visitLoadInst(LoadInst &I) {
+ LatticeVal &IV = ValueState[&I];
+ if (IV.isOverdefined()) return;
+
+ LatticeVal &PtrVal = getValueState(I.getOperand(0));
+ if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
+ if (PtrVal.isConstant() && !I.isVolatile()) {
+ Value *Ptr = PtrVal.getConstant();
+ if (isa<ConstantPointerNull>(Ptr)) {
+ // load null -> null
+ markConstant(IV, &I, Constant::getNullValue(I.getType()));
+ return;
}
- return;
- }
- case Instruction::Switch: {
- SwitchInst *SI = cast<SwitchInst>(I);
- InstVal &SCValue = getValueState(SI->getCondition());
- if (SCValue.isOverdefined()) { // Overdefined condition? All dests are exe
- for(unsigned i = 0; BasicBlock *Succ = SI->getSuccessor(i); ++i)
- markExecutable(Succ);
- } else if (SCValue.isConstant()) {
- Constant *CPV = SCValue.getConstant();
- // Make sure to skip the "default value" which isn't a value
- for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i) {
- if (SI->getSuccessorValue(i) == CPV) {// Found the right branch...
- markExecutable(SI->getSuccessor(i));
+ // Transform load (constant global) into the value loaded.
+ if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
+ if (GV->isConstant()) {
+ if (!GV->isExternal()) {
+ markConstant(IV, &I, GV->getInitializer());
+ return;
+ }
+ } else if (!TrackedGlobals.empty()) {
+ // If we are tracking this global, merge in the known value for it.
+ hash_map<GlobalVariable*, LatticeVal>::iterator It =
+ TrackedGlobals.find(GV);
+ if (It != TrackedGlobals.end()) {
+ mergeInValue(IV, &I, It->second);
return;
}
}
+ }
- // Constant value not equal to any of the branches... must execute
- // default branch then...
- markExecutable(SI->getDefaultDest());
+ // Transform load (constantexpr_GEP global, 0, ...) into the value loaded.
+ if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
+ if (CE->getOpcode() == Instruction::GetElementPtr)
+ if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
+ if (GV->isConstant() && !GV->isExternal())
+ if (Constant *V =
+ GetGEPGlobalInitializer(GV->getInitializer(), CE)) {
+ markConstant(IV, &I, V);
+ return;
+ }
+ }
+
+ // Otherwise we cannot say for certain what value this load will produce.
+ // Bail out.
+ markOverdefined(IV, &I);
+}
+
+void SCCPSolver::visitCallSite(CallSite CS) {
+ Function *F = CS.getCalledFunction();
+
+ // If we are tracking this function, we must make sure to bind arguments as
+ // appropriate.
+ hash_map<Function*, LatticeVal>::iterator TFRVI =TrackedFunctionRetVals.end();
+ if (F && F->hasInternalLinkage())
+ TFRVI = TrackedFunctionRetVals.find(F);
+
+ if (TFRVI != TrackedFunctionRetVals.end()) {
+ // If this is the first call to the function hit, mark its entry block
+ // executable.
+ if (!BBExecutable.count(F->begin()))
+ MarkBlockExecutable(F->begin());
+
+ CallSite::arg_iterator CAI = CS.arg_begin();
+ for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
+ AI != E; ++AI, ++CAI) {
+ LatticeVal &IV = ValueState[AI];
+ if (!IV.isOverdefined())
+ mergeInValue(IV, AI, getValueState(*CAI));
}
+ }
+ Instruction *I = CS.getInstruction();
+ if (I->getType() == Type::VoidTy) return;
+
+ LatticeVal &IV = ValueState[I];
+ if (IV.isOverdefined()) return;
+
+ // Propagate the return value of the function to the value of the instruction.
+ if (TFRVI != TrackedFunctionRetVals.end()) {
+ mergeInValue(IV, I, TFRVI->second);
return;
}
- default: break; // Handle math operators as groups.
- } // end switch(I->getOpcode())
+ if (F == 0 || !F->isExternal() || !canConstantFoldCallTo(F)) {
+ markOverdefined(IV, I);
+ return;
+ }
+ std::vector<Constant*> Operands;
+ Operands.reserve(I->getNumOperands()-1);
+
+ for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
+ AI != E; ++AI) {
+ LatticeVal &State = getValueState(*AI);
+ if (State.isUndefined())
+ return; // Operands are not resolved yet...
+ else if (State.isOverdefined()) {
+ markOverdefined(IV, I);
+ return;
+ }
+ assert(State.isConstant() && "Unknown state!");
+ Operands.push_back(State.getConstant());
+ }
- //===-------------------------------------------------------------------===//
- // Handle Unary and cast instructions...
- //
- if (isa<UnaryOperator>(I) || isa<CastInst>(I)) {
- Value *V = I->getOperand(0);
- InstVal &VState = getValueState(V);
- if (VState.isOverdefined()) { // Inherit overdefinedness of operand
- markOverdefined(I);
- } else if (VState.isConstant()) { // Propogate constant value
- Constant *Result = isa<CastInst>(I)
- ? ConstantFoldCastInstruction(VState.getConstant(), I->getType())
- : ConstantFoldUnaryInstruction(I->getOpcode(), VState.getConstant());
-
- if (Result) {
- // This instruction constant folds!
- markConstant(I, Result);
- } else {
- markOverdefined(I); // Don't know how to fold this instruction. :(
- }
+ if (Constant *C = ConstantFoldCall(F, Operands))
+ markConstant(IV, I, C);
+ else
+ markOverdefined(IV, I);
+}
+
+
+void SCCPSolver::Solve() {
+ // Process the work lists until they are empty!
+ while (!BBWorkList.empty() || !InstWorkList.empty() ||
+ !OverdefinedInstWorkList.empty()) {
+ // Process the instruction work list...
+ while (!OverdefinedInstWorkList.empty()) {
+ Value *I = OverdefinedInstWorkList.back();
+ OverdefinedInstWorkList.pop_back();
+
+ DEBUG(std::cerr << "\nPopped off OI-WL: " << *I);
+
+ // "I" got into the work list because it either made the transition from
+ // bottom to constant
+ //
+ // Anything on this worklist that is overdefined need not be visited
+ // since all of its users will have already been marked as overdefined
+ // Update all of the users of this instruction's value...
+ //
+ for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
+ UI != E; ++UI)
+ OperandChangedState(*UI);
+ }
+ // Process the instruction work list...
+ while (!InstWorkList.empty()) {
+ Value *I = InstWorkList.back();
+ InstWorkList.pop_back();
+
+ DEBUG(std::cerr << "\nPopped off I-WL: " << *I);
+
+ // "I" got into the work list because it either made the transition from
+ // bottom to constant
+ //
+ // Anything on this worklist that is overdefined need not be visited
+ // since all of its users will have already been marked as overdefined.
+ // Update all of the users of this instruction's value...
+ //
+ if (!getValueState(I).isOverdefined())
+ for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
+ UI != E; ++UI)
+ OperandChangedState(*UI);
+ }
+
+ // Process the basic block work list...
+ while (!BBWorkList.empty()) {
+ BasicBlock *BB = BBWorkList.back();
+ BBWorkList.pop_back();
+
+ DEBUG(std::cerr << "\nPopped off BBWL: " << *BB);
+
+ // Notify all instructions in this basic block that they are newly
+ // executable.
+ visit(BB);
}
- return;
}
+}
+/// ResolveBranchesIn - While solving the dataflow for a function, we assume
+/// that branches on undef values cannot reach any of their successors.
+/// However, this is not a safe assumption. After we solve dataflow, this
+/// method should be use to handle this. If this returns true, the solver
+/// should be rerun.
+bool SCCPSolver::ResolveBranchesIn(Function &F) {
+ bool BranchesResolved = false;
+ for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
+ if (BBExecutable.count(BB)) {
+ TerminatorInst *TI = BB->getTerminator();
+ if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
+ if (BI->isConditional()) {
+ LatticeVal &BCValue = getValueState(BI->getCondition());
+ if (BCValue.isUndefined()) {
+ BI->setCondition(ConstantBool::True);
+ BranchesResolved = true;
+ visit(BI);
+ }
+ }
+ } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
+ LatticeVal &SCValue = getValueState(SI->getCondition());
+ if (SCValue.isUndefined()) {
+ const Type *CondTy = SI->getCondition()->getType();
+ SI->setCondition(Constant::getNullValue(CondTy));
+ BranchesResolved = true;
+ visit(SI);
+ }
+ }
+ }
+
+ return BranchesResolved;
+}
+
+
+namespace {
+ Statistic<> NumInstRemoved("sccp", "Number of instructions removed");
+ Statistic<> NumDeadBlocks ("sccp", "Number of basic blocks unreachable");
- //===-----------------------------------------------------------------===//
- // Handle GetElementPtr instructions...
+ //===--------------------------------------------------------------------===//
//
- if (isa<GetElementPtrInst>(I)) {
- markOverdefined(I);
- return;
+ /// SCCP Class - This class uses the SCCPSolver to implement a per-function
+ /// Sparse Conditional COnstant Propagator.
+ ///
+ struct SCCP : public FunctionPass {
+ // runOnFunction - Run the Sparse Conditional Constant Propagation
+ // algorithm, and return true if the function was modified.
+ //
+ bool runOnFunction(Function &F);
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesCFG();
+ }
+ };
+
+ RegisterOpt<SCCP> X("sccp", "Sparse Conditional Constant Propagation");
+} // end anonymous namespace
+
+
+// createSCCPPass - This is the public interface to this file...
+FunctionPass *llvm::createSCCPPass() {
+ return new SCCP();
+}
+
+
+// runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
+// and return true if the function was modified.
+//
+bool SCCP::runOnFunction(Function &F) {
+ DEBUG(std::cerr << "SCCP on function '" << F.getName() << "'\n");
+ SCCPSolver Solver;
+
+ // Mark the first block of the function as being executable.
+ Solver.MarkBlockExecutable(F.begin());
+
+ // Mark all arguments to the function as being overdefined.
+ hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
+ for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E; ++AI)
+ Values[AI].markOverdefined();
+
+ // Solve for constants.
+ bool ResolvedBranches = true;
+ while (ResolvedBranches) {
+ Solver.Solve();
+ DEBUG(std::cerr << "RESOLVING UNDEF BRANCHES\n");
+ ResolvedBranches = Solver.ResolveBranchesIn(F);
}
+ bool MadeChanges = false;
- //===-----------------------------------------------------------------===//
- // Handle Binary instructions...
+ // If we decided that there are basic blocks that are dead in this function,
+ // delete their contents now. Note that we cannot actually delete the blocks,
+ // as we cannot modify the CFG of the function.
//
- if (isa<BinaryOperator>(I) || isa<ShiftInst>(I)) {
- Value *V1 = I->getOperand(0);
- Value *V2 = I->getOperand(1);
-
- InstVal &V1State = getValueState(V1);
- InstVal &V2State = getValueState(V2);
- if (V1State.isOverdefined() || V2State.isOverdefined()) {
- markOverdefined(I);
- } else if (V1State.isConstant() && V2State.isConstant()) {
- Constant *Result =
- ConstantFoldBinaryInstruction(I->getOpcode(),
- V1State.getConstant(),
- V2State.getConstant());
- if (Result) {
- // This instruction constant folds!
- markConstant(I, Result);
- } else {
- markOverdefined(I); // Don't know how to fold this instruction. :(
+ std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
+ for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
+ if (!ExecutableBBs.count(BB)) {
+ DEBUG(std::cerr << " BasicBlock Dead:" << *BB);
+ ++NumDeadBlocks;
+
+ // Delete the instructions backwards, as it has a reduced likelihood of
+ // having to update as many def-use and use-def chains.
+ std::vector<Instruction*> Insts;
+ for (BasicBlock::iterator I = BB->begin(), E = BB->getTerminator();
+ I != E; ++I)
+ Insts.push_back(I);
+ while (!Insts.empty()) {
+ Instruction *I = Insts.back();
+ Insts.pop_back();
+ if (!I->use_empty())
+ I->replaceAllUsesWith(UndefValue::get(I->getType()));
+ BB->getInstList().erase(I);
+ MadeChanges = true;
+ ++NumInstRemoved;
+ }
+ } else {
+ // Iterate over all of the instructions in a function, replacing them with
+ // constants if we have found them to be of constant values.
+ //
+ for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
+ Instruction *Inst = BI++;
+ if (Inst->getType() != Type::VoidTy) {
+ LatticeVal &IV = Values[Inst];
+ if (IV.isConstant() || IV.isUndefined() &&
+ !isa<TerminatorInst>(Inst)) {
+ Constant *Const = IV.isConstant()
+ ? IV.getConstant() : UndefValue::get(Inst->getType());
+ DEBUG(std::cerr << " Constant: " << *Const << " = " << *Inst);
+
+ // Replaces all of the uses of a variable with uses of the constant.
+ Inst->replaceAllUsesWith(Const);
+
+ // Delete the instruction.
+ BB->getInstList().erase(Inst);
+
+ // Hey, we just changed something!
+ MadeChanges = true;
+ ++NumInstRemoved;
+ }
+ }
}
}
- return;
- }
- // Shouldn't get here... either the switch statement or one of the group
- // handlers should have kicked in...
- //
- cerr << "SCCP: Don't know how to handle: " << I;
- markOverdefined(I); // Just in case
+ return MadeChanges;
}
+namespace {
+ Statistic<> IPNumInstRemoved("ipsccp", "Number of instructions removed");
+ Statistic<> IPNumDeadBlocks ("ipsccp", "Number of basic blocks unreachable");
+ Statistic<> IPNumArgsElimed ("ipsccp",
+ "Number of arguments constant propagated");
+ Statistic<> IPNumGlobalConst("ipsccp",
+ "Number of globals found to be constant");
+ //===--------------------------------------------------------------------===//
+ //
+ /// IPSCCP Class - This class implements interprocedural Sparse Conditional
+ /// Constant Propagation.
+ ///
+ struct IPSCCP : public ModulePass {
+ bool runOnModule(Module &M);
+ };
-// OperandChangedState - This method is invoked on all of the users of an
-// instruction that was just changed state somehow.... Based on this
-// information, we need to update the specified user of this instruction.
-//
-void SCCP::OperandChangedState(User *U) {
- // Only instructions use other variable values!
- Instruction *I = cast<Instruction>(U);
- if (!BBExecutable.count(I->getParent())) return; // Inst not executable yet!
+ RegisterOpt<IPSCCP>
+ Y("ipsccp", "Interprocedural Sparse Conditional Constant Propagation");
+} // end anonymous namespace
- UpdateInstruction(I);
+// createIPSCCPPass - This is the public interface to this file...
+ModulePass *llvm::createIPSCCPPass() {
+ return new IPSCCP();
}
-namespace {
- // SCCPPass - Use Sparse Conditional Constant Propogation
- // to prove whether a value is constant and whether blocks are used.
- //
- struct SCCPPass : public MethodPass {
- inline bool runOnMethod(Function *F) {
- SCCP S(F);
- return S.doSCCP();
+
+static bool AddressIsTaken(GlobalValue *GV) {
+ // Delete any dead constantexpr klingons.
+ GV->removeDeadConstantUsers();
+
+ for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
+ UI != E; ++UI)
+ if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
+ if (SI->getOperand(0) == GV || SI->isVolatile())
+ return true; // Storing addr of GV.
+ } else if (isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) {
+ // Make sure we are calling the function, not passing the address.
+ CallSite CS = CallSite::get(cast<Instruction>(*UI));
+ for (CallSite::arg_iterator AI = CS.arg_begin(),
+ E = CS.arg_end(); AI != E; ++AI)
+ if (*AI == GV)
+ return true;
+ } else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
+ if (LI->isVolatile())
+ return true;
+ } else {
+ return true;
}
- };
+ return false;
}
-Pass *createSCCPPass() {
- return new SCCPPass();
+bool IPSCCP::runOnModule(Module &M) {
+ SCCPSolver Solver;
+
+ // Loop over all functions, marking arguments to those with their addresses
+ // taken or that are external as overdefined.
+ //
+ hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
+ for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
+ if (!F->hasInternalLinkage() || AddressIsTaken(F)) {
+ if (!F->isExternal())
+ Solver.MarkBlockExecutable(F->begin());
+ for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
+ AI != E; ++AI)
+ Values[AI].markOverdefined();
+ } else {
+ Solver.AddTrackedFunction(F);
+ }
+
+ // Loop over global variables. We inform the solver about any internal global
+ // variables that do not have their 'addresses taken'. If they don't have
+ // their addresses taken, we can propagate constants through them.
+ for (Module::global_iterator G = M.global_begin(), E = M.global_end();
+ G != E; ++G)
+ if (!G->isConstant() && G->hasInternalLinkage() && !AddressIsTaken(G))
+ Solver.TrackValueOfGlobalVariable(G);
+
+ // Solve for constants.
+ bool ResolvedBranches = true;
+ while (ResolvedBranches) {
+ Solver.Solve();
+
+ DEBUG(std::cerr << "RESOLVING UNDEF BRANCHES\n");
+ ResolvedBranches = false;
+ for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
+ ResolvedBranches |= Solver.ResolveBranchesIn(*F);
+ }
+
+ bool MadeChanges = false;
+
+ // Iterate over all of the instructions in the module, replacing them with
+ // constants if we have found them to be of constant values.
+ //
+ std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
+ for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
+ for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
+ AI != E; ++AI)
+ if (!AI->use_empty()) {
+ LatticeVal &IV = Values[AI];
+ if (IV.isConstant() || IV.isUndefined()) {
+ Constant *CST = IV.isConstant() ?
+ IV.getConstant() : UndefValue::get(AI->getType());
+ DEBUG(std::cerr << "*** Arg " << *AI << " = " << *CST <<"\n");
+
+ // Replaces all of the uses of a variable with uses of the
+ // constant.
+ AI->replaceAllUsesWith(CST);
+ ++IPNumArgsElimed;
+ }
+ }
+
+ std::vector<BasicBlock*> BlocksToErase;
+ for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
+ if (!ExecutableBBs.count(BB)) {
+ DEBUG(std::cerr << " BasicBlock Dead:" << *BB);
+ ++IPNumDeadBlocks;
+
+ // Delete the instructions backwards, as it has a reduced likelihood of
+ // having to update as many def-use and use-def chains.
+ std::vector<Instruction*> Insts;
+ TerminatorInst *TI = BB->getTerminator();
+ for (BasicBlock::iterator I = BB->begin(), E = TI; I != E; ++I)
+ Insts.push_back(I);
+
+ while (!Insts.empty()) {
+ Instruction *I = Insts.back();
+ Insts.pop_back();
+ if (!I->use_empty())
+ I->replaceAllUsesWith(UndefValue::get(I->getType()));
+ BB->getInstList().erase(I);
+ MadeChanges = true;
+ ++IPNumInstRemoved;
+ }
+
+ for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
+ BasicBlock *Succ = TI->getSuccessor(i);
+ if (Succ->begin() != Succ->end() && isa<PHINode>(Succ->begin()))
+ TI->getSuccessor(i)->removePredecessor(BB);
+ }
+ if (!TI->use_empty())
+ TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
+ BB->getInstList().erase(TI);
+
+ if (&*BB != &F->front())
+ BlocksToErase.push_back(BB);
+ else
+ new UnreachableInst(BB);
+
+ } else {
+ for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
+ Instruction *Inst = BI++;
+ if (Inst->getType() != Type::VoidTy) {
+ LatticeVal &IV = Values[Inst];
+ if (IV.isConstant() || IV.isUndefined() &&
+ !isa<TerminatorInst>(Inst)) {
+ Constant *Const = IV.isConstant()
+ ? IV.getConstant() : UndefValue::get(Inst->getType());
+ DEBUG(std::cerr << " Constant: " << *Const << " = " << *Inst);
+
+ // Replaces all of the uses of a variable with uses of the
+ // constant.
+ Inst->replaceAllUsesWith(Const);
+
+ // Delete the instruction.
+ if (!isa<TerminatorInst>(Inst) && !isa<CallInst>(Inst))
+ BB->getInstList().erase(Inst);
+
+ // Hey, we just changed something!
+ MadeChanges = true;
+ ++IPNumInstRemoved;
+ }
+ }
+ }
+ }
+
+ // Now that all instructions in the function are constant folded, erase dead
+ // blocks, because we can now use ConstantFoldTerminator to get rid of
+ // in-edges.
+ for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
+ // If there are any PHI nodes in this successor, drop entries for BB now.
+ BasicBlock *DeadBB = BlocksToErase[i];
+ while (!DeadBB->use_empty()) {
+ Instruction *I = cast<Instruction>(DeadBB->use_back());
+ bool Folded = ConstantFoldTerminator(I->getParent());
+ assert(Folded && "Didn't fold away reference to block!");
+ }
+
+ // Finally, delete the basic block.
+ F->getBasicBlockList().erase(DeadBB);
+ }
+ }
+
+ // If we inferred constant or undef return values for a function, we replaced
+ // all call uses with the inferred value. This means we don't need to bother
+ // actually returning anything from the function. Replace all return
+ // instructions with return undef.
+ const hash_map<Function*, LatticeVal> &RV =Solver.getTrackedFunctionRetVals();
+ for (hash_map<Function*, LatticeVal>::const_iterator I = RV.begin(),
+ E = RV.end(); I != E; ++I)
+ if (!I->second.isOverdefined() &&
+ I->first->getReturnType() != Type::VoidTy) {
+ Function *F = I->first;
+ for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
+ if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
+ if (!isa<UndefValue>(RI->getOperand(0)))
+ RI->setOperand(0, UndefValue::get(F->getReturnType()));
+ }
+
+ // If we infered constant or undef values for globals variables, we can delete
+ // the global and any stores that remain to it.
+ const hash_map<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
+ for (hash_map<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
+ E = TG.end(); I != E; ++I) {
+ GlobalVariable *GV = I->first;
+ assert(!I->second.isOverdefined() &&
+ "Overdefined values should have been taken out of the map!");
+ DEBUG(std::cerr << "Found that GV '" << GV->getName()<< "' is constant!\n");
+ while (!GV->use_empty()) {
+ StoreInst *SI = cast<StoreInst>(GV->use_back());
+ SI->eraseFromParent();
+ }
+ M.getGlobalList().erase(GV);
+ ++IPNumGlobalConst;
+ }
+
+ return MadeChanges;
}
projects / oota-llvm.git / blobdiff