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This is the initial implementation of IPSCCP, as requested by Brian.

Browse Source 
This implements SCCP/ipsccp-basic.ll, rips apart Olden/mst (as described in
PR415), and does other nice things.

There is still more to come with this, but it's a start.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@18752 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-12-10 08:02:06 +00:00
parent 3c05176526
commit 59acc7d4ef
1 changed files with 275 additions and 65 deletions
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340
lib/Transforms/Scalar/SCCP.cpp
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@ -23,6 +23,7 @@
#define DEBUG_TYPE "sccp"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Constants.h"
#include "llvm/Function.h"
#include "llvm/GlobalVariable.h"
@ -31,6 +32,7 @@
#include "llvm/Type.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"
@ -43,8 +45,6 @@ using namespace llvm;
// instruction may occupy. It is a simple class with value semantics.
//
namespace {
Statistic<> NumInstRemoved("sccp", "Number of instructions removed");
Statistic<> NumDeadBlocks ("sccp", "Number of basic blocks unreachable");
class LatticeVal {
enum {
@ -99,15 +99,19 @@ class SCCPSolver : public InstVisitor<SCCPSolver> {
std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
hash_map<Value*, LatticeVal> ValueState; // The state each value is in...
/// 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<Instruction*> OverdefinedInstWorkList;// The overdefined
// instruction work list
std::vector<Instruction*> InstWorkList;// The instruction work list
std::vector<Value*> OverdefinedInstWorkList;
std::vector<Value*> InstWorkList;
std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
@ -130,6 +134,21 @@ public:
BBWorkList.push_back(BB); // Add the block to the work list!
}
/// TrackValueOfGlobalVariableIfPossible - 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 TrackValueOfGlobalVariableIfPossible(GlobalVariable *GV);
/// 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();
@ -151,29 +170,40 @@ private:
// is not already a constant, add it to the instruction work list so that
// the users of the instruction are updated later.
//
inline void markConstant(LatticeVal &IV, Instruction *I, Constant *C) {
inline void markConstant(LatticeVal &IV, Value *V, Constant *C) {
if (IV.markConstant(C)) {
DEBUG(std::cerr << "markConstant: " << *C << ": " << *I);
InstWorkList.push_back(I);
DEBUG(std::cerr << "markConstant: " << *C << ": " << *V);
InstWorkList.push_back(V);
}
}
inline void markConstant(Instruction *I, Constant *C) {
markConstant(ValueState[I], I, C);
inline void markConstant(Value *V, Constant *C) {
markConstant(ValueState[V], V, C);
}
// 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, Instruction *I) {
inline void markOverdefined(LatticeVal &IV, Value *V) {
if (IV.markOverdefined()) {
DEBUG(std::cerr << "markOverdefined: " << *I);
DEBUG(std::cerr << "markOverdefined: " << *V);
// Only instructions go on the work list
OverdefinedInstWorkList.push_back(I);
OverdefinedInstWorkList.push_back(V);
}
}
inline void markOverdefined(Instruction *I) {
markOverdefined(ValueState[I], I);
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 LatticeVal object that corresponds to the value.
@ -211,10 +241,8 @@ private:
// 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) {
PHINode *PN = cast<PHINode>(I);
visitPHINode(*PN);
}
for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
visitPHINode(*cast<PHINode>(I));
} else {
MarkBlockExecutable(Dest);
@ -252,7 +280,7 @@ private:
void visitPHINode(PHINode &I);
// Terminators
void visitReturnInst(ReturnInst &I) { /*does not have an effect*/ }
void visitReturnInst(ReturnInst &I);
void visitTerminatorInst(TerminatorInst &TI);
void visitCastInst(CastInst &I);
@ -264,11 +292,12 @@ private:
void visitStoreInst (Instruction &I) { /*returns void*/ }
void visitLoadInst (LoadInst &I);
void visitGetElementPtrInst(GetElementPtrInst &I);
void visitCallInst (CallInst &I);
void visitInvokeInst (TerminatorInst &I) {
if (I.getType() != Type::VoidTy) markOverdefined(&I);
visitTerminatorInst(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); }
@ -482,6 +511,23 @@ void SCCPSolver::visitPHINode(PHINode &PN) {
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);
@ -704,25 +750,56 @@ void SCCPSolver::visitLoadInst(LoadInst &I) {
markOverdefined(IV, &I);
}
void SCCPSolver::visitCallInst(CallInst &I) {
LatticeVal &IV = ValueState[&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::aiterator AI = F->abegin(), E = F->aend();
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;
Function *F = I.getCalledFunction();
if (F == 0 || !canConstantFoldCallTo(F)) {
markOverdefined(IV, &I);
// Propagate the return value of the function to the value of the instruction.
if (TFRVI != TrackedFunctionRetVals.end()) {
mergeInValue(IV, I, TFRVI->second);
return;
}
if (F == 0 || !F->isExternal() || !canConstantFoldCallTo(F)) {
markOverdefined(IV, I);
return;
}
std::vector<Constant*> Operands;
Operands.reserve(I.getNumOperands()-1);
Operands.reserve(I->getNumOperands()-1);
for (unsigned i = 1, e = I.getNumOperands(); i != e; ++i) {
LatticeVal &State = getValueState(I.getOperand(i));
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);
markOverdefined(IV, I);
return;
}
assert(State.isConstant() && "Unknown state!");
@ -730,9 +807,9 @@ void SCCPSolver::visitCallInst(CallInst &I) {
}
if (Constant *C = ConstantFoldCall(F, Operands))
markConstant(IV, &I, C);
markConstant(IV, I, C);
else
markOverdefined(IV, &I);
markOverdefined(IV, I);
}
@ -742,10 +819,10 @@ void SCCPSolver::Solve() {
!OverdefinedInstWorkList.empty()) {
// Process the instruction work list...
while (!OverdefinedInstWorkList.empty()) {
Instruction *I = OverdefinedInstWorkList.back();
Value *I = OverdefinedInstWorkList.back();
OverdefinedInstWorkList.pop_back();
DEBUG(std::cerr << "\nPopped off OI-WL: " << I);
DEBUG(std::cerr << "\nPopped off OI-WL: " << *I);
// "I" got into the work list because it either made the transition from
// bottom to constant
@ -760,7 +837,7 @@ void SCCPSolver::Solve() {
}
// Process the instruction work list...
while (!InstWorkList.empty()) {
Instruction *I = InstWorkList.back();
Value *I = InstWorkList.back();
InstWorkList.pop_back();
DEBUG(std::cerr << "\nPopped off I-WL: " << *I);
@ -794,6 +871,9 @@ void SCCPSolver::Solve() {
namespace {
Statistic<> NumInstRemoved("sccp", "Number of instructions removed");
Statistic<> NumDeadBlocks ("sccp", "Number of basic blocks unreachable");
//===--------------------------------------------------------------------===//
//
/// SCCP Class - This class uses the SCCPSolver to implement a per-function
@ -865,38 +945,168 @@ bool SCCP::runOnFunction(Function &F) {
MadeChanges = true;
++NumInstRemoved;
}
}
// Iterate over all of the instructions in a function, replacing them with
// constants if we have found them to be of constant values.
//
for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB)
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;
if (IV.isConstant()) {
Const = IV.getConstant();
} 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);
} else {
Const = UndefValue::get(Inst->getType());
DEBUG(std::cerr << " Undefined: " << *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;
}
// 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 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");
//===--------------------------------------------------------------------===//
//
/// IPSCCP Class - This class implements interprocedural Sparse Conditional
/// Constant Propagation.
///
struct IPSCCP : public ModulePass {
bool runOnModule(Module &M);
};
RegisterOpt<IPSCCP>
Y("ipsccp", "Interprocedural Sparse Conditional Constant Propagation");
} // end anonymous namespace
// createIPSCCPPass - This is the public interface to this file...
ModulePass *llvm::createIPSCCPPass() {
return new IPSCCP();
}
static bool AddressIsTaken(GlobalValue *GV) {
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) 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 (!isa<LoadInst>(*UI)) {
return true;
}
return false;
}
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::aiterator AI = F->abegin(), E = F->aend(); AI != E; ++AI)
Values[AI].markOverdefined();
} else {
Solver.AddTrackedFunction(F);
}
// Solve for constants.
Solver.Solve();
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::aiterator AI = F->abegin(), E = F->aend(); 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;
}
}
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;
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;
++IPNumInstRemoved;
}
} 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;
}
}
}
}
}
return MadeChanges;
}