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llvm-mirror/lib/Analysis/PHITransAddr.cpp
Dan Gohman 1add31cc93 Move Instruction::isSafeToSpeculativelyExecute out of VMCore and 
into Analysis as a standalone function, since there's no need for
it to be in VMCore. Also, update it to use isKnownNonZero and
other goodies available in Analysis, making it more precise,
enabling more aggressive optimization.

llvm-svn: 146610
2011-12-14 23:49:11 +00:00

444 lines
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//===- PHITransAddr.cpp - PHI Translation for Addresses -------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the PHITransAddr class.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/PHITransAddr.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
static bool CanPHITrans(Instruction *Inst) {
if (isa<PHINode>(Inst) ||
isa<GetElementPtrInst>(Inst))
return true;
if (isa<CastInst>(Inst) &&
isSafeToSpeculativelyExecute(Inst))
return true;
if (Inst->getOpcode() == Instruction::Add &&
isa<ConstantInt>(Inst->getOperand(1)))
return true;
// cerr << "MEMDEP: Could not PHI translate: " << *Pointer;
// if (isa<BitCastInst>(PtrInst) || isa<GetElementPtrInst>(PtrInst))
// cerr << "OP:\t\t\t\t" << *PtrInst->getOperand(0);
return false;
}
void PHITransAddr::dump() const {
if (Addr == 0) {
dbgs() << "PHITransAddr: null\n";
return;
}
dbgs() << "PHITransAddr: " << *Addr << "\n";
for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
dbgs() << " Input #" << i << " is " << *InstInputs[i] << "\n";
}
static bool VerifySubExpr(Value *Expr,
SmallVectorImpl<Instruction*> &InstInputs) {
// If this is a non-instruction value, there is nothing to do.
Instruction *I = dyn_cast<Instruction>(Expr);
if (I == 0) return true;
// If it's an instruction, it is either in Tmp or its operands recursively
// are.
SmallVectorImpl<Instruction*>::iterator Entry =
std::find(InstInputs.begin(), InstInputs.end(), I);
if (Entry != InstInputs.end()) {
InstInputs.erase(Entry);
return true;
}
// If it isn't in the InstInputs list it is a subexpr incorporated into the
// address. Sanity check that it is phi translatable.
if (!CanPHITrans(I)) {
errs() << "Non phi translatable instruction found in PHITransAddr:\n";
errs() << *I << '\n';
llvm_unreachable("Either something is missing from InstInputs or "
"CanPHITrans is wrong.");
return false;
}
// Validate the operands of the instruction.
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
if (!VerifySubExpr(I->getOperand(i), InstInputs))
return false;
return true;
}
/// Verify - Check internal consistency of this data structure. If the
/// structure is valid, it returns true. If invalid, it prints errors and
/// returns false.
bool PHITransAddr::Verify() const {
if (Addr == 0) return true;
SmallVector<Instruction*, 8> Tmp(InstInputs.begin(), InstInputs.end());
if (!VerifySubExpr(Addr, Tmp))
return false;
if (!Tmp.empty()) {
errs() << "PHITransAddr contains extra instructions:\n";
for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
errs() << " InstInput #" << i << " is " << *InstInputs[i] << "\n";
llvm_unreachable("This is unexpected.");
return false;
}
// a-ok.
return true;
}
/// IsPotentiallyPHITranslatable - If this needs PHI translation, return true
/// if we have some hope of doing it. This should be used as a filter to
/// avoid calling PHITranslateValue in hopeless situations.
bool PHITransAddr::IsPotentiallyPHITranslatable() const {
// If the input value is not an instruction, or if it is not defined in CurBB,
// then we don't need to phi translate it.
Instruction *Inst = dyn_cast<Instruction>(Addr);
return Inst == 0 || CanPHITrans(Inst);
}
static void RemoveInstInputs(Value *V,
SmallVectorImpl<Instruction*> &InstInputs) {
Instruction *I = dyn_cast<Instruction>(V);
if (I == 0) return;
// If the instruction is in the InstInputs list, remove it.
SmallVectorImpl<Instruction*>::iterator Entry =
std::find(InstInputs.begin(), InstInputs.end(), I);
if (Entry != InstInputs.end()) {
InstInputs.erase(Entry);
return;
}
assert(!isa<PHINode>(I) && "Error, removing something that isn't an input");
// Otherwise, it must have instruction inputs itself. Zap them recursively.
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
RemoveInstInputs(Op, InstInputs);
}
}
Value *PHITransAddr::PHITranslateSubExpr(Value *V, BasicBlock *CurBB,
BasicBlock *PredBB,
const DominatorTree *DT) {
// If this is a non-instruction value, it can't require PHI translation.
Instruction *Inst = dyn_cast<Instruction>(V);
if (Inst == 0) return V;
// Determine whether 'Inst' is an input to our PHI translatable expression.
bool isInput = std::count(InstInputs.begin(), InstInputs.end(), Inst);
// Handle inputs instructions if needed.
if (isInput) {
if (Inst->getParent() != CurBB) {
// If it is an input defined in a different block, then it remains an
// input.
return Inst;
}
// If 'Inst' is defined in this block and is an input that needs to be phi
// translated, we need to incorporate the value into the expression or fail.
// In either case, the instruction itself isn't an input any longer.
InstInputs.erase(std::find(InstInputs.begin(), InstInputs.end(), Inst));
// If this is a PHI, go ahead and translate it.
if (PHINode *PN = dyn_cast<PHINode>(Inst))
return AddAsInput(PN->getIncomingValueForBlock(PredBB));
// If this is a non-phi value, and it is analyzable, we can incorporate it
// into the expression by making all instruction operands be inputs.
if (!CanPHITrans(Inst))
return 0;
// All instruction operands are now inputs (and of course, they may also be
// defined in this block, so they may need to be phi translated themselves.
for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
if (Instruction *Op = dyn_cast<Instruction>(Inst->getOperand(i)))
InstInputs.push_back(Op);
}
// Ok, it must be an intermediate result (either because it started that way
// or because we just incorporated it into the expression). See if its
// operands need to be phi translated, and if so, reconstruct it.
if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
if (!isSafeToSpeculativelyExecute(Cast)) return 0;
Value *PHIIn = PHITranslateSubExpr(Cast->getOperand(0), CurBB, PredBB, DT);
if (PHIIn == 0) return 0;
if (PHIIn == Cast->getOperand(0))
return Cast;
// Find an available version of this cast.
// Constants are trivial to find.
if (Constant *C = dyn_cast<Constant>(PHIIn))
return AddAsInput(ConstantExpr::getCast(Cast->getOpcode(),
C, Cast->getType()));
// Otherwise we have to see if a casted version of the incoming pointer
// is available. If so, we can use it, otherwise we have to fail.
for (Value::use_iterator UI = PHIIn->use_begin(), E = PHIIn->use_end();
UI != E; ++UI) {
if (CastInst *CastI = dyn_cast<CastInst>(*UI))
if (CastI->getOpcode() == Cast->getOpcode() &&
CastI->getType() == Cast->getType() &&
(!DT || DT->dominates(CastI->getParent(), PredBB)))
return CastI;
}
return 0;
}
// Handle getelementptr with at least one PHI translatable operand.
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
SmallVector<Value*, 8> GEPOps;
bool AnyChanged = false;
for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
Value *GEPOp = PHITranslateSubExpr(GEP->getOperand(i), CurBB, PredBB, DT);
if (GEPOp == 0) return 0;
AnyChanged |= GEPOp != GEP->getOperand(i);
GEPOps.push_back(GEPOp);
}
if (!AnyChanged)
return GEP;
// Simplify the GEP to handle 'gep x, 0' -> x etc.
if (Value *V = SimplifyGEPInst(GEPOps, TD, DT)) {
for (unsigned i = 0, e = GEPOps.size(); i != e; ++i)
RemoveInstInputs(GEPOps[i], InstInputs);
return AddAsInput(V);
}
// Scan to see if we have this GEP available.
Value *APHIOp = GEPOps[0];
for (Value::use_iterator UI = APHIOp->use_begin(), E = APHIOp->use_end();
UI != E; ++UI) {
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI))
if (GEPI->getType() == GEP->getType() &&
GEPI->getNumOperands() == GEPOps.size() &&
GEPI->getParent()->getParent() == CurBB->getParent() &&
(!DT || DT->dominates(GEPI->getParent(), PredBB))) {
bool Mismatch = false;
for (unsigned i = 0, e = GEPOps.size(); i != e; ++i)
if (GEPI->getOperand(i) != GEPOps[i]) {
Mismatch = true;
break;
}
if (!Mismatch)
return GEPI;
}
}
return 0;
}
// Handle add with a constant RHS.
if (Inst->getOpcode() == Instruction::Add &&
isa<ConstantInt>(Inst->getOperand(1))) {
// PHI translate the LHS.
Constant *RHS = cast<ConstantInt>(Inst->getOperand(1));
bool isNSW = cast<BinaryOperator>(Inst)->hasNoSignedWrap();
bool isNUW = cast<BinaryOperator>(Inst)->hasNoUnsignedWrap();
Value *LHS = PHITranslateSubExpr(Inst->getOperand(0), CurBB, PredBB, DT);
if (LHS == 0) return 0;
// If the PHI translated LHS is an add of a constant, fold the immediates.
if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(LHS))
if (BOp->getOpcode() == Instruction::Add)
if (ConstantInt *CI = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
LHS = BOp->getOperand(0);
RHS = ConstantExpr::getAdd(RHS, CI);
isNSW = isNUW = false;
// If the old 'LHS' was an input, add the new 'LHS' as an input.
if (std::count(InstInputs.begin(), InstInputs.end(), BOp)) {
RemoveInstInputs(BOp, InstInputs);
AddAsInput(LHS);
}
}
// See if the add simplifies away.
if (Value *Res = SimplifyAddInst(LHS, RHS, isNSW, isNUW, TD, TLI, DT)) {
// If we simplified the operands, the LHS is no longer an input, but Res
// is.
RemoveInstInputs(LHS, InstInputs);
return AddAsInput(Res);
}
// If we didn't modify the add, just return it.
if (LHS == Inst->getOperand(0) && RHS == Inst->getOperand(1))
return Inst;
// Otherwise, see if we have this add available somewhere.
for (Value::use_iterator UI = LHS->use_begin(), E = LHS->use_end();
UI != E; ++UI) {
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(*UI))
if (BO->getOpcode() == Instruction::Add &&
BO->getOperand(0) == LHS && BO->getOperand(1) == RHS &&
BO->getParent()->getParent() == CurBB->getParent() &&
(!DT || DT->dominates(BO->getParent(), PredBB)))
return BO;
}
return 0;
}
// Otherwise, we failed.
return 0;
}
/// PHITranslateValue - PHI translate the current address up the CFG from
/// CurBB to Pred, updating our state to reflect any needed changes. If the
/// dominator tree DT is non-null, the translated value must dominate
/// PredBB. This returns true on failure and sets Addr to null.
bool PHITransAddr::PHITranslateValue(BasicBlock *CurBB, BasicBlock *PredBB,
const DominatorTree *DT) {
assert(Verify() && "Invalid PHITransAddr!");
Addr = PHITranslateSubExpr(Addr, CurBB, PredBB, DT);
assert(Verify() && "Invalid PHITransAddr!");
if (DT) {
// Make sure the value is live in the predecessor.
if (Instruction *Inst = dyn_cast_or_null<Instruction>(Addr))
if (!DT->dominates(Inst->getParent(), PredBB))
Addr = 0;
}
return Addr == 0;
}
/// PHITranslateWithInsertion - PHI translate this value into the specified
/// predecessor block, inserting a computation of the value if it is
/// unavailable.
///
/// All newly created instructions are added to the NewInsts list. This
/// returns null on failure.
///
Value *PHITransAddr::
PHITranslateWithInsertion(BasicBlock *CurBB, BasicBlock *PredBB,
const DominatorTree &DT,
SmallVectorImpl<Instruction*> &NewInsts) {
unsigned NISize = NewInsts.size();
// Attempt to PHI translate with insertion.
Addr = InsertPHITranslatedSubExpr(Addr, CurBB, PredBB, DT, NewInsts);
// If successful, return the new value.
if (Addr) return Addr;
// If not, destroy any intermediate instructions inserted.
while (NewInsts.size() != NISize)
NewInsts.pop_back_val()->eraseFromParent();
return 0;
}
/// InsertPHITranslatedPointer - Insert a computation of the PHI translated
/// version of 'V' for the edge PredBB->CurBB into the end of the PredBB
/// block. All newly created instructions are added to the NewInsts list.
/// This returns null on failure.
///
Value *PHITransAddr::
InsertPHITranslatedSubExpr(Value *InVal, BasicBlock *CurBB,
BasicBlock *PredBB, const DominatorTree &DT,
SmallVectorImpl<Instruction*> &NewInsts) {
// See if we have a version of this value already available and dominating
// PredBB. If so, there is no need to insert a new instance of it.
PHITransAddr Tmp(InVal, TD);
if (!Tmp.PHITranslateValue(CurBB, PredBB, &DT))
return Tmp.getAddr();
// If we don't have an available version of this value, it must be an
// instruction.
Instruction *Inst = cast<Instruction>(InVal);
// Handle cast of PHI translatable value.
if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
if (!isSafeToSpeculativelyExecute(Cast)) return 0;
Value *OpVal = InsertPHITranslatedSubExpr(Cast->getOperand(0),
CurBB, PredBB, DT, NewInsts);
if (OpVal == 0) return 0;
// Otherwise insert a cast at the end of PredBB.
CastInst *New = CastInst::Create(Cast->getOpcode(),
OpVal, InVal->getType(),
InVal->getName()+".phi.trans.insert",
PredBB->getTerminator());
NewInsts.push_back(New);
return New;
}
// Handle getelementptr with at least one PHI operand.
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
SmallVector<Value*, 8> GEPOps;
BasicBlock *CurBB = GEP->getParent();
for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
Value *OpVal = InsertPHITranslatedSubExpr(GEP->getOperand(i),
CurBB, PredBB, DT, NewInsts);
if (OpVal == 0) return 0;
GEPOps.push_back(OpVal);
}
GetElementPtrInst *Result =
GetElementPtrInst::Create(GEPOps[0], makeArrayRef(GEPOps).slice(1),
InVal->getName()+".phi.trans.insert",
PredBB->getTerminator());
Result->setIsInBounds(GEP->isInBounds());
NewInsts.push_back(Result);
return Result;
}
#if 0
// FIXME: This code works, but it is unclear that we actually want to insert
// a big chain of computation in order to make a value available in a block.
// This needs to be evaluated carefully to consider its cost trade offs.
// Handle add with a constant RHS.
if (Inst->getOpcode() == Instruction::Add &&
isa<ConstantInt>(Inst->getOperand(1))) {
// PHI translate the LHS.
Value *OpVal = InsertPHITranslatedSubExpr(Inst->getOperand(0),
CurBB, PredBB, DT, NewInsts);
if (OpVal == 0) return 0;
BinaryOperator *Res = BinaryOperator::CreateAdd(OpVal, Inst->getOperand(1),
InVal->getName()+".phi.trans.insert",
PredBB->getTerminator());
Res->setHasNoSignedWrap(cast<BinaryOperator>(Inst)->hasNoSignedWrap());
Res->setHasNoUnsignedWrap(cast<BinaryOperator>(Inst)->hasNoUnsignedWrap());
NewInsts.push_back(Res);
return Res;
}
#endif
return 0;
}
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