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Teach LSR about loop-variant expressions, such as loops like this: 

for (i = 0; i < N; ++i)
    A[i][foo()] = 0;

here we still want to strength reduce the A[i] part, even though foo() is
l-v.

This also simplifies some of the 'CanReduce' logic.

This implements Transforms/LoopStrengthReduce/ops_after_indvar.ll

llvm-svn: 22652
This commit is contained in:
Chris Lattner 2005-08-04 19:08:16 +00:00
parent faf17b43da
commit acc42c4df1
1 changed files with 93 additions and 68 deletions
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157
llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
View File

@ -167,7 +167,9 @@ Value *LoopStrengthReduce::getCastedVersionOf(Value *V) {
while (isa<PHINode>(InsertPt)) ++InsertPt;
}
return New = new CastInst(V, UIntPtrTy, V->getName(), InsertPt);
New = new CastInst(V, UIntPtrTy, V->getName(), InsertPt);
DeadInsts.insert(cast<Instruction>(New));
return New;
}
@ -191,30 +193,6 @@ DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts) {
}
/// CanReduceSCEV - Return true if we can strength reduce this scalar evolution
/// in the specified loop.
static bool CanReduceSCEV(const SCEVHandle &SH, Loop *L) {
SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SH);
if (!AddRec || AddRec->getLoop() != L) return false;
// FIXME: Generalize to non-affine IV's.
if (!AddRec->isAffine()) return false;
// FIXME: generalize to IV's with more complex strides (must emit stride
// expression outside of loop!)
if (isa<SCEVConstant>(AddRec->getOperand(1)))
return true;
// We handle steps by unsigned values, because we know we won't have to insert
// a cast for them.
if (SCEVUnknown *SU = dyn_cast<SCEVUnknown>(AddRec->getOperand(1)))
if (SU->getValue()->getType()->isUnsigned())
return true;
// Otherwise, no, we can't handle it yet.
return false;
}
/// GetExpressionSCEV - Compute and return the SCEV for the specified
/// instruction.
SCEVHandle LoopStrengthReduce::GetExpressionSCEV(Instruction *Exp, Loop *L) {
@ -243,7 +221,9 @@ SCEVHandle LoopStrengthReduce::GetExpressionSCEV(Instruction *Exp, Loop *L) {
GEPVal = SCEVAddExpr::get(GEPVal,
SCEVUnknown::getIntegerSCEV(Offset, UIntPtrTy));
} else {
SCEVHandle Idx = SE->getSCEV(getCastedVersionOf(GEP->getOperand(i)));
Value *OpVal = getCastedVersionOf(GEP->getOperand(i));
SCEVHandle Idx = SE->getSCEV(OpVal);
uint64_t TypeSize = TD->getTypeSize(GTI.getIndexedType());
if (TypeSize != 1)
Idx = SCEVMulExpr::get(Idx,
@ -253,10 +233,58 @@ SCEVHandle LoopStrengthReduce::GetExpressionSCEV(Instruction *Exp, Loop *L) {
}
}
//assert(CanReduceSCEV(GEPVal, L) && "Cannot reduce this use of IV?");
return GEPVal;
}
/// getSCEVStartAndStride - Compute the start and stride of this expression,
/// returning false if the expression is not a start/stride pair, or true if it
/// is. The stride must be a loop invariant expression, but the start may be
/// a mix of loop invariant and loop variant expressions.
static bool getSCEVStartAndStride(const SCEVHandle &SH, Loop *L,
SCEVHandle &Start, Value *&Stride) {
SCEVHandle TheAddRec = Start; // Initialize to zero.
// If the outer level is an AddExpr, the operands are all start values except
// for a nested AddRecExpr.
if (SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(SH)) {
for (unsigned i = 0, e = AE->getNumOperands(); i != e; ++i)
if (SCEVAddRecExpr *AddRec =
dyn_cast<SCEVAddRecExpr>(AE->getOperand(i))) {
if (AddRec->getLoop() == L)
TheAddRec = SCEVAddExpr::get(AddRec, TheAddRec);
else
return false; // Nested IV of some sort?
} else {
Start = SCEVAddExpr::get(Start, AE->getOperand(i));
}
} else if (SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SH)) {
TheAddRec = SH;
} else {
return false; // not analyzable.
}
SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(TheAddRec);
if (!AddRec || AddRec->getLoop() != L) return false;
// FIXME: Generalize to non-affine IV's.
if (!AddRec->isAffine()) return false;
Start = SCEVAddExpr::get(Start, AddRec->getOperand(0));
// FIXME: generalize to IV's with more complex strides (must emit stride
// expression outside of loop!)
if (!isa<SCEVConstant>(AddRec->getOperand(1)))
return false;
SCEVConstant *StrideC = cast<SCEVConstant>(AddRec->getOperand(1));
Stride = StrideC->getValue();
assert(Stride->getType()->isUnsigned() &&
"Constants should be canonicalized to unsigned!");
return true;
}
/// AddUsersIfInteresting - Inspect the specified instruction. If it is a
/// reducible SCEV, recursively add its users to the IVUsesByStride set and
/// return true. Otherwise, return false.
@ -266,24 +294,15 @@ bool LoopStrengthReduce::AddUsersIfInteresting(Instruction *I, Loop *L,
if (!Processed.insert(I).second)
return true; // Instruction already handled.
// Get the symbolic expression for this instruction.
SCEVHandle ISE = GetExpressionSCEV(I, L);
if (!CanReduceSCEV(ISE, L))
return false; // Non-analyzable expression, e.g. a rem instr.
if (isa<SCEVCouldNotCompute>(ISE)) return false;
// NOT SAFE with generalized EXPRS
SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(ISE);
SCEVHandle Start = AR->getStart();
// Get the step value, canonicalizing to an unsigned integer type so that
// lookups in the map will match.
Value *Step = 0; // Step of ISE.
if (SCEVConstant *SC = dyn_cast<SCEVConstant>(AR->getOperand(1)))
/// Always get the step value as an unsigned value.
Step = ConstantExpr::getCast(SC->getValue(),
SC->getValue()->getType()->getUnsignedVersion());
else
Step = cast<SCEVUnknown>(AR->getOperand(1))->getValue();
assert(Step->getType()->isUnsigned() && "Bad step value!");
// Get the start and stride for this expression.
SCEVHandle Start = SCEVUnknown::getIntegerSCEV(0, ISE->getType());
Value *Stride = 0;
if (!getSCEVStartAndStride(ISE, L, Start, Stride))
return false; // Non-reducible symbolic expression, bail out.
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;++UI){
Instruction *User = cast<Instruction>(*UI);
@ -294,20 +313,21 @@ bool LoopStrengthReduce::AddUsersIfInteresting(Instruction *I, Loop *L,
// If this is an instruction defined in a nested loop, or outside this loop,
// don't recurse into it.
bool AddUserToIVUsers = false;
if (LI->getLoopFor(User->getParent()) != L) {
DEBUG(std::cerr << "FOUND USER in nested loop: " << *User
<< " OF SCEV: " << *ISE << "\n");
// Okay, we found a user that we cannot reduce. Analyze the instruction
// and decide what to do with it.
IVUsesByStride[Step].addUser(Start, User, I);
AddUserToIVUsers = true;
} else if (!AddUsersIfInteresting(User, L, Processed)) {
DEBUG(std::cerr << "FOUND USER: " << *User
<< " OF SCEV: " << *ISE << "\n");
AddUserToIVUsers = true;
}
if (AddUserToIVUsers) {
// Okay, we found a user that we cannot reduce. Analyze the instruction
// and decide what to do with it.
IVUsesByStride[Step].addUser(Start, User, I);
IVUsesByStride[Stride].addUser(Start, User, I);
}
}
return true;
@ -372,28 +392,27 @@ static bool isTargetConstant(const SCEVHandle &V) {
/// GetImmediateValues - Look at Val, and pull out any additions of constants
/// that can fit into the immediate field of instructions in the target.
static SCEVHandle GetImmediateValues(SCEVHandle Val, bool isAddress) {
if (!isAddress)
return SCEVUnknown::getIntegerSCEV(0, Val->getType());
if (isTargetConstant(Val))
static SCEVHandle GetImmediateValues(SCEVHandle Val, bool isAddress, Loop *L) {
if (isAddress && isTargetConstant(Val))
return Val;
if (SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) {
unsigned i = 0;
for (; i != SAE->getNumOperands(); ++i)
if (isTargetConstant(SAE->getOperand(i))) {
SCEVHandle ImmVal = SAE->getOperand(i);
SCEVHandle Imm = SCEVUnknown::getIntegerSCEV(0, Val->getType());
// If there are any other immediates that we can handle here, pull them
// out too.
for (++i; i != SAE->getNumOperands(); ++i)
if (isTargetConstant(SAE->getOperand(i)))
ImmVal = SCEVAddExpr::get(ImmVal, SAE->getOperand(i));
return ImmVal;
for (; i != SAE->getNumOperands(); ++i)
if (isAddress && isTargetConstant(SAE->getOperand(i))) {
Imm = SCEVAddExpr::get(Imm, SAE->getOperand(i));
} else if (!SAE->getOperand(i)->isLoopInvariant(L)) {
// If this is a loop-variant expression, it must stay in the immediate
// field of the expression.
Imm = SCEVAddExpr::get(Imm, SAE->getOperand(i));
}
return Imm;
} else if (SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) {
// Try to pull immediates out of the start value of nested addrec's.
return GetImmediateValues(SARE->getStart(), isAddress);
return GetImmediateValues(SARE->getStart(), isAddress, L);
}
return SCEVUnknown::getIntegerSCEV(0, Val->getType());
@ -427,10 +446,16 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(Value *Stride,
// instructions. If we can represent anything there, move it to the imm
// fields of the BasedUsers.
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) {
bool isAddress = isa<LoadInst>(UsersToProcess[i].second.Inst) ||
isa<StoreInst>(UsersToProcess[i].second.Inst);
UsersToProcess[i].second.Imm = GetImmediateValues(UsersToProcess[i].first,
isAddress);
// Addressing modes can be folded into loads and stores. Be careful that
// the store is through the expression, not of the expression though.
bool isAddress = isa<LoadInst>(UsersToProcess[i].second.Inst);
if (StoreInst *SI = dyn_cast<StoreInst>(UsersToProcess[i].second.Inst))
if (SI->getOperand(1) == UsersToProcess[i].second.OperandValToReplace)
isAddress = true;
UsersToProcess[i].second.Imm =
GetImmediateValues(UsersToProcess[i].first, isAddress, L);
UsersToProcess[i].first = SCEV::getMinusSCEV(UsersToProcess[i].first,
UsersToProcess[i].second.Imm);