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Refactor this code substantially with the following improvements: 

1. We only analyze instructions once, guaranteed
  2. AnalyzeGetElementPtrUsers has been ripped apart and replaced with
     something much simpler.

The next step is to handle expressions that are not all indvar+loop-invariant
values (e.g. handling indvar+loopvariant).

llvm-svn: 22649
This commit is contained in:
Chris Lattner 2005-08-04 17:40:30 +00:00
parent 5adb830b30
commit eaf24725b2
1 changed files with 38 additions and 138 deletions
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172
llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
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@ -138,9 +138,10 @@ namespace {
Value *getCastedVersionOf(Value *V); Value *getCastedVersionOf(Value *V);
private: private:
void runOnLoop(Loop *L); void runOnLoop(Loop *L);
bool AddUsersIfInteresting(Instruction *I, Loop *L); bool AddUsersIfInteresting(Instruction *I, Loop *L,
void AnalyzeGetElementPtrUsers(GetElementPtrInst *GEP, Instruction *I, std::set<Instruction*> &Processed);
Loop *L); SCEVHandle GetExpressionSCEV(Instruction *E, Loop *L);
void StrengthReduceStridedIVUsers(Value *Stride, IVUsersOfOneStride &Uses, void StrengthReduceStridedIVUsers(Value *Stride, IVUsersOfOneStride &Uses,
Loop *L, bool isOnlyStride); Loop *L, bool isOnlyStride);
@ -234,48 +235,24 @@ static bool CanReduceSCEV(const SCEVHandle &SH, Loop *L) {
return false; return false;
} }
/// GetExpressionSCEV - Compute and return the SCEV for the specified
/// instruction.
SCEVHandle LoopStrengthReduce::GetExpressionSCEV(Instruction *Exp, Loop *L) {
GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Exp);
if (!GEP)
return SE->getSCEV(Exp);
/// GetAdjustedIndex - Adjust the specified GEP sequential type index to match
/// the size of the pointer type, and scale it by the type size.
static SCEVHandle GetAdjustedIndex(const SCEVHandle &Idx, uint64_t TySize,
const Type *UIntPtrTy) {
SCEVHandle Result = Idx;
if (Result->getType()->getUnsignedVersion() != UIntPtrTy) {
if (UIntPtrTy->getPrimitiveSize() < Result->getType()->getPrimitiveSize())
Result = SCEVTruncateExpr::get(Result, UIntPtrTy);
else
Result = SCEVZeroExtendExpr::get(Result, UIntPtrTy);
}
// This index is scaled by the type size being indexed.
if (TySize != 1)
Result = SCEVMulExpr::get(Result,
SCEVConstant::get(ConstantUInt::get(UIntPtrTy,
TySize)));
return Result;
}
/// AnalyzeGetElementPtrUsers - Analyze all of the users of the specified
/// getelementptr instruction, adding them to the IVUsesByStride table. Note
/// that we only want to analyze a getelementptr instruction once, and it can
/// have multiple operands that are uses of the indvar (e.g. A[i][i]). Because
/// of this, we only process a GEP instruction if its first recurrent operand is
/// "op", otherwise we will either have already processed it or we will sometime
/// later.
void LoopStrengthReduce::AnalyzeGetElementPtrUsers(GetElementPtrInst *GEP,
Instruction *Op, Loop *L) {
// Analyze all of the subscripts of this getelementptr instruction, looking // Analyze all of the subscripts of this getelementptr instruction, looking
// for uses that are determined by the trip count of L. First, skip all // for uses that are determined by the trip count of L. First, skip all
// operands the are not dependent on the IV. // operands the are not dependent on the IV.
// Build up the base expression. Insert an LLVM cast of the pointer to // Build up the base expression. Insert an LLVM cast of the pointer to
// uintptr_t first. // uintptr_t first.
SCEVHandle Base = SCEVUnknown::get(getCastedVersionOf(GEP->getOperand(0))); SCEVHandle GEPVal = SCEVUnknown::get(getCastedVersionOf(GEP->getOperand(0)));
gep_type_iterator GTI = gep_type_begin(GEP); gep_type_iterator GTI = gep_type_begin(GEP);
unsigned i = 1;
for (; GEP->getOperand(i) != Op; ++i, ++GTI) { for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
// If this is a use of a recurrence that we can analyze, and it comes before // If this is a use of a recurrence that we can analyze, and it comes before
// Op does in the GEP operand list, we will handle this when we process this // Op does in the GEP operand list, we will handle this when we process this
// operand. // operand.
@ -283,104 +260,37 @@ void LoopStrengthReduce::AnalyzeGetElementPtrUsers(GetElementPtrInst *GEP,
const StructLayout *SL = TD->getStructLayout(STy); const StructLayout *SL = TD->getStructLayout(STy);
unsigned Idx = cast<ConstantUInt>(GEP->getOperand(i))->getValue(); unsigned Idx = cast<ConstantUInt>(GEP->getOperand(i))->getValue();
uint64_t Offset = SL->MemberOffsets[Idx]; uint64_t Offset = SL->MemberOffsets[Idx];
Base = SCEVAddExpr::get(Base, SCEVUnknown::getIntegerSCEV(Offset, GEPVal = SCEVAddExpr::get(GEPVal,
UIntPtrTy)); SCEVUnknown::getIntegerSCEV(Offset, UIntPtrTy));
} else { } else {
SCEVHandle Idx = SE->getSCEV(GEP->getOperand(i)); SCEVHandle Idx = SE->getSCEV(getCastedVersionOf(GEP->getOperand(i)));
uint64_t TypeSize = TD->getTypeSize(GTI.getIndexedType());
// If this operand is reducible, and it's not the one we are looking at if (TypeSize != 1)
// currently, do not process the GEP at this time. Idx = SCEVMulExpr::get(Idx,
if (CanReduceSCEV(Idx, L)) SCEVConstant::get(ConstantUInt::get(UIntPtrTy,
return; TypeSize)));
Base = SCEVAddExpr::get(Base, GetAdjustedIndex(Idx, GEPVal = SCEVAddExpr::get(GEPVal, Idx);
TD->getTypeSize(GTI.getIndexedType()), UIntPtrTy));
} }
} }
// Get the index, convert it to intptr_t. //assert(CanReduceSCEV(GEPVal, L) && "Cannot reduce this use of IV?");
SCEVHandle GEPIndexExpr = return GEPVal;
GetAdjustedIndex(SE->getSCEV(Op), TD->getTypeSize(GTI.getIndexedType()),
UIntPtrTy);
// Process all remaining subscripts in the GEP instruction.
for (++i, ++GTI; i != GEP->getNumOperands(); ++i, ++GTI)
if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
const StructLayout *SL = TD->getStructLayout(STy);
unsigned Idx = cast<ConstantUInt>(GEP->getOperand(i))->getValue();
uint64_t Offset = SL->MemberOffsets[Idx];
Base = SCEVAddExpr::get(Base, SCEVUnknown::getIntegerSCEV(Offset,
UIntPtrTy));
} else {
SCEVHandle Idx = SE->getSCEV(GEP->getOperand(i));
if (CanReduceSCEV(Idx, L)) { // Another IV subscript
GEPIndexExpr = SCEVAddExpr::get(GEPIndexExpr,
GetAdjustedIndex(Idx, TD->getTypeSize(GTI.getIndexedType()),
UIntPtrTy));
assert(CanReduceSCEV(GEPIndexExpr, L) &&
"Cannot reduce the sum of two reducible SCEV's??");
} else {
Base = SCEVAddExpr::get(Base, GetAdjustedIndex(Idx,
TD->getTypeSize(GTI.getIndexedType()), UIntPtrTy));
}
}
assert(CanReduceSCEV(GEPIndexExpr, L) && "Non reducible idx??");
// FIXME: If the base is not loop invariant, we currently cannot emit this.
if (!Base->isLoopInvariant(L)) {
DEBUG(std::cerr << "IGNORING GEP due to non-invariant base: "
<< *Base << "\n");
return;
}
Base = SCEVAddExpr::get(Base, cast<SCEVAddRecExpr>(GEPIndexExpr)->getStart());
SCEVHandle Stride = cast<SCEVAddRecExpr>(GEPIndexExpr)->getOperand(1);
DEBUG(std::cerr << "GEP BASE : " << *Base << "\n");
DEBUG(std::cerr << "GEP STRIDE: " << *Stride << "\n");
Value *Step = 0; // Step of ISE.
if (SCEVConstant *SC = dyn_cast<SCEVConstant>(Stride))
/// Always get the step value as an unsigned value.
Step = ConstantExpr::getCast(SC->getValue(),
SC->getValue()->getType()->getUnsignedVersion());
else
Step = cast<SCEVUnknown>(Stride)->getValue();
assert(Step->getType()->isUnsigned() && "Bad step value!");
// Now that we know the base and stride contributed by the GEP instruction,
// process all users.
for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end();
UI != E; ++UI) {
Instruction *User = cast<Instruction>(*UI);
// Do not infinitely recurse on PHI nodes.
if (isa<PHINode>(User) && User->getParent() == L->getHeader())
continue;
// If this is an instruction defined in a nested loop, or outside this loop,
// don't mess with it.
if (LI->getLoopFor(User->getParent()) != L)
continue;
DEBUG(std::cerr << "FOUND USER: " << *User
<< " OF STRIDE: " << *Step << " BASE = " << *Base << "\n");
// Okay, we found a user that we cannot reduce. Analyze the instruction
// and decide what to do with it.
IVUsesByStride[Step].addUser(Base, User, GEP);
}
} }
/// AddUsersIfInteresting - Inspect the specified instruction. If it is a /// AddUsersIfInteresting - Inspect the specified instruction. If it is a
/// reducible SCEV, recursively add its users to the IVUsesByStride set and /// reducible SCEV, recursively add its users to the IVUsesByStride set and
/// return true. Otherwise, return false. /// return true. Otherwise, return false.
bool LoopStrengthReduce::AddUsersIfInteresting(Instruction *I, Loop *L) { bool LoopStrengthReduce::AddUsersIfInteresting(Instruction *I, Loop *L,
std::set<Instruction*> &Processed) {
if (I->getType() == Type::VoidTy) return false; if (I->getType() == Type::VoidTy) return false;
SCEVHandle ISE = SE->getSCEV(I); if (!Processed.insert(I).second)
if (!CanReduceSCEV(ISE, L)) return false; return true; // Instruction already handled.
SCEVHandle ISE = GetExpressionSCEV(I, L);
if (!CanReduceSCEV(ISE, L))
return false; // Non-analyzable expression, e.g. a rem instr.
// NOT SAFE with generalized EXPRS
SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(ISE); SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(ISE);
SCEVHandle Start = AR->getStart(); SCEVHandle Start = AR->getStart();
@ -395,8 +305,6 @@ bool LoopStrengthReduce::AddUsersIfInteresting(Instruction *I, Loop *L) {
Step = cast<SCEVUnknown>(AR->getOperand(1))->getValue(); Step = cast<SCEVUnknown>(AR->getOperand(1))->getValue();
assert(Step->getType()->isUnsigned() && "Bad step value!"); assert(Step->getType()->isUnsigned() && "Bad step value!");
std::set<GetElementPtrInst*> AnalyzedGEPs;
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;++UI){ for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;++UI){
Instruction *User = cast<Instruction>(*UI); Instruction *User = cast<Instruction>(*UI);
@ -413,16 +321,7 @@ bool LoopStrengthReduce::AddUsersIfInteresting(Instruction *I, Loop *L) {
// Okay, we found a user that we cannot reduce. Analyze the instruction // Okay, we found a user that we cannot reduce. Analyze the instruction
// and decide what to do with it. // and decide what to do with it.
IVUsesByStride[Step].addUser(Start, User, I); IVUsesByStride[Step].addUser(Start, User, I);
continue; } else if (!AddUsersIfInteresting(User, L, Processed)) {
}
// Next, see if this user is analyzable itself!
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) {
// If this is a getelementptr instruction, figure out what linear
// expression of induction variable is actually being used.
if (AnalyzedGEPs.insert(GEP).second) // Not already analyzed?
AnalyzeGetElementPtrUsers(GEP, I, L);
} else if (!AddUsersIfInteresting(User, L)) {
DEBUG(std::cerr << "FOUND USER: " << *User DEBUG(std::cerr << "FOUND USER: " << *User
<< " OF SCEV: " << *ISE << "\n"); << " OF SCEV: " << *ISE << "\n");
@ -655,8 +554,9 @@ void LoopStrengthReduce::runOnLoop(Loop *L) {
// Next, find all uses of induction variables in this loop, and catagorize // Next, find all uses of induction variables in this loop, and catagorize
// them by stride. Start by finding all of the PHI nodes in the header for // them by stride. Start by finding all of the PHI nodes in the header for
// this loop. If they are induction variables, inspect their uses. // this loop. If they are induction variables, inspect their uses.
std::set<Instruction*> Processed; // Don't reprocess instructions.
for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
AddUsersIfInteresting(I, L); AddUsersIfInteresting(I, L, Processed);
// If we have nothing to do, return. // If we have nothing to do, return.
//if (IVUsesByStride.empty()) return; //if (IVUsesByStride.empty()) return;