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For each loop, keep track of all the IV expressions inserted indexed by 

stride. For a set of uses of the IV of a stride which is a multiple
of another stride, do not insert a new IV expression. Rather, reuse the
previous IV and rewrite the uses as uses of IV expression multiplied by
the factor.

e.g.
x = 0 ...; x ++
y = 0 ...; y += 4
then use of y can be rewritten as use of 4*x for x86.

llvm-svn: 26803
This commit is contained in:
Evan Cheng 2006-03-16 21:53:05 +00:00
parent 20931a798e
commit 3df447d354
2 changed files with 119 additions and 44 deletions
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12
llvm/include/llvm/Transforms/Scalar.h
View File

@ -132,15 +132,11 @@ FunctionPass *createLICMPass();
//===----------------------------------------------------------------------===//
//
// LoopStrengthReduce - This pass is strength reduces GEP instructions that use
// a loop's canonical induction variable as one of their indices. The
// MaxTargetAMSize is the largest element size that the target architecture
// can handle in its addressing modes. Power of two multipliers less than or
// equal to this value are not reduced. It also takes an optional second
// parameter used to consult the target machine whether certain transformations
// are profitable.
// a loop's canonical induction variable as one of their indices. It takes an
// optional parameter used to consult the target machine whether certain
// transformations are profitable.
//
FunctionPass *createLoopStrengthReducePass(unsigned MaxTargetAMSize = 1,
const TargetLowering *TLI = NULL);
FunctionPass *createLoopStrengthReducePass(const TargetLowering *TLI = NULL);
//===----------------------------------------------------------------------===//
//

151
llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
View File

@ -76,6 +76,27 @@ namespace {
}
};
/// IVInfo - This structure keeps track of one IV expression inserted during
/// StrengthReduceStridedIVUsers. It contains the base value, as well as the
/// PHI node and increment value created for rewrite.
struct IVExpr {
SCEVHandle Base;
PHINode *PHI;
Value *IncV;
IVExpr(const SCEVHandle &base, PHINode *phi, Value *incv)
: Base(base), PHI(phi), IncV(incv) {}
};
/// IVsOfOneStride - This structure keeps track of all IV expression inserted
/// during StrengthReduceStridedIVUsers for a particular stride of the IV.
struct IVsOfOneStride {
std::vector<IVExpr> IVs;
void addIV(const SCEVHandle &Base, PHINode *PHI, Value *IncV) {
IVs.push_back(IVExpr(Base, PHI, IncV));
}
};
class LoopStrengthReduce : public FunctionPass {
LoopInfo *LI;
@ -85,14 +106,14 @@ namespace {
const Type *UIntPtrTy;
bool Changed;
/// MaxTargetAMSize - This is the maximum power-of-two scale value that the
/// target can handle for free with its addressing modes.
unsigned MaxTargetAMSize;
/// IVUsesByStride - Keep track of all uses of induction variables that we
/// are interested in. The key of the map is the stride of the access.
std::map<SCEVHandle, IVUsersOfOneStride> IVUsesByStride;
/// IVsByStride - Keep track of all IVs that have been inserted for a
/// particular stride.
std::map<SCEVHandle, IVsOfOneStride> IVsByStride;
/// StrideOrder - An ordering of the keys in IVUsesByStride that is stable:
/// We use this to iterate over the IVUsesByStride collection without being
/// dependent on random ordering of pointers in the process.
@ -112,8 +133,8 @@ namespace {
const TargetLowering *TLI;
public:
LoopStrengthReduce(unsigned MTAMS = 1, const TargetLowering *tli = NULL)
: MaxTargetAMSize(MTAMS), TLI(tli) {
LoopStrengthReduce(const TargetLowering *tli = NULL)
: TLI(tli) {
}
virtual bool runOnFunction(Function &) {
@ -168,9 +189,8 @@ private:
"Loop Strength Reduction");
}
FunctionPass *llvm::createLoopStrengthReducePass(unsigned MaxTargetAMSize,
const TargetLowering *TLI) {
return new LoopStrengthReduce(MaxTargetAMSize, TLI);
FunctionPass *llvm::createLoopStrengthReducePass(const TargetLowering *TLI) {
return new LoopStrengthReduce(TLI);
}
/// getCastedVersionOf - Return the specified value casted to uintptr_t.
@ -829,6 +849,14 @@ RemoveCommonExpressionsFromUseBases(std::vector<BasedUser> &Uses) {
return Result;
}
/// isZero - returns true if the scalar evolution expression is zero.
///
static bool isZero(SCEVHandle &V) {
if (SCEVConstant *SC = dyn_cast<SCEVConstant>(V))
return SC->getValue()->getRawValue() == 0;
return false;
}
/// StrengthReduceStridedIVUsers - Strength reduce all of the users of a single
/// stride of IV. All of the users may have different starting values, and this
@ -863,7 +891,8 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
// for the strides (e.g. if we have "A+C+B" and "A+B+D" as our bases, find
// "A+B"), emit it to the preheader, then remove the expression from the
// UsersToProcess base values.
SCEVHandle CommonExprs = RemoveCommonExpressionsFromUseBases(UsersToProcess);
SCEVHandle CommonExprs =
RemoveCommonExpressionsFromUseBases(UsersToProcess);
// Next, figure out what we can represent in the immediate fields of
// instructions. If we can represent anything there, move it to the imm
@ -891,12 +920,12 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
isAddress, L);
}
}
// Now that we know what we need to do, insert the PHI node itself.
//
DEBUG(std::cerr << "INSERTING IV of STRIDE " << *Stride << " and BASE "
<< *CommonExprs << " :\n");
SCEVExpander Rewriter(*SE, *LI);
SCEVExpander PreheaderRewriter(*SE, *LI);
@ -905,33 +934,68 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
Instruction *PhiInsertBefore = L->getHeader()->begin();
BasicBlock *LatchBlock = L->getLoopLatch();
// Create a new Phi for this base, and stick it in the loop header.
unsigned RewriteFactor = 1;
PHINode *NewPHI = NULL;
Value *IncV = NULL;
// FIXME: Only handle base == 0 for now.
if (TLI && isZero(CommonExprs)) {
if (SCEVConstant *SC = dyn_cast<SCEVConstant>(Stride)) {
unsigned SInt = SC->getValue()->getRawValue();
for (TargetLowering::legal_am_scale_iterator
I = TLI->legal_am_scale_begin(), E = TLI->legal_am_scale_end();
I != E; ++I) {
unsigned Scale = *I;
if ((SInt % Scale) != 0)
continue;
std::map<SCEVHandle, IVsOfOneStride>::iterator SI =
IVsByStride.find(SCEVUnknown::getIntegerSCEV(SInt/Scale, Type::UIntTy));
if (SI == IVsByStride.end())
continue;
for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
IE = SI->second.IVs.end(); II != IE; ++II)
if (isZero(II->Base)) {
RewriteFactor = Scale;
NewPHI = II->PHI;
IncV = II->IncV;
break;
}
if (RewriteFactor != 1)
break;
}
}
}
const Type *ReplacedTy = CommonExprs->getType();
PHINode *NewPHI = new PHINode(ReplacedTy, "iv.", PhiInsertBefore);
++NumInserted;
if (RewriteFactor == 1) {
// Create a new Phi for this base, and stick it in the loop header.
NewPHI = new PHINode(ReplacedTy, "iv.", PhiInsertBefore);
++NumInserted;
// Insert the stride into the preheader.
Value *StrideV = PreheaderRewriter.expandCodeFor(Stride, PreInsertPt,
ReplacedTy);
if (!isa<ConstantInt>(StrideV)) ++NumVariable;
// Insert the stride into the preheader.
Value *StrideV = PreheaderRewriter.expandCodeFor(Stride, PreInsertPt,
ReplacedTy);
if (!isa<ConstantInt>(StrideV)) ++NumVariable;
// Emit the initial base value into the loop preheader, and add it to the
// Phi node.
Value *PHIBaseV = PreheaderRewriter.expandCodeFor(CommonExprs, PreInsertPt,
ReplacedTy);
NewPHI->addIncoming(PHIBaseV, Preheader);
// Emit the initial base value into the loop preheader, and add it to the
// Phi node.
Value *PHIBaseV = PreheaderRewriter.expandCodeFor(CommonExprs, PreInsertPt,
ReplacedTy);
NewPHI->addIncoming(PHIBaseV, Preheader);
// Emit the increment of the base value before the terminator of the loop
// latch block, and add it to the Phi node.
SCEVHandle IncExp = SCEVAddExpr::get(SCEVUnknown::get(NewPHI),
SCEVUnknown::get(StrideV));
// Emit the increment of the base value before the terminator of the loop
// latch block, and add it to the Phi node.
SCEVHandle IncExp = SCEVAddExpr::get(SCEVUnknown::get(NewPHI),
SCEVUnknown::get(StrideV));
Value *IncV = Rewriter.expandCodeFor(IncExp, LatchBlock->getTerminator(),
ReplacedTy);
IncV->setName(NewPHI->getName()+".inc");
NewPHI->addIncoming(IncV, LatchBlock);
IncV = Rewriter.expandCodeFor(IncExp, LatchBlock->getTerminator(),
ReplacedTy);
IncV->setName(NewPHI->getName()+".inc");
NewPHI->addIncoming(IncV, LatchBlock);
IVsByStride[Stride].addIV(CommonExprs, NewPHI, IncV);
}
// Sort by the base value, so that all IVs with identical bases are next to
// each other.
@ -977,13 +1041,20 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
// Clear the SCEVExpander's expression map so that we are guaranteed
// to have the code emitted where we expect it.
Rewriter.clear();
// If we are reusing the iv, then it must be multiplied by a constant
// factor take advantage of addressing mode scale component.
if (RewriteFactor != 1)
RewriteExpr =
SCEVMulExpr::get(SCEVUnknown::getIntegerSCEV(RewriteFactor,
RewriteExpr->getType()), RewriteExpr);
// Now that we know what we need to do, insert code before User for the
// immediate and any loop-variant expressions.
if (!isa<ConstantInt>(BaseV) || !cast<ConstantInt>(BaseV)->isNullValue())
// Add BaseV to the PHI value if needed.
RewriteExpr = SCEVAddExpr::get(RewriteExpr, SCEVUnknown::get(BaseV));
User.RewriteInstructionToUseNewBase(RewriteExpr, Rewriter, L, this);
// Mark old value we replaced as possibly dead, so that it is elminated
@ -1119,7 +1190,15 @@ void LoopStrengthReduce::runOnLoop(Loop *L) {
// If we only have one stride, we can more aggressively eliminate some things.
bool HasOneStride = IVUsesByStride.size() == 1;
#ifndef NDEBUG
DEBUG(std::cerr << "\nLSR on ");
DEBUG(L->dump());
#endif
// IVsByStride keeps IVs for one particular loop.
IVsByStride.clear();
// Note: this processes each stride/type pair individually. All users passed
// into StrengthReduceStridedIVUsers have the same type AND stride. Also,
// node that we iterate over IVUsesByStride indirectly by using StrideOrder.