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Allow users of iv / stride to be rewritten with expression that is a multiply

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of a smaller stride even if they have a common loop invariant expression part.

llvm-svn: 26828
This commit is contained in:
Evan Cheng 2006-03-17 19:52:23 +00:00
parent 0517ea7b2b
commit fa1b885135
1 changed files with 83 additions and 41 deletions
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124
lib/Transforms/Scalar/LoopStrengthReduce.cpp
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@ -180,6 +180,8 @@ private:
void OptimizeIndvars(Loop *L);
unsigned CheckForIVReuse(const SCEVHandle &Stride, IVExpr &IV);
void StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
IVUsersOfOneStride &Uses,
Loop *L, bool isOnlyStride);
@ -858,6 +860,44 @@ static bool isZero(SCEVHandle &V) {
}
/// CheckForIVReuse - Returns the multiple if the stride is the multiple
/// of a previous stride and it is a legal value for the target addressing
/// mode scale component. This allows the users of this stride to be rewritten
/// as prev iv * factor. It returns 1 if no reuse is possible.
unsigned LoopStrengthReduce::CheckForIVReuse(const SCEVHandle &Stride,
IVExpr &IV) {
if (!TLI)
return 1;
if (SCEVConstant *SC = dyn_cast<SCEVConstant>(Stride)) {
unsigned SInt = SC->getValue()->getRawValue();
if (SInt == 1)
return 1;
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 && (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)
// FIXME: Only handle base == 0 for now.
if (isZero(II->Base)) {
IV = *II;
return Scale;
}
}
}
return 1;
}
/// StrengthReduceStridedIVUsers - Strength reduce all of the users of a single
/// stride of IV. All of the users may have different starting values, and this
/// may not be the only stride (we know it is if isOnlyStride is true).
@ -883,7 +923,19 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
assert(UsersToProcess.back().Base->isLoopInvariant(L) &&
"Base value is not loop invariant!");
}
// Check if it is possible to reuse a IV with stride that is factor of this
// stride. And the multiple is a number that can be encoded in the scale
// field of the target addressing mode.
PHINode *NewPHI = NULL;
Value *IncV = NULL;
IVExpr ReuseIV(Stride, NULL, NULL);
unsigned RewriteFactor = CheckForIVReuse(Stride, ReuseIV);
if (RewriteFactor > 1) {
NewPHI = ReuseIV.PHI;
IncV = ReuseIV.IncV;
}
// We now have a whole bunch of uses of like-strided induction variables, but
// they might all have different bases. We want to emit one PHI node for this
// stride which we fold as many common expressions (between the IVs) into as
@ -935,55 +987,26 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
BasicBlock *LatchBlock = L->getLoopLatch();
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();
// Emit the initial base value into the loop preheader.
Value *CommonBaseV
= PreheaderRewriter.expandCodeFor(CommonExprs, PreInsertPt,
ReplacedTy);
if (RewriteFactor == 1) {
// Create a new Phi for this base, and stick it in the loop header.
NewPHI = new PHINode(ReplacedTy, "iv.", PhiInsertBefore);
++NumInserted;
// Add common base to the new Phi node.
NewPHI->addIncoming(CommonBaseV, Preheader);
// 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 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),
@ -994,7 +1017,16 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
IncV->setName(NewPHI->getName()+".inc");
NewPHI->addIncoming(IncV, LatchBlock);
// Remember this in case a later stride is multiple of this.
IVsByStride[Stride].addIV(CommonExprs, NewPHI, IncV);
} else {
Constant *C = dyn_cast<Constant>(CommonBaseV);
if (!C ||
(!C->isNullValue() &&
!isTargetConstant(SCEVUnknown::get(CommonBaseV), TLI)))
// We want the common base emitted into the preheader!
CommonBaseV = new CastInst(CommonBaseV, CommonBaseV->getType(),
"commonbase", PreInsertPt);
}
// Sort by the base value, so that all IVs with identical bases are next to
@ -1044,10 +1076,20 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
// 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)
if (RewriteFactor != 1) {
RewriteExpr =
SCEVMulExpr::get(SCEVUnknown::getIntegerSCEV(RewriteFactor,
RewriteExpr->getType()), RewriteExpr);
RewriteExpr->getType()),
RewriteExpr);
// The common base is emitted in the loop preheader. But since we
// are reusing an IV, it has not been used to initialize the PHI node.
// Add it to the expression used to rewrite the uses.
if (!isa<ConstantInt>(CommonBaseV) ||
!cast<ConstantInt>(CommonBaseV)->isNullValue())
RewriteExpr = SCEVAddExpr::get(RewriteExpr,
SCEVUnknown::get(CommonBaseV));
}
// Now that we know what we need to do, insert code before User for the
// immediate and any loop-variant expressions.