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Generalize IVUsers to track arbitrary expressions rather than expressions

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explicitly split into stride-and-offset pairs. Also, add the
ability to track multiple post-increment loops on the same expression.

This refines the concept of "normalizing" SCEV expressions used for
to post-increment uses, and introduces a dedicated utility routine for
normalizing and denormalizing expressions.

This fixes the expansion of expressions which are post-increment users
of more than one loop at a time. More broadly, this takes LSR another
step closer to being able to reason about more than one loop at a time.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@100699 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2010-04-07 22:27:08 +00:00
parent b72e59e361
commit 448db1cdef
10 changed files with 743 additions and 279 deletions
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lib/Analysis/IVUsers.cpp
+83 -161
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@@ -62,120 +62,34 @@ static void CollectSubexprs(const SCEV *S,
Ops.push_back(S);
}
/// 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. The start cannot,
/// however, contain an AddRec from a different loop, unless that loop is an
/// outer loop of the current loop.
static bool getSCEVStartAndStride(const SCEV *&SH, Loop *L, Loop *UseLoop,
const SCEV *&Start, const SCEV *&Stride,
ScalarEvolution *SE, DominatorTree *DT) {
const SCEV *TheAddRec = Start; // Initialize to zero.
// If the outer level is an AddExpr, the operands are all start values except
// for a nested AddRecExpr.
if (const SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(SH)) {
for (unsigned i = 0, e = AE->getNumOperands(); i != e; ++i)
if (const SCEVAddRecExpr *AddRec =
dyn_cast<SCEVAddRecExpr>(AE->getOperand(i)))
TheAddRec = SE->getAddExpr(AddRec, TheAddRec);
else
Start = SE->getAddExpr(Start, AE->getOperand(i));
} else if (isa<SCEVAddRecExpr>(SH)) {
TheAddRec = SH;
} else {
return false; // not analyzable.
}
// Break down TheAddRec into its component parts.
SmallVector<const SCEV *, 4> Subexprs;
CollectSubexprs(TheAddRec, Subexprs, *SE);
// Look for an addrec on the current loop among the parts.
const SCEV *AddRecStride = 0;
for (SmallVectorImpl<const SCEV *>::iterator I = Subexprs.begin(),
E = Subexprs.end(); I != E; ++I) {
const SCEV *S = *I;
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S))
if (AR->getLoop() == L) {
*I = AR->getStart();
AddRecStride = AR->getStepRecurrence(*SE);
break;
}
}
if (!AddRecStride)
return false;
// Add up everything else into a start value (which may not be
// loop-invariant).
const SCEV *AddRecStart = SE->getAddExpr(Subexprs);
// Use getSCEVAtScope to attempt to simplify other loops out of
// the picture.
AddRecStart = SE->getSCEVAtScope(AddRecStart, UseLoop);
Start = SE->getAddExpr(Start, AddRecStart);
// If stride is an instruction, make sure it properly dominates the header.
// Otherwise we could end up with a use before def situation.
if (!isa<SCEVConstant>(AddRecStride)) {
BasicBlock *Header = L->getHeader();
if (!AddRecStride->properlyDominates(Header, DT))
return false;
DEBUG(dbgs() << "[";
WriteAsOperand(dbgs(), L->getHeader(), /*PrintType=*/false);
dbgs() << "] Variable stride: " << *AddRecStride << "\n");
}
Stride = AddRecStride;
return true;
}
/// IVUseShouldUsePostIncValue - We have discovered a "User" of an IV expression
/// and now we need to decide whether the user should use the preinc or post-inc
/// value. If this user should use the post-inc version of the IV, return true.
///
/// Choosing wrong here can break dominance properties (if we choose to use the
/// post-inc value when we cannot) or it can end up adding extra live-ranges to
/// the loop, resulting in reg-reg copies (if we use the pre-inc value when we
/// should use the post-inc value).
static bool IVUseShouldUsePostIncValue(Instruction *User, Instruction *IV,
const Loop *L, DominatorTree *DT) {
// If the user is in the loop, use the preinc value.
if (L->contains(User)) return false;
BasicBlock *LatchBlock = L->getLoopLatch();
if (!LatchBlock)
return false;
// Ok, the user is outside of the loop. If it is dominated by the latch
// block, use the post-inc value.
if (DT->dominates(LatchBlock, User->getParent()))
/// isInteresting - Test whether the given expression is "interesting" when
/// used by the given expression, within the context of analyzing the
/// given loop.
static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L) {
// Anything loop-invariant is interesting.
if (!isa<SCEVUnknown>(S) && S->isLoopInvariant(L))
return true;
// There is one case we have to be careful of: PHI nodes. These little guys
// can live in blocks that are not dominated by the latch block, but (since
// their uses occur in the predecessor block, not the block the PHI lives in)
// should still use the post-inc value. Check for this case now.
PHINode *PN = dyn_cast<PHINode>(User);
if (!PN) return false; // not a phi, not dominated by latch block.
// An addrec is interesting if it's affine or if it has an interesting start.
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
// Keep things simple. Don't touch loop-variant strides.
if (AR->getLoop() == L && (AR->isAffine() || !L->contains(I)))
return true;
// Otherwise recurse to see if the start value is interesting.
return isInteresting(AR->getStart(), I, L);
}
// Look at all of the uses of IV by the PHI node. If any use corresponds to
// a block that is not dominated by the latch block, give up and use the
// preincremented value.
unsigned NumUses = 0;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (PN->getIncomingValue(i) == IV) {
++NumUses;
if (!DT->dominates(LatchBlock, PN->getIncomingBlock(i)))
return false;
}
// An add is interesting if any of its operands is.
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
OI != OE; ++OI)
if (isInteresting(*OI, I, L))
return true;
return false;
}
// Okay, all uses of IV by PN are in predecessor blocks that really are
// dominated by the latch block. Use the post-incremented value.
return true;
// Nothing else is interesting here.
return false;
}
/// AddUsersIfInteresting - Inspect the specified instruction. If it is a
@@ -196,16 +110,9 @@ bool IVUsers::AddUsersIfInteresting(Instruction *I) {
const SCEV *ISE = SE->getSCEV(I);
if (isa<SCEVCouldNotCompute>(ISE)) return false;
// Get the start and stride for this expression.
Loop *UseLoop = LI->getLoopFor(I->getParent());
const SCEV *Start = SE->getIntegerSCEV(0, ISE->getType());
const SCEV *Stride = Start;
if (!getSCEVStartAndStride(ISE, L, UseLoop, Start, Stride, SE, DT))
return false; // Non-reducible symbolic expression, bail out.
// Keep things simple. Don't touch loop-variant strides.
if (!Stride->isLoopInvariant(L) && L->contains(I))
// If we've come to an uninteresting expression, stop the traversal and
// call this a user.
if (!isInteresting(ISE, I, L))
return false;
SmallPtrSet<Instruction *, 4> UniqueUsers;
@@ -241,27 +148,24 @@ bool IVUsers::AddUsersIfInteresting(Instruction *I) {
}
if (AddUserToIVUsers) {
// Okay, we found a user that we cannot reduce. Analyze the instruction
// and decide what to do with it. If we are a use inside of the loop, use
// the value before incrementation, otherwise use it after incrementation.
if (IVUseShouldUsePostIncValue(User, I, L, DT)) {
// The value used will be incremented by the stride more than we are
// expecting, so subtract this off.
const SCEV *NewStart = SE->getMinusSCEV(Start, Stride);
IVUses.push_back(new IVStrideUse(this, Stride, NewStart, User, I));
IVUses.back().setIsUseOfPostIncrementedValue(true);
DEBUG(dbgs() << " USING POSTINC SCEV, START=" << *NewStart<< "\n");
} else {
IVUses.push_back(new IVStrideUse(this, Stride, Start, User, I));
}
// Okay, we found a user that we cannot reduce.
IVUses.push_back(new IVStrideUse(this, ISE, User, I));
IVStrideUse &NewUse = IVUses.back();
// Transform the expression into a normalized form.
NewUse.Expr =
TransformForPostIncUse(NormalizeAutodetect, NewUse.Expr,
User, I,
NewUse.PostIncLoops,
*SE, *DT);
DEBUG(dbgs() << " NORMALIZED TO: " << *NewUse.Expr << '\n');
}
}
return true;
}
IVStrideUse &IVUsers::AddUser(const SCEV *Stride, const SCEV *Offset,
IVStrideUse &IVUsers::AddUser(const SCEV *Expr,
Instruction *User, Value *Operand) {
IVUses.push_back(new IVStrideUse(this, Stride, Offset, User, Operand));
IVUses.push_back(new IVStrideUse(this, Expr, User, Operand));
return IVUses.back();
}
@@ -295,30 +199,10 @@ bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
/// getReplacementExpr - Return a SCEV expression which computes the
/// value of the OperandValToReplace of the given IVStrideUse.
const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &U) const {
// Start with zero.
const SCEV *RetVal = SE->getIntegerSCEV(0, U.getStride()->getType());
// Create the basic add recurrence.
RetVal = SE->getAddRecExpr(RetVal, U.getStride(), L);
// Add the offset in a separate step, because it may be loop-variant.
RetVal = SE->getAddExpr(RetVal, U.getOffset());
// For uses of post-incremented values, add an extra stride to compute
// the actual replacement value.
if (U.isUseOfPostIncrementedValue())
RetVal = SE->getAddExpr(RetVal, U.getStride());
return RetVal;
}
/// getCanonicalExpr - Return a SCEV expression which computes the
/// value of the SCEV of the given IVStrideUse, ignoring the
/// isUseOfPostIncrementedValue flag.
const SCEV *IVUsers::getCanonicalExpr(const IVStrideUse &U) const {
// Start with zero.
const SCEV *RetVal = SE->getIntegerSCEV(0, U.getStride()->getType());
// Create the basic add recurrence.
RetVal = SE->getAddRecExpr(RetVal, U.getStride(), L);
// Add the offset in a separate step, because it may be loop-variant.
RetVal = SE->getAddExpr(RetVal, U.getOffset());
return RetVal;
PostIncLoopSet &Loops = const_cast<PostIncLoopSet &>(U.PostIncLoops);
return TransformForPostIncUse(Denormalize, U.getExpr(),
U.getUser(), U.getOperandValToReplace(),
Loops, *SE, *DT);
}
void IVUsers::print(raw_ostream &OS, const Module *M) const {
@@ -339,8 +223,13 @@ void IVUsers::print(raw_ostream &OS, const Module *M) const {
WriteAsOperand(OS, UI->getOperandValToReplace(), false);
OS << " = "
<< *getReplacementExpr(*UI);
if (UI->isUseOfPostIncrementedValue())
OS << " (post-inc)";
for (PostIncLoopSet::const_iterator
I = UI->PostIncLoops.begin(),
E = UI->PostIncLoops.end(); I != E; ++I) {
OS << " (post-inc with loop ";
WriteAsOperand(OS, (*I)->getHeader(), false);
OS << ")";
}
OS << " in ";
UI->getUser()->print(OS, &Annotator);
OS << '\n';
@@ -356,6 +245,39 @@ void IVUsers::releaseMemory() {
IVUses.clear();
}
static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
if (AR->getLoop() == L)
return AR;
return findAddRecForLoop(AR->getStart(), L);
}
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
I != E; ++I)
if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
return AR;
return 0;
}
return 0;
}
const SCEV *IVStrideUse::getStride(const Loop *L) const {
if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(), L))
return AR->getStepRecurrence(*Parent->SE);
return 0;
}
void IVStrideUse::transformToPostInc(const Loop *L) {
PostIncLoopSet Loops;
Loops.insert(L);
Expr = TransformForPostIncUse(Normalize, Expr,
getUser(), getOperandValToReplace(),
Loops, *Parent->SE, *Parent->DT);
PostIncLoops.insert(L);
}
void IVStrideUse::deleted() {
// Remove this user from the list.
Parent->IVUses.erase(this);