Generalize IVUsers to track arbitrary expressions rather than expressions
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
diff --git a/lib/Analysis/IVUsers.cpp b/lib/Analysis/IVUsers.cpp
index 47b5d4a..467f9dd 100644
--- a/lib/Analysis/IVUsers.cpp
+++ b/lib/Analysis/IVUsers.cpp
@@ -62,120 +62,34 @@
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 @@
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 @@
}
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 @@
/// 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 @@
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 @@
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);