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

1 files changed, 82 insertions, 160 deletions

diff --git a/lib/Analysis/IVUsers.cpp b/lib/Analysis/IVUsers.cpp
index 47b5d4a0f0..467f9dd840 100644
--- a/lib/Analysis/IVUsers.cpp
+++ b/lib/Analysis/IVUsers.cpp
@@ -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;
+/// 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;
 
-    DEBUG(dbgs() << "[";
-          WriteAsOperand(dbgs(), L->getHeader(), /*PrintType=*/false);
-          dbgs() << "] Variable stride: " << *AddRecStride << "\n");
+  // 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);
   }
 
-  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)
+  // 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;
+  }
 
-  // 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()))
-    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.
-
-  // 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;
-    }
-
-  // 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);