[SCEV][LAA] Re-commit r260085 and r260086, this time with a fix for the memory

sanitizer issue. The PredicatedScalarEvolution's copy constructor
wasn't copying the Generation value, and was leaving it un-initialized.

Original commit message:

[SCEV][LAA] Add no wrap SCEV predicates and use use them to improve strided pointer detection

Summary:
This change adds no wrap SCEV predicates with:
  - support for runtime checking
  - support for expression rewriting:
      (sext ({x,+,y}) -> {sext(x),+,sext(y)}
      (zext ({x,+,y}) -> {zext(x),+,sext(y)}

Note that we are sign extending the increment of the SCEV, even for
the zext case. This is needed to cover the fairly common case where y would
be a (small) negative integer. In order to do this, this change adds two new
flags: nusw and nssw that are applicable to AddRecExprs and permit the
transformations above.

We also change isStridedPtr in LAA to be able to make use of
these predicates. With this feature we should now always be able to
work around overflow issues in the dependence analysis.

Reviewers: mzolotukhin, sanjoy, anemet

Subscribers: mzolotukhin, sanjoy, llvm-commits, rengolin, jmolloy, hfinkel

Differential Revision: http://reviews.llvm.org/D15412

llvm-svn: 260112

1 files changed, 188 insertions, 10 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 32bf11ac5c5..c618791272e 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -9627,17 +9627,40 @@ ScalarEvolution::getEqualPredicate(const SCEVUnknown *LHS,
   return Eq;
 }
 
+const SCEVPredicate *ScalarEvolution::getWrapPredicate(
+    const SCEVAddRecExpr *AR,
+    SCEVWrapPredicate::IncrementWrapFlags AddedFlags) {
+  FoldingSetNodeID ID;
+  // Unique this node based on the arguments
+  ID.AddInteger(SCEVPredicate::P_Wrap);
+  ID.AddPointer(AR);
+  ID.AddInteger(AddedFlags);
+  void *IP = nullptr;
+  if (const auto *S = UniquePreds.FindNodeOrInsertPos(ID, IP))
+    return S;
+  auto *OF = new (SCEVAllocator)
+      SCEVWrapPredicate(ID.Intern(SCEVAllocator), AR, AddedFlags);
+  UniquePreds.InsertNode(OF, IP);
+  return OF;
+}
+
 namespace {
+
 class SCEVPredicateRewriter : public SCEVRewriteVisitor<SCEVPredicateRewriter> {
 public:
-  static const SCEV *rewrite(const SCEV *Scev, ScalarEvolution &SE,
-                             SCEVUnionPredicate &A) {
-    SCEVPredicateRewriter Rewriter(SE, A);
+  // Rewrites Scev in the context of a loop L and the predicate A.
+  // If Assume is true, rewrite is free to add further predicates to A
+  // such that the result will be an AddRecExpr.
+  static const SCEV *rewrite(const SCEV *Scev, const Loop *L,
+                             ScalarEvolution &SE, SCEVUnionPredicate &A,
+                             bool Assume) {
+    SCEVPredicateRewriter Rewriter(L, SE, A, Assume);
     return Rewriter.visit(Scev);
   }
 
-  SCEVPredicateRewriter(ScalarEvolution &SE, SCEVUnionPredicate &P)
-      : SCEVRewriteVisitor(SE), P(P) {}
+  SCEVPredicateRewriter(const Loop *L, ScalarEvolution &SE,
+                        SCEVUnionPredicate &P, bool Assume)
+      : SCEVRewriteVisitor(SE), P(P), L(L), Assume(Assume) {}
 
   const SCEV *visitUnknown(const SCEVUnknown *Expr) {
     auto ExprPreds = P.getPredicatesForExpr(Expr);
@@ -9649,14 +9672,67 @@ public:
     return Expr;
   }
 
+  const SCEV *visitZeroExtendExpr(const SCEVZeroExtendExpr *Expr) {
+    const SCEV *Operand = visit(Expr->getOperand());
+    const SCEVAddRecExpr *AR = dyn_cast<const SCEVAddRecExpr>(Operand);
+    if (AR && AR->getLoop() == L && AR->isAffine()) {
+      // This couldn't be folded because the operand didn't have the nuw
+      // flag. Add the nusw flag as an assumption that we could make.
+      const SCEV *Step = AR->getStepRecurrence(SE);
+      Type *Ty = Expr->getType();
+      if (addOverflowAssumption(AR, SCEVWrapPredicate::IncrementNUSW))
+        return SE.getAddRecExpr(SE.getZeroExtendExpr(AR->getStart(), Ty),
+                                SE.getSignExtendExpr(Step, Ty), L,
+                                AR->getNoWrapFlags());
+    }
+    return SE.getZeroExtendExpr(Operand, Expr->getType());
+  }
+
+  const SCEV *visitSignExtendExpr(const SCEVSignExtendExpr *Expr) {
+    const SCEV *Operand = visit(Expr->getOperand());
+    const SCEVAddRecExpr *AR = dyn_cast<const SCEVAddRecExpr>(Operand);
+    if (AR && AR->getLoop() == L && AR->isAffine()) {
+      // This couldn't be folded because the operand didn't have the nsw
+      // flag. Add the nssw flag as an assumption that we could make.
+      const SCEV *Step = AR->getStepRecurrence(SE);
+      Type *Ty = Expr->getType();
+      if (addOverflowAssumption(AR, SCEVWrapPredicate::IncrementNSSW))
+        return SE.getAddRecExpr(SE.getSignExtendExpr(AR->getStart(), Ty),
+                                SE.getSignExtendExpr(Step, Ty), L,
+                                AR->getNoWrapFlags());
+    }
+    return SE.getSignExtendExpr(Operand, Expr->getType());
+  }
+
 private:
+  bool addOverflowAssumption(const SCEVAddRecExpr *AR,
+                             SCEVWrapPredicate::IncrementWrapFlags AddedFlags) {
+    auto *A = SE.getWrapPredicate(AR, AddedFlags);
+    if (!Assume) {
+      // Check if we've already made this assumption.
+      if (P.implies(A))
+        return true;
+      return false;
+    }
+    P.add(A);
+    return true;
+  }
+
   SCEVUnionPredicate &P;
+  const Loop *L;
+  bool Assume;
 };
 } // end anonymous namespace
 
 const SCEV *ScalarEvolution::rewriteUsingPredicate(const SCEV *Scev,
+                                                   const Loop *L,
                                                    SCEVUnionPredicate &Preds) {
-  return SCEVPredicateRewriter::rewrite(Scev, *this, Preds);
+  return SCEVPredicateRewriter::rewrite(Scev, L, *this, Preds, false);
+}
+
+const SCEV *ScalarEvolution::convertSCEVToAddRecWithPredicates(
+    const SCEV *Scev, const Loop *L, SCEVUnionPredicate &Preds) {
+  return SCEVPredicateRewriter::rewrite(Scev, L, *this, Preds, true);
 }
 
 /// SCEV predicates
@@ -9686,6 +9762,59 @@ void SCEVEqualPredicate::print(raw_ostream &OS, unsigned Depth) const {
   OS.indent(Depth) << "Equal predicate: " << *LHS << " == " << *RHS << "\n";
 }
 
+SCEVWrapPredicate::SCEVWrapPredicate(const FoldingSetNodeIDRef ID,
+                                     const SCEVAddRecExpr *AR,
+                                     IncrementWrapFlags Flags)
+    : SCEVPredicate(ID, P_Wrap), AR(AR), Flags(Flags) {}
+
+const SCEV *SCEVWrapPredicate::getExpr() const { return AR; }
+
+bool SCEVWrapPredicate::implies(const SCEVPredicate *N) const {
+  const auto *Op = dyn_cast<SCEVWrapPredicate>(N);
+
+  return Op && Op->AR == AR && setFlags(Flags, Op->Flags) == Flags;
+}
+
+bool SCEVWrapPredicate::isAlwaysTrue() const {
+  SCEV::NoWrapFlags ScevFlags = AR->getNoWrapFlags();
+  IncrementWrapFlags IFlags = Flags;
+
+  if (ScalarEvolution::setFlags(ScevFlags, SCEV::FlagNSW) == ScevFlags)
+    IFlags = clearFlags(IFlags, IncrementNSSW);
+
+  return IFlags == IncrementAnyWrap;
+}
+
+void SCEVWrapPredicate::print(raw_ostream &OS, unsigned Depth) const {
+  OS.indent(Depth) << *getExpr() << " Added Flags: ";
+  if (SCEVWrapPredicate::IncrementNUSW & getFlags())
+    OS << "<nusw>";
+  if (SCEVWrapPredicate::IncrementNSSW & getFlags())
+    OS << "<nssw>";
+  OS << "\n";
+}
+
+SCEVWrapPredicate::IncrementWrapFlags
+SCEVWrapPredicate::getImpliedFlags(const SCEVAddRecExpr *AR,
+                                   ScalarEvolution &SE) {
+  IncrementWrapFlags ImpliedFlags = IncrementAnyWrap;
+  SCEV::NoWrapFlags StaticFlags = AR->getNoWrapFlags();
+
+  // We can safely transfer the NSW flag as NSSW.
+  if (ScalarEvolution::setFlags(StaticFlags, SCEV::FlagNSW) == StaticFlags)
+    ImpliedFlags = IncrementNSSW;
+
+  if (ScalarEvolution::setFlags(StaticFlags, SCEV::FlagNUW) == StaticFlags) {
+    // If the increment is positive, the SCEV NUW flag will also imply the
+    // WrapPredicate NUSW flag.
+    if (const auto *Step = dyn_cast<SCEVConstant>(AR->getStepRecurrence(SE)))
+      if (Step->getValue()->getValue().isNonNegative())
+        ImpliedFlags = setFlags(ImpliedFlags, IncrementNUSW);
+  }
+
+  return ImpliedFlags;
+}
+
 /// Union predicates don't get cached so create a dummy set ID for it.
 SCEVUnionPredicate::SCEVUnionPredicate()
     : SCEVPredicate(FoldingSetNodeIDRef(nullptr, 0), P_Union) {}
@@ -9742,8 +9871,9 @@ void SCEVUnionPredicate::add(const SCEVPredicate *N) {
   Preds.push_back(N);
 }
 
-PredicatedScalarEvolution::PredicatedScalarEvolution(ScalarEvolution &SE)
-    : SE(SE), Generation(0) {}
+PredicatedScalarEvolution::PredicatedScalarEvolution(ScalarEvolution &SE,
+                                                     Loop &L)
+    : SE(SE), L(L), Generation(0) {}
 
 const SCEV *PredicatedScalarEvolution::getSCEV(Value *V) {
   const SCEV *Expr = SE.getSCEV(V);
@@ -9758,7 +9888,7 @@ const SCEV *PredicatedScalarEvolution::getSCEV(Value *V) {
   if (Entry.second)
     Expr = Entry.second;
 
-  const SCEV *NewSCEV = SE.rewriteUsingPredicate(Expr, Preds);
+  const SCEV *NewSCEV = SE.rewriteUsingPredicate(Expr, &L, Preds);
   Entry = {Generation, NewSCEV};
 
   return NewSCEV;
@@ -9780,7 +9910,55 @@ void PredicatedScalarEvolution::updateGeneration() {
   if (++Generation == 0) {
     for (auto &II : RewriteMap) {
       const SCEV *Rewritten = II.second.second;
-      II.second = {Generation, SE.rewriteUsingPredicate(Rewritten, Preds)};
+      II.second = {Generation, SE.rewriteUsingPredicate(Rewritten, &L, Preds)};
     }
   }
 }
+
+void PredicatedScalarEvolution::setNoOverflow(
+    Value *V, SCEVWrapPredicate::IncrementWrapFlags Flags) {
+  const SCEV *Expr = getSCEV(V);
+  const auto *AR = cast<SCEVAddRecExpr>(Expr);
+
+  auto ImpliedFlags = SCEVWrapPredicate::getImpliedFlags(AR, SE);
+
+  // Clear the statically implied flags.
+  Flags = SCEVWrapPredicate::clearFlags(Flags, ImpliedFlags);
+  addPredicate(*SE.getWrapPredicate(AR, Flags));
+
+  auto II = FlagsMap.insert({V, Flags});
+  if (!II.second)
+    II.first->second = SCEVWrapPredicate::setFlags(Flags, II.first->second);
+}
+
+bool PredicatedScalarEvolution::hasNoOverflow(
+    Value *V, SCEVWrapPredicate::IncrementWrapFlags Flags) {
+  const SCEV *Expr = getSCEV(V);
+  const auto *AR = cast<SCEVAddRecExpr>(Expr);
+
+  Flags = SCEVWrapPredicate::clearFlags(
+      Flags, SCEVWrapPredicate::getImpliedFlags(AR, SE));
+
+  auto II = FlagsMap.find(V);
+
+  if (II != FlagsMap.end())
+    Flags = SCEVWrapPredicate::clearFlags(Flags, II->second);
+
+  return Flags == SCEVWrapPredicate::IncrementAnyWrap;
+}
+
+const SCEV *PredicatedScalarEvolution::getAsAddRec(Value *V) {
+  const SCEV *Expr = this->getSCEV(V);
+  const SCEV *New = SE.convertSCEVToAddRecWithPredicates(Expr, &L, Preds);
+  updateGeneration();
+  RewriteMap[SE.getSCEV(V)] = {Generation, New};
+  return New;
+}
+
+PredicatedScalarEvolution::
+PredicatedScalarEvolution(const PredicatedScalarEvolution &Init) :
+  RewriteMap(Init.RewriteMap), SE(Init.SE), L(Init.L), Preds(Init.Preds),
+  Generation(Init.Generation) {
+  for (auto I = Init.FlagsMap.begin(), E = Init.FlagsMap.end(); I != E; ++I)
+    FlagsMap.insert(*I);
+}