[PATCH] Enable unrolling of multi-exit loops

[Mark Heffernan]

================
Comment at: lib/Analysis/ScalarEvolution.cpp:4723
@@ -4469,3 +4722,3 @@
     //
     // (a) Its ExitLimit.MustExit flag must be set which indicates that the exit
     // test condition cannot be skipped (the tested variable has unit stride or
----------------
jingyue wrote:
> Since MustExit is gone, comments need to be updated. 
Done.

================
Comment at: lib/Analysis/ScalarEvolution.cpp:6045
@@ -5800,3 +6044,3 @@
     const SCEV *Exact =
-      getUDivExpr(Distance, CountDown ? getNegativeSCEV(Step) : Step);
-    return ExitLimit(Exact, Exact, /*MustExit=*/false);
+        getUDivExpr(Distance, CountDown ? getNegativeSCEV(Step) : Step);
+    return ExitLimit(Exact, Exact);
----------------
jingyue wrote:
> Can we use getUDivExactExpr when R is zero? 
Done.

================
Comment at: lib/Analysis/ScalarEvolution.cpp:7104
@@ -6868,213 +7103,3 @@
                          R1->getValue(), R2->getValue()))) {
-        if (CB->getZExtValue() == false)
-          std::swap(R1, R2);   // R1 is the minimum root now.
-
-        // Make sure the root is not off by one.  The returned iteration should
-        // not be in the range, but the previous one should be.  When solving
-        // for "X*X < 5", for example, we should not return a root of 2.
-        ConstantInt *R1Val = EvaluateConstantChrecAtConstant(this,
-                                                             R1->getValue(),
-                                                             SE);
-        if (Range.contains(R1Val->getValue())) {
-          // The next iteration must be out of the range...
-          ConstantInt *NextVal =
-                ConstantInt::get(SE.getContext(), R1->getValue()->getValue()+1);
-
-          R1Val = EvaluateConstantChrecAtConstant(this, NextVal, SE);
-          if (!Range.contains(R1Val->getValue()))
-            return SE.getConstant(NextVal);
-          return SE.getCouldNotCompute();  // Something strange happened
-        }
-
-        // If R1 was not in the range, then it is a good return value.  Make
-        // sure that R1-1 WAS in the range though, just in case.
-        ConstantInt *NextVal =
-               ConstantInt::get(SE.getContext(), R1->getValue()->getValue()-1);
-        R1Val = EvaluateConstantChrecAtConstant(this, NextVal, SE);
-        if (Range.contains(R1Val->getValue()))
-          return R1;
-        return SE.getCouldNotCompute();  // Something strange happened
-      }
-    }
-  }
-
-  return SE.getCouldNotCompute();
-}
-
-namespace {
-struct FindUndefs {
-  bool Found;
-  FindUndefs() : Found(false) {}
-
-  bool follow(const SCEV *S) {
-    if (const SCEVUnknown *C = dyn_cast<SCEVUnknown>(S)) {
-      if (isa<UndefValue>(C->getValue()))
-        Found = true;
-    } else if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S)) {
-      if (isa<UndefValue>(C->getValue()))
-        Found = true;
-    }
-
-    // Keep looking if we haven't found it yet.
-    return !Found;
-  }
-  bool isDone() const {
-    // Stop recursion if we have found an undef.
-    return Found;
-  }
-};
-}
-
-// Return true when S contains at least an undef value.
-static inline bool
-containsUndefs(const SCEV *S) {
-  FindUndefs F;
-  SCEVTraversal<FindUndefs> ST(F);
-  ST.visitAll(S);
-
-  return F.Found;
-}
-
-namespace {
-// Collect all steps of SCEV expressions.
-struct SCEVCollectStrides {
-  ScalarEvolution &SE;
-  SmallVectorImpl<const SCEV *> &Strides;
-
-  SCEVCollectStrides(ScalarEvolution &SE, SmallVectorImpl<const SCEV *> &S)
-      : SE(SE), Strides(S) {}
-
-  bool follow(const SCEV *S) {
-    if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S))
-      Strides.push_back(AR->getStepRecurrence(SE));
-    return true;
-  }
-  bool isDone() const { return false; }
-};
-
-// Collect all SCEVUnknown and SCEVMulExpr expressions.
-struct SCEVCollectTerms {
-  SmallVectorImpl<const SCEV *> &Terms;
-
-  SCEVCollectTerms(SmallVectorImpl<const SCEV *> &T)
-      : Terms(T) {}
-
-  bool follow(const SCEV *S) {
-    if (isa<SCEVUnknown>(S) || isa<SCEVMulExpr>(S)) {
-      if (!containsUndefs(S))
-        Terms.push_back(S);
-
-      // Stop recursion: once we collected a term, do not walk its operands.
-      return false;
-    }
-
-    // Keep looking.
-    return true;
-  }
-  bool isDone() const { return false; }
-};
-}
-
-/// Find parametric terms in this SCEVAddRecExpr.
-void SCEVAddRecExpr::collectParametricTerms(
-    ScalarEvolution &SE, SmallVectorImpl<const SCEV *> &Terms) const {
-  SmallVector<const SCEV *, 4> Strides;
-  SCEVCollectStrides StrideCollector(SE, Strides);
-  visitAll(this, StrideCollector);
-
-  DEBUG({
-      dbgs() << "Strides:\n";
-      for (const SCEV *S : Strides)
-        dbgs() << *S << "\n";
-    });
-
-  for (const SCEV *S : Strides) {
-    SCEVCollectTerms TermCollector(Terms);
-    visitAll(S, TermCollector);
-  }
-
-  DEBUG({
-      dbgs() << "Terms:\n";
-      for (const SCEV *T : Terms)
-        dbgs() << *T << "\n";
-    });
-}
-
-static const APInt srem(const SCEVConstant *C1, const SCEVConstant *C2) {
-  APInt A = C1->getValue()->getValue();
-  APInt B = C2->getValue()->getValue();
-  uint32_t ABW = A.getBitWidth();
-  uint32_t BBW = B.getBitWidth();
-
-  if (ABW > BBW)
-    B = B.sext(ABW);
-  else if (ABW < BBW)
-    A = A.sext(BBW);
-
-  return APIntOps::srem(A, B);
-}
-
-static const APInt sdiv(const SCEVConstant *C1, const SCEVConstant *C2) {
-  APInt A = C1->getValue()->getValue();
-  APInt B = C2->getValue()->getValue();
-  uint32_t ABW = A.getBitWidth();
-  uint32_t BBW = B.getBitWidth();
-
-  if (ABW > BBW)
-    B = B.sext(ABW);
-  else if (ABW < BBW)
-    A = A.sext(BBW);
-
-  return APIntOps::sdiv(A, B);
-}
-
-namespace {
-struct FindSCEVSize {
-  int Size;
-  FindSCEVSize() : Size(0) {}
-
-  bool follow(const SCEV *S) {
-    ++Size;
-    // Keep looking at all operands of S.
-    return true;
-  }
-  bool isDone() const {
-    return false;
-  }
-};
-}
-
-// Returns the size of the SCEV S.
-static inline int sizeOfSCEV(const SCEV *S) {
-  FindSCEVSize F;
-  SCEVTraversal<FindSCEVSize> ST(F);
-  ST.visitAll(S);
-  return F.Size;
-}
-
-namespace {
-
-struct SCEVDivision : public SCEVVisitor<SCEVDivision, void> {
-public:
-  // Computes the Quotient and Remainder of the division of Numerator by
-  // Denominator.
-  static void divide(ScalarEvolution &SE, const SCEV *Numerator,
-                     const SCEV *Denominator, const SCEV **Quotient,
-                     const SCEV **Remainder) {
-    assert(Numerator && Denominator && "Uninitialized SCEV");
-
-    SCEVDivision D(SE, Numerator, Denominator);
-
-    // Check for the trivial case here to avoid having to check for it in the
-    // rest of the code.
-    if (Numerator == Denominator) {
-      *Quotient = D.One;
-      *Remainder = D.Zero;
-      return;
-    }
-
-    if (Numerator->isZero()) {
-      *Quotient = D.Zero;
-      *Remainder = D.Zero;
-      return;
-    }
+        if (CB->getZExtValue() == false)
+          std::swap(R1, R2);   // R1 is the minimum root now.
----------------
jingyue wrote:
> Looks like the diff tool is not doing a good job :) Are the remaining differences in this file simply copy and paste? 
Yeah, there is a big cut and paste.  Evidently there is some very similar code elsewhere in the file which is confusing the diff.

http://reviews.llvm.org/D5550