1 files changed, 259 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/ScalarEvolutionDivision.cpp b/llvm/lib/Analysis/ScalarEvolutionDivision.cpp
new file mode 100644
index 000000000000..19bf5766f448
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+++ b/llvm/lib/Analysis/ScalarEvolutionDivision.cpp
@@ -0,0 +1,259 @@
+//===- ScalarEvolutionDivision.h - See below --------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the class that knows how to divide SCEV's.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/ScalarEvolutionDivision.h"
+#include "llvm/ADT/APInt.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/ErrorHandling.h"
+#include <cassert>
+#include <cstdint>
+
+namespace llvm {
+class Type;
+}
+
+using namespace llvm;
+
+namespace {
+
+static inline int sizeOfSCEV(const SCEV *S) {
+  struct FindSCEVSize {
+    int Size = 0;
+
+    FindSCEVSize() = default;
+
+    bool follow(const SCEV *S) {
+      ++Size;
+      // Keep looking at all operands of S.
+      return true;
+    }
+
+    bool isDone() const { return false; }
+  };
+
+  FindSCEVSize F;
+  SCEVTraversal<FindSCEVSize> ST(F);
+  ST.visitAll(S);
+  return F.Size;
+}
+
+} // namespace
+
+// Computes the Quotient and Remainder of the division of Numerator by
+// Denominator.
+void SCEVDivision::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;
+  }
+
+  // A simple case when N/1. The quotient is N.
+  if (Denominator->isOne()) {
+    *Quotient = Numerator;
+    *Remainder = D.Zero;
+    return;
+  }
+
+  // Split the Denominator when it is a product.
+  if (const SCEVMulExpr *T = dyn_cast<SCEVMulExpr>(Denominator)) {
+    const SCEV *Q, *R;
+    *Quotient = Numerator;
+    for (const SCEV *Op : T->operands()) {
+      divide(SE, *Quotient, Op, &Q, &R);
+      *Quotient = Q;
+
+      // Bail out when the Numerator is not divisible by one of the terms of
+      // the Denominator.
+      if (!R->isZero()) {
+        *Quotient = D.Zero;
+        *Remainder = Numerator;
+        return;
+      }
+    }
+    *Remainder = D.Zero;
+    return;
+  }
+
+  D.visit(Numerator);
+  *Quotient = D.Quotient;
+  *Remainder = D.Remainder;
+}
+
+void SCEVDivision::visitConstant(const SCEVConstant *Numerator) {
+  if (const SCEVConstant *D = dyn_cast<SCEVConstant>(Denominator)) {
+    APInt NumeratorVal = Numerator->getAPInt();
+    APInt DenominatorVal = D->getAPInt();
+    uint32_t NumeratorBW = NumeratorVal.getBitWidth();
+    uint32_t DenominatorBW = DenominatorVal.getBitWidth();
+
+    if (NumeratorBW > DenominatorBW)
+      DenominatorVal = DenominatorVal.sext(NumeratorBW);
+    else if (NumeratorBW < DenominatorBW)
+      NumeratorVal = NumeratorVal.sext(DenominatorBW);
+
+    APInt QuotientVal(NumeratorVal.getBitWidth(), 0);
+    APInt RemainderVal(NumeratorVal.getBitWidth(), 0);
+    APInt::sdivrem(NumeratorVal, DenominatorVal, QuotientVal, RemainderVal);
+    Quotient = SE.getConstant(QuotientVal);
+    Remainder = SE.getConstant(RemainderVal);
+    return;
+  }
+}
+
+void SCEVDivision::visitAddRecExpr(const SCEVAddRecExpr *Numerator) {
+  const SCEV *StartQ, *StartR, *StepQ, *StepR;
+  if (!Numerator->isAffine())
+    return cannotDivide(Numerator);
+  divide(SE, Numerator->getStart(), Denominator, &StartQ, &StartR);
+  divide(SE, Numerator->getStepRecurrence(SE), Denominator, &StepQ, &StepR);
+  // Bail out if the types do not match.
+  Type *Ty = Denominator->getType();
+  if (Ty != StartQ->getType() || Ty != StartR->getType() ||
+      Ty != StepQ->getType() || Ty != StepR->getType())
+    return cannotDivide(Numerator);
+  Quotient = SE.getAddRecExpr(StartQ, StepQ, Numerator->getLoop(),
+                              Numerator->getNoWrapFlags());
+  Remainder = SE.getAddRecExpr(StartR, StepR, Numerator->getLoop(),
+                               Numerator->getNoWrapFlags());
+}
+
+void SCEVDivision::visitAddExpr(const SCEVAddExpr *Numerator) {
+  SmallVector<const SCEV *, 2> Qs, Rs;
+  Type *Ty = Denominator->getType();
+
+  for (const SCEV *Op : Numerator->operands()) {
+    const SCEV *Q, *R;
+    divide(SE, Op, Denominator, &Q, &R);
+
+    // Bail out if types do not match.
+    if (Ty != Q->getType() || Ty != R->getType())
+      return cannotDivide(Numerator);
+
+    Qs.push_back(Q);
+    Rs.push_back(R);
+  }
+
+  if (Qs.size() == 1) {
+    Quotient = Qs[0];
+    Remainder = Rs[0];
+    return;
+  }
+
+  Quotient = SE.getAddExpr(Qs);
+  Remainder = SE.getAddExpr(Rs);
+}
+
+void SCEVDivision::visitMulExpr(const SCEVMulExpr *Numerator) {
+  SmallVector<const SCEV *, 2> Qs;
+  Type *Ty = Denominator->getType();
+
+  bool FoundDenominatorTerm = false;
+  for (const SCEV *Op : Numerator->operands()) {
+    // Bail out if types do not match.
+    if (Ty != Op->getType())
+      return cannotDivide(Numerator);
+
+    if (FoundDenominatorTerm) {
+      Qs.push_back(Op);
+      continue;
+    }
+
+    // Check whether Denominator divides one of the product operands.
+    const SCEV *Q, *R;
+    divide(SE, Op, Denominator, &Q, &R);
+    if (!R->isZero()) {
+      Qs.push_back(Op);
+      continue;
+    }
+
+    // Bail out if types do not match.
+    if (Ty != Q->getType())
+      return cannotDivide(Numerator);
+
+    FoundDenominatorTerm = true;
+    Qs.push_back(Q);
+  }
+
+  if (FoundDenominatorTerm) {
+    Remainder = Zero;
+    if (Qs.size() == 1)
+      Quotient = Qs[0];
+    else
+      Quotient = SE.getMulExpr(Qs);
+    return;
+  }
+
+  if (!isa<SCEVUnknown>(Denominator))
+    return cannotDivide(Numerator);
+
+  // The Remainder is obtained by replacing Denominator by 0 in Numerator.
+  ValueToValueMap RewriteMap;
+  RewriteMap[cast<SCEVUnknown>(Denominator)->getValue()] =
+      cast<SCEVConstant>(Zero)->getValue();
+  Remainder = SCEVParameterRewriter::rewrite(Numerator, SE, RewriteMap, true);
+
+  if (Remainder->isZero()) {
+    // The Quotient is obtained by replacing Denominator by 1 in Numerator.
+    RewriteMap[cast<SCEVUnknown>(Denominator)->getValue()] =
+        cast<SCEVConstant>(One)->getValue();
+    Quotient = SCEVParameterRewriter::rewrite(Numerator, SE, RewriteMap, true);
+    return;
+  }
+
+  // Quotient is (Numerator - Remainder) divided by Denominator.
+  const SCEV *Q, *R;
+  const SCEV *Diff = SE.getMinusSCEV(Numerator, Remainder);
+  // This SCEV does not seem to simplify: fail the division here.
+  if (sizeOfSCEV(Diff) > sizeOfSCEV(Numerator))
+    return cannotDivide(Numerator);
+  divide(SE, Diff, Denominator, &Q, &R);
+  if (R != Zero)
+    return cannotDivide(Numerator);
+  Quotient = Q;
+}
+
+SCEVDivision::SCEVDivision(ScalarEvolution &S, const SCEV *Numerator,
+                           const SCEV *Denominator)
+    : SE(S), Denominator(Denominator) {
+  Zero = SE.getZero(Denominator->getType());
+  One = SE.getOne(Denominator->getType());
+
+  // We generally do not know how to divide Expr by Denominator. We initialize
+  // the division to a "cannot divide" state to simplify the rest of the code.
+  cannotDivide(Numerator);
+}
+
+// Convenience function for giving up on the division. We set the quotient to
+// be equal to zero and the remainder to be equal to the numerator.
+void SCEVDivision::cannotDivide(const SCEV *Numerator) {
+  Quotient = Zero;
+  Remainder = Numerator;
+}