Revert "[ScalarEvolution] Re-enable Predicate implication from operations"

This reverts commit rL298690

Causes failures on clang.

llvm-svn: 298693

1 files changed, 16 insertions, 159 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index afa4e464ed3..58634064d09 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -137,11 +137,6 @@ static cl::opt<unsigned> MaxSCEVCompareDepth(
     cl::desc("Maximum depth of recursive SCEV complexity comparisons"),
     cl::init(32));
 
-static cl::opt<unsigned> MaxSCEVOperationsImplicationDepth(
-    "scalar-evolution-max-scev-operations-implication-depth", cl::Hidden,
-    cl::desc("Maximum depth of recursive SCEV operations implication analysis"),
-    cl::init(4));
-
 static cl::opt<unsigned> MaxValueCompareDepth(
     "scalar-evolution-max-value-compare-depth", cl::Hidden,
     cl::desc("Maximum depth of recursive value complexity comparisons"),
@@ -3423,10 +3418,6 @@ Type *ScalarEvolution::getEffectiveSCEVType(Type *Ty) const {
   return getDataLayout().getIntPtrType(Ty);
 }
 
-Type *ScalarEvolution::getWiderType(Type *T1, Type *T2) const {
-  return  getTypeSizeInBits(T1) >= getTypeSizeInBits(T2) ? T1 : T2;
-}
-
 const SCEV *ScalarEvolution::getCouldNotCompute() {
   return CouldNotCompute.get();
 }
@@ -8568,149 +8559,19 @@ static bool IsKnownPredicateViaMinOrMax(ScalarEvolution &SE,
   llvm_unreachable("covered switch fell through?!");
 }
 
-bool ScalarEvolution::isImpliedViaOperations(ICmpInst::Predicate Pred,
-                                             const SCEV *LHS, const SCEV *RHS,
-                                             const SCEV *FoundLHS,
-                                             const SCEV *FoundRHS,
-                                             unsigned Depth) {
-  // We want to avoid hurting the compile time with analysis of too big trees.
-  if (Depth > MaxSCEVOperationsImplicationDepth)
-    return false;
-  // We only want to work with ICMP_SGT comparison so far.
-  // TODO: Extend to ICMP_UGT?
-  if (Pred == ICmpInst::ICMP_SLT) {
-    Pred = ICmpInst::ICMP_SGT;
-    std::swap(LHS, RHS);
-    std::swap(FoundLHS, FoundRHS);
-  }
-  if (Pred != ICmpInst::ICMP_SGT)
-    return false;
-
-  auto GetOpFromSExt = [&](const SCEV *S) {
-    if (auto *Ext = dyn_cast<SCEVSignExtendExpr>(S))
-      return Ext->getOperand();
-    // TODO: If S is a SCEVConstant then you can cheaply "strip" the sext off
-    // the constant in some cases.
-    return S;
-  };
-
-  // Acquire values from extensions.
-  auto *OrigFoundLHS = FoundLHS;
-  LHS = GetOpFromSExt(LHS);
-  FoundLHS = GetOpFromSExt(FoundLHS);
-
-  // Is the SGT predicate can be proved trivially or using the found context.
-  auto IsSGTViaContext = [&](const SCEV *S1, const SCEV *S2) {
-    assert(S1->getType() == S2->getType() && "Proving for wrong types?");
-    return isKnownViaSimpleReasoning(ICmpInst::ICMP_SGT, S1, S2) ||
-           isImpliedViaOperations(ICmpInst::ICMP_SGT, S1, S2, OrigFoundLHS,
-                                  FoundRHS, Depth + 1);
-  };
-
-  if (auto *LHSAddExpr = dyn_cast<SCEVAddExpr>(LHS)) {
-    // We want to avoid creation of any new non-constant SCEV. Since we are
-    // going to compare the operands to RHS, we should be certain that we don't
-    // need any type conversions for this. So let's decline all cases when the
-    // types of LHS and RHS do not match.
-    // TODO: Maybe try to get RHS from sext to catch more cases?
-    if (LHSAddExpr->getType() != RHS->getType())
-      return false;
-
-    // Should not overflow.
-    if (!LHSAddExpr->hasNoSignedWrap())
-      return false;
-
-    auto *LL = LHSAddExpr->getOperand(0);
-    auto *LR = LHSAddExpr->getOperand(1);
-    auto *MinusOne = getNegativeSCEV(getOne(RHS->getType()));
-
-    // Checks that S1 >= 0 && S2 > RHS, trivially or using the found context.
-    auto IsSumGreaterThanRHS = [&](const SCEV *S1, const SCEV *S2) {
-      return IsSGTViaContext(S1, MinusOne) && IsSGTViaContext(S2, RHS);
-    };
-    // Try to prove the following rule:
-    // (LHS = LL + LR) && (LL >= 0) && (LR > RHS) => (LHS > RHS).
-    // (LHS = LL + LR) && (LR >= 0) && (LL > RHS) => (LHS > RHS).
-    if (IsSumGreaterThanRHS(LL, LR) || IsSumGreaterThanRHS(LR, LL))
-      return true;
-  } else if (auto *LHSUnknownExpr = dyn_cast<SCEVUnknown>(LHS)) {
-    Value *LL, *LR;
-    // FIXME: Once we have SDiv implemented, we can get rid of this matching.
-    using namespace llvm::PatternMatch;
-    if (match(LHSUnknownExpr->getValue(), m_SDiv(m_Value(LL), m_Value(LR)))) {
-      // Rules for division.
-      // We are going to perform some comparisons with Denominator and its
-      // derivative expressions. In general case, creating a SCEV for it may
-      // lead to a complex analysis of the entire graph, and in particular it
-      // can request trip count recalculation for the same loop. This would
-      // cache as SCEVCouldNotCompute to avoid the infinite recursion. This is a
-      // sad thing. To avoid this, we only want to create SCEVs that are
-      // constants in this section. So we bail if Denominator is not a constant.
-      if (!isa<ConstantInt>(LR))
-        return false;
-
-      auto *Denominator = cast<SCEVConstant>(getSCEV(LR));
-
-      // We want to make sure that LHS = FoundLHS / Denominator. If it is so,
-      // then a SCEV for the numerator already exists and matches with FoundLHS.
-      auto *Numerator = getExistingSCEV(LL);
-
-      // Make sure that it exists and has the same type.
-      if (!Numerator || Numerator->getType() != FoundLHS->getType())
-        return false;
-
-      // Make sure that the numerator matches with FoundLHs and the denominator
-      // is positive.
-      if (!HasSameValue(Numerator, FoundLHS) || !isKnownPositive(Denominator))
-        return false;
-
-      // Given that:
-      // FoundLHS > FoundRHS, LHS = FoundLHS / Denominator, Denominator > 0.
-      auto *Ty2 = getWiderType(Denominator->getType(), FoundRHS->getType());
-      auto *DenominatorExt = getNoopOrSignExtend(Denominator, Ty2);
-      auto *FoundRHSExt = getNoopOrSignExtend(FoundRHS, Ty2);
-
-      // Try to prove the following rule:
-      // (FoundRHS > Denominator - 2) && (RHS <= 0) => (LHS > RHS).
-      // For example, given that FoundLHS > 2. It means that FoundLHS is at
-      // least 3. If we divide it by Denominator < 4, we will have at least 1.
-      auto *DenomMinusTwo = getMinusSCEV(DenominatorExt, getConstant(Ty2, 2));
-      if (isKnownNonPositive(RHS) &&
-          IsSGTViaContext(FoundRHSExt, DenomMinusTwo))
-        return true;
-
-      // Try to prove the following rule:
-      // (FoundRHS > -1 - Denominator) && (RHS < 0) => (LHS > RHS).
-      // For example, given that FoundLHS > -3. Then FoundLHS is at least -2.
-      // If we divide it by Denominator > 2, then:
-      // 1. If FoundLHS is negative, then the result is 0.
-      // 2. If FoundLHS is non-negative, then the result is non-negative.
-      // Anyways, the result is non-negative.
-      auto *MinusOne = getNegativeSCEV(getOne(Ty2));
-      auto *NegDenomMinusOne = getMinusSCEV(MinusOne, DenominatorExt);
-      if (isKnownNegative(RHS) &&
-          IsSGTViaContext(FoundRHSExt, NegDenomMinusOne))
-        return true;
-    }
-  }
-
-  return false;
-}
-
-bool
-ScalarEvolution::isKnownViaSimpleReasoning(ICmpInst::Predicate Pred,
-                                           const SCEV *LHS, const SCEV *RHS) {
-  return isKnownPredicateViaConstantRanges(Pred, LHS, RHS) ||
-         IsKnownPredicateViaMinOrMax(*this, Pred, LHS, RHS) ||
-         IsKnownPredicateViaAddRecStart(*this, Pred, LHS, RHS) ||
-         isKnownPredicateViaNoOverflow(Pred, LHS, RHS);
-}
-
 bool
 ScalarEvolution::isImpliedCondOperandsHelper(ICmpInst::Predicate Pred,
                                              const SCEV *LHS, const SCEV *RHS,
                                              const SCEV *FoundLHS,
                                              const SCEV *FoundRHS) {
+  auto IsKnownPredicateFull =
+      [this](ICmpInst::Predicate Pred, const SCEV *LHS, const SCEV *RHS) {
+    return isKnownPredicateViaConstantRanges(Pred, LHS, RHS) ||
+           IsKnownPredicateViaMinOrMax(*this, Pred, LHS, RHS) ||
+           IsKnownPredicateViaAddRecStart(*this, Pred, LHS, RHS) ||
+           isKnownPredicateViaNoOverflow(Pred, LHS, RHS);
+  };
+
   switch (Pred) {
   default: llvm_unreachable("Unexpected ICmpInst::Predicate value!");
   case ICmpInst::ICMP_EQ:
@@ -8720,34 +8581,30 @@ ScalarEvolution::isImpliedCondOperandsHelper(ICmpInst::Predicate Pred,
     break;
   case ICmpInst::ICMP_SLT:
   case ICmpInst::ICMP_SLE:
-    if (isKnownViaSimpleReasoning(ICmpInst::ICMP_SLE, LHS, FoundLHS) &&
-        isKnownViaSimpleReasoning(ICmpInst::ICMP_SGE, RHS, FoundRHS))
+    if (IsKnownPredicateFull(ICmpInst::ICMP_SLE, LHS, FoundLHS) &&
+        IsKnownPredicateFull(ICmpInst::ICMP_SGE, RHS, FoundRHS))
       return true;
     break;
   case ICmpInst::ICMP_SGT:
   case ICmpInst::ICMP_SGE:
-    if (isKnownViaSimpleReasoning(ICmpInst::ICMP_SGE, LHS, FoundLHS) &&
-        isKnownViaSimpleReasoning(ICmpInst::ICMP_SLE, RHS, FoundRHS))
+    if (IsKnownPredicateFull(ICmpInst::ICMP_SGE, LHS, FoundLHS) &&
+        IsKnownPredicateFull(ICmpInst::ICMP_SLE, RHS, FoundRHS))
       return true;
     break;
   case ICmpInst::ICMP_ULT:
   case ICmpInst::ICMP_ULE:
-    if (isKnownViaSimpleReasoning(ICmpInst::ICMP_ULE, LHS, FoundLHS) &&
-        isKnownViaSimpleReasoning(ICmpInst::ICMP_UGE, RHS, FoundRHS))
+    if (IsKnownPredicateFull(ICmpInst::ICMP_ULE, LHS, FoundLHS) &&
+        IsKnownPredicateFull(ICmpInst::ICMP_UGE, RHS, FoundRHS))
       return true;
     break;
   case ICmpInst::ICMP_UGT:
   case ICmpInst::ICMP_UGE:
-    if (isKnownViaSimpleReasoning(ICmpInst::ICMP_UGE, LHS, FoundLHS) &&
-        isKnownViaSimpleReasoning(ICmpInst::ICMP_ULE, RHS, FoundRHS))
+    if (IsKnownPredicateFull(ICmpInst::ICMP_UGE, LHS, FoundLHS) &&
+        IsKnownPredicateFull(ICmpInst::ICMP_ULE, RHS, FoundRHS))
       return true;
     break;
   }
 
-  // Maybe it can be proved via operations?
-  if (isImpliedViaOperations(Pred, LHS, RHS, FoundLHS, FoundRHS))
-    return true;
-
   return false;
 }