vendor/llvm-project/llvmorg-12-init-17869-g8e464dd76bef

1 files changed, 271 insertions, 218 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 17124f717af7..f26c194d31b9 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -38,6 +38,7 @@
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/KnownBits.h"
 #include "llvm/Transforms/InstCombine/InstCombineWorklist.h"
+#include "llvm/Transforms/InstCombine/InstCombiner.h"
 #include <cassert>
 #include <utility>
 
@@ -46,6 +47,11 @@ using namespace PatternMatch;
 
 #define DEBUG_TYPE "instcombine"
 
+/// FIXME: Enabled by default until the pattern is supported well.
+static cl::opt<bool> EnableUnsafeSelectTransform(
+    "instcombine-unsafe-select-transform", cl::init(true),
+    cl::desc("Enable poison-unsafe select to and/or transform"));
+
 static Value *createMinMax(InstCombiner::BuilderTy &Builder,
                            SelectPatternFlavor SPF, Value *A, Value *B) {
   CmpInst::Predicate Pred = getMinMaxPred(SPF);
@@ -57,7 +63,7 @@ static Value *createMinMax(InstCombiner::BuilderTy &Builder,
 /// constant of a binop.
 static Instruction *foldSelectBinOpIdentity(SelectInst &Sel,
                                             const TargetLibraryInfo &TLI,
-                                            InstCombiner &IC) {
+                                            InstCombinerImpl &IC) {
   // The select condition must be an equality compare with a constant operand.
   Value *X;
   Constant *C;
@@ -258,29 +264,9 @@ static unsigned getSelectFoldableOperands(BinaryOperator *I) {
   }
 }
 
-/// For the same transformation as the previous function, return the identity
-/// constant that goes into the select.
-static APInt getSelectFoldableConstant(BinaryOperator *I) {
-  switch (I->getOpcode()) {
-  default: llvm_unreachable("This cannot happen!");
-  case Instruction::Add:
-  case Instruction::Sub:
-  case Instruction::Or:
-  case Instruction::Xor:
-  case Instruction::Shl:
-  case Instruction::LShr:
-  case Instruction::AShr:
-    return APInt::getNullValue(I->getType()->getScalarSizeInBits());
-  case Instruction::And:
-    return APInt::getAllOnesValue(I->getType()->getScalarSizeInBits());
-  case Instruction::Mul:
-    return APInt(I->getType()->getScalarSizeInBits(), 1);
-  }
-}
-
 /// We have (select c, TI, FI), and we know that TI and FI have the same opcode.
-Instruction *InstCombiner::foldSelectOpOp(SelectInst &SI, Instruction *TI,
-                                          Instruction *FI) {
+Instruction *InstCombinerImpl::foldSelectOpOp(SelectInst &SI, Instruction *TI,
+                                              Instruction *FI) {
   // Don't break up min/max patterns. The hasOneUse checks below prevent that
   // for most cases, but vector min/max with bitcasts can be transformed. If the
   // one-use restrictions are eased for other patterns, we still don't want to
@@ -302,10 +288,9 @@ Instruction *InstCombiner::foldSelectOpOp(SelectInst &SI, Instruction *TI,
     // The select condition may be a vector. We may only change the operand
     // type if the vector width remains the same (and matches the condition).
     if (auto *CondVTy = dyn_cast<VectorType>(CondTy)) {
-      if (!FIOpndTy->isVectorTy())
-        return nullptr;
-      if (CondVTy->getNumElements() !=
-          cast<VectorType>(FIOpndTy)->getNumElements())
+      if (!FIOpndTy->isVectorTy() ||
+          CondVTy->getElementCount() !=
+              cast<VectorType>(FIOpndTy)->getElementCount())
         return nullptr;
 
       // TODO: If the backend knew how to deal with casts better, we could
@@ -418,8 +403,8 @@ static bool isSelect01(const APInt &C1I, const APInt &C2I) {
 
 /// Try to fold the select into one of the operands to allow further
 /// optimization.
-Instruction *InstCombiner::foldSelectIntoOp(SelectInst &SI, Value *TrueVal,
-                                            Value *FalseVal) {
+Instruction *InstCombinerImpl::foldSelectIntoOp(SelectInst &SI, Value *TrueVal,
+                                                Value *FalseVal) {
   // See the comment above GetSelectFoldableOperands for a description of the
   // transformation we are doing here.
   if (auto *TVI = dyn_cast<BinaryOperator>(TrueVal)) {
@@ -433,14 +418,15 @@ Instruction *InstCombiner::foldSelectIntoOp(SelectInst &SI, Value *TrueVal,
         }
 
         if (OpToFold) {
-          APInt CI = getSelectFoldableConstant(TVI);
+          Constant *C = ConstantExpr::getBinOpIdentity(TVI->getOpcode(),
+                                                       TVI->getType(), true);
           Value *OOp = TVI->getOperand(2-OpToFold);
           // Avoid creating select between 2 constants unless it's selecting
           // between 0, 1 and -1.
           const APInt *OOpC;
           bool OOpIsAPInt = match(OOp, m_APInt(OOpC));
-          if (!isa<Constant>(OOp) || (OOpIsAPInt && isSelect01(CI, *OOpC))) {
-            Value *C = ConstantInt::get(OOp->getType(), CI);
+          if (!isa<Constant>(OOp) ||
+              (OOpIsAPInt && isSelect01(C->getUniqueInteger(), *OOpC))) {
             Value *NewSel = Builder.CreateSelect(SI.getCondition(), OOp, C);
             NewSel->takeName(TVI);
             BinaryOperator *BO = BinaryOperator::Create(TVI->getOpcode(),
@@ -464,14 +450,15 @@ Instruction *InstCombiner::foldSelectIntoOp(SelectInst &SI, Value *TrueVal,
         }
 
         if (OpToFold) {
-          APInt CI = getSelectFoldableConstant(FVI);
+          Constant *C = ConstantExpr::getBinOpIdentity(FVI->getOpcode(),
+                                                       FVI->getType(), true);
           Value *OOp = FVI->getOperand(2-OpToFold);
           // Avoid creating select between 2 constants unless it's selecting
           // between 0, 1 and -1.
           const APInt *OOpC;
           bool OOpIsAPInt = match(OOp, m_APInt(OOpC));
-          if (!isa<Constant>(OOp) || (OOpIsAPInt && isSelect01(CI, *OOpC))) {
-            Value *C = ConstantInt::get(OOp->getType(), CI);
+          if (!isa<Constant>(OOp) ||
+              (OOpIsAPInt && isSelect01(C->getUniqueInteger(), *OOpC))) {
             Value *NewSel = Builder.CreateSelect(SI.getCondition(), C, OOp);
             NewSel->takeName(FVI);
             BinaryOperator *BO = BinaryOperator::Create(FVI->getOpcode(),
@@ -782,25 +769,24 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
 
   // Match unsigned saturated add of 2 variables with an unnecessary 'not'.
   // There are 8 commuted variants.
-  // Canonicalize -1 (saturated result) to true value of the select. Just
-  // swapping the compare operands is legal, because the selected value is the
-  // same in case of equality, so we can interchange u< and u<=.
+  // Canonicalize -1 (saturated result) to true value of the select.
   if (match(FVal, m_AllOnes())) {
     std::swap(TVal, FVal);
-    std::swap(Cmp0, Cmp1);
+    Pred = CmpInst::getInversePredicate(Pred);
   }
   if (!match(TVal, m_AllOnes()))
     return nullptr;
 
-  // Canonicalize predicate to 'ULT'.
-  if (Pred == ICmpInst::ICMP_UGT) {
-    Pred = ICmpInst::ICMP_ULT;
+  // Canonicalize predicate to less-than or less-or-equal-than.
+  if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_UGE) {
     std::swap(Cmp0, Cmp1);
+    Pred = CmpInst::getSwappedPredicate(Pred);
   }
-  if (Pred != ICmpInst::ICMP_ULT)
+  if (Pred != ICmpInst::ICMP_ULT && Pred != ICmpInst::ICMP_ULE)
     return nullptr;
 
   // Match unsigned saturated add of 2 variables with an unnecessary 'not'.
+  // Strictness of the comparison is irrelevant.
   Value *Y;
   if (match(Cmp0, m_Not(m_Value(X))) &&
       match(FVal, m_c_Add(m_Specific(X), m_Value(Y))) && Y == Cmp1) {
@@ -809,6 +795,7 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
     return Builder.CreateBinaryIntrinsic(Intrinsic::uadd_sat, X, Y);
   }
   // The 'not' op may be included in the sum but not the compare.
+  // Strictness of the comparison is irrelevant.
   X = Cmp0;
   Y = Cmp1;
   if (match(FVal, m_c_Add(m_Not(m_Specific(X)), m_Specific(Y)))) {
@@ -819,7 +806,9 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
         Intrinsic::uadd_sat, BO->getOperand(0), BO->getOperand(1));
   }
   // The overflow may be detected via the add wrapping round.
-  if (match(Cmp0, m_c_Add(m_Specific(Cmp1), m_Value(Y))) &&
+  // This is only valid for strict comparison!
+  if (Pred == ICmpInst::ICMP_ULT &&
+      match(Cmp0, m_c_Add(m_Specific(Cmp1), m_Value(Y))) &&
       match(FVal, m_c_Add(m_Specific(Cmp1), m_Specific(Y)))) {
     // ((X + Y) u< X) ? -1 : (X + Y) --> uadd.sat(X, Y)
     // ((X + Y) u< Y) ? -1 : (X + Y) --> uadd.sat(X, Y)
@@ -1024,9 +1013,9 @@ static bool adjustMinMax(SelectInst &Sel, ICmpInst &Cmp) {
 /// select (icmp Pred X, C1), C2, X --> select (icmp Pred' X, C2), X, C2
 /// Note: if C1 != C2, this will change the icmp constant to the existing
 /// constant operand of the select.
-static Instruction *
-canonicalizeMinMaxWithConstant(SelectInst &Sel, ICmpInst &Cmp,
-                               InstCombiner &IC) {
+static Instruction *canonicalizeMinMaxWithConstant(SelectInst &Sel,
+                                                   ICmpInst &Cmp,
+                                                   InstCombinerImpl &IC) {
   if (!Cmp.hasOneUse() || !isa<Constant>(Cmp.getOperand(1)))
     return nullptr;
 
@@ -1063,105 +1052,29 @@ canonicalizeMinMaxWithConstant(SelectInst &Sel, ICmpInst &Cmp,
   return &Sel;
 }
 
-/// There are many select variants for each of ABS/NABS.
-/// In matchSelectPattern(), there are different compare constants, compare
-/// predicates/operands and select operands.
-/// In isKnownNegation(), there are different formats of negated operands.
-/// Canonicalize all these variants to 1 pattern.
-/// This makes CSE more likely.
 static Instruction *canonicalizeAbsNabs(SelectInst &Sel, ICmpInst &Cmp,
-                                        InstCombiner &IC) {
+                                        InstCombinerImpl &IC) {
   if (!Cmp.hasOneUse() || !isa<Constant>(Cmp.getOperand(1)))
     return nullptr;
 
-  // Choose a sign-bit check for the compare (likely simpler for codegen).
-  // ABS:  (X <s 0) ? -X : X
-  // NABS: (X <s 0) ? X : -X
   Value *LHS, *RHS;
   SelectPatternFlavor SPF = matchSelectPattern(&Sel, LHS, RHS).Flavor;
   if (SPF != SelectPatternFlavor::SPF_ABS &&
       SPF != SelectPatternFlavor::SPF_NABS)
     return nullptr;
 
-  Value *TVal = Sel.getTrueValue();
-  Value *FVal = Sel.getFalseValue();
-  assert(isKnownNegation(TVal, FVal) &&
-         "Unexpected result from matchSelectPattern");
-
-  // The compare may use the negated abs()/nabs() operand, or it may use
-  // negation in non-canonical form such as: sub A, B.
-  bool CmpUsesNegatedOp = match(Cmp.getOperand(0), m_Neg(m_Specific(TVal))) ||
-                          match(Cmp.getOperand(0), m_Neg(m_Specific(FVal)));
-
-  bool CmpCanonicalized = !CmpUsesNegatedOp &&
-                          match(Cmp.getOperand(1), m_ZeroInt()) &&
-                          Cmp.getPredicate() == ICmpInst::ICMP_SLT;
-  bool RHSCanonicalized = match(RHS, m_Neg(m_Specific(LHS)));
-
-  // Is this already canonical?
-  if (CmpCanonicalized && RHSCanonicalized)
-    return nullptr;
+  // Note that NSW flag can only be propagated for normal, non-negated abs!
+  bool IntMinIsPoison = SPF == SelectPatternFlavor::SPF_ABS &&
+                        match(RHS, m_NSWNeg(m_Specific(LHS)));
+  Constant *IntMinIsPoisonC =
+      ConstantInt::get(Type::getInt1Ty(Sel.getContext()), IntMinIsPoison);
+  Instruction *Abs =
+      IC.Builder.CreateBinaryIntrinsic(Intrinsic::abs, LHS, IntMinIsPoisonC);
 
-  // If RHS is not canonical but is used by other instructions, don't
-  // canonicalize it and potentially increase the instruction count.
-  if (!RHSCanonicalized)
-    if (!(RHS->hasOneUse() || (RHS->hasNUses(2) && CmpUsesNegatedOp)))
-      return nullptr;
+  if (SPF == SelectPatternFlavor::SPF_NABS)
+    return BinaryOperator::CreateNeg(Abs); // Always without NSW flag!
 
-  // Create the canonical compare: icmp slt LHS 0.
-  if (!CmpCanonicalized) {
-    Cmp.setPredicate(ICmpInst::ICMP_SLT);
-    Cmp.setOperand(1, ConstantInt::getNullValue(Cmp.getOperand(0)->getType()));
-    if (CmpUsesNegatedOp)
-      Cmp.setOperand(0, LHS);
-  }
-
-  // Create the canonical RHS: RHS = sub (0, LHS).
-  if (!RHSCanonicalized) {
-    assert(RHS->hasOneUse() && "RHS use number is not right");
-    RHS = IC.Builder.CreateNeg(LHS);
-    if (TVal == LHS) {
-      // Replace false value.
-      IC.replaceOperand(Sel, 2, RHS);
-      FVal = RHS;
-    } else {
-      // Replace true value.
-      IC.replaceOperand(Sel, 1, RHS);
-      TVal = RHS;
-    }
-  }
-
-  // If the select operands do not change, we're done.
-  if (SPF == SelectPatternFlavor::SPF_NABS) {
-    if (TVal == LHS)
-      return &Sel;
-    assert(FVal == LHS && "Unexpected results from matchSelectPattern");
-  } else {
-    if (FVal == LHS)
-      return &Sel;
-    assert(TVal == LHS && "Unexpected results from matchSelectPattern");
-  }
-
-  // We are swapping the select operands, so swap the metadata too.
-  Sel.swapValues();
-  Sel.swapProfMetadata();
-  return &Sel;
-}
-
-static Value *simplifyWithOpReplaced(Value *V, Value *Op, Value *ReplaceOp,
-                                     const SimplifyQuery &Q) {
-  // If this is a binary operator, try to simplify it with the replaced op
-  // because we know Op and ReplaceOp are equivalant.
-  // For example: V = X + 1, Op = X, ReplaceOp = 42
-  // Simplifies as: add(42, 1) --> 43
-  if (auto *BO = dyn_cast<BinaryOperator>(V)) {
-    if (BO->getOperand(0) == Op)
-      return SimplifyBinOp(BO->getOpcode(), ReplaceOp, BO->getOperand(1), Q);
-    if (BO->getOperand(1) == Op)
-      return SimplifyBinOp(BO->getOpcode(), BO->getOperand(0), ReplaceOp, Q);
-  }
-
-  return nullptr;
+  return IC.replaceInstUsesWith(Sel, Abs);
 }
 
 /// If we have a select with an equality comparison, then we know the value in
@@ -1180,30 +1093,97 @@ static Value *simplifyWithOpReplaced(Value *V, Value *Op, Value *ReplaceOp,
 ///
 /// We can't replace %sel with %add unless we strip away the flags.
 /// TODO: Wrapping flags could be preserved in some cases with better analysis.
-static Value *foldSelectValueEquivalence(SelectInst &Sel, ICmpInst &Cmp,
-                                         const SimplifyQuery &Q) {
+Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
+                                                          ICmpInst &Cmp) {
   if (!Cmp.isEquality())
     return nullptr;
 
   // Canonicalize the pattern to ICMP_EQ by swapping the select operands.
   Value *TrueVal = Sel.getTrueValue(), *FalseVal = Sel.getFalseValue();
-  if (Cmp.getPredicate() == ICmpInst::ICMP_NE)
+  bool Swapped = false;
+  if (Cmp.getPredicate() == ICmpInst::ICMP_NE) {
     std::swap(TrueVal, FalseVal);
+    Swapped = true;
+  }
+
+  // In X == Y ? f(X) : Z, try to evaluate f(Y) and replace the operand.
+  // Make sure Y cannot be undef though, as we might pick different values for
+  // undef in the icmp and in f(Y). Additionally, take care to avoid replacing
+  // X == Y ? X : Z with X == Y ? Y : Z, as that would lead to an infinite
+  // replacement cycle.
+  Value *CmpLHS = Cmp.getOperand(0), *CmpRHS = Cmp.getOperand(1);
+  if (TrueVal != CmpLHS &&
+      isGuaranteedNotToBeUndefOrPoison(CmpRHS, SQ.AC, &Sel, &DT)) {
+    if (Value *V = SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, SQ,
+                                          /* AllowRefinement */ true))
+      return replaceOperand(Sel, Swapped ? 2 : 1, V);
+
+    // Even if TrueVal does not simplify, we can directly replace a use of
+    // CmpLHS with CmpRHS, as long as the instruction is not used anywhere
+    // else and is safe to speculatively execute (we may end up executing it
+    // with different operands, which should not cause side-effects or trigger
+    // undefined behavior). Only do this if CmpRHS is a constant, as
+    // profitability is not clear for other cases.
+    // FIXME: The replacement could be performed recursively.
+    if (match(CmpRHS, m_ImmConstant()) && !match(CmpLHS, m_ImmConstant()))
+      if (auto *I = dyn_cast<Instruction>(TrueVal))
+        if (I->hasOneUse() && isSafeToSpeculativelyExecute(I))
+          for (Use &U : I->operands())
+            if (U == CmpLHS) {
+              replaceUse(U, CmpRHS);
+              return &Sel;
+            }
+  }
+  if (TrueVal != CmpRHS &&
+      isGuaranteedNotToBeUndefOrPoison(CmpLHS, SQ.AC, &Sel, &DT))
+    if (Value *V = SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, SQ,
+                                          /* AllowRefinement */ true))
+      return replaceOperand(Sel, Swapped ? 2 : 1, V);
+
+  auto *FalseInst = dyn_cast<Instruction>(FalseVal);
+  if (!FalseInst)
+    return nullptr;
+
+  // InstSimplify already performed this fold if it was possible subject to
+  // current poison-generating flags. Try the transform again with
+  // poison-generating flags temporarily dropped.
+  bool WasNUW = false, WasNSW = false, WasExact = false, WasInBounds = false;
+  if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(FalseVal)) {
+    WasNUW = OBO->hasNoUnsignedWrap();
+    WasNSW = OBO->hasNoSignedWrap();
+    FalseInst->setHasNoUnsignedWrap(false);
+    FalseInst->setHasNoSignedWrap(false);
+  }
+  if (auto *PEO = dyn_cast<PossiblyExactOperator>(FalseVal)) {
+    WasExact = PEO->isExact();
+    FalseInst->setIsExact(false);
+  }
+  if (auto *GEP = dyn_cast<GetElementPtrInst>(FalseVal)) {
+    WasInBounds = GEP->isInBounds();
+    GEP->setIsInBounds(false);
+  }
 
   // Try each equivalence substitution possibility.
   // We have an 'EQ' comparison, so the select's false value will propagate.
   // Example:
   // (X == 42) ? 43 : (X + 1) --> (X == 42) ? (X + 1) : (X + 1) --> X + 1
-  // (X == 42) ? (X + 1) : 43 --> (X == 42) ? (42 + 1) : 43 --> 43
-  Value *CmpLHS = Cmp.getOperand(0), *CmpRHS = Cmp.getOperand(1);
-  if (simplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, Q) == TrueVal ||
-      simplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, Q) == TrueVal ||
-      simplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, Q) == FalseVal ||
-      simplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, Q) == FalseVal) {
-    if (auto *FalseInst = dyn_cast<Instruction>(FalseVal))
-      FalseInst->dropPoisonGeneratingFlags();
-    return FalseVal;
+  if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, SQ,
+                             /* AllowRefinement */ false) == TrueVal ||
+      SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, SQ,
+                             /* AllowRefinement */ false) == TrueVal) {
+    return replaceInstUsesWith(Sel, FalseVal);
   }
+
+  // Restore poison-generating flags if the transform did not apply.
+  if (WasNUW)
+    FalseInst->setHasNoUnsignedWrap();
+  if (WasNSW)
+    FalseInst->setHasNoSignedWrap();
+  if (WasExact)
+    FalseInst->setIsExact();
+  if (WasInBounds)
+    cast<GetElementPtrInst>(FalseInst)->setIsInBounds();
+
   return nullptr;
 }
 
@@ -1253,7 +1233,7 @@ static Instruction *canonicalizeClampLike(SelectInst &Sel0, ICmpInst &Cmp0,
                                   APInt::getAllOnesValue(
                                       C0->getType()->getScalarSizeInBits()))))
       return nullptr; // Can't do, have all-ones element[s].
-    C0 = AddOne(C0);
+    C0 = InstCombiner::AddOne(C0);
     std::swap(X, Sel1);
     break;
   case ICmpInst::Predicate::ICMP_UGE:
@@ -1313,7 +1293,7 @@ static Instruction *canonicalizeClampLike(SelectInst &Sel0, ICmpInst &Cmp0,
                                   APInt::getSignedMaxValue(
                                       C2->getType()->getScalarSizeInBits()))))
       return nullptr; // Can't do, have signed max element[s].
-    C2 = AddOne(C2);
+    C2 = InstCombiner::AddOne(C2);
     LLVM_FALLTHROUGH;
   case ICmpInst::Predicate::ICMP_SGE:
     // Also non-canonical, but here we don't need to change C2,
@@ -1360,7 +1340,7 @@ static Instruction *canonicalizeClampLike(SelectInst &Sel0, ICmpInst &Cmp0,
 // and swap the hands of select.
 static Instruction *
 tryToReuseConstantFromSelectInComparison(SelectInst &Sel, ICmpInst &Cmp,
-                                         InstCombiner &IC) {
+                                         InstCombinerImpl &IC) {
   ICmpInst::Predicate Pred;
   Value *X;
   Constant *C0;
@@ -1375,7 +1355,7 @@ tryToReuseConstantFromSelectInComparison(SelectInst &Sel, ICmpInst &Cmp,
 
   // If comparison predicate is non-canonical, then we certainly won't be able
   // to make it canonical; canonicalizeCmpWithConstant() already tried.
-  if (!isCanonicalPredicate(Pred))
+  if (!InstCombiner::isCanonicalPredicate(Pred))
     return nullptr;
 
   // If the [input] type of comparison and select type are different, lets abort
@@ -1403,7 +1383,8 @@ tryToReuseConstantFromSelectInComparison(SelectInst &Sel, ICmpInst &Cmp,
     return nullptr;
 
   // Check the constant we'd have with flipped-strictness predicate.
-  auto FlippedStrictness = getFlippedStrictnessPredicateAndConstant(Pred, C0);
+  auto FlippedStrictness =
+      InstCombiner::getFlippedStrictnessPredicateAndConstant(Pred, C0);
   if (!FlippedStrictness)
     return nullptr;
 
@@ -1426,10 +1407,10 @@ tryToReuseConstantFromSelectInComparison(SelectInst &Sel, ICmpInst &Cmp,
 }
 
 /// Visit a SelectInst that has an ICmpInst as its first operand.
-Instruction *InstCombiner::foldSelectInstWithICmp(SelectInst &SI,
-                                                  ICmpInst *ICI) {
-  if (Value *V = foldSelectValueEquivalence(SI, *ICI, SQ))
-    return replaceInstUsesWith(SI, V);
+Instruction *InstCombinerImpl::foldSelectInstWithICmp(SelectInst &SI,
+                                                      ICmpInst *ICI) {
+  if (Instruction *NewSel = foldSelectValueEquivalence(SI, *ICI))
+    return NewSel;
 
   if (Instruction *NewSel = canonicalizeMinMaxWithConstant(SI, *ICI, *this))
     return NewSel;
@@ -1579,11 +1560,11 @@ static bool canSelectOperandBeMappingIntoPredBlock(const Value *V,
 
 /// We have an SPF (e.g. a min or max) of an SPF of the form:
 ///   SPF2(SPF1(A, B), C)
-Instruction *InstCombiner::foldSPFofSPF(Instruction *Inner,
-                                        SelectPatternFlavor SPF1,
-                                        Value *A, Value *B,
-                                        Instruction &Outer,
-                                        SelectPatternFlavor SPF2, Value *C) {
+Instruction *InstCombinerImpl::foldSPFofSPF(Instruction *Inner,
+                                            SelectPatternFlavor SPF1, Value *A,
+                                            Value *B, Instruction &Outer,
+                                            SelectPatternFlavor SPF2,
+                                            Value *C) {
   if (Outer.getType() != Inner->getType())
     return nullptr;
 
@@ -1900,7 +1881,7 @@ foldOverflowingAddSubSelect(SelectInst &SI, InstCombiner::BuilderTy &Builder) {
   return CallInst::Create(F, {X, Y});
 }
 
-Instruction *InstCombiner::foldSelectExtConst(SelectInst &Sel) {
+Instruction *InstCombinerImpl::foldSelectExtConst(SelectInst &Sel) {
   Constant *C;
   if (!match(Sel.getTrueValue(), m_Constant(C)) &&
       !match(Sel.getFalseValue(), m_Constant(C)))
@@ -1966,10 +1947,11 @@ Instruction *InstCombiner::foldSelectExtConst(SelectInst &Sel) {
 static Instruction *canonicalizeSelectToShuffle(SelectInst &SI) {
   Value *CondVal = SI.getCondition();
   Constant *CondC;
-  if (!CondVal->getType()->isVectorTy() || !match(CondVal, m_Constant(CondC)))
+  auto *CondValTy = dyn_cast<FixedVectorType>(CondVal->getType());
+  if (!CondValTy || !match(CondVal, m_Constant(CondC)))
     return nullptr;
 
-  unsigned NumElts = cast<VectorType>(CondVal->getType())->getNumElements();
+  unsigned NumElts = CondValTy->getNumElements();
   SmallVector<int, 16> Mask;
   Mask.reserve(NumElts);
   for (unsigned i = 0; i != NumElts; ++i) {
@@ -2001,8 +1983,8 @@ static Instruction *canonicalizeSelectToShuffle(SelectInst &SI) {
 /// to a vector select by splatting the condition. A splat may get folded with
 /// other operations in IR and having all operands of a select be vector types
 /// is likely better for vector codegen.
-static Instruction *canonicalizeScalarSelectOfVecs(
-    SelectInst &Sel, InstCombiner &IC) {
+static Instruction *canonicalizeScalarSelectOfVecs(SelectInst &Sel,
+                                                   InstCombinerImpl &IC) {
   auto *Ty = dyn_cast<VectorType>(Sel.getType());
   if (!Ty)
     return nullptr;
@@ -2015,8 +1997,8 @@ static Instruction *canonicalizeScalarSelectOfVecs(
   // select (extelt V, Index), T, F --> select (splat V, Index), T, F
   // Splatting the extracted condition reduces code (we could directly create a
   // splat shuffle of the source vector to eliminate the intermediate step).
-  unsigned NumElts = Ty->getNumElements();
-  return IC.replaceOperand(Sel, 0, IC.Builder.CreateVectorSplat(NumElts, Cond));
+  return IC.replaceOperand(
+      Sel, 0, IC.Builder.CreateVectorSplat(Ty->getElementCount(), Cond));
 }
 
 /// Reuse bitcasted operands between a compare and select:
@@ -2172,7 +2154,7 @@ static Instruction *moveAddAfterMinMax(SelectPatternFlavor SPF, Value *X,
 }
 
 /// Match a sadd_sat or ssub_sat which is using min/max to clamp the value.
-Instruction *InstCombiner::matchSAddSubSat(SelectInst &MinMax1) {
+Instruction *InstCombinerImpl::matchSAddSubSat(SelectInst &MinMax1) {
   Type *Ty = MinMax1.getType();
 
   // We are looking for a tree of:
@@ -2293,34 +2275,42 @@ static Instruction *factorizeMinMaxTree(SelectPatternFlavor SPF, Value *LHS,
   return SelectInst::Create(CmpABC, MinMaxOp, ThirdOp);
 }
 
-/// Try to reduce a rotate pattern that includes a compare and select into a
-/// funnel shift intrinsic. Example:
+/// Try to reduce a funnel/rotate pattern that includes a compare and select
+/// into a funnel shift intrinsic. Example:
 /// rotl32(a, b) --> (b == 0 ? a : ((a >> (32 - b)) | (a << b)))
 ///              --> call llvm.fshl.i32(a, a, b)
-static Instruction *foldSelectRotate(SelectInst &Sel) {
-  // The false value of the select must be a rotate of the true value.
-  Value *Or0, *Or1;
-  if (!match(Sel.getFalseValue(), m_OneUse(m_Or(m_Value(Or0), m_Value(Or1)))))
+/// fshl32(a, b, c) --> (c == 0 ? a : ((b >> (32 - c)) | (a << c)))
+///                 --> call llvm.fshl.i32(a, b, c)
+/// fshr32(a, b, c) --> (c == 0 ? b : ((a >> (32 - c)) | (b << c)))
+///                 --> call llvm.fshr.i32(a, b, c)
+static Instruction *foldSelectFunnelShift(SelectInst &Sel,
+                                          InstCombiner::BuilderTy &Builder) {
+  // This must be a power-of-2 type for a bitmasking transform to be valid.
+  unsigned Width = Sel.getType()->getScalarSizeInBits();
+  if (!isPowerOf2_32(Width))
     return nullptr;
 
-  Value *TVal = Sel.getTrueValue();
-  Value *SA0, *SA1;
-  if (!match(Or0, m_OneUse(m_LogicalShift(m_Specific(TVal), m_Value(SA0)))) ||
-      !match(Or1, m_OneUse(m_LogicalShift(m_Specific(TVal), m_Value(SA1)))))
+  BinaryOperator *Or0, *Or1;
+  if (!match(Sel.getFalseValue(), m_OneUse(m_Or(m_BinOp(Or0), m_BinOp(Or1)))))
     return nullptr;
 
-  auto ShiftOpcode0 = cast<BinaryOperator>(Or0)->getOpcode();
-  auto ShiftOpcode1 = cast<BinaryOperator>(Or1)->getOpcode();
-  if (ShiftOpcode0 == ShiftOpcode1)
+  Value *SV0, *SV1, *SA0, *SA1;
+  if (!match(Or0, m_OneUse(m_LogicalShift(m_Value(SV0),
+                                          m_ZExtOrSelf(m_Value(SA0))))) ||
+      !match(Or1, m_OneUse(m_LogicalShift(m_Value(SV1),
+                                          m_ZExtOrSelf(m_Value(SA1))))) ||
+      Or0->getOpcode() == Or1->getOpcode())
     return nullptr;
 
-  // We have one of these patterns so far:
-  // select ?, TVal, (or (lshr TVal, SA0), (shl TVal, SA1))
-  // select ?, TVal, (or (shl TVal, SA0), (lshr TVal, SA1))
-  // This must be a power-of-2 rotate for a bitmasking transform to be valid.
-  unsigned Width = Sel.getType()->getScalarSizeInBits();
-  if (!isPowerOf2_32(Width))
-    return nullptr;
+  // Canonicalize to or(shl(SV0, SA0), lshr(SV1, SA1)).
+  if (Or0->getOpcode() == BinaryOperator::LShr) {
+    std::swap(Or0, Or1);
+    std::swap(SV0, SV1);
+    std::swap(SA0, SA1);
+  }
+  assert(Or0->getOpcode() == BinaryOperator::Shl &&
+         Or1->getOpcode() == BinaryOperator::LShr &&
+         "Illegal or(shift,shift) pair");
 
   // Check the shift amounts to see if they are an opposite pair.
   Value *ShAmt;
@@ -2331,6 +2321,15 @@ static Instruction *foldSelectRotate(SelectInst &Sel) {
   else
     return nullptr;
 
+  // We should now have this pattern:
+  // select ?, TVal, (or (shl SV0, SA0), (lshr SV1, SA1))
+  // The false value of the select must be a funnel-shift of the true value:
+  // IsFShl -> TVal must be SV0 else TVal must be SV1.
+  bool IsFshl = (ShAmt == SA0);
+  Value *TVal = Sel.getTrueValue();
+  if ((IsFshl && TVal != SV0) || (!IsFshl && TVal != SV1))
+    return nullptr;
+
   // Finally, see if the select is filtering out a shift-by-zero.
   Value *Cond = Sel.getCondition();
   ICmpInst::Predicate Pred;
@@ -2338,13 +2337,21 @@ static Instruction *foldSelectRotate(SelectInst &Sel) {
       Pred != ICmpInst::ICMP_EQ)
     return nullptr;
 
-  // This is a rotate that avoids shift-by-bitwidth UB in a suboptimal way.
+  // If this is not a rotate then the select was blocking poison from the
+  // 'shift-by-zero' non-TVal, but a funnel shift won't - so freeze it.
+  if (SV0 != SV1) {
+    if (IsFshl && !llvm::isGuaranteedNotToBePoison(SV1))
+      SV1 = Builder.CreateFreeze(SV1);
+    else if (!IsFshl && !llvm::isGuaranteedNotToBePoison(SV0))
+      SV0 = Builder.CreateFreeze(SV0);
+  }
+
+  // This is a funnel/rotate that avoids shift-by-bitwidth UB in a suboptimal way.
   // Convert to funnel shift intrinsic.
-  bool IsFshl = (ShAmt == SA0 && ShiftOpcode0 == BinaryOperator::Shl) ||
-                (ShAmt == SA1 && ShiftOpcode1 == BinaryOperator::Shl);
   Intrinsic::ID IID = IsFshl ? Intrinsic::fshl : Intrinsic::fshr;
   Function *F = Intrinsic::getDeclaration(Sel.getModule(), IID, Sel.getType());
-  return IntrinsicInst::Create(F, { TVal, TVal, ShAmt });
+  ShAmt = Builder.CreateZExt(ShAmt, Sel.getType());
+  return IntrinsicInst::Create(F, { SV0, SV1, ShAmt });
 }
 
 static Instruction *foldSelectToCopysign(SelectInst &Sel,
@@ -2368,7 +2375,8 @@ static Instruction *foldSelectToCopysign(SelectInst &Sel,
   bool IsTrueIfSignSet;
   ICmpInst::Predicate Pred;
   if (!match(Cond, m_OneUse(m_ICmp(Pred, m_BitCast(m_Value(X)), m_APInt(C)))) ||
-      !isSignBitCheck(Pred, *C, IsTrueIfSignSet) || X->getType() != SelType)
+      !InstCombiner::isSignBitCheck(Pred, *C, IsTrueIfSignSet) ||
+      X->getType() != SelType)
     return nullptr;
 
   // If needed, negate the value that will be the sign argument of the copysign:
@@ -2389,7 +2397,7 @@ static Instruction *foldSelectToCopysign(SelectInst &Sel,
   return CopySign;
 }
 
-Instruction *InstCombiner::foldVectorSelect(SelectInst &Sel) {
+Instruction *InstCombinerImpl::foldVectorSelect(SelectInst &Sel) {
   auto *VecTy = dyn_cast<FixedVectorType>(Sel.getType());
   if (!VecTy)
     return nullptr;
@@ -2469,6 +2477,10 @@ static Instruction *foldSelectToPhiImpl(SelectInst &Sel, BasicBlock *BB,
   } else
     return nullptr;
 
+  // Make sure the branches are actually different.
+  if (TrueSucc == FalseSucc)
+    return nullptr;
+
   // We want to replace select %cond, %a, %b with a phi that takes value %a
   // for all incoming edges that are dominated by condition `%cond == true`,
   // and value %b for edges dominated by condition `%cond == false`. If %a
@@ -2515,7 +2527,33 @@ static Instruction *foldSelectToPhi(SelectInst &Sel, const DominatorTree &DT,
   return nullptr;
 }
 
-Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
+static Value *foldSelectWithFrozenICmp(SelectInst &Sel, InstCombiner::BuilderTy &Builder) {
+  FreezeInst *FI = dyn_cast<FreezeInst>(Sel.getCondition());
+  if (!FI)
+    return nullptr;
+
+  Value *Cond = FI->getOperand(0);
+  Value *TrueVal = Sel.getTrueValue(), *FalseVal = Sel.getFalseValue();
+
+  //   select (freeze(x == y)), x, y --> y
+  //   select (freeze(x != y)), x, y --> x
+  // The freeze should be only used by this select. Otherwise, remaining uses of
+  // the freeze can observe a contradictory value.
+  //   c = freeze(x == y)   ; Let's assume that y = poison & x = 42; c is 0 or 1
+  //   a = select c, x, y   ;
+  //   f(a, c)              ; f(poison, 1) cannot happen, but if a is folded
+  //                        ; to y, this can happen.
+  CmpInst::Predicate Pred;
+  if (FI->hasOneUse() &&
+      match(Cond, m_c_ICmp(Pred, m_Specific(TrueVal), m_Specific(FalseVal))) &&
+      (Pred == ICmpInst::ICMP_EQ || Pred == ICmpInst::ICMP_NE)) {
+    return Pred == ICmpInst::ICMP_EQ ? FalseVal : TrueVal;
+  }
+
+  return nullptr;
+}
+
+Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
   Value *CondVal = SI.getCondition();
   Value *TrueVal = SI.getTrueValue();
   Value *FalseVal = SI.getFalseValue();
@@ -2551,38 +2589,45 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
 
   if (SelType->isIntOrIntVectorTy(1) &&
       TrueVal->getType() == CondVal->getType()) {
-    if (match(TrueVal, m_One())) {
+    if (match(TrueVal, m_One()) &&
+        (EnableUnsafeSelectTransform || impliesPoison(FalseVal, CondVal))) {
       // Change: A = select B, true, C --> A = or B, C
       return BinaryOperator::CreateOr(CondVal, FalseVal);
     }
-    if (match(TrueVal, m_Zero())) {
-      // Change: A = select B, false, C --> A = and !B, C
-      Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
-      return BinaryOperator::CreateAnd(NotCond, FalseVal);
-    }
-    if (match(FalseVal, m_Zero())) {
+    if (match(FalseVal, m_Zero()) &&
+        (EnableUnsafeSelectTransform || impliesPoison(TrueVal, CondVal))) {
       // Change: A = select B, C, false --> A = and B, C
       return BinaryOperator::CreateAnd(CondVal, TrueVal);
     }
+
+    // select a, false, b -> select !a, b, false
+    if (match(TrueVal, m_Zero())) {
+      Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
+      return SelectInst::Create(NotCond, FalseVal,
+                                ConstantInt::getFalse(SelType));
+    }
+    // select a, b, true -> select !a, true, b
     if (match(FalseVal, m_One())) {
-      // Change: A = select B, C, true --> A = or !B, C
       Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
-      return BinaryOperator::CreateOr(NotCond, TrueVal);
+      return SelectInst::Create(NotCond, ConstantInt::getTrue(SelType),
+                                TrueVal);
     }
 
-    // select a, a, b  -> a | b
-    // select a, b, a  -> a & b
+    // select a, a, b -> select a, true, b
     if (CondVal == TrueVal)
-      return BinaryOperator::CreateOr(CondVal, FalseVal);
+      return replaceOperand(SI, 1, ConstantInt::getTrue(SelType));
+    // select a, b, a -> select a, b, false
     if (CondVal == FalseVal)
-      return BinaryOperator::CreateAnd(CondVal, TrueVal);
+      return replaceOperand(SI, 2, ConstantInt::getFalse(SelType));
 
-    // select a, ~a, b -> (~a) & b
-    // select a, b, ~a -> (~a) | b
+    // select a, !a, b -> select !a, b, false
     if (match(TrueVal, m_Not(m_Specific(CondVal))))
-      return BinaryOperator::CreateAnd(TrueVal, FalseVal);
+      return SelectInst::Create(TrueVal, FalseVal,
+                                ConstantInt::getFalse(SelType));
+    // select a, b, !a -> select !a, true, b
     if (match(FalseVal, m_Not(m_Specific(CondVal))))
-      return BinaryOperator::CreateOr(TrueVal, FalseVal);
+      return SelectInst::Create(FalseVal, ConstantInt::getTrue(SelType),
+                                TrueVal);
   }
 
   // Selecting between two integer or vector splat integer constants?
@@ -2591,7 +2636,10 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
   // select i1 %c, <2 x i8> <1, 1>, <2 x i8> <0, 0>
   // because that may need 3 instructions to splat the condition value:
   // extend, insertelement, shufflevector.
-  if (SelType->isIntOrIntVectorTy() &&
+  //
+  // Do not handle i1 TrueVal and FalseVal otherwise would result in
+  // zext/sext i1 to i1.
+  if (SelType->isIntOrIntVectorTy() && !SelType->isIntOrIntVectorTy(1) &&
       CondVal->getType()->isVectorTy() == SelType->isVectorTy()) {
     // select C, 1, 0 -> zext C to int
     if (match(TrueVal, m_One()) && match(FalseVal, m_Zero()))
@@ -2838,8 +2886,9 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
         return replaceOperand(SI, 1, TrueSI->getTrueValue());
       }
       // select(C0, select(C1, a, b), b) -> select(C0&C1, a, b)
-      // We choose this as normal form to enable folding on the And and shortening
-      // paths for the values (this helps GetUnderlyingObjects() for example).
+      // We choose this as normal form to enable folding on the And and
+      // shortening paths for the values (this helps getUnderlyingObjects() for
+      // example).
       if (TrueSI->getFalseValue() == FalseVal && TrueSI->hasOneUse()) {
         Value *And = Builder.CreateAnd(CondVal, TrueSI->getCondition());
         replaceOperand(SI, 0, And);
@@ -2922,7 +2971,8 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
   }
 
   Value *NotCond;
-  if (match(CondVal, m_Not(m_Value(NotCond)))) {
+  if (match(CondVal, m_Not(m_Value(NotCond))) &&
+      !InstCombiner::shouldAvoidAbsorbingNotIntoSelect(SI)) {
     replaceOperand(SI, 0, NotCond);
     SI.swapValues();
     SI.swapProfMetadata();
@@ -2956,8 +3006,8 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
   if (Instruction *Select = foldSelectBinOpIdentity(SI, TLI, *this))
     return Select;
 
-  if (Instruction *Rot = foldSelectRotate(SI))
-    return Rot;
+  if (Instruction *Funnel = foldSelectFunnelShift(SI, Builder))
+    return Funnel;
 
   if (Instruction *Copysign = foldSelectToCopysign(SI, Builder))
     return Copysign;
@@ -2965,5 +3015,8 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
   if (Instruction *PN = foldSelectToPhi(SI, DT, Builder))
     return replaceInstUsesWith(SI, PN);
 
+  if (Value *Fr = foldSelectWithFrozenICmp(SI, Builder))
+    return replaceInstUsesWith(SI, Fr);
+
   return nullptr;
 }