[InstCombine] Improve folding of icmp pred (and X, Mask/~Mask), Y)

llvm/include/llvm/IR/PatternMatch.h

@@ -564,6 +564,19 @@ inline api_pred_ty<is_negated_power2> m_NegatedPower2(const APInt *&V) {
   return V;
 }
 
+struct is_negated_power2_or_zero {
+  bool isValue(const APInt &C) { return !C || C.isNegatedPowerOf2(); }
+};
+/// Match a integer or vector negated power-of-2.
+/// For vectors, this includes constants with undefined elements.
+inline cst_pred_ty<is_negated_power2_or_zero> m_NegatedPower2OrZero() {
+  return cst_pred_ty<is_negated_power2_or_zero>();
+}
+inline api_pred_ty<is_negated_power2_or_zero>
+m_NegatedPower2OrZero(const APInt *&V) {
+  return V;
+}
+
 struct is_power2_or_zero {
   bool isValue(const APInt &C) { return !C || C.isPowerOf2(); }
 };
@@ -595,6 +608,18 @@ inline cst_pred_ty<is_lowbit_mask> m_LowBitMask() {
 }
 inline api_pred_ty<is_lowbit_mask> m_LowBitMask(const APInt *&V) { return V; }
 
+struct is_lowbit_mask_or_zero {
+  bool isValue(const APInt &C) { return !C || C.isMask(); }
+};
+/// Match an integer or vector with only the low bit(s) set.
+/// For vectors, this includes constants with undefined elements.
+inline cst_pred_ty<is_lowbit_mask_or_zero> m_LowBitMaskOrZero() {
+  return cst_pred_ty<is_lowbit_mask_or_zero>();
+}
+inline api_pred_ty<is_lowbit_mask_or_zero> m_LowBitMaskOrZero(const APInt *&V) {
+  return V;
+}
+
 struct icmp_pred_with_threshold {
   ICmpInst::Predicate Pred;
   const APInt *Thr;

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -4069,11 +4069,101 @@ Instruction *InstCombinerImpl::foldSelectICmp(ICmpInst::Predicate Pred,
   return nullptr;
 }
 
+// Returns whether V is a Mask ((X + 1) & X == 0) or ~Mask (-Pow2OrZero)
+static bool isMaskOrZero(const Value *V, bool Not, const SimplifyQuery &Q,
+                         unsigned Depth = 0) {
+  if (Not ? match(V, m_NegatedPower2OrZero()) : match(V, m_LowBitMaskOrZero()))
+    return true;
+  if (V->getType()->getScalarSizeInBits() == 1)
+    return true;
+  if (Depth++ >= MaxAnalysisRecursionDepth)
+    return false;
+  Value *X;
+  const Instruction *I = dyn_cast<Instruction>(V);
+  if (!I)
+    return false;
+  switch (I->getOpcode()) {
+  case Instruction::ZExt:
+    // ZExt(Mask) is a Mask.
+    return !Not && isMaskOrZero(I->getOperand(0), Not, Q, Depth);
+  case Instruction::SExt:
+    // SExt(Mask) is a Mask.
+    // SExt(~Mask) is a ~Mask.
+    return isMaskOrZero(I->getOperand(0), Not, Q, Depth);
+  case Instruction::And:
+  case Instruction::Or:
+    // Mask0 | Mask1 is a Mask.
+    // Mask0 & Mask1 is a Mask.
+    // ~Mask0 | ~Mask1 is a ~Mask.
+    // ~Mask0 & ~Mask1 is a ~Mask.
+    return isMaskOrZero(I->getOperand(1), Not, Q, Depth) &&
+           isMaskOrZero(I->getOperand(0), Not, Q, Depth);
+  case Instruction::Xor:
+    if (match(V, m_Not(m_Value(X))))
+      return isMaskOrZero(X, !Not, Q, Depth);
+
+    // (X ^ (X - 1)) is a Mask
+    return !Not &&
+           match(V, m_c_Xor(m_Value(X), m_Add(m_Deferred(X), m_AllOnes())));
+  case Instruction::Select:
+    // c ? Mask0 : Mask1 is a Mask.
+    return isMaskOrZero(I->getOperand(1), Not, Q, Depth) &&
+           isMaskOrZero(I->getOperand(2), Not, Q, Depth);
+  case Instruction::Shl:
+    // (~Mask) << X is a ~Mask.
+    return Not && isMaskOrZero(I->getOperand(0), Not, Q, Depth);
+  case Instruction::LShr:
+    // Mask >> X is a Mask.
+    return !Not && isMaskOrZero(I->getOperand(0), Not, Q, Depth);
+  case Instruction::AShr:
+    // Mask s>> X is a Mask.
+    // ~Mask s>> X is a ~Mask.
+    return isMaskOrZero(I->getOperand(0), Not, Q, Depth);
+  case Instruction::Add:
+    // Pow2 - 1 is a Mask.
+    if (!Not && match(I->getOperand(1), m_AllOnes()))
+      return isKnownToBeAPowerOfTwo(I->getOperand(0), Q.DL, /*OrZero*/ true,
+                                    Depth, Q.AC, Q.CxtI, Q.DT);
+    break;
+  case Instruction::Sub:
+    // -Pow2 is a ~Mask.
+    if (Not && match(I->getOperand(0), m_Zero()))
+      return isKnownToBeAPowerOfTwo(I->getOperand(1), Q.DL, /*OrZero*/ true,
+                                    Depth, Q.AC, Q.CxtI, Q.DT);
+    break;
+  case Instruction::Call: {
+    if (auto *II = dyn_cast<IntrinsicInst>(I)) {
+      switch (II->getIntrinsicID()) {
+        // min/max(Mask0, Mask1) is a Mask.
+        // min/max(~Mask0, ~Mask1) is a ~Mask.
+      case Intrinsic::umax:
+      case Intrinsic::smax:
+      case Intrinsic::umin:
+      case Intrinsic::smin:
+        return isMaskOrZero(II->getArgOperand(1), Not, Q, Depth) &&
+               isMaskOrZero(II->getArgOperand(0), Not, Q, Depth);
+
+        // In the context of masks, bitreverse(Mask) == ~Mask
+      case Intrinsic::bitreverse:
+        return isMaskOrZero(II->getArgOperand(0), !Not, Q, Depth);
+      default:
+        break;
+      }
+    }
+    break;
+  }
+  default:
+    break;
+  }
+  return false;
+}
+
 /// Some comparisons can be simplified.
 /// In this case, we are looking for comparisons that look like
 /// a check for a lossy truncation.
 /// Folds:
 ///   icmp SrcPred (x & Mask), x    to    icmp DstPred x, Mask
+///   icmp eq/ne (x & ~Mask), 0     to    icmp DstPred x, Mask
 /// Where Mask is some pattern that produces all-ones in low bits:
 ///    (-1 >> y)
 ///    ((-1 << y) >> y)     <- non-canonical, has extra uses
@@ -4082,23 +4172,35 @@ Instruction *InstCombinerImpl::foldSelectICmp(ICmpInst::Predicate Pred,
 /// The Mask can be a constant, too.
 /// For some predicates, the operands are commutative.
 /// For others, x can only be on a specific side.
-static Value *foldICmpWithLowBitMaskedVal(ICmpInst &I,
-                                          InstCombiner::BuilderTy &Builder) {
-  ICmpInst::Predicate SrcPred;
-  Value *X, *M, *Y;
-  auto m_VariableMask = m_CombineOr(
-      m_CombineOr(m_Not(m_Shl(m_AllOnes(), m_Value())),
-                  m_Add(m_Shl(m_One(), m_Value()), m_AllOnes())),
-      m_CombineOr(m_LShr(m_AllOnes(), m_Value()),
-                  m_LShr(m_Shl(m_AllOnes(), m_Value(Y)), m_Deferred(Y))));
-  auto m_Mask = m_CombineOr(m_VariableMask, m_LowBitMask());
-  if (!match(&I, m_c_ICmp(SrcPred,
-                          m_c_And(m_CombineAnd(m_Mask, m_Value(M)), m_Value(X)),
-                          m_Deferred(X))))
+static Value *foldICmpWithLowBitMaskedVal(ICmpInst::Predicate Pred, Value *Op0,
+                                          Value *Op1, const SimplifyQuery &Q,
+                                          InstCombiner &IC) {
+  Value *X, *M;
+  bool NeedsNot = false;
+
+  auto CheckMask = [&](Value *V, bool Not) {
+    if (ICmpInst::isSigned(Pred) && !match(V, m_ImmConstant()))
+      return false;
+    return isMaskOrZero(V, Not, Q);
+  };
+
+  if (match(Op0, m_c_And(m_Specific(Op1), m_Value(M))) &&
+      CheckMask(M, /*Not*/ false)) {
+    X = Op1;
+  } else if (match(Op1, m_Zero()) && ICmpInst::isEquality(Pred) &&
+             match(Op0, m_OneUse(m_And(m_Value(X), m_Value(M))))) {
+    NeedsNot = true;
+    if (IC.isFreeToInvert(X, X->hasOneUse()) && CheckMask(X, /*Not*/ true))
+      std::swap(X, M);
+    else if (!IC.isFreeToInvert(M, M->hasOneUse()) ||
+             !CheckMask(M, /*Not*/ true))
+      return nullptr;
+  } else {
     return nullptr;
+  }
 
   ICmpInst::Predicate DstPred;
-  switch (SrcPred) {
+  switch (Pred) {
   case ICmpInst::Predicate::ICMP_EQ:
     //  x & (-1 >> y) == x    ->    x u<= (-1 >> y)
     DstPred = ICmpInst::Predicate::ICMP_ULE;
@@ -4164,7 +4266,9 @@ static Value *foldICmpWithLowBitMaskedVal(ICmpInst &I,
     M = Constant::replaceUndefsWith(VecC, SafeReplacementConstant);
   }
 
-  return Builder.CreateICmp(DstPred, X, M);
+  if (NeedsNot)
+    M = IC.Builder.CreateNot(M);
+  return IC.Builder.CreateICmp(DstPred, X, M);
 }
 
 /// Some comparisons can be simplified.
@@ -5081,9 +5185,6 @@ Instruction *InstCombinerImpl::foldICmpBinOp(ICmpInst &I,
   if (Value *V = foldMultiplicationOverflowCheck(I))
     return replaceInstUsesWith(I, V);
 
-  if (Value *V = foldICmpWithLowBitMaskedVal(I, Builder))
-    return replaceInstUsesWith(I, V);
-
   if (Instruction *R = foldICmpAndXX(I, Q, *this))
     return R;
 
@@ -6984,6 +7085,10 @@ Instruction *InstCombinerImpl::foldICmpCommutative(ICmpInst::Predicate Pred,
     }
   }
 
+  const SimplifyQuery Q = SQ.getWithInstruction(&CxtI);
+  if (Value *V = foldICmpWithLowBitMaskedVal(Pred, Op0, Op1, Q, *this))
+    return replaceInstUsesWith(CxtI, V);
+
   return nullptr;
 }
 

llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-eq-to-icmp-ule.ll

@@ -62,8 +62,7 @@ define <2 x i1> @p2_vec_nonsplat(<2 x i8> %x) {
 
 define <2 x i1> @p2_vec_nonsplat_edgecase0(<2 x i8> %x) {
 ; CHECK-LABEL: @p2_vec_nonsplat_edgecase0(
-; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i8> [[X:%.*]], <i8 -4, i8 -1>
-; CHECK-NEXT:    [[RET:%.*]] = icmp eq <2 x i8> [[TMP1]], zeroinitializer
+; CHECK-NEXT:    [[RET:%.*]] = icmp ult <2 x i8> [[X:%.*]], <i8 4, i8 1>
 ; CHECK-NEXT:    ret <2 x i1> [[RET]]
 ;
   %tmp0 = and <2 x i8> %x, <i8 3, i8 0>

llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-ne-to-icmp-ugt.ll

@@ -62,8 +62,7 @@ define <2 x i1> @p2_vec_nonsplat(<2 x i8> %x) {
 
 define <2 x i1> @p2_vec_nonsplat_edgecase0(<2 x i8> %x) {
 ; CHECK-LABEL: @p2_vec_nonsplat_edgecase0(
-; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i8> [[X:%.*]], <i8 -4, i8 -1>
-; CHECK-NEXT:    [[RET:%.*]] = icmp ne <2 x i8> [[TMP1]], zeroinitializer
+; CHECK-NEXT:    [[RET:%.*]] = icmp ugt <2 x i8> [[X:%.*]], <i8 3, i8 0>
 ; CHECK-NEXT:    ret <2 x i1> [[RET]]
 ;
   %tmp0 = and <2 x i8> %x, <i8 3, i8 0>

llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-sge-to-icmp-sle.ll

@@ -50,8 +50,7 @@ define <2 x i1> @p2_vec_nonsplat(<2 x i8> %x) {
 
 define <2 x i1> @p2_vec_nonsplat_edgecase(<2 x i8> %x) {
 ; CHECK-LABEL: @p2_vec_nonsplat_edgecase(
-; CHECK-NEXT:    [[TMP0:%.*]] = and <2 x i8> [[X:%.*]], <i8 3, i8 0>
-; CHECK-NEXT:    [[RET:%.*]] = icmp sge <2 x i8> [[TMP0]], [[X]]
+; CHECK-NEXT:    [[RET:%.*]] = icmp slt <2 x i8> [[X:%.*]], <i8 4, i8 1>
 ; CHECK-NEXT:    ret <2 x i1> [[RET]]
 ;
   %tmp0 = and <2 x i8> %x, <i8 3, i8 0>

llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-sgt-to-icmp-sgt.ll

@@ -63,8 +63,7 @@ define <2 x i1> @p2_vec_nonsplat() {
 define <2 x i1> @p2_vec_nonsplat_edgecase() {
 ; CHECK-LABEL: @p2_vec_nonsplat_edgecase(
 ; CHECK-NEXT:    [[X:%.*]] = call <2 x i8> @gen2x8()
-; CHECK-NEXT:    [[TMP0:%.*]] = and <2 x i8> [[X]], <i8 3, i8 0>
-; CHECK-NEXT:    [[RET:%.*]] = icmp sgt <2 x i8> [[X]], [[TMP0]]
+; CHECK-NEXT:    [[RET:%.*]] = icmp sgt <2 x i8> [[X]], <i8 3, i8 0>
 ; CHECK-NEXT:    ret <2 x i1> [[RET]]
 ;
   %x = call <2 x i8> @gen2x8()

llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-sle-to-icmp-sle.ll

@@ -63,8 +63,7 @@ define <2 x i1> @p2_vec_nonsplat() {
 define <2 x i1> @p2_vec_nonsplat_edgecase() {
 ; CHECK-LABEL: @p2_vec_nonsplat_edgecase(
 ; CHECK-NEXT:    [[X:%.*]] = call <2 x i8> @gen2x8()
-; CHECK-NEXT:    [[TMP0:%.*]] = and <2 x i8> [[X]], <i8 3, i8 0>
-; CHECK-NEXT:    [[RET:%.*]] = icmp sle <2 x i8> [[X]], [[TMP0]]
+; CHECK-NEXT:    [[RET:%.*]] = icmp slt <2 x i8> [[X]], <i8 4, i8 1>
 ; CHECK-NEXT:    ret <2 x i1> [[RET]]
 ;
   %x = call <2 x i8> @gen2x8()

llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-slt-to-icmp-sgt.ll

@@ -50,8 +50,7 @@ define <2 x i1> @p2_vec_nonsplat(<2 x i8> %x) {
 
 define <2 x i1> @p2_vec_nonsplat_edgecase(<2 x i8> %x) {
 ; CHECK-LABEL: @p2_vec_nonsplat_edgecase(
-; CHECK-NEXT:    [[TMP0:%.*]] = and <2 x i8> [[X:%.*]], <i8 3, i8 0>
-; CHECK-NEXT:    [[RET:%.*]] = icmp slt <2 x i8> [[TMP0]], [[X]]
+; CHECK-NEXT:    [[RET:%.*]] = icmp sgt <2 x i8> [[X:%.*]], <i8 3, i8 0>
 ; CHECK-NEXT:    ret <2 x i1> [[RET]]
 ;
   %tmp0 = and <2 x i8> %x, <i8 3, i8 0>

llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-uge-to-icmp-ule.ll

@@ -62,8 +62,7 @@ define <2 x i1> @p2_vec_nonsplat(<2 x i8> %x) {
 
 define <2 x i1> @p2_vec_nonsplat_edgecase0(<2 x i8> %x) {
 ; CHECK-LABEL: @p2_vec_nonsplat_edgecase0(
-; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i8> [[X:%.*]], <i8 -4, i8 -1>
-; CHECK-NEXT:    [[RET:%.*]] = icmp eq <2 x i8> [[TMP1]], zeroinitializer
+; CHECK-NEXT:    [[RET:%.*]] = icmp ult <2 x i8> [[X:%.*]], <i8 4, i8 1>
 ; CHECK-NEXT:    ret <2 x i1> [[RET]]
 ;
   %tmp0 = and <2 x i8> %x, <i8 3, i8 0>

llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-ugt-to-icmp-ugt.ll

@@ -75,8 +75,7 @@ define <2 x i1> @p2_vec_nonsplat() {
 define <2 x i1> @p2_vec_nonsplat_edgecase0() {
 ; CHECK-LABEL: @p2_vec_nonsplat_edgecase0(
 ; CHECK-NEXT:    [[X:%.*]] = call <2 x i8> @gen2x8()
-; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i8> [[X]], <i8 -4, i8 -1>
-; CHECK-NEXT:    [[RET:%.*]] = icmp ne <2 x i8> [[TMP1]], zeroinitializer
+; CHECK-NEXT:    [[RET:%.*]] = icmp ugt <2 x i8> [[X]], <i8 3, i8 0>
 ; CHECK-NEXT:    ret <2 x i1> [[RET]]
 ;
   %x = call <2 x i8> @gen2x8()

llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-ule-to-icmp-ule.ll

@@ -75,8 +75,7 @@ define <2 x i1> @p2_vec_nonsplat() {
 define <2 x i1> @p2_vec_nonsplat_edgecase0() {
 ; CHECK-LABEL: @p2_vec_nonsplat_edgecase0(
 ; CHECK-NEXT:    [[X:%.*]] = call <2 x i8> @gen2x8()
-; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i8> [[X]], <i8 -4, i8 -1>
-; CHECK-NEXT:    [[RET:%.*]] = icmp eq <2 x i8> [[TMP1]], zeroinitializer
+; CHECK-NEXT:    [[RET:%.*]] = icmp ult <2 x i8> [[X]], <i8 4, i8 1>
 ; CHECK-NEXT:    ret <2 x i1> [[RET]]
 ;
   %x = call <2 x i8> @gen2x8()

llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-ult-to-icmp-ugt.ll

@@ -62,8 +62,7 @@ define <2 x i1> @p2_vec_nonsplat(<2 x i8> %x) {
 
 define <2 x i1> @p2_vec_nonsplat_edgecase0(<2 x i8> %x) {
 ; CHECK-LABEL: @p2_vec_nonsplat_edgecase0(
-; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i8> [[X:%.*]], <i8 -4, i8 -1>
-; CHECK-NEXT:    [[RET:%.*]] = icmp ne <2 x i8> [[TMP1]], zeroinitializer
+; CHECK-NEXT:    [[RET:%.*]] = icmp ugt <2 x i8> [[X:%.*]], <i8 3, i8 0>
 ; CHECK-NEXT:    ret <2 x i1> [[RET]]
 ;
   %tmp0 = and <2 x i8> %x, <i8 3, i8 0>