Recommit "[DAGCombiner] Transform (icmp eq/ne (and X,C0),(shift X,C1)) to use rotate or to getter constants." (2nd Try)

Added missing check that the mask and shift amount added up to correct
bitwidth as well as test cases for the bug.

Closes #71729

Author: goldsteinn

llvm/include/llvm/CodeGen/TargetLowering.h

@@ -832,6 +832,24 @@ class TargetLoweringBase {
     return N->getOpcode() == ISD::FDIV;
   }
 
+  // Given:
+  //    (icmp eq/ne (and X, C0), (shift X, C1))
+  // or
+  //    (icmp eq/ne X, (rotate X, CPow2))
+
+  // If C0 is a mask or shifted mask and the shift amt (C1) isolates the
+  // remaining bits (i.e something like `(x64 & UINT32_MAX) == (x64 >> 32)`)
+  // Do we prefer the shift to be shift-right, shift-left, or rotate.
+  // Note: Its only valid to convert the rotate version to the shift version iff
+  // the shift-amt (`C1`) is a power of 2 (including 0).
+  // If ShiftOpc (current Opcode) is returned, do nothing.
+  virtual unsigned preferedOpcodeForCmpEqPiecesOfOperand(
+      EVT VT, unsigned ShiftOpc, bool MayTransformRotate,
+      const APInt &ShiftOrRotateAmt,
+      const std::optional<APInt> &AndMask) const {
+    return ShiftOpc;
+  }
+
   /// These two forms are equivalent:
   ///   sub %y, (xor %x, -1)
   ///   add (add %x, 1), %y

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -12466,27 +12466,132 @@ SDValue DAGCombiner::visitSETCC(SDNode *N) {
 
   ISD::CondCode Cond = cast<CondCodeSDNode>(N->getOperand(2))->get();
   EVT VT = N->getValueType(0);
+  SDValue N0 = N->getOperand(0), N1 = N->getOperand(1);
 
-  SDValue Combined = SimplifySetCC(VT, N->getOperand(0), N->getOperand(1), Cond,
-                                   SDLoc(N), !PreferSetCC);
-
-  if (!Combined)
-    return SDValue();
+  SDValue Combined = SimplifySetCC(VT, N0, N1, Cond, SDLoc(N), !PreferSetCC);
 
-  // If we prefer to have a setcc, and we don't, we'll try our best to
-  // recreate one using rebuildSetCC.
-  if (PreferSetCC && Combined.getOpcode() != ISD::SETCC) {
-    SDValue NewSetCC = rebuildSetCC(Combined);
+  if (Combined) {
+    // If we prefer to have a setcc, and we don't, we'll try our best to
+    // recreate one using rebuildSetCC.
+    if (PreferSetCC && Combined.getOpcode() != ISD::SETCC) {
+      SDValue NewSetCC = rebuildSetCC(Combined);
 
-    // We don't have anything interesting to combine to.
-    if (NewSetCC.getNode() == N)
-      return SDValue();
+      // We don't have anything interesting to combine to.
+      if (NewSetCC.getNode() == N)
+        return SDValue();
 
-    if (NewSetCC)
-      return NewSetCC;
+      if (NewSetCC)
+        return NewSetCC;
+    }
+    return Combined;
   }
 
-  return Combined;
+  // Optimize
+  //    1) (icmp eq/ne (and X, C0), (shift X, C1))
+  // or
+  //    2) (icmp eq/ne X, (rotate X, C1))
+  // If C0 is a mask or shifted mask and the shift amt (C1) isolates the
+  // remaining bits (i.e something like `(x64 & UINT32_MAX) == (x64 >> 32)`)
+  // Then:
+  // If C1 is a power of 2, then the rotate and shift+and versions are
+  // equivilent, so we can interchange them depending on target preference.
+  // Otherwise, if we have the shift+and version we can interchange srl/shl
+  // which inturn affects the constant C0. We can use this to get better
+  // constants again determined by target preference.
+  if (Cond == ISD::SETNE || Cond == ISD::SETEQ) {
+    auto IsAndWithShift = [](SDValue A, SDValue B) {
+      return A.getOpcode() == ISD::AND &&
+             (B.getOpcode() == ISD::SRL || B.getOpcode() == ISD::SHL) &&
+             A.getOperand(0) == B.getOperand(0);
+    };
+    auto IsRotateWithOp = [](SDValue A, SDValue B) {
+      return (B.getOpcode() == ISD::ROTL || B.getOpcode() == ISD::ROTR) &&
+             B.getOperand(0) == A;
+    };
+    SDValue AndOrOp = SDValue(), ShiftOrRotate = SDValue();
+    bool IsRotate = false;
+
+    // Find either shift+and or rotate pattern.
+    if (IsAndWithShift(N0, N1)) {
+      AndOrOp = N0;
+      ShiftOrRotate = N1;
+    } else if (IsAndWithShift(N1, N0)) {
+      AndOrOp = N1;
+      ShiftOrRotate = N0;
+    } else if (IsRotateWithOp(N0, N1)) {
+      IsRotate = true;
+      AndOrOp = N0;
+      ShiftOrRotate = N1;
+    } else if (IsRotateWithOp(N1, N0)) {
+      IsRotate = true;
+      AndOrOp = N1;
+      ShiftOrRotate = N0;
+    }
+
+    if (AndOrOp && ShiftOrRotate && ShiftOrRotate.hasOneUse() &&
+        (IsRotate || AndOrOp.hasOneUse())) {
+      EVT OpVT = N0.getValueType();
+      // Get constant shift/rotate amount and possibly mask (if its shift+and
+      // variant).
+      auto GetAPIntValue = [](SDValue Op) -> std::optional<APInt> {
+        ConstantSDNode *CNode = isConstOrConstSplat(Op, /*AllowUndefs*/ false,
+                                                    /*AllowTrunc*/ false);
+        if (CNode == nullptr)
+          return std::nullopt;
+        return CNode->getAPIntValue();
+      };
+      std::optional<APInt> AndCMask =
+          IsRotate ? std::nullopt : GetAPIntValue(AndOrOp.getOperand(1));
+      std::optional<APInt> ShiftCAmt =
+          GetAPIntValue(ShiftOrRotate.getOperand(1));
+      unsigned NumBits = OpVT.getScalarSizeInBits();
+
+      // We found constants.
+      if (ShiftCAmt && (IsRotate || AndCMask) && ShiftCAmt->ult(NumBits)) {
+        unsigned ShiftOpc = ShiftOrRotate.getOpcode();
+        // Check that the constants meet the constraints.
+        bool CanTransform = IsRotate;
+        if (!CanTransform) {
+          // Check that mask and shift compliment eachother
+          CanTransform = *ShiftCAmt == (~*AndCMask).popcount();
+          // Check that we are comparing all bits
+          CanTransform &= (*ShiftCAmt + AndCMask->popcount()) == NumBits;
+          // Check that the and mask is correct for the shift
+          CanTransform &=
+              ShiftOpc == ISD::SHL ? (~*AndCMask).isMask() : AndCMask->isMask();
+        }
+
+        // See if target prefers another shift/rotate opcode.
+        unsigned NewShiftOpc = TLI.preferedOpcodeForCmpEqPiecesOfOperand(
+            OpVT, ShiftOpc, ShiftCAmt->isPowerOf2(), *ShiftCAmt, AndCMask);
+        // Transform is valid and we have a new preference.
+        if (CanTransform && NewShiftOpc != ShiftOpc) {
+          SDLoc DL(N);
+          SDValue NewShiftOrRotate =
+              DAG.getNode(NewShiftOpc, DL, OpVT, ShiftOrRotate.getOperand(0),
+                          ShiftOrRotate.getOperand(1));
+          SDValue NewAndOrOp = SDValue();
+
+          if (NewShiftOpc == ISD::SHL || NewShiftOpc == ISD::SRL) {
+            APInt NewMask =
+                NewShiftOpc == ISD::SHL
+                    ? APInt::getHighBitsSet(NumBits,
+                                            NumBits - ShiftCAmt->getZExtValue())
+                    : APInt::getLowBitsSet(NumBits,
+                                           NumBits - ShiftCAmt->getZExtValue());
+            NewAndOrOp =
+                DAG.getNode(ISD::AND, DL, OpVT, ShiftOrRotate.getOperand(0),
+                            DAG.getConstant(NewMask, DL, OpVT));
+          } else {
+            NewAndOrOp = ShiftOrRotate.getOperand(0);
+          }
+
+          return DAG.getSetCC(DL, VT, NewAndOrOp, NewShiftOrRotate, Cond);
+        }
+      }
+    }
+  }
+  return SDValue();
 }
 
 SDValue DAGCombiner::visitSETCCCARRY(SDNode *N) {

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -3263,6 +3263,73 @@ bool X86TargetLowering::
   return NewShiftOpcode == ISD::SHL;
 }
 
+unsigned X86TargetLowering::preferedOpcodeForCmpEqPiecesOfOperand(
+    EVT VT, unsigned ShiftOpc, bool MayTransformRotate,
+    const APInt &ShiftOrRotateAmt, const std::optional<APInt> &AndMask) const {
+  if (!VT.isInteger())
+    return ShiftOpc;
+
+  bool PreferRotate = false;
+  if (VT.isVector()) {
+    // For vectors, if we have rotate instruction support, then its definetly
+    // best. Otherwise its not clear what the best so just don't make changed.
+    PreferRotate = Subtarget.hasAVX512() && (VT.getScalarType() == MVT::i32 ||
+                                             VT.getScalarType() == MVT::i64);
+  } else {
+    // For scalar, if we have bmi prefer rotate for rorx. Otherwise prefer
+    // rotate unless we have a zext mask+shr.
+    PreferRotate = Subtarget.hasBMI2();
+    if (!PreferRotate) {
+      unsigned MaskBits =
+          VT.getScalarSizeInBits() - ShiftOrRotateAmt.getZExtValue();
+      PreferRotate = (MaskBits != 8) && (MaskBits != 16) && (MaskBits != 32);
+    }
+  }
+
+  if (ShiftOpc == ISD::SHL || ShiftOpc == ISD::SRL) {
+    assert(AndMask.has_value() && "Null andmask when querying about shift+and");
+
+    if (PreferRotate && MayTransformRotate)
+      return ISD::ROTL;
+
+    // If vector we don't really get much benefit swapping around constants.
+    // Maybe we could check if the DAG has the flipped node already in the
+    // future.
+    if (VT.isVector())
+      return ShiftOpc;
+
+    // See if the beneficial to swap shift type.
+    if (ShiftOpc == ISD::SHL) {
+      // If the current setup has imm64 mask, then inverse will have
+      // at least imm32 mask (or be zext i32 -> i64).
+      if (VT == MVT::i64)
+        return AndMask->getSignificantBits() > 32 ? (unsigned)ISD::SRL
+                                                  : ShiftOpc;
+
+      // We can only benefit if req at least 7-bit for the mask. We
+      // don't want to replace shl of 1,2,3 as they can be implemented
+      // with lea/add.
+      return ShiftOrRotateAmt.uge(7) ? (unsigned)ISD::SRL : ShiftOpc;
+    }
+
+    if (VT == MVT::i64)
+      // Keep exactly 32-bit imm64, this is zext i32 -> i64 which is
+      // extremely efficient.
+      return AndMask->getSignificantBits() > 33 ? (unsigned)ISD::SHL : ShiftOpc;
+
+    // Keep small shifts as shl so we can generate add/lea.
+    return ShiftOrRotateAmt.ult(7) ? (unsigned)ISD::SHL : ShiftOpc;
+  }
+
+  // We prefer rotate for vectors of if we won't get a zext mask with SRL
+  // (PreferRotate will be set in the latter case).
+  if (PreferRotate || VT.isVector())
+    return ShiftOpc;
+
+  // Non-vector type and we have a zext mask with SRL.
+  return ISD::SRL;
+}
+
 bool X86TargetLowering::preferScalarizeSplat(SDNode *N) const {
   return N->getOpcode() != ISD::FP_EXTEND;
 }

llvm/lib/Target/X86/X86ISelLowering.h

@@ -1138,6 +1138,11 @@ namespace llvm {
         unsigned OldShiftOpcode, unsigned NewShiftOpcode,
         SelectionDAG &DAG) const override;
 
+    unsigned preferedOpcodeForCmpEqPiecesOfOperand(
+        EVT VT, unsigned ShiftOpc, bool MayTransformRotate,
+        const APInt &ShiftOrRotateAmt,
+        const std::optional<APInt> &AndMask) const override;
+
     bool preferScalarizeSplat(SDNode *N) const override;
 
     bool shouldFoldConstantShiftPairToMask(const SDNode *N,