[DAG] Expose NoSignedWrap, NoUnsignedWrap and Exact flags to SelectionDAG.

This patch modifies SelectionDAGBuilder to construct SDNodes with associated
NoSignedWrap, NoUnsignedWrap and Exact flags coming from IR BinaryOperator
instructions.

Added a new SDNode type called 'BinaryWithFlagsSDNode' to allow accessing
nsw/nuw/exact flags during codegen.

Patch by Marcello Maggioni.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210467 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/SelectionDAG.h

@@ -612,14 +612,14 @@ public:
   ///
   SDValue getNode(unsigned Opcode, SDLoc DL, EVT VT);
   SDValue getNode(unsigned Opcode, SDLoc DL, EVT VT, SDValue N);
-  SDValue getNode(unsigned Opcode, SDLoc DL, EVT VT, SDValue N1, SDValue N2);
+  SDValue getNode(unsigned Opcode, SDLoc DL, EVT VT, SDValue N1, SDValue N2,
-  SDValue getNode(unsigned Opcode, SDLoc DL, EVT VT,
+                  bool nuw = false, bool nsw = false, bool exact = false);
-                  SDValue N1, SDValue N2, SDValue N3);
+  SDValue getNode(unsigned Opcode, SDLoc DL, EVT VT, SDValue N1, SDValue N2,
-  SDValue getNode(unsigned Opcode, SDLoc DL, EVT VT,
+                  SDValue N3);
-                  SDValue N1, SDValue N2, SDValue N3, SDValue N4);
+  SDValue getNode(unsigned Opcode, SDLoc DL, EVT VT, SDValue N1, SDValue N2,
-  SDValue getNode(unsigned Opcode, SDLoc DL, EVT VT,
+                  SDValue N3, SDValue N4);
-                  SDValue N1, SDValue N2, SDValue N3, SDValue N4,
+  SDValue getNode(unsigned Opcode, SDLoc DL, EVT VT, SDValue N1, SDValue N2,
-                  SDValue N5);
+                  SDValue N3, SDValue N4, SDValue N5);
   SDValue getNode(unsigned Opcode, SDLoc DL, EVT VT, ArrayRef<SDUse> Ops);
   SDValue getNode(unsigned Opcode, SDLoc DL, EVT VT,
                   ArrayRef<SDValue> Ops);
@@ -927,7 +927,9 @@ public:
 
   /// getNodeIfExists - Get the specified node if it's already available, or
   /// else return NULL.
-  SDNode *getNodeIfExists(unsigned Opcode, SDVTList VTs, ArrayRef<SDValue> Ops);
+  SDNode *getNodeIfExists(unsigned Opcode, SDVTList VTs, ArrayRef<SDValue> Ops,
+                          bool nuw = false, bool nsw = false,
+                          bool exact = false);
 
   /// getDbgValue - Creates a SDDbgValue node.
   ///
@@ -1184,6 +1186,10 @@ private:
 
   void allnodes_clear();
 
+  BinarySDNode *GetBinarySDNode(unsigned Opcode, SDLoc DL, SDVTList VTs,
+                                SDValue N1, SDValue N2, bool nuw, bool nsw,
+                                bool exact);
+
   /// VTList - List of non-single value types.
   FoldingSet<SDVTListNode> VTListMap;
 

include/llvm/CodeGen/SelectionDAGNodes.h

@@ -49,6 +49,24 @@ template <typename T> struct DenseMapInfo;
 template <typename T> struct simplify_type;
 template <typename T> struct ilist_traits;
 
+/// isBinOpWithFlags - Returns true if the opcode is a binary operation
+/// with flags.
+static bool isBinOpWithFlags(unsigned Opcode) {
+  switch (Opcode) {
+  case ISD::SDIV:
+  case ISD::UDIV:
+  case ISD::SRA:
+  case ISD::SRL:
+  case ISD::MUL:
+  case ISD::ADD:
+  case ISD::SUB:
+  case ISD::SHL:
+    return true;
+  default:
+    return false;
+  }
+}
+
 void checkForCycles(const SDNode *N, const SelectionDAG *DAG = nullptr,
                     bool force = false);
 
@@ -939,6 +957,36 @@ public:
   }
 };
 
+/// BinaryWithFlagsSDNode - This class is an extension of BinarySDNode
+/// used from those opcodes that have associated extra flags.
+class BinaryWithFlagsSDNode : public BinarySDNode {
+  enum { NUW = (1 << 0), NSW = (1 << 1), EXACT = (1 << 2) };
+
+public:
+  BinaryWithFlagsSDNode(unsigned Opc, unsigned Order, DebugLoc dl, SDVTList VTs,
+                        SDValue X, SDValue Y)
+      : BinarySDNode(Opc, Order, dl, VTs, X, Y) {}
+  /// getRawSubclassData - Return the SubclassData value, which contains an
+  /// encoding of the flags.
+  /// This function should be used to add subclass data to the NodeID value.
+  unsigned getRawSubclassData() const { return SubclassData; }
+  void setHasNoUnsignedWrap(bool b) {
+    SubclassData = (SubclassData & ~NUW) | (b ? NUW : 0);
+  }
+  void setHasNoSignedWrap(bool b) {
+    SubclassData = (SubclassData & ~NSW) | (b ? NSW : 0);
+  }
+  void setIsExact(bool b) {
+    SubclassData = (SubclassData & ~EXACT) | (b ? EXACT : 0);
+  }
+  bool hasNoUnsignedWrap() const { return SubclassData & NUW; }
+  bool hasNoSignedWrap() const { return SubclassData & NSW; }
+  bool isExact() const { return SubclassData & EXACT; }
+  static bool classof(const SDNode *N) {
+    return isBinOpWithFlags(N->getOpcode());
+  }
+};
+
 /// TernarySDNode - This class is used for three-operand SDNodes. This is solely
 /// to allow co-allocation of node operands with the node itself.
 class TernarySDNode : public SDNode {

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -1325,9 +1325,16 @@ SDValue DAGCombiner::combine(SDNode *N) {
 
     // Constant operands are canonicalized to RHS.
     if (isa<ConstantSDNode>(N0) || !isa<ConstantSDNode>(N1)) {
-      SDValue Ops[] = { N1, N0 };
+      SDValue Ops[] = {N1, N0};
-      SDNode *CSENode = DAG.getNodeIfExists(N->getOpcode(), N->getVTList(),
+      SDNode *CSENode;
-                                            Ops);
+      if (const BinaryWithFlagsSDNode *BinNode =
+              dyn_cast<BinaryWithFlagsSDNode>(N)) {
+        CSENode = DAG.getNodeIfExists(
+            N->getOpcode(), N->getVTList(), Ops, BinNode->hasNoUnsignedWrap(),
+            BinNode->hasNoSignedWrap(), BinNode->isExact());
+      } else {
+        CSENode = DAG.getNodeIfExists(N->getOpcode(), N->getVTList(), Ops);
+      }
       if (CSENode)
         return SDValue(CSENode, 0);
     }

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -48,6 +48,7 @@
 #include "llvm/Target/TargetSelectionDAGInfo.h"
 #include <algorithm>
 #include <cmath>
+
 using namespace llvm;
 
 /// makeVTList - Return an instance of the SDVTList struct initialized with the
@@ -381,6 +382,20 @@ static void AddNodeIDOperands(FoldingSetNodeID &ID,
   }
 }
 
+static void AddBinaryNodeIDCustom(FoldingSetNodeID &ID, bool nuw, bool nsw,
+                                  bool exact) {
+  ID.AddBoolean(nuw);
+  ID.AddBoolean(nsw);
+  ID.AddBoolean(exact);
+}
+
+/// AddBinaryNodeIDCustom - Add BinarySDNodes special infos
+static void AddBinaryNodeIDCustom(FoldingSetNodeID &ID, unsigned Opcode,
+                                  bool nuw, bool nsw, bool exact) {
+  if (isBinOpWithFlags(Opcode))
+    AddBinaryNodeIDCustom(ID, nuw, nsw, exact);
+}
+
 static void AddNodeIDNode(FoldingSetNodeID &ID, unsigned short OpC,
                           SDVTList VTList, ArrayRef<SDValue> OpList) {
   AddNodeIDOpcode(ID, OpC);
@@ -473,6 +488,19 @@ static void AddNodeIDCustom(FoldingSetNodeID &ID, const SDNode *N) {
     ID.AddInteger(ST->getPointerInfo().getAddrSpace());
     break;
   }
+  case ISD::SDIV:
+  case ISD::UDIV:
+  case ISD::SRA:
+  case ISD::SRL:
+  case ISD::MUL:
+  case ISD::ADD:
+  case ISD::SUB:
+  case ISD::SHL: {
+    const BinaryWithFlagsSDNode *BinNode = cast<BinaryWithFlagsSDNode>(N);
+    AddBinaryNodeIDCustom(ID, N->getOpcode(), BinNode->hasNoUnsignedWrap(),
+                          BinNode->hasNoSignedWrap(), BinNode->isExact());
+    break;
+  }
   case ISD::ATOMIC_CMP_SWAP:
   case ISD::ATOMIC_SWAP:
   case ISD::ATOMIC_LOAD_ADD:
@@ -926,6 +954,25 @@ void SelectionDAG::allnodes_clear() {
     DeallocateNode(AllNodes.begin());
 }
 
+BinarySDNode *SelectionDAG::GetBinarySDNode(unsigned Opcode, SDLoc DL,
+                                            SDVTList VTs, SDValue N1,
+                                            SDValue N2, bool nuw, bool nsw,
+                                            bool exact) {
+  if (isBinOpWithFlags(Opcode)) {
+    BinaryWithFlagsSDNode *FN = new (NodeAllocator) BinaryWithFlagsSDNode(
+        Opcode, DL.getIROrder(), DL.getDebugLoc(), VTs, N1, N2);
+    FN->setHasNoUnsignedWrap(nuw);
+    FN->setHasNoSignedWrap(nsw);
+    FN->setIsExact(exact);
+
+    return FN;
+  }
+
+  BinarySDNode *N = new (NodeAllocator)
+      BinarySDNode(Opcode, DL.getIROrder(), DL.getDebugLoc(), VTs, N1, N2);
+  return N;
+}
+
 void SelectionDAG::clear() {
   allnodes_clear();
   OperandAllocator.Reset();
@@ -2936,7 +2983,7 @@ SDValue SelectionDAG::FoldConstantArithmetic(unsigned Opcode, EVT VT,
 }
 
 SDValue SelectionDAG::getNode(unsigned Opcode, SDLoc DL, EVT VT, SDValue N1,
-                              SDValue N2) {
+                              SDValue N2, bool nuw, bool nsw, bool exact) {
   ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1.getNode());
   ConstantSDNode *N2C = dyn_cast<ConstantSDNode>(N2.getNode());
   switch (Opcode) {
@@ -3376,22 +3423,25 @@ SDValue SelectionDAG::getNode(unsigned Opcode, SDLoc DL, EVT VT, SDValue N1,
   }
 
   // Memoize this node if possible.
-  SDNode *N;
+  BinarySDNode *N;
   SDVTList VTs = getVTList(VT);
+  const bool BinOpHasFlags = isBinOpWithFlags(Opcode);
   if (VT != MVT::Glue) {
-    SDValue Ops[] = { N1, N2 };
+    SDValue Ops[] = {N1, N2};
     FoldingSetNodeID ID;
     AddNodeIDNode(ID, Opcode, VTs, Ops);
+    if (BinOpHasFlags)
+      AddBinaryNodeIDCustom(ID, Opcode, nuw, nsw, exact);
     void *IP = nullptr;
     if (SDNode *E = CSEMap.FindNodeOrInsertPos(ID, IP))
       return SDValue(E, 0);
 
-    N = new (NodeAllocator) BinarySDNode(Opcode, DL.getIROrder(),
+    N = GetBinarySDNode(Opcode, DL, VTs, N1, N2, nuw, nsw, exact);
-                                         DL.getDebugLoc(), VTs, N1, N2);
+
     CSEMap.InsertNode(N, IP);
   } else {
-    N = new (NodeAllocator) BinarySDNode(Opcode, DL.getIROrder(),
+
-                                         DL.getDebugLoc(), VTs, N1, N2);
+    N = GetBinarySDNode(Opcode, DL, VTs, N1, N2, nuw, nsw, exact);
   }
 
   AllNodes.push_back(N);
@@ -5606,10 +5656,13 @@ SelectionDAG::getTargetInsertSubreg(int SRIdx, SDLoc DL, EVT VT,
 /// getNodeIfExists - Get the specified node if it's already available, or
 /// else return NULL.
 SDNode *SelectionDAG::getNodeIfExists(unsigned Opcode, SDVTList VTList,
-                                      ArrayRef<SDValue> Ops) {
+                                      ArrayRef<SDValue> Ops, bool nuw, bool nsw,
-  if (VTList.VTs[VTList.NumVTs-1] != MVT::Glue) {
+                                      bool exact) {
+  if (VTList.VTs[VTList.NumVTs - 1] != MVT::Glue) {
     FoldingSetNodeID ID;
     AddNodeIDNode(ID, Opcode, VTList, Ops);
+    if (isBinOpWithFlags(Opcode))
+      AddBinaryNodeIDCustom(ID, nuw, nsw, exact);
     void *IP = nullptr;
     if (SDNode *E = CSEMap.FindNodeOrInsertPos(ID, IP))
       return E;

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -2784,8 +2784,22 @@ void SelectionDAGBuilder::visitFSub(const User &I) {
 void SelectionDAGBuilder::visitBinary(const User &I, unsigned OpCode) {
   SDValue Op1 = getValue(I.getOperand(0));
   SDValue Op2 = getValue(I.getOperand(1));
-  setValue(&I, DAG.getNode(OpCode, getCurSDLoc(),
+
-                           Op1.getValueType(), Op1, Op2));
+  bool nuw = false;
+  bool nsw = false;
+  bool exact = false;
+  if (const OverflowingBinaryOperator *OFBinOp =
+          dyn_cast<const OverflowingBinaryOperator>(&I)) {
+    nuw = OFBinOp->hasNoUnsignedWrap();
+    nsw = OFBinOp->hasNoSignedWrap();
+  }
+  if (const PossiblyExactOperator *ExactOp =
+          dyn_cast<const PossiblyExactOperator>(&I))
+    exact = ExactOp->isExact();
+
+  SDValue BinNodeValue = DAG.getNode(OpCode, getCurSDLoc(), Op1.getValueType(),
+                                     Op1, Op2, nuw, nsw, exact);
+  setValue(&I, BinNodeValue);
 }
 
 void SelectionDAGBuilder::visitShift(const User &I, unsigned Opcode) {
@@ -2816,8 +2830,25 @@ void SelectionDAGBuilder::visitShift(const User &I, unsigned Opcode) {
       Op2 = DAG.getZExtOrTrunc(Op2, DL, MVT::i32);
   }
 
-  setValue(&I, DAG.getNode(Opcode, getCurSDLoc(),
+  bool nuw = false;
-                           Op1.getValueType(), Op1, Op2));
+  bool nsw = false;
+  bool exact = false;
+
+  if (Opcode == ISD::SRL || Opcode == ISD::SRA || Opcode == ISD::SHL) {
+
+    if (const OverflowingBinaryOperator *OFBinOp =
+            dyn_cast<const OverflowingBinaryOperator>(&I)) {
+      nuw = OFBinOp->hasNoUnsignedWrap();
+      nsw = OFBinOp->hasNoSignedWrap();
+    }
+    if (const PossiblyExactOperator *ExactOp =
+            dyn_cast<const PossiblyExactOperator>(&I))
+      exact = ExactOp->isExact();
+  }
+
+  SDValue Res = DAG.getNode(Opcode, getCurSDLoc(), Op1.getValueType(), Op1, Op2,
+                            nuw, nsw, exact);
+  setValue(&I, Res);
 }
 
 void SelectionDAGBuilder::visitSDiv(const User &I) {

lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -2617,7 +2617,8 @@ SDValue TargetLowering::BuildExactSDIV(SDValue Op1, SDValue Op2, SDLoc dl,
   if (ShAmt) {
     // TODO: For UDIV use SRL instead of SRA.
     SDValue Amt = DAG.getConstant(ShAmt, getShiftAmountTy(Op1.getValueType()));
-    Op1 = DAG.getNode(ISD::SRA, dl, Op1.getValueType(), Op1, Amt);
+    Op1 = DAG.getNode(ISD::SRA, dl, Op1.getValueType(), Op1, Amt, false, false,
+                      true);
     d = d.ashr(ShAmt);
   }
 

test/CodeGen/X86/2014-05-30-CombineAddNSW.ll

@@ -0,0 +1,20 @@
+; RUN: llc < %s -march=x86-64 | FileCheck %s
+; CHECK: addl
+
+; The two additions are the same , but have different flags.
+; In theory this code should never be generated by the frontend, but this 
+; tries to test that two identical instructions with two different flags
+; actually generate two different nodes.
+;
+; Normally the combiner would see this condition without the flags 
+; and optimize the result of the sub into a register clear
+; (the final result would be 0). With the different flags though the combiner 
+; needs to keep the add + sub nodes, because the two nodes result as different
+; nodes and so cannot assume that the subtraction of the two nodes
+; generates 0 as result
+define i32 @foo(i32 %a, i32 %b) {
+  %1 = add i32 %a, %b
+  %2 = add nsw i32 %a, %b
+  %3 = sub i32 %1, %2
+  ret i32 %3
+}