[SelectionDAG] Add preliminary plumbing for samesign flag

Extend recently-added poison-generating IR flag to codegen as well.

Author: antoniofrighetto

llvm/include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h

@@ -1267,7 +1267,7 @@ class MachineIRBuilder {
   /// \return a MachineInstrBuilder for the newly created instruction.
   MachineInstrBuilder buildICmp(CmpInst::Predicate Pred, const DstOp &Res,
                                 const SrcOp &Op0, const SrcOp &Op1,
-                                std::optional<unsigned> Flgs = std::nullopt);
+                                std::optional<unsigned> Flags = std::nullopt);
 
   /// Build and insert a \p Res = G_FCMP \p Pred\p Op0, \p Op1
   ///

llvm/include/llvm/CodeGen/SelectionDAGNodes.h

@@ -411,12 +411,14 @@ struct SDNodeFlags {
     NoFPExcept = 1 << 12,
     // Instructions with attached 'unpredictable' metadata on IR level.
     Unpredictable = 1 << 13,
+    // Compare instructions which may carry the samesign flag.
+    SameSign = 1 << 14,
 
     // NOTE: Please update LargestValue in LLVM_DECLARE_ENUM_AS_BITMASK below
     // the class definition when adding new flags.
 
     PoisonGeneratingFlags = NoUnsignedWrap | NoSignedWrap | Exact | Disjoint |
-                            NonNeg | NoNaNs | NoInfs,
+                            NonNeg | NoNaNs | NoInfs | SameSign,
   };
 
   /// Default constructor turns off all optimization flags.
@@ -438,6 +440,7 @@ struct SDNodeFlags {
   void setNoSignedWrap(bool b) { setFlag<NoSignedWrap>(b); }
   void setExact(bool b) { setFlag<Exact>(b); }
   void setDisjoint(bool b) { setFlag<Disjoint>(b); }
+  void setSameSign(bool b) { setFlag<SameSign>(b); }
   void setNonNeg(bool b) { setFlag<NonNeg>(b); }
   void setNoNaNs(bool b) { setFlag<NoNaNs>(b); }
   void setNoInfs(bool b) { setFlag<NoInfs>(b); }
@@ -454,6 +457,7 @@ struct SDNodeFlags {
   bool hasNoSignedWrap() const { return Flags & NoSignedWrap; }
   bool hasExact() const { return Flags & Exact; }
   bool hasDisjoint() const { return Flags & Disjoint; }
+  bool hasSameSign() const { return Flags & SameSign; }
   bool hasNonNeg() const { return Flags & NonNeg; }
   bool hasNoNaNs() const { return Flags & NoNaNs; }
   bool hasNoInfs() const { return Flags & NoInfs; }
@@ -473,7 +477,7 @@ struct SDNodeFlags {
 };
 
 LLVM_DECLARE_ENUM_AS_BITMASK(decltype(SDNodeFlags::None),
-                             SDNodeFlags::Unpredictable);
+                             SDNodeFlags::SameSign);
 
 inline SDNodeFlags operator|(SDNodeFlags LHS, SDNodeFlags RHS) {
   LHS |= RHS;

llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp

@@ -1105,6 +1105,9 @@ EmitMachineNode(SDNode *Node, bool IsClone, bool IsCloned,
 
     if (Flags.hasDisjoint())
       MI->setFlag(MachineInstr::MIFlag::Disjoint);
+
+    if (Flags.hasSameSign())
+      MI->setFlag(MachineInstr::MIFlag::SameSign);
   }
 
   // Emit all of the actual operands of this instruction, adding them to the

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -3652,6 +3652,10 @@ void SelectionDAGBuilder::visitICmp(const ICmpInst &I) {
     Op2 = DAG.getPtrExtOrTrunc(Op2, getCurSDLoc(), MemVT);
   }
 
+  SDNodeFlags Flags;
+  Flags.setSameSign(I.hasSameSign());
+  SelectionDAG::FlagInserter FlagsInserter(DAG, Flags);
+
   EVT DestVT = DAG.getTargetLoweringInfo().getValueType(DAG.getDataLayout(),
                                                         I.getType());
   setValue(&I, DAG.getSetCC(getCurSDLoc(), DestVT, Op1, Op2, Opcode));

llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp

@@ -653,6 +653,9 @@ void SDNode::print_details(raw_ostream &OS, const SelectionDAG *G) const {
   if (getFlags().hasDisjoint())
     OS << " disjoint";
 
+  if (getFlags().hasSameSign())
+    OS << " samesign";
+
   if (getFlags().hasNonNeg())
     OS << " nneg";