[TableGen] Add bang-operators !getop and !setop.

[simon_tatham]

Summary

These allow you to get and set the operator of a dag node, without
affecting its list of arguments.

!getop is slightly fiddly because in many contexts you need its
return value to have a static type more specific than 'any record'. It
works to say !cast<BaseClass>(!getop(...)), but it's cumbersome, so
I made !getop take an optional type suffix itself, so that can be
written as the shorter !getop<BaseClass>(...).

[simon_tatham]

Suddenly realised that it wasn't as hard as I thought to make
!getop(...) usable as the operator of a new dag literal expression.

[nhaehnle]

This looks fine, but have you thought through !setop discarding the name on the operand? The only use of this feature seems to be naming DAG pattern nodes, a feature that seems to have been around forever but I haven't seen used in the code I've touched...

[simon_tatham]

I'm sorry, I'm not sure I understand that question.

!setop affects the operator of a dag value, not the operands. The :$name suffix can only be applied to an operand. So !setop leaves all the operand names completely alone, since the part of the dag value it's replacing is nothing to do with them.

(Perhaps !setop is a bad name, for that reason, since it could very easily mean either 'operator' or 'operand'...)

[nhaehnle]

The name suffix _can_ be applied to the operator:

def op;
def Foo {
  dag x = (op:$blah 1:$foo, 2, 3);
}
// produces:
------------- Defs -----------------
def Foo {
  dag x = (op:blah 1:$foo, 2, 3);
}
def op {
}

Though the inconsistent output and undocumented nature of it suggests that this feature is hardly ever used...

[nhaehnle]

Okay, digging in further, the feature is actually used quite a bit in pattern definitions like:

def : GCNPat <
  (VGPRImm<(i32 imm)>:$imm),
  (V_MOV_B32_e32 imm:$imm)
>;

or

def: Pat<(s32_0ImmPred:$s16), (A2_tfrsi imm:$s16)>;

The first really ought to be expressible by placing the $imm inside the inner DAG expression, but for some reason the TableGen backend doesn't allow that. I don't know about the second... maybe if it was wrapped as (i32 s32_0ImmPred:$s16)? Fundamentally, the feature seems to be used as a hacky workaround for the fact that SelectionDAG patterns don't have an "outer" DAG, and having a naked expression like s32_0ImmPred:$s16 is not possible.

So here we are. I think your change is okay as-is though. It strips such names, but this naming feature seems kind of awkward to me anyway, and its use should probably be discouraged.

[simon_tatham]

OK, I'll commit it as is. Thanks!

I must admit that I hadn't known about that feature of dags at all, and I probably should have found out about it, because I did see that nullptr argument when I copied the form of an existing call to DagInit::get, but I lazily didn't dig down to find out what it was for. Ahem.

llvm/docs/TableGen/LangIntro.rst

``!dag(op, children, names)``
     Due to limitations of the type system, 'children' must be a list of items
     of a common type. In practice, this means that they should either have the
     same type or be records with a common superclass. Mixing dag and non-dag
     items is not possible. However, '?' can be used.
 
     Example: !dag(op, [a1, a2, ?], ["name1", "name2", "name3"]) results in
     (op a1:$name1, a2:$name2, ?:$name3).
 
+``!setop(dag, op)``
+    Return a DAG node with the same arguments as ``dag``, but with its
+    operator replaced with ``op``.
+
+    Example: ``!setop((foo 1, 2), bar)`` results in ``(bar 1, 2)``.
+
+``!getop(dag)``
+
+``!getop<type>(dag)``
+    Return the operator of the given DAG node.
+    Example: ``!getop((foo 1, 2))`` results in ``foo``.
+
+    The result of ``!getop`` can be used directly in a context where
+    any record value at all is acceptable (typically placing it into
+    another dag value). But in other contexts, it must be explicitly
+    cast to a particular class type. The ``!getop<type>`` syntax is
+    provided to make this easy.
+
+    For example, to assign the result to a class-typed value, you
+    could write either of these:
+      ``BaseClass b = !getop<BaseClass>(someDag);``
+
+      ``BaseClass b = !cast<BaseClass>(!getop(someDag));``
+
+    But to build a new dag node reusing the operator from another, no
+    cast is necessary:
+      ``dag d = !dag(!getop(someDag), args, names);``
+
 ``!listconcat(a, b, ...)``
     A list value that is the result of concatenating the 'a' and 'b' lists.
     The lists must have the same element type.
     More than two arguments are accepted with the result being the concatenation
     of all the lists given.
 
 ``!listsplat(a, size)``
     A list value that contains the value ``a`` ``size`` times.

llvm/docs/TableGen/LangRef.rst

 
 .. productionlist::
    BangOperator: one of
                :!eq     !if      !head    !tail      !con
                :!add    !shl     !sra     !srl       !and
                :!or     !empty   !subst   !foreach   !strconcat
                :!cast   !listconcat       !size      !foldl
                :!isa    !dag     !le      !lt        !ge
-               :!gt     !ne      !mul     !listsplat
+               :!gt     !ne      !mul     !listsplat !setop
+               :!getop
 
 TableGen also has !cond operator that needs a slightly different
 syntax compared to other "bang operators":
 
 .. productionlist::
    CondOperator: !cond
 
 

llvm/include/llvm/TableGen/Record.h

public:
 
   Init *getBit(unsigned Bit) const override;
 };
 
 /// !op (X) - Transform an init.
 ///
 class UnOpInit : public OpInit, public FoldingSetNode {
 public:
-  enum UnaryOp : uint8_t { CAST, HEAD, TAIL, SIZE, EMPTY };
+  enum UnaryOp : uint8_t { CAST, HEAD, TAIL, SIZE, EMPTY, GETOP };
 
 private:
   Init *LHS;
 
   UnOpInit(UnaryOp opc, Init *lhs, RecTy *Type)
     : OpInit(IK_UnOpInit, Type, opc), LHS(lhs) {}
 
 public:
public:
   std::string getAsString() const override;
 };
 
 /// !op (X, Y) - Combine two inits.
 class BinOpInit : public OpInit, public FoldingSetNode {
 public:
   enum BinaryOp : uint8_t { ADD, MUL, AND, OR, SHL, SRA, SRL, LISTCONCAT,
                             LISTSPLAT, STRCONCAT, CONCAT, EQ, NE, LE, LT, GE,
-                            GT };
+                            GT, SETOP };
 
 private:
   Init *LHS, *RHS;
 
   BinOpInit(BinaryOp opc, Init *lhs, Init *rhs, RecTy *Type) :
       OpInit(IK_BinOpInit, Type, opc), LHS(lhs), RHS(rhs) {}
 
 public:

llvm/lib/TableGen/Record.cpp

case SIZE:
     break;
 
   case EMPTY:
     if (ListInit *LHSl = dyn_cast<ListInit>(LHS))
       return IntInit::get(LHSl->empty());
     if (StringInit *LHSs = dyn_cast<StringInit>(LHS))
       return IntInit::get(LHSs->getValue().empty());
     break;
+
+  case GETOP:
+    if (DagInit *Dag = dyn_cast<DagInit>(LHS)) {
+      DefInit *DI = DefInit::get(Dag->getOperatorAsDef({}));
+      if (!DI->getType()->typeIsA(getType())) {
+        PrintFatalError(CurRec->getLoc(),
+                        Twine("Expected type '") +
+                        getType()->getAsString() + "', got '" +
+                        DI->getType()->getAsString() + "' in: " +
+                        getAsString() + "\n");
+      } else {
+        return DI;
+      }
+    }
+    break;
   }
   return const_cast<UnOpInit *>(this);
 }
 
 Init *UnOpInit::resolveReferences(Resolver &R) const {
   Init *lhs = LHS->resolveReferences(R);
 
   if (LHS != lhs || (R.isFinal() && getOpcode() == CAST))
     return (UnOpInit::get(getOpcode(), lhs, getType()))
         ->Fold(R.getCurrentRecord(), R.isFinal());
   return const_cast<UnOpInit *>(this);
 }
 
 std::string UnOpInit::getAsString() const {
   std::string Result;
   switch (getOpcode()) {
   case CAST: Result = "!cast<" + getType()->getAsString() + ">"; break;
   case HEAD: Result = "!head"; break;
   case TAIL: Result = "!tail"; break;
   case SIZE: Result = "!size"; break;
   case EMPTY: Result = "!empty"; break;
+  case GETOP: Result = "!getop"; break;
   }
   return Result + "(" + LHS->getAsString() + ")";
 }
 
 static void
 ProfileBinOpInit(FoldingSetNodeID &ID, unsigned Opcode, Init *LHS, Init *RHS,
                  RecTy *Type) {
   ID.AddInteger(Opcode);
if (getOpcode() == EQ || getOpcode() == NE) {
       if (LHSs && RHSs) {
         bool Equal = LHSs->getValue() == RHSs->getValue();
         return BitInit::get(getOpcode() == EQ ? Equal : !Equal);
       }
     }
 
     break;
   }
+  case SETOP: {
+    DagInit *Dag = dyn_cast<DagInit>(LHS);
+    DefInit *Op = dyn_cast<DefInit>(RHS);
+    if (Dag && Op) {
+      SmallVector<Init*, 8> Args;
+      SmallVector<StringInit*, 8> ArgNames;
+      for (unsigned i = 0, e = Dag->getNumArgs(); i != e; ++i) {
+        Args.push_back(Dag->getArg(i));
+        ArgNames.push_back(Dag->getArgName(i));
+      }
+      return DagInit::get(Op, nullptr, Args, ArgNames);
+    }
+    break;
+  }
   case ADD:
   case MUL:
   case AND:
   case OR:
   case SHL:
   case SRA:
   case SRL: {
     IntInit *LHSi =
std::string BinOpInit::getAsString() const {
   case NE: Result = "!ne"; break;
   case LE: Result = "!le"; break;
   case LT: Result = "!lt"; break;
   case GE: Result = "!ge"; break;
   case GT: Result = "!gt"; break;
   case LISTCONCAT: Result = "!listconcat"; break;
   case LISTSPLAT: Result = "!listsplat"; break;
   case STRCONCAT: Result = "!strconcat"; break;
+  case SETOP: Result = "!setop"; break;
   }
   return Result + "(" + LHS->getAsString() + ", " + RHS->getAsString() + ")";
 }
 
 static void
 ProfileTernOpInit(FoldingSetNodeID &ID, unsigned Opcode, Init *LHS, Init *MHS,
                   Init *RHS, RecTy *Type) {
   ID.AddInteger(Opcode);

llvm/lib/TableGen/TGLexer.h

enum TokKind {
 
     // Keywords.
     Bit, Bits, Class, Code, Dag, Def, Foreach, Defm, Field, In, Int, Let, List,
     MultiClass, String, Defset,
 
     // !keywords.
     XConcat, XADD, XMUL, XAND, XOR, XSRA, XSRL, XSHL, XListConcat, XListSplat,
     XStrConcat, XCast, XSubst, XForEach, XFoldl, XHead, XTail, XSize, XEmpty,
-    XIf, XCond, XEq, XIsA, XDag, XNe, XLe, XLt, XGe, XGt,
+    XIf, XCond, XEq, XIsA, XDag, XNe, XLe, XLt, XGe, XGt, XSetOp, XGetOp,
 
     // Integer value.
     IntVal,
 
     // Binary constant.  Note that these are sized according to the number of
     // bits given.
     BinaryIntVal,
 

llvm/lib/TableGen/TGLexer.cpp

tgtok::TokKind Kind =
     .Case("cast", tgtok::XCast)
     .Case("empty", tgtok::XEmpty)
     .Case("subst", tgtok::XSubst)
     .Case("foldl", tgtok::XFoldl)
     .Case("foreach", tgtok::XForEach)
     .Case("listconcat", tgtok::XListConcat)
     .Case("listsplat", tgtok::XListSplat)
     .Case("strconcat", tgtok::XStrConcat)
+    .Case("setop", tgtok::XSetOp)
+    .Case("getop", tgtok::XGetOp)
     .Default(tgtok::Error);
 
   return Kind != tgtok::Error ? Kind : ReturnError(Start-1, "Unknown operator");
 }
 
 bool TGLexer::prepExitInclude(bool IncludeStackMustBeEmpty) {
   // Report an error, if preprocessor control stack for the current
   // file is not empty.

llvm/lib/TableGen/TGParser.cpp

Init *TGParser::ParseOperation(Record *CurRec, RecTy *ItemType) {
   switch (Lex.getCode()) {
   default:
     TokError("unknown operation");
     return nullptr;
   case tgtok::XHead:
   case tgtok::XTail:
   case tgtok::XSize:
   case tgtok::XEmpty:
-  case tgtok::XCast: {  // Value ::= !unop '(' Value ')'
+  case tgtok::XCast:
+  case tgtok::XGetOp: {  // Value ::= !unop '(' Value ')'
     UnOpInit::UnaryOp Code;
     RecTy *Type = nullptr;
 
     switch (Lex.getCode()) {
     default: llvm_unreachable("Unhandled code!");
     case tgtok::XCast:
       Lex.Lex();  // eat the operation
       Code = UnOpInit::CAST;
case tgtok::XSize:
       Code = UnOpInit::SIZE;
       Type = IntRecTy::get();
       break;
     case tgtok::XEmpty:
       Lex.Lex();  // eat the operation
       Code = UnOpInit::EMPTY;
       Type = IntRecTy::get();
       break;
+    case tgtok::XGetOp:
+      Lex.Lex();  // eat the operation
+      if (Lex.getCode() == tgtok::less) {
+        // Parse an optional type suffix, so that you can say
+        // !getop<BaseClass>(someDag) as a shorthand for
+        // !cast<BaseClass>(!getop(someDag)).
+        Type = ParseOperatorType();
+
+        if (!Type) {
+          TokError("did not get type for unary operator");
+          return nullptr;
+        }
+
+        if (!isa<RecordRecTy>(Type)) {
+          TokError("type for !getop must be a record type");
+          // but keep parsing, to consume the operand
+        }
+      } else {
+        Type = RecordRecTy::get({});
+      }
+      Code = UnOpInit::GETOP;
+      break;
     }
     if (Lex.getCode() != tgtok::l_paren) {
       TokError("expected '(' after unary operator");
       return nullptr;
     }
     Lex.Lex();  // eat the '('
 
     Init *LHS = ParseValue(CurRec);
Init *TGParser::ParseOperation(Record *CurRec, RecTy *ItemType) {
   case tgtok::XEq:
   case tgtok::XNe:
   case tgtok::XLe:
   case tgtok::XLt:
   case tgtok::XGe:
   case tgtok::XGt:
   case tgtok::XListConcat:
   case tgtok::XListSplat:
-  case tgtok::XStrConcat: {  // Value ::= !binop '(' Value ',' Value ')'
+  case tgtok::XStrConcat:
+  case tgtok::XSetOp: {  // Value ::= !binop '(' Value ',' Value ')'
     tgtok::TokKind OpTok = Lex.getCode();
     SMLoc OpLoc = Lex.getLoc();
     Lex.Lex();  // eat the operation
 
     BinOpInit::BinaryOp Code;
     switch (OpTok) {
     default: llvm_unreachable("Unhandled code!");
     case tgtok::XConcat: Code = BinOpInit::CONCAT; break;
     case tgtok::XADD:    Code = BinOpInit::ADD; break;
     case tgtok::XMUL:    Code = BinOpInit::MUL; break;
     case tgtok::XAND:    Code = BinOpInit::AND; break;
     case tgtok::XOR:     Code = BinOpInit::OR; break;
     case tgtok::XSRA:    Code = BinOpInit::SRA; break;
     case tgtok::XSRL:    Code = BinOpInit::SRL; break;
     case tgtok::XSHL:    Code = BinOpInit::SHL; break;
     case tgtok::XEq:     Code = BinOpInit::EQ; break;
     case tgtok::XNe:     Code = BinOpInit::NE; break;
     case tgtok::XLe:     Code = BinOpInit::LE; break;
     case tgtok::XLt:     Code = BinOpInit::LT; break;
     case tgtok::XGe:     Code = BinOpInit::GE; break;
     case tgtok::XGt:     Code = BinOpInit::GT; break;
     case tgtok::XListConcat: Code = BinOpInit::LISTCONCAT; break;
     case tgtok::XListSplat: Code = BinOpInit::LISTSPLAT; break;
     case tgtok::XStrConcat: Code = BinOpInit::STRCONCAT; break;
+    case tgtok::XSetOp: Code = BinOpInit::SETOP; break;
     }
 
     RecTy *Type = nullptr;
     RecTy *ArgType = nullptr;
     switch (OpTok) {
     default:
       llvm_unreachable("Unhandled code!");
     case tgtok::XConcat:
+    case tgtok::XSetOp:
       Type = DagRecTy::get();
       ArgType = DagRecTy::get();
       break;
     case tgtok::XAND:
     case tgtok::XOR:
     case tgtok::XSRA:
     case tgtok::XSRL:
     case tgtok::XSHL:
case tgtok::XSetOp: {  // Value ::= !binop '(' Value ',' Value ')'
 
     SmallVector<Init*, 2> InitList;
 
     for (;;) {
       SMLoc InitLoc = Lex.getLoc();
       InitList.push_back(ParseValue(CurRec, ArgType));
       if (!InitList.back()) return nullptr;
 
-      // All BinOps require their arguments to be of compatible types.
       RecTy *ListType = cast<TypedInit>(InitList.back())->getType();
       if (!ArgType) {
         ArgType = ListType;
 
         switch (Code) {
         case BinOpInit::LISTCONCAT:
           if (!isa<ListRecTy>(ArgType)) {
             Error(InitLoc, Twine("expected a list, got value of type '") +
for (;;) {
         }
         if (Code != BinOpInit::ADD && Code != BinOpInit::AND &&
             Code != BinOpInit::OR && Code != BinOpInit::SRA &&
             Code != BinOpInit::SRL && Code != BinOpInit::SHL &&
             Code != BinOpInit::MUL)
           ArgType = Resolved;
       }
 
+      // Deal with BinOps whose arguments have different types, by
+      // rewriting ArgType in between them.
+      switch (Code) {
+        case BinOpInit::SETOP:
+          // After parsing the first dag argument, switch to expecting
+          // a record, with no restriction on its superclasses.
+          ArgType = RecordRecTy::get({});
+          break;
+        default:
+          break;
+      }
+
       if (Lex.getCode() != tgtok::comma)
         break;
       Lex.Lex();  // eat the ','
     }
 
     if (Lex.getCode() != tgtok::r_paren) {
       TokError("expected ')' in operator");
       return nullptr;
if (!EltTy) {
       DeducedEltTy = EltTy;
     }
 
     return ListInit::get(Vals, DeducedEltTy);
   }
   case tgtok::l_paren: {         // Value ::= '(' IDValue DagArgList ')'
     Lex.Lex();   // eat the '('
     if (Lex.getCode() != tgtok::Id && Lex.getCode() != tgtok::XCast &&
-        Lex.getCode() != tgtok::question) {
+        Lex.getCode() != tgtok::question && Lex.getCode() != tgtok::XGetOp) {
       TokError("expected identifier in dag init");
       return nullptr;
     }
 
     Init *Operator = ParseValue(CurRec);
     if (!Operator) return nullptr;
 
     // If the operator name is present, parse it.
case tgtok::l_paren: {         // Value ::= '(' IDValue DagArgList ')'
 
     return DagInit::get(Operator, OperatorName, DagArgs);
   }
 
   case tgtok::XHead:
   case tgtok::XTail:
   case tgtok::XSize:
   case tgtok::XEmpty:
-  case tgtok::XCast:  // Value ::= !unop '(' Value ')'
+  case tgtok::XCast:
+  case tgtok::XGetOp:  // Value ::= !unop '(' Value ')'
   case tgtok::XIsA:
   case tgtok::XConcat:
   case tgtok::XDag:
   case tgtok::XADD:
   case tgtok::XMUL:
   case tgtok::XAND:
   case tgtok::XOR:
   case tgtok::XSRA:
   case tgtok::XSRL:
   case tgtok::XSHL:
   case tgtok::XEq:
   case tgtok::XNe:
   case tgtok::XLe:
   case tgtok::XLt:
   case tgtok::XGe:
   case tgtok::XGt:
   case tgtok::XListConcat:
   case tgtok::XListSplat:
-  case tgtok::XStrConcat:   // Value ::= !binop '(' Value ',' Value ')'
+  case tgtok::XStrConcat:
+  case tgtok::XSetOp:   // Value ::= !binop '(' Value ',' Value ')'
   case tgtok::XIf:
   case tgtok::XCond:
   case tgtok::XFoldl:
   case tgtok::XForEach:
   case tgtok::XSubst: {  // Value ::= !ternop '(' Value ',' Value ',' Value ')'
     return ParseOperation(CurRec, ItemType);
   }
   }

llvm/test/TableGen/getsetop.td

+// RUN: llvm-tblgen %s | FileCheck %s
+// RUN: not llvm-tblgen -DERROR1 %s 2>&1 | FileCheck --check-prefix=ERROR1 %s
+// RUN: not llvm-tblgen -DERROR2 %s 2>&1 | FileCheck --check-prefix=ERROR2 %s
+// RUN: not llvm-tblgen -DERROR3 %s 2>&1 | FileCheck --check-prefix=ERROR3 %s
+
+class Base;
+class OtherBase;
+
+def foo: Base;
+def bar: Base;
+def qux: OtherBase;
+
+def test {
+  dag orig = (foo 1, 2:$a, $b);
+  dag another = (qux "hello", $world);
+
+  // CHECK: dag replaceWithBar = (bar 1, 2:$a, ?:$b);
+  dag replaceWithBar = !setop(orig, bar);
+
+  // CHECK: dag replaceWithBaz = (qux 1, 2:$a, ?:$b);
+  dag replaceWithBaz = !setop(orig, qux);
+
+  // CHECK: Base getopWithCast = foo;
+  Base getopWithCast = !getop<Base>(orig);
+
+  // CHECK: dag getopToSetop = (foo "hello", ?:$world);
+  dag getopToSetop = !setop(another, !getop(orig));
+
+  // CHECK: dag getopToBangDag = (foo 1:$a, 2:$b, 3:$c);
+  dag getopToBangDag = !dag(!getop(orig), [1, 2, 3], ["a", "b", "c"]);
+
+  // CHECK: dag getopToDagInit = (foo "it worked");
+  dag getopToDagInit = (!getop(orig) "it worked");
+
+#ifdef ERROR1
+  // !getop(...) has a static type of 'any record at all, with no
+  // required superclasses'. That's too general to use in an
+  // assignment whose LHS demands an instance of Base, so we expect a
+  // static (parse-time) type-checking error.
+
+  // ERROR1: error: Value 'noCast' of type 'Base' is incompatible with initializer '!getop(orig)' of type '{}'
+  Base noCast = !getop(orig);
+#endif
+
+#ifdef ERROR2
+  // Here, we expect a _dynamic_ type error, when it turns out at
+  // evaluation time that the operator of 'another' is a record that
+  // isn't an instance of the specified base class.
+
+  // ERROR2: error: Expected type 'Base', got 'OtherBase' in: !getop((qux "hello", ?:$world))
+  Base badCast = !getop<Base>(another);
+#endif
+
+#ifdef ERROR3
+  // Obviously, you shouldn't be able to give any type to !getop that
+  // isn't a class type.
+
+  // ERROR3: error: type for !getop must be a record type
+  int ridiculousCast = !getop<int>(orig);
+#endif
+}