[llvm-dev] C++ compiler error I do not understand

[Krzysztof Parzyszek via llvm-dev]

The 4th constructor takes a (unique) pointer, not a reference, but you pass an rvalue reference.

If you really need an unique pointer, you can make one with std::make_unique.

--
Krzysztof Parzyszek  kparzysz at quicinc.com<mailto:kparzysz at quicinc.com>   AI tools development

From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of Paul C. Anagnostopoulos via llvm-dev
Sent: Tuesday, March 30, 2021 7:03 PM
To: LLVM dev <llvm-dev at lists.llvm.org>
Subject: [EXT] [llvm-dev] C++ compiler error I do not understand


I have the following situation with which I could use some enlightenment. As usual, the context is TableGen.

in class Record:

public:
  using AssertionTuple = std::tuple<SMLoc, Init *, Init *>;
...
  SmallVector<AssertionTuple, 0> Assertions;

then there exists:

  struct RecordsEntry {
    std::unique_ptr<Record> Rec;
    std::unique_ptr<ForeachLoop> Loop;
    std::unique_ptr<Record::AssertionTuple> Assertion;

    void dump() const;

    RecordsEntry() {}
    RecordsEntry(std::unique_ptr<Record> Rec) : Rec(std::move(Rec)) {}
    RecordsEntry(std::unique_ptr<ForeachLoop> Loop)
      : Loop(std::move(Loop)) {}
    RecordsEntry(std::unique_ptr<Record::AssertionTuple> Assertion) // 4th constructor
      : Assertion(std::move(Assertion)) {}
  };

...

bool TGParser::addEntry(RecordsEntry E) { ...

Note that I expect to create a RecordsEntry by passing an AssertionTuple to addEntry and having the 4th constructor do the trick. The other three constructors all work fine. However, when I do this:

    Record::AssertionTuple tuple = std::make_tuple(ConditionLoc, Condition, Message);
    addEntry(std::move(tuple));

I get this:

C:\LLVM\llvm-project\llvm\lib\TableGen\TGParser.cpp(3190): error C2664: 'bool llvm::TGParser::addEntry(llvm::RecordsEntry)': cannot convert argument 1 from 'llvm::Record::AssertionTuple' to 'llvm::RecordsEntry'
C:\LLVM\llvm-project\llvm\lib\TableGen\TGParser.cpp(3190): note: No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
C:\LLVM\llvm-project\llvm\lib\TableGen\TGParser.cpp(344): note: see declaration of 'llvm::TGParser::addEntry'

Ah, I guess I should show the definitions of the three arguments passed to make_tuple() above:

  SMLoc ConditionLoc = Lex.getLoc();
  Init *Condition = ParseValue(CurRec);
  Init *Message = ParseValue(CurRec);

Since there is no complaint about making the tuple, I assume those three arguments have the correct type. The problem is the 4th RecordsEntry constructor, which cannot convert the addEntry argument 'std::move(tuple)' to a Record::AssertionTuple, even though that's exactly what it is.

P.S.: Regardless of what I learn here, I'm going to change the assertion tuple into a little struct, which should work fine as demonstrated by constructor 3 above.


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