[llvm] r338175 - [Support] Remove unnecessary MemoryBuffer::anchor (where the destructor serves as the key function)

[Fāng-ruì Sòng via llvm-commits]

> Oh, looks like the key function/weak vtable issue was removed from the style guide at some point - maybe we can/should just rip out all the explicit anchors, then?

Is it still there at
https://llvm.org/docs/CodingStandards.html#provide-a-virtual-method-anchor-for-classes-in-headers.
There is no wording about prefererence of dtor or an explicit
'anchor()'. For MemoryBuffer, the out-of-line dtors is already there
`virtual ~MemoryBuffer();` and removing the unnecessary `anchor()`
might be fine?
On Mon, Jul 30, 2018 at 12:48 PM David Blaikie <dblaikie at gmail.com> wrote:
>
> What's the advantage of moving the dtor to be out of line and act as a key function? I Think when I originally added a bunch of these Chris Lattner mentioned a slight preference towards an explicit anchor rather than placing the dtor out of line (if it wasn't already) - since the latter might inhibit optimizations like inlining of the dtor in some cases (even with a virtual dtor - not all dtor calls might be virtual, and derived dtors need to call the base dtor, etc).
>
> Oh, looks like the key function/weak vtable issue was removed from the style guide at some point - maybe we can/should just rip out all the explicit anchors, then?
>
> On Fri, Jul 27, 2018 at 4:12 PM Fangrui Song via llvm-commits <llvm-commits at lists.llvm.org> wrote:
>>
>> Author: maskray
>> Date: Fri Jul 27 16:12:11 2018
>> New Revision: 338175
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=338175&view=rev
>> Log:
>> [Support] Remove unnecessary MemoryBuffer::anchor (where the destructor serves as the key function)
>>
>> Modified:
>>     llvm/trunk/include/llvm/Support/MemoryBuffer.h
>>     llvm/trunk/include/llvm/Support/SmallVectorMemoryBuffer.h
>>     llvm/trunk/lib/Support/MemoryBuffer.cpp
>>
>> Modified: llvm/trunk/include/llvm/Support/MemoryBuffer.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/MemoryBuffer.h?rev=338175&r1=338174&r2=338175&view=diff
>> ==============================================================================
>> --- llvm/trunk/include/llvm/Support/MemoryBuffer.h (original)
>> +++ llvm/trunk/include/llvm/Support/MemoryBuffer.h Fri Jul 27 16:12:11 2018
>> @@ -43,7 +43,6 @@ class MemoryBuffer {
>>    const char *BufferStart; // Start of the buffer.
>>    const char *BufferEnd;   // End of the buffer.
>>
>> -
>>  protected:
>>    MemoryBuffer() = default;
>>
>> @@ -148,9 +147,6 @@ public:
>>    virtual BufferKind getBufferKind() const = 0;
>>
>>    MemoryBufferRef getMemBufferRef() const;
>> -
>> -private:
>> -  virtual void anchor();
>>  };
>>
>>  /// This class is an extension of MemoryBuffer, which allows copy-on-write
>>
>> Modified: llvm/trunk/include/llvm/Support/SmallVectorMemoryBuffer.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/SmallVectorMemoryBuffer.h?rev=338175&r1=338174&r2=338175&view=diff
>> ==============================================================================
>> --- llvm/trunk/include/llvm/Support/SmallVectorMemoryBuffer.h (original)
>> +++ llvm/trunk/include/llvm/Support/SmallVectorMemoryBuffer.h Fri Jul 27 16:12:11 2018
>> @@ -49,6 +49,9 @@ public:
>>      init(this->SV.begin(), this->SV.end(), false);
>>    }
>>
>> +  // Key function.
>> +  ~SmallVectorMemoryBuffer() override;
>> +
>>    StringRef getBufferIdentifier() const override { return BufferName; }
>>
>>    BufferKind getBufferKind() const override { return MemoryBuffer_Malloc; }
>> @@ -56,7 +59,6 @@ public:
>>  private:
>>    SmallVector<char, 0> SV;
>>    std::string BufferName;
>> -  void anchor() override;
>>  };
>>
>>  } // namespace llvm
>>
>> Modified: llvm/trunk/lib/Support/MemoryBuffer.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/MemoryBuffer.cpp?rev=338175&r1=338174&r2=338175&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Support/MemoryBuffer.cpp (original)
>> +++ llvm/trunk/lib/Support/MemoryBuffer.cpp Fri Jul 27 16:12:11 2018
>> @@ -533,5 +533,4 @@ MemoryBufferRef MemoryBuffer::getMemBuff
>>    return MemoryBufferRef(Data, Identifier);
>>  }
>>
>> -void MemoryBuffer::anchor() {}
>> -void SmallVectorMemoryBuffer::anchor() {}
>> +SmallVectorMemoryBuffer::~SmallVectorMemoryBuffer() {}
>>
>>
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