[llvm-dev] Change coding style for argument alignment?

Krzysztof Parzyszek via llvm-dev llvm-dev at lists.llvm.org
Thu Dec 3 13:32:43 PST 2020

I support this proposal.  I very much dislike the current function parameter formatting (in function declarations/definitions).  It just adds a bunch of whitespace without improvement in readability.

In practice there are already various mixtures of formatting being used.  For example:

  bool tailDuplicate(bool IsSimple,
                     MachineBasicBlock *TailBB,
                     MachineBasicBlock *ForcedLayoutPred,
                     SmallVectorImpl<MachineBasicBlock *> &TDBBs,
                     SmallVectorImpl<MachineInstr *> &Copies,
                     SmallVectorImpl<MachineBasicBlock *> *CandidatePtr);
  void appendCopies(MachineBasicBlock *MBB,
                 SmallVectorImpl<std::pair<Register, RegSubRegPair>> &CopyInfos,
                 SmallVectorImpl<MachineInstr *> &Copies);

  void removeDeadBlock(
      MachineBasicBlock *MBB,
      function_ref<void(MachineBasicBlock *)> *RemovalCallback = nullptr);

These are 3 adjacent declarations in the same file (llvm/include/llvm/CodeGen/TailDuplicator.h).

I don’t think that the alternative format would make call sites immune to renaming, since it can still cause fewer or more function arguments to fit in a given line of code.  I still think it’s a worthwhile change in style.

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 Nikita Popov via llvm-dev
Sent: Thursday, December 3, 2020 3:01 PM
To: llvm-dev <llvm-dev at lists.llvm.org>
Subject: [EXT] [llvm-dev] Change coding style for argument alignment?


LLVM currently uses a coding style where arguments and parameters need to be aligned to the opening parenthesis "(".

    someFunctionCall(Arg1, Arg2,
                     Arg3, Arg4);

This style guideline is unfortunate for a couple of reasons:

1. If a function is renamed, it is necessary to also reindent the arguments at all call-sites. For functions with many or complex arguments, this may require significant reflow.

2. It causes significant right-ward drift. Especially for declarations, it's somewhat common for code ending up like this...

   Foo SomeClassName::someMethodName(Bar &Arg1,
                                      Bar &Arg2,
                                      Bar &Arg3,
                                      Bar &Arg4) {

... because there is just enough space to fit each argument individually, but still a need to break each one out on a separate line. Closure arguments are another common case of very awkward formatting.

3. There are some arcane rules about when this is not the preferred style and you're supposed to indent arguments on the following line instead.

Is there any chance that the style could be changed towards indenting (but not aligning) the following line instead?

        Arg1, Arg2, Arg3, Arg4);

This is unaffected by renames, does not cause rightward drift and results in very predictable formatting.

Based on past discussions, LLVM seems to be open to improving coding style for the better, so I thought I'd give this a shot, as this is a continuous source of friction for me.

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