[llvm] ef89409 - Fix 'unused-lambda-capture' gcc warning. NFCI.

[David Blaikie via llvm-commits]

On Mon, Oct 17, 2022 at 4:58 PM Alexey Bataev <a.bataev at hotmail.com> wrote:
>
>
>
> Best regards,
> Alexey Bataev
>
> > 17 окт. 2022 г., в 7:26 PM, David Blaikie <dblaikie at gmail.com> написал(а):
> >
> > ping on this
> >
> >> On Mon, Oct 3, 2022 at 12:44 PM David Blaikie <dblaikie at gmail.com> wrote:
> >>
> >>> On Tue, Sep 27, 2022 at 7:16 AM Simon Pilgrim via llvm-commits
> >>> <llvm-commits at lists.llvm.org> wrote:
> >>>
> >>>
> >>> Author: Simon Pilgrim
> >>> Date: 2022-09-27T15:15:43+01:00
> >>> New Revision: ef89409a59f3b79ae143b33b7d8e6ee6285aa42f
> >>>
> >>> URL: https://github.com/llvm/llvm-project/commit/ef89409a59f3b79ae143b33b7d8e6ee6285aa42f
> >>> DIFF: https://github.com/llvm/llvm-project/commit/ef89409a59f3b79ae143b33b7d8e6ee6285aa42f.diff
> >>>
> >>> LOG: Fix 'unused-lambda-capture' gcc warning. NFCI.
> >>>
> >>> Added:
> >>>
> >>>
> >>> Modified:
> >>>    llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
> >>>
> >>> Removed:
> >>>
> >>>
> >>>
> >>> ################################################################################
> >>> diff  --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
> >>> index b5c73819335e..9584c421bcca 100644
> >>> --- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
> >>> +++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
> >>> @@ -6075,7 +6075,7 @@ InstructionCost BoUpSLP::getEntryCost(const TreeEntry *E,
> >>>   bool NeedToShuffleReuses = !E->ReuseShuffleIndices.empty();
> >>>   // FIXME: it tries to fix a problem with MSVC buildbots.
> >>>   TargetTransformInfo &TTIRef = *TTI;
> >>> -  auto &&AdjustExtractsCost = [this, &TTIRef, CostKind, VL, VecTy,
> >>> +  auto &&AdjustExtractsCost = [this, &TTIRef, CostKind, VL,
> >>>                                VectorizedVals, E](InstructionCost &Cost) {
> >>
> >> Generally if a lambda's only going to be used in the current scope,
> >> I'd suggest using default capture "[&]" so the list doesn't need to be
> >> maintained.
>
> Thera are no strict rules about it, I prefer to keep explicit list where possible to be sure what's used or can be dropped.

It's a bit of a maintenance burden, though - in the same way that we
don't enumerate what variables are used in a while loop or other scope
- I think it's suitable for local lambdas not to enumerate them so
it's easier to update/modify the code without having to maintain the
list.

> >> Also rvalue reference lifetime extension's probably not helpful here,
> >> and just plain `auto AdjustExtractsCost` could be used.
>
> It saves us from one move constructor call in AST (not in codegen, it is elided then).

Yeah, nothing to save there - as you say, it doesn't get codegen'd
that way. Using `auto` non-reference is used in almost all cases - be
nice to change this for consistency, so it doesn't raise questions of
"why is this different? is there something importantly odd/unique
going on here?"

- Dave

> >>>     ScalarizationOverheadBuilder ScalarizationCost;
> >>>     SmallPtrSet<Value *, 4> CheckedExtracts;
> >>>
> >>>
> >>>
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