[llvm] r263866 - Compute some Debug Info Metadata hash key partially (NFC)

[David Blaikie via llvm-commits]

Might be worth leaving a comment trail in each of these to explain why only
some fields are being hashed?

On Fri, Mar 18, 2016 at 5:59 PM, Mehdi Amini via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: mehdi_amini
> Date: Fri Mar 18 19:59:26 2016
> New Revision: 263866
>
> URL: http://llvm.org/viewvc/llvm-project?rev=263866&view=rev
> Log:
> Compute some Debug Info Metadata hash key partially (NFC)
>
> Summary:
> This patch changes the computation of the hash key for DISubprogram to
> be computed on a small subset of the fields. The hash is computed a
> lot faster, but there might be more collision in the table.
> However by carefully selecting the fields, colisions should be rare.
>
> Using `opt` to load the IR for FastISelEmitter.cpp.o, with this patch:
>  - DISubprogram::getImpl() goes from 28ms to 15ms.
>  - DICompositeType::getImpl() goes from 6ms to 2ms
>  - DIDerivedType::getImpl() goes from 18 to 12ms
>
> Reviewers: dexonsmith
>
> Subscribers: llvm-commits
>
> Differential Revision: http://reviews.llvm.org/D16571
>
> From: Mehdi Amini <mehdi.amini at apple.com>
>
> Modified:
>     llvm/trunk/lib/IR/LLVMContextImpl.h
>
> Modified: llvm/trunk/lib/IR/LLVMContextImpl.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/LLVMContextImpl.h?rev=263866&r1=263865&r2=263866&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/IR/LLVMContextImpl.h (original)
> +++ llvm/trunk/lib/IR/LLVMContextImpl.h Fri Mar 18 19:59:26 2016
> @@ -365,8 +365,7 @@ template <> struct MDNodeKeyImpl<DIDeriv
>             ExtraData == RHS->getRawExtraData();
>    }
>    unsigned getHashValue() const {
> -    return hash_combine(Tag, Name, File, Line, Scope, BaseType,
> SizeInBits,
> -                        AlignInBits, OffsetInBits, Flags, ExtraData);
> +    return hash_combine(Tag, Name, File, Line, Scope, BaseType, Flags);
>    }
>  };
>
> @@ -422,9 +421,8 @@ template <> struct MDNodeKeyImpl<DICompo
>             Identifier == RHS->getIdentifier();
>    }
>    unsigned getHashValue() const {
> -    return hash_combine(Tag, Name, File, Line, Scope, BaseType,
> SizeInBits,
> -                        AlignInBits, OffsetInBits, Flags, Elements,
> RuntimeLang,
> -                        VTableHolder, TemplateParams, Identifier);
> +    return hash_combine(Name, File, Line, BaseType, Scope, Elements,
> +                        TemplateParams);
>    }
>  };
>
> @@ -518,10 +516,7 @@ template <> struct MDNodeKeyImpl<DISubpr
>             Variables == RHS->getRawVariables();
>    }
>    unsigned getHashValue() const {
> -    return hash_combine(Scope, Name, LinkageName, File, Line, Type,
> -                        IsLocalToUnit, IsDefinition, ScopeLine,
> ContainingType,
> -                        Virtuality, VirtualIndex, Flags, IsOptimized,
> -                        TemplateParams, Declaration, Variables);
> +    return hash_combine(Name, Scope, File, Type, Line);
>    }
>  };
>
>
>
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