r233228 - Keep track of canonical decls in Redeclarable.

[Richard Smith]

On Wed, Mar 25, 2015 at 6:01 PM, Sean Silva <chisophugis at gmail.com> wrote:

>
>
> On Wed, Mar 25, 2015 at 5:56 PM, Sean Silva <chisophugis at gmail.com> wrote:
>
>> Awesome performance numbers!
>>
>> When we discussed this previously, one alternative (should we ever need
>> it; not sure we do) if the memory overhead is excessive is to use a
>> waymarking scheme to find the canonical decl in constant time (unlike Use
>> http://www.llvm.org/docs/ProgrammersManual.html#the-waymarking-algorithm
>> , we don't have random access, but we can instead take advantage of the
>> stable address of the canonical decl and directly store bits of the stable
>> address).
>>
>
> D'oh, just saw the review thread and
> https://llvm.org/bugs/show_bug.cgi?id=21264 where Richard suggests a more
> elaborate (but not guaranteed constant time?) scheme.
>

It's guaranteed constant time to get the canonical decl (because every decl
either is it or has a pointer to it) and to find the previous decl
(although the constant on that is a bit higher if there are multiple
redeclarations, as is the memory usage).


> -- Sean Silva
>
>
>>
>> -- Sean Silva
>>
>> On Wed, Mar 25, 2015 at 4:18 PM, Manuel Klimek <klimek at google.com> wrote:
>>
>>> Author: klimek
>>> Date: Wed Mar 25 18:18:30 2015
>>> New Revision: 233228
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=233228&view=rev
>>> Log:
>>> Keep track of canonical decls in Redeclarable.
>>>
>>> More than 2x speedup on modules builds with large redecl chains.
>>> Roughly 15-20% speedup on non-modules builds for very large TUs.
>>> Between 2-3% cost in memory on large TUs.
>>>
>>> Modified:
>>>     cfe/trunk/include/clang/AST/Decl.h
>>>     cfe/trunk/include/clang/AST/Redeclarable.h
>>>     cfe/trunk/lib/Serialization/ASTReaderDecl.cpp
>>>
>>> Modified: cfe/trunk/include/clang/AST/Decl.h
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/AST/Decl.h?rev=233228&r1=233227&r2=233228&view=diff
>>>
>>> ==============================================================================
>>> --- cfe/trunk/include/clang/AST/Decl.h (original)
>>> +++ cfe/trunk/include/clang/AST/Decl.h Wed Mar 25 18:18:30 2015
>>> @@ -3738,8 +3738,6 @@ void Redeclarable<decl_type>::setPreviou
>>>    assert(RedeclLink.NextIsLatest() &&
>>>           "setPreviousDecl on a decl already in a redeclaration chain");
>>>
>>> -  decl_type *First;
>>> -
>>>    if (PrevDecl) {
>>>      // Point to previous. Make sure that this is actually the most
>>> recent
>>>      // redeclaration, or we can build invalid chains. If the most recent
>>>
>>> Modified: cfe/trunk/include/clang/AST/Redeclarable.h
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/AST/Redeclarable.h?rev=233228&r1=233227&r2=233228&view=diff
>>>
>>> ==============================================================================
>>> --- cfe/trunk/include/clang/AST/Redeclarable.h (original)
>>> +++ cfe/trunk/include/clang/AST/Redeclarable.h Wed Mar 25 18:18:30 2015
>>> @@ -121,14 +121,15 @@ protected:
>>>    ///
>>>    /// If there is only one declaration, it is <pointer to self, true>
>>>    DeclLink RedeclLink;
>>> +  decl_type *First;
>>>
>>>    decl_type *getNextRedeclaration() const {
>>>      return RedeclLink.getNext(static_cast<const decl_type *>(this));
>>>    }
>>>
>>>  public:
>>> -  Redeclarable(const ASTContext &Ctx)
>>> -      : RedeclLink(LatestDeclLink(Ctx)) {}
>>> + Redeclarable(const ASTContext &Ctx)
>>> +     : RedeclLink(LatestDeclLink(Ctx)), First(static_cast<decl_type
>>> *>(this)) {}
>>>
>>>    /// \brief Return the previous declaration of this declaration or
>>> NULL if this
>>>    /// is the first declaration.
>>> @@ -144,21 +145,11 @@ public:
>>>
>>>    /// \brief Return the first declaration of this declaration or itself
>>> if this
>>>    /// is the only declaration.
>>> -  decl_type *getFirstDecl() {
>>> -    decl_type *D = static_cast<decl_type*>(this);
>>> -    while (D->getPreviousDecl())
>>> -      D = D->getPreviousDecl();
>>> -    return D;
>>> -  }
>>> +  decl_type *getFirstDecl() { return First; }
>>>
>>>    /// \brief Return the first declaration of this declaration or itself
>>> if this
>>>    /// is the only declaration.
>>> -  const decl_type *getFirstDecl() const {
>>> -    const decl_type *D = static_cast<const decl_type*>(this);
>>> -    while (D->getPreviousDecl())
>>> -      D = D->getPreviousDecl();
>>> -    return D;
>>> -  }
>>> +  const decl_type *getFirstDecl() const { return First; }
>>>
>>>    /// \brief True if this is the first declaration in its redeclaration
>>> chain.
>>>    bool isFirstDecl() const { return RedeclLink.NextIsLatest(); }
>>>
>>> Modified: cfe/trunk/lib/Serialization/ASTReaderDecl.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Serialization/ASTReaderDecl.cpp?rev=233228&r1=233227&r2=233228&view=diff
>>>
>>> ==============================================================================
>>> --- cfe/trunk/lib/Serialization/ASTReaderDecl.cpp (original)
>>> +++ cfe/trunk/lib/Serialization/ASTReaderDecl.cpp Wed Mar 25 18:18:30
>>> 2015
>>> @@ -2106,6 +2106,7 @@ ASTDeclReader::VisitRedeclarable(Redecla
>>>      // which is the one that matters and mark the real previous DeclID
>>> to be
>>>      // loaded & attached later on.
>>>      D->RedeclLink = Redeclarable<T>::PreviousDeclLink(FirstDecl);
>>> +    D->First = FirstDecl->getCanonicalDecl();
>>>    }
>>>
>>>    // Note that this declaration has been deserialized.
>>> @@ -2209,6 +2210,7 @@ void ASTDeclReader::mergeRedeclarable(Re
>>>      // of the existing declaration, so that this declaration has the
>>>      // appropriate canonical declaration.
>>>      D->RedeclLink = Redeclarable<T>::PreviousDeclLink(ExistingCanon);
>>> +    D->First = ExistingCanon;
>>>
>>>      // When we merge a namespace, update its pointer to the first
>>> namespace.
>>>      // We cannot have loaded any redeclarations of this declaration
>>> yet, so
>>> @@ -2828,6 +2830,7 @@ void ASTDeclReader::attachPreviousDeclIm
>>>                                             Redeclarable<DeclT> *D,
>>>                                             Decl *Previous, Decl *Canon)
>>> {
>>>    D->RedeclLink.setPrevious(cast<DeclT>(Previous));
>>> +  D->First = cast<DeclT>(Previous)->First;
>>>  }
>>>  namespace clang {
>>>  template<>
>>> @@ -2838,6 +2841,7 @@ void ASTDeclReader::attachPreviousDeclIm
>>>    FunctionDecl *PrevFD = cast<FunctionDecl>(Previous);
>>>
>>>    FD->RedeclLink.setPrevious(PrevFD);
>>> +  FD->First = PrevFD->First;
>>>
>>>    // If the previous declaration is an inline function declaration,
>>> then this
>>>    // declaration is too.
>>>
>>>
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>>>
>>
>>
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