[lld] r243496 - [ELF2] Devirtualize SymbolBody.
Rui Ueyama
ruiu at google.com
Tue Jul 28 16:43:16 PDT 2015
On Tue, Jul 28, 2015 at 4:37 PM, Michael Spencer <bigcheesegs at gmail.com>
wrote:
> On Tue, Jul 28, 2015 at 4:22 PM, Chandler Carruth <chandlerc at google.com>
> wrote:
> > On Tue, Jul 28, 2015 at 4:01 PM Michael J. Spencer <
> bigcheesegs at gmail.com>
> > wrote:
> >>
> >> Author: mspencer
> >> Date: Tue Jul 28 17:58:25 2015
> >> New Revision: 243496
> >>
> >> URL: http://llvm.org/viewvc/llvm-project?rev=243496&view=rev
> >> Log:
> >> [ELF2] Devirtualize SymbolBody.
> >
> >
> > Could you outline the specific benefits you're hoping to achieve here?
> > Memory reduction, speed, even just readability?
> >
> > I just think a bit more context would help folks reading the patches.
>
> The goal here is to reduce divergence from the COFF linker. It is also
> expected that the same performance issues addressed by this change
> (r241001) in the COFF linker will be encountered by the ELF linker,
> and it's easier to build it right the first time.
>
Thank you for doing this!
>
> - Michael Spencer
>
> >>
> >>
> >> Modified:
> >> lld/trunk/ELF/InputFiles.cpp
> >> lld/trunk/ELF/Symbols.cpp
> >> lld/trunk/ELF/Symbols.h
> >>
> >> Modified: lld/trunk/ELF/InputFiles.cpp
> >> URL:
> >>
> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputFiles.cpp?rev=243496&r1=243495&r2=243496&view=diff
> >>
> >>
> ==============================================================================
> >> --- lld/trunk/ELF/InputFiles.cpp (original)
> >> +++ lld/trunk/ELF/InputFiles.cpp Tue Jul 28 17:58:25 2015
> >> @@ -65,7 +65,7 @@ SymbolBody *elf2::ObjectFile<ELFT>::crea
> >> StringRef Name = *NameOrErr;
> >> if (Sym->isUndefined())
> >> return new (Alloc) Undefined(Name);
> >> - return new (Alloc) DefinedRegular<ELFT>(Name);
> >> + return new (Alloc) DefinedRegular<ELFT>(this, Sym);
> >> }
> >>
> >> namespace lld {
> >>
> >> Modified: lld/trunk/ELF/Symbols.cpp
> >> URL:
> >>
> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.cpp?rev=243496&r1=243495&r2=243496&view=diff
> >>
> >>
> >>
> ==============================================================================
> >> --- lld/trunk/ELF/Symbols.cpp (original)
> >> +++ lld/trunk/ELF/Symbols.cpp Tue Jul 28 17:58:25 2015
> >> @@ -9,12 +9,30 @@
> >>
> >> #include "Symbols.h"
> >> #include "Chunks.h"
> >> +#include "InputFiles.h"
> >>
> >> using namespace llvm::object;
> >>
> >> using namespace lld;
> >> using namespace lld::elf2;
> >>
> >> +template <class ELFT>
> >> +StringRef
> >> +getSymbolName(const llvm::object::ELFFile<ELFT> *F,
> >> + const typename llvm::object::ELFFile<ELFT>::Elf_Sym *S) {
> >> + ErrorOr<StringRef> StrTab =
> >> F->getStringTableForSymtab(*F->getDotSymtabSec());
> >> + if (!StrTab || S->st_name >= StrTab->size())
> >> + llvm::report_fatal_error("Invalid string table.");
> >> + return StrTab->data() + S->st_name;
> >> +}
> >> +
> >> +template <class ELFT>
> >> +DefinedRegular<ELFT>::DefinedRegular(ObjectFile<ELFT> *F, const Elf_Sym
> >> *S)
> >> + : Defined(DefinedRegularKind, getSymbolName<ELFT>(F->getObj(), S)),
> >> File(F),
> >> + Sym(S) {
> >> + IsExternal = S->isExternal();
> >> +}
> >> +
> >> // Returns 1, 0 or -1 if this symbol should take precedence
> >> // over the Other, tie or lose, respectively.
> >> int SymbolBody::compare(SymbolBody *Other) {
> >>
> >> Modified: lld/trunk/ELF/Symbols.h
> >> URL:
> >>
> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.h?rev=243496&r1=243495&r2=243496&view=diff
> >>
> >>
> >>
> ==============================================================================
> >> --- lld/trunk/ELF/Symbols.h (original)
> >> +++ lld/trunk/ELF/Symbols.h Tue Jul 28 17:58:25 2015
> >> @@ -21,6 +21,7 @@ using llvm::object::ELFFile;
> >> class Chunk;
> >> class InputFile;
> >> class SymbolBody;
> >> +template <class ELFT> class ObjectFile;
> >>
> >> // A real symbol object, SymbolBody, is usually accessed indirectly
> >> // through a Symbol. There's always one Symbol for each symbol name.
> >> @@ -40,14 +41,13 @@ public:
> >> UndefinedKind,
> >> };
> >>
> >> - Kind kind() const { return SymbolKind; }
> >> - virtual ~SymbolBody() {}
> >> + Kind kind() const { return static_cast<Kind>(SymbolKind); }
> >>
> >> // Returns true if this is an external symbol.
> >> - virtual bool isExternal() { return true; }
> >> + bool isExternal() const { return true; }
> >>
> >> // Returns the symbol name.
> >> - virtual StringRef getName() = 0;
> >> + StringRef getName() const { return Name; }
> >>
> >> // A SymbolBody has a backreference to a Symbol. Originally they are
> >> // doubly-linked. A backreference will never change. But the pointer
> >> @@ -64,10 +64,13 @@ public:
> >> int compare(SymbolBody *Other);
> >>
> >> protected:
> >> - SymbolBody(Kind K) : SymbolKind(K) {}
> >> + SymbolBody(Kind K, StringRef N = "")
> >> + : SymbolKind(K), IsExternal(true), Name(N) {}
> >>
> >> -private:
> >> - const Kind SymbolKind;
> >> +protected:
> >> + const unsigned SymbolKind : 8;
> >> + unsigned IsExternal : 1;
> >> + StringRef Name;
> >> Symbol *Backref = nullptr;
> >> };
> >>
> >> @@ -75,7 +78,7 @@ private:
> >> // etc.
> >> class Defined : public SymbolBody {
> >> public:
> >> - Defined(Kind K) : SymbolBody(K) {}
> >> + Defined(Kind K, StringRef N = "") : SymbolBody(K, N) {}
> >>
> >> static bool classof(const SymbolBody *S) {
> >> Kind K = S->kind();
> >> @@ -85,31 +88,28 @@ public:
> >>
> >> // Regular defined symbols read from object file symbol tables.
> >> template <class ELFT> class DefinedRegular : public Defined {
> >> + typedef typename llvm::object::ELFFile<ELFT>::Elf_Sym Elf_Sym;
> >> +
> >> public:
> >> - DefinedRegular(StringRef Name) : Defined(DefinedRegularKind),
> >> Name(Name) {}
> >> + DefinedRegular(ObjectFile<ELFT> *F, const Elf_Sym *S);
> >>
> >> static bool classof(const SymbolBody *S) {
> >> return S->kind() == DefinedRegularKind;
> >> }
> >>
> >> - StringRef getName() override { return Name; }
> >> -
> >> private:
> >> - StringRef Name;
> >> + ObjectFile<ELFT> *File;
> >> + const Elf_Sym *Sym;
> >> };
> >>
> >> // Undefined symbols.
> >> class Undefined : public SymbolBody {
> >> public:
> >> - explicit Undefined(StringRef N) : SymbolBody(UndefinedKind), Name(N)
> {}
> >> + explicit Undefined(StringRef N) : SymbolBody(UndefinedKind, N) {}
> >>
> >> static bool classof(const SymbolBody *S) {
> >> return S->kind() == UndefinedKind;
> >> }
> >> - StringRef getName() override { return Name; }
> >> -
> >> -private:
> >> - StringRef Name;
> >> };
> >>
> >> } // namespace elf2
> >>
> >>
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