[lld] r270340 - Define SectionPiece and use it instead of std::pair<uint_t, uint_t>.
Rui Ueyama via llvm-commits
llvm-commits at lists.llvm.org
Tue May 24 21:42:03 PDT 2016
It is I think actually spent in StringTableBuilder. More specifically,
StringTableBuilder spends time on inserting given strings (all pieces of
splittable sections) into a hash table in order to uniquify them.
On Tue, May 24, 2016 at 9:39 PM, Sean Silva <chisophugis at gmail.com> wrote:
> Be very careful with this code (e.g. changing data layouts). We spend over
> 20% of non-LTO time in it last time I looked (mostly the call to
> lower_bound IIRC).
>
> -- Sean Silva
>
> On Sat, May 21, 2016 at 5:13 PM, Rui Ueyama via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: ruiu
>> Date: Sat May 21 19:13:04 2016
>> New Revision: 270340
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=270340&view=rev
>> Log:
>> Define SectionPiece and use it instead of std::pair<uint_t, uint_t>.
>>
>> We were using std::pair to represents pieces of splittable section
>> contents. It hurt readability because "first" and "second" are not
>> meaningful. This patch give them names.
>>
>> One more thing is that piecewise liveness information is stored to
>> the second element of the pair as a special value of output section
>> offset. It was confusing, so I defiend a new bit, "Live", in the
>> new struct.
>>
>> Modified:
>> lld/trunk/ELF/InputSection.cpp
>> lld/trunk/ELF/InputSection.h
>> lld/trunk/ELF/MarkLive.cpp
>> lld/trunk/ELF/OutputSections.cpp
>> lld/trunk/ELF/Writer.cpp
>>
>> Modified: lld/trunk/ELF/InputSection.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputSection.cpp?rev=270340&r1=270339&r2=270340&view=diff
>>
>> ==============================================================================
>> --- lld/trunk/ELF/InputSection.cpp (original)
>> +++ lld/trunk/ELF/InputSection.cpp Sat May 21 19:13:04 2016
>> @@ -414,13 +414,12 @@ typename ELFT::uint EHInputSection<ELFT>
>> // identify the start of the output .eh_frame. Handle this special
>> case.
>> if (this->getSectionHdr()->sh_size == 0)
>> return Offset;
>> - std::pair<uintX_t, uintX_t> *I = this->getRangeAndSize(Offset).first;
>> - uintX_t Base = I->second;
>> - if (Base == uintX_t(-1))
>> + SectionPiece *Piece = this->getRangeAndSize(Offset).first;
>> + if (Piece->OutputOff == size_t(-1))
>> return -1; // Not in the output
>>
>> - uintX_t Addend = Offset - I->first;
>> - return Base + Addend;
>> + uintX_t Addend = Offset - Piece->InputOff;
>> + return Piece->OutputOff + Addend;
>> }
>>
>> static size_t findNull(StringRef S, size_t EntSize) {
>> @@ -443,17 +442,14 @@ MergeInputSection<ELFT>::MergeInputSecti
>> uintX_t EntSize = Header->sh_entsize;
>> ArrayRef<uint8_t> D = this->getSectionData();
>> StringRef Data((const char *)D.data(), D.size());
>> - std::vector<std::pair<uintX_t, uintX_t>> &Offsets = this->Offsets;
>>
>> - uintX_t V = Config->GcSections ? MergeInputSection<ELFT>::PieceDead
>> - : MergeInputSection<ELFT>::PieceLive;
>> if (Header->sh_flags & SHF_STRINGS) {
>> uintX_t Offset = 0;
>> while (!Data.empty()) {
>> size_t End = findNull(Data, EntSize);
>> if (End == StringRef::npos)
>> fatal("string is not null terminated");
>> - Offsets.push_back(std::make_pair(Offset, V));
>> + this->Pieces.emplace_back(Offset);
>> uintX_t Size = End + EntSize;
>> Data = Data.substr(Size);
>> Offset += Size;
>> @@ -465,7 +461,7 @@ MergeInputSection<ELFT>::MergeInputSecti
>> size_t Size = Data.size();
>> assert((Size % EntSize) == 0);
>> for (unsigned I = 0, N = Size; I != N; I += EntSize)
>> - Offsets.push_back(std::make_pair(I, V));
>> + this->Pieces.emplace_back(I);
>> }
>>
>> template <class ELFT>
>> @@ -474,8 +470,7 @@ bool MergeInputSection<ELFT>::classof(co
>> }
>>
>> template <class ELFT>
>> -std::pair<std::pair<typename ELFT::uint, typename ELFT::uint> *,
>> - typename ELFT::uint>
>> +std::pair<SectionPiece *, typename ELFT::uint>
>> SplitInputSection<ELFT>::getRangeAndSize(uintX_t Offset) {
>> ArrayRef<uint8_t> D = this->getSectionData();
>> StringRef Data((const char *)D.data(), D.size());
>> @@ -485,37 +480,32 @@ SplitInputSection<ELFT>::getRangeAndSize
>>
>> // Find the element this offset points to.
>> auto I = std::upper_bound(
>> - Offsets.begin(), Offsets.end(), Offset,
>> - [](const uintX_t &A, const std::pair<uintX_t, uintX_t> &B) {
>> - return A < B.first;
>> - });
>> - uintX_t End = I == Offsets.end() ? Data.size() : I->first;
>> + Pieces.begin(), Pieces.end(), Offset,
>> + [](const uintX_t &A, const SectionPiece &B) { return A <
>> B.InputOff; });
>> + uintX_t End = (I == Pieces.end()) ? Data.size() : I->InputOff;
>> --I;
>> - return std::make_pair(&*I, End);
>> + return {&*I, End};
>> }
>>
>> template <class ELFT>
>> typename ELFT::uint MergeInputSection<ELFT>::getOffset(uintX_t Offset) {
>> - std::pair<std::pair<uintX_t, uintX_t> *, uintX_t> T =
>> - this->getRangeAndSize(Offset);
>> - std::pair<uintX_t, uintX_t> *I = T.first;
>> + std::pair<SectionPiece *, uintX_t> T = this->getRangeAndSize(Offset);
>> + SectionPiece &Piece = *T.first;
>> uintX_t End = T.second;
>> - uintX_t Start = I->first;
>> + assert(Piece.Live);
>>
>> // Compute the Addend and if the Base is cached, return.
>> - uintX_t Addend = Offset - Start;
>> - uintX_t &Base = I->second;
>> - assert(Base != MergeInputSection<ELFT>::PieceDead);
>> - if (Base != MergeInputSection<ELFT>::PieceLive)
>> - return Base + Addend;
>> + uintX_t Addend = Offset - Piece.InputOff;
>> + if (Piece.OutputOff != size_t(-1))
>> + return Piece.OutputOff + Addend;
>>
>> // Map the base to the offset in the output section and cache it.
>> ArrayRef<uint8_t> D = this->getSectionData();
>> StringRef Data((const char *)D.data(), D.size());
>> - StringRef Entry = Data.substr(Start, End - Start);
>> + StringRef Entry = Data.substr(Piece.InputOff, End - Piece.InputOff);
>> auto *MOS = static_cast<MergeOutputSection<ELFT> *>(this->OutSec);
>> - Base = MOS->getOffset(Entry);
>> - return Base + Addend;
>> + Piece.OutputOff = MOS->getOffset(Entry);
>> + return Piece.OutputOff + Addend;
>> }
>>
>> template <class ELFT>
>>
>> Modified: lld/trunk/ELF/InputSection.h
>> URL:
>> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputSection.h?rev=270340&r1=270339&r2=270340&view=diff
>>
>> ==============================================================================
>> --- lld/trunk/ELF/InputSection.h (original)
>> +++ lld/trunk/ELF/InputSection.h Sat May 21 19:13:04 2016
>> @@ -130,6 +130,14 @@ public:
>>
>> template <class ELFT> InputSectionBase<ELFT>
>> InputSectionBase<ELFT>::Discarded;
>>
>> +// SectionPiece represents a piece of splittable section contents.
>> +struct SectionPiece {
>> + SectionPiece(size_t I) : InputOff(I), Live(!Config->GcSections) {}
>> + size_t InputOff;
>> + size_t OutputOff = -1;
>> + bool Live;
>> +};
>> +
>> // Usually sections are copied to the output as atomic chunks of data,
>> // but some special types of sections are split into small pieces of data
>> // and each piece is copied to a different place in the output.
>> @@ -142,24 +150,11 @@ public:
>> SplitInputSection(ObjectFile<ELFT> *File, const Elf_Shdr *Header,
>> typename InputSectionBase<ELFT>::Kind SectionKind);
>>
>> - // For each piece of data, we maintain the offsets in the input
>> section and
>> - // in the output section.
>> - std::vector<std::pair<uintX_t, uintX_t>> Offsets;
>> -
>> - // Merge input sections may use the following special values as the
>> output
>> - // section offset:
>> - enum {
>> - // The piece is dead.
>> - PieceDead = uintX_t(-1),
>> - // The piece is live, but an offset has not yet been assigned. After
>> offsets
>> - // have been assigned, if the output section uses tail merging, the
>> field
>> - // will still have this value and the output section offset is
>> computed
>> - // lazilly.
>> - PieceLive = uintX_t(-2),
>> - };
>> + // Splittable sections are handled as a sequence of data
>> + // rather than a single large blob of data.
>> + std::vector<SectionPiece> Pieces;
>>
>> - std::pair<std::pair<uintX_t, uintX_t> *, uintX_t>
>> - getRangeAndSize(uintX_t Offset);
>> + std::pair<SectionPiece *, uintX_t> getRangeAndSize(uintX_t Offset);
>> };
>>
>> // This corresponds to a SHF_MERGE section of an input file.
>>
>> Modified: lld/trunk/ELF/MarkLive.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/MarkLive.cpp?rev=270340&r1=270339&r2=270340&view=diff
>>
>> ==============================================================================
>> --- lld/trunk/ELF/MarkLive.cpp (original)
>> +++ lld/trunk/ELF/MarkLive.cpp Sat May 21 19:13:04 2016
>> @@ -143,9 +143,8 @@ template <class ELFT> void elf::markLive
>> if (!R.Sec)
>> return;
>> if (auto *MS = dyn_cast<MergeInputSection<ELFT>>(R.Sec)) {
>> - std::pair<std::pair<uintX_t, uintX_t> *, uintX_t> T =
>> - MS->getRangeAndSize(R.Offset);
>> - T.first->second = MergeInputSection<ELFT>::PieceLive;
>> + std::pair<SectionPiece *, uintX_t> T =
>> MS->getRangeAndSize(R.Offset);
>> + T.first->Live = true;
>> }
>> if (R.Sec->Live)
>> return;
>>
>> Modified: lld/trunk/ELF/OutputSections.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.cpp?rev=270340&r1=270339&r2=270340&view=diff
>>
>> ==============================================================================
>> --- lld/trunk/ELF/OutputSections.cpp (original)
>> +++ lld/trunk/ELF/OutputSections.cpp Sat May 21 19:13:04 2016
>> @@ -978,10 +978,9 @@ EHRegion<ELFT>::EHRegion(EHInputSection<
>>
>> template <class ELFT> StringRef EHRegion<ELFT>::data() const {
>> ArrayRef<uint8_t> SecData = S->getSectionData();
>> - ArrayRef<std::pair<uintX_t, uintX_t>> Offsets = S->Offsets;
>> - size_t Start = Offsets[Index].first;
>> - size_t End =
>> - Index == Offsets.size() - 1 ? SecData.size() : Offsets[Index +
>> 1].first;
>> + size_t Start = S->Pieces[Index].InputOff;
>> + size_t End = (Index == S->Pieces.size() - 1) ? SecData.size()
>> + : S->Pieces[Index +
>> 1].InputOff;
>> return StringRef((const char *)SecData.data() + Start, End - Start);
>> }
>>
>> @@ -1142,8 +1141,8 @@ void EHOutputSection<ELFT>::addSectionAu
>>
>> DenseMap<uintX_t, uintX_t> OffsetToIndex;
>> while (!D.empty()) {
>> - unsigned Index = S->Offsets.size();
>> - S->Offsets.push_back(std::make_pair(Offset, -1));
>> + unsigned Index = S->Pieces.size();
>> + S->Pieces.emplace_back(Offset);
>>
>> uintX_t Length = readEntryLength<ELFT>(D);
>> // If CIE/FDE data length is zero then Length is 4, this
>> @@ -1227,11 +1226,11 @@ template <class ELFT> void EHOutputSecti
>>
>> size_t Offset = 0;
>> for (const Cie<ELFT> &C : Cies) {
>> - C.S->Offsets[C.Index].second = Offset;
>> + C.S->Pieces[C.Index].OutputOff = Offset;
>> Offset += alignTo(C.data().size(), sizeof(uintX_t));
>>
>> for (const EHRegion<ELFT> &F : C.Fdes) {
>> - F.S->Offsets[F.Index].second = Offset;
>> + F.S->Pieces[F.Index].OutputOff = Offset;
>> Offset += alignTo(F.data().size(), sizeof(uintX_t));
>> }
>> }
>> @@ -1240,11 +1239,11 @@ template <class ELFT> void EHOutputSecti
>> template <class ELFT> void EHOutputSection<ELFT>::writeTo(uint8_t *Buf) {
>> const endianness E = ELFT::TargetEndianness;
>> for (const Cie<ELFT> &C : Cies) {
>> - size_t CieOffset = C.S->Offsets[C.Index].second;
>> + size_t CieOffset = C.S->Pieces[C.Index].OutputOff;
>> writeCieFde<ELFT>(Buf + CieOffset, C.data());
>>
>> for (const EHRegion<ELFT> &F : C.Fdes) {
>> - size_t Offset = F.S->Offsets[F.Index].second;
>> + size_t Offset = F.S->Pieces[F.Index].OutputOff;
>> writeCieFde<ELFT>(Buf + Offset, F.data());
>> write32<E>(Buf + Offset + 4, Offset + 4 - CieOffset); // Pointer
>>
>> @@ -1284,32 +1283,30 @@ void MergeOutputSection<ELFT>::addSectio
>> StringRef Data((const char *)D.data(), D.size());
>> uintX_t EntSize = S->getSectionHdr()->sh_entsize;
>> this->Header.sh_entsize = EntSize;
>> - MutableArrayRef<std::pair<uintX_t, uintX_t>> Offsets = S->Offsets;
>>
>> // If this is of type string, the contents are null-terminated strings.
>> if (this->Header.sh_flags & SHF_STRINGS) {
>> - for (unsigned I = 0, N = Offsets.size(); I != N; ++I) {
>> - auto &P = Offsets[I];
>> - if (P.second == MergeInputSection<ELFT>::PieceDead)
>> + for (unsigned I = 0, N = S->Pieces.size(); I != N; ++I) {
>> + SectionPiece &Piece = S->Pieces[I];
>> + if (!Piece.Live)
>> continue;
>>
>> - uintX_t Start = P.first;
>> - uintX_t End = (I == N - 1) ? Data.size() : Offsets[I + 1].first;
>> + uintX_t Start = Piece.InputOff;
>> + uintX_t End = (I == N - 1) ? Data.size() : S->Pieces[I +
>> 1].InputOff;
>> StringRef Entry = Data.substr(Start, End - Start);
>> uintX_t OutputOffset = Builder.add(Entry);
>> - if (shouldTailMerge())
>> - OutputOffset = MergeInputSection<ELFT>::PieceLive;
>> - P.second = OutputOffset;
>> + if (!shouldTailMerge())
>> + Piece.OutputOff = OutputOffset;
>> }
>> return;
>> }
>>
>> // If this is not of type string, every entry has the same size.
>> - for (auto &P : Offsets) {
>> - if (P.second == (uintX_t)-1)
>> + for (SectionPiece &Piece : S->Pieces) {
>> + if (!Piece.Live)
>> continue;
>> - StringRef Entry = Data.substr(P.first, EntSize);
>> - P.second = Builder.add(Entry);
>> + StringRef Entry = Data.substr(Piece.InputOff, EntSize);
>> + Piece.OutputOff = Builder.add(Entry);
>> }
>> }
>>
>>
>> Modified: lld/trunk/ELF/Writer.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=270340&r1=270339&r2=270340&view=diff
>>
>> ==============================================================================
>> --- lld/trunk/ELF/Writer.cpp (original)
>> +++ lld/trunk/ELF/Writer.cpp Sat May 21 19:13:04 2016
>> @@ -855,8 +855,7 @@ template <class ELFT> static bool includ
>> if (!D->Section->Live)
>> return false;
>> if (auto *S = dyn_cast<MergeInputSection<ELFT>>(D->Section))
>> - if (S->getRangeAndSize(D->Value).first->second ==
>> - MergeInputSection<ELFT>::PieceDead)
>> + if (!S->getRangeAndSize(D->Value).first->Live)
>> return false;
>> }
>> return true;
>>
>>
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>
>
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