[lld] r270340 - Define SectionPiece and use it instead of std::pair<uint_t, uint_t>.
Sean Silva via llvm-commits
llvm-commits at lists.llvm.org
Tue May 24 21:39:37 PDT 2016
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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