[lld] r244934 - Template OutputSection only over Is64Bit.
Sean Silva via llvm-commits
llvm-commits at lists.llvm.org
Thu Aug 13 16:36:06 PDT 2015
On Thu, Aug 13, 2015 at 11:37 AM, Rafael Espindola via llvm-commits <
llvm-commits at lists.llvm.org> wrote:
> Author: rafael
> Date: Thu Aug 13 13:37:23 2015
> New Revision: 244934
>
> URL: http://llvm.org/viewvc/llvm-project?rev=244934&view=rev
> Log:
> Template OutputSection only over Is64Bit.
>
> This is a bit more c++ code, but:
> * It is less machine code: lld's text is 44688 bytes smaller.
> * It should be a bit more efficient in the non native endian case.
> * It should be a bit more efficient on architectures with slow unaligned
> access.
>
Feel free to add this sort of thing to a TODO list of interesting things to
look at in the future, but please avoid doing
microoptimization-without-a-measured-performance-benefit until we have a
working linker (and then, hopefully dropping the
"without-a-measured-performance-benefit"). Almost every single one of these
"NFC" patches are stepping on Michael's toes and holding up real "FC"
patches that are what we need to get a working linker.
-- Sean Silva
>
> Modified:
> lld/trunk/ELF/Writer.cpp
>
> Modified: lld/trunk/ELF/Writer.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=244934&r1=244933&r2=244934&view=diff
>
> ==============================================================================
> --- lld/trunk/ELF/Writer.cpp (original)
> +++ lld/trunk/ELF/Writer.cpp Thu Aug 13 13:37:23 2015
> @@ -32,14 +32,15 @@ namespace {
> // Chunks cannot belong to more than one OutputSections. The writer
> // creates multiple OutputSections and assign them unique,
> // non-overlapping file offsets and VAs.
> -template <class ELFT> class OutputSection {
> +template <bool Is64Bits> class OutputSection {
> public:
> - typedef typename llvm::object::ELFFile<ELFT>::uintX_t uintX_t;
> - typedef typename llvm::object::ELFFile<ELFT>::Elf_Shdr Elf_Shdr;
> + typedef typename std::conditional<Is64Bits, uint64_t, uint32_t>::type
> uintX_t;
> + typedef
> + typename std::conditional<Is64Bits, Elf64_Shdr, Elf32_Shdr>::type
> HeaderT;
>
> OutputSection(StringRef Name, uint32_t sh_type, uintX_t sh_flags)
> : Name(Name) {
> - memset(&Header, 0, sizeof(Elf_Shdr));
> + memset(&Header, 0, sizeof(HeaderT));
> Header.sh_type = sh_type;
> Header.sh_flags = sh_flags;
> }
> @@ -47,7 +48,8 @@ public:
> void setFileOffset(uintX_t Off) { Header.sh_offset = Off; }
> void addChunk(Chunk *C);
> std::vector<Chunk *> &getChunks() { return Chunks; }
> - void writeHeaderTo(Elf_Shdr *SHdr);
> + template <endianness E>
> + void writeHeaderTo(typename ELFFile<ELFType<E, Is64Bits>>::Elf_Shdr
> *SHdr);
> StringRef getName() { return Name; }
> void setNameOffset(uintX_t Offset) { Header.sh_name = Offset; }
>
> @@ -58,7 +60,7 @@ public:
>
> private:
> StringRef Name;
> - Elf_Shdr Header;
> + HeaderT Header;
> std::vector<Chunk *> Chunks;
> };
>
> @@ -79,8 +81,8 @@ private:
>
> SymbolTable *Symtab;
> std::unique_ptr<llvm::FileOutputBuffer> Buffer;
> - llvm::SpecificBumpPtrAllocator<OutputSection<ELFT>> CAlloc;
> - std::vector<OutputSection<ELFT> *> OutputSections;
> + llvm::SpecificBumpPtrAllocator<OutputSection<ELFT::Is64Bits>> CAlloc;
> + std::vector<OutputSection<ELFT::Is64Bits> *> OutputSections;
>
> uintX_t FileSize;
> uintX_t SizeOfHeaders;
> @@ -118,7 +120,7 @@ template <class ELFT> void Writer<ELFT>:
> error(Buffer->commit());
> }
>
> -template <class ELFT> void OutputSection<ELFT>::addChunk(Chunk *C) {
> +template <bool Is64Bits> void OutputSection<Is64Bits>::addChunk(Chunk *C)
> {
> Chunks.push_back(C);
> uintX_t Off = Header.sh_size;
> Off = RoundUpToAlignment(Off, C->getAlign());
> @@ -127,8 +129,20 @@ template <class ELFT> void OutputSection
> Header.sh_size = Off;
> }
>
> -template <class ELFT> void OutputSection<ELFT>::writeHeaderTo(Elf_Shdr
> *SHdr) {
> - *SHdr = Header;
> +template <bool Is64Bits>
> +template <endianness E>
> +void OutputSection<Is64Bits>::writeHeaderTo(
> + typename ELFFile<ELFType<E, Is64Bits>>::Elf_Shdr *SHdr) {
> + SHdr->sh_name = Header.sh_name;
> + SHdr->sh_type = Header.sh_type;
> + SHdr->sh_flags = Header.sh_flags;
> + SHdr->sh_addr = Header.sh_addr;
> + SHdr->sh_offset = Header.sh_offset;
> + SHdr->sh_size = Header.sh_size;
> + SHdr->sh_link = Header.sh_link;
> + SHdr->sh_info = Header.sh_info;
> + SHdr->sh_addralign = Header.sh_addralign;
> + SHdr->sh_entsize = Header.sh_entsize;
> }
>
> namespace {
> @@ -161,17 +175,18 @@ template <bool Is64Bits> struct DenseMap
>
> // Create output section objects and add them to OutputSections.
> template <class ELFT> void Writer<ELFT>::createSections() {
> - SmallDenseMap<SectionKey<ELFT::Is64Bits>, OutputSection<ELFT> *> Map;
> + SmallDenseMap<SectionKey<ELFT::Is64Bits>, OutputSection<ELFT::Is64Bits>
> *>
> + Map;
> for (std::unique_ptr<ObjectFileBase> &FileB : Symtab->ObjectFiles) {
> auto &File = cast<ObjectFile<ELFT>>(*FileB);
> for (SectionChunk<ELFT> *C : File.getChunks()) {
> const Elf_Shdr *H = C->getSectionHdr();
> SectionKey<ELFT::Is64Bits> Key{C->getSectionName(), H->sh_type,
> H->sh_flags};
> - OutputSection<ELFT> *&Sec = Map[Key];
> + OutputSection<ELFT::Is64Bits> *&Sec = Map[Key];
> if (!Sec) {
> Sec = new (CAlloc.Allocate())
> - OutputSection<ELFT>(Key.Name, Key.sh_type, Key.sh_flags);
> + OutputSection<ELFT::Is64Bits>(Key.Name, Key.sh_type,
> Key.sh_flags);
> OutputSections.push_back(Sec);
> }
> Sec->addChunk(C);
> @@ -179,8 +194,8 @@ template <class ELFT> void Writer<ELFT>:
> }
> }
>
> -template <class ELFT>
> -static bool compSec(OutputSection<ELFT> *A, OutputSection<ELFT> *B) {
> +template <bool Is64Bits>
> +static bool compSec(OutputSection<Is64Bits> *A, OutputSection<Is64Bits>
> *B) {
> // Place SHF_ALLOC sections first.
> return (A->getFlags() & SHF_ALLOC) && !(B->getFlags() & SHF_ALLOC);
> }
> @@ -192,9 +207,10 @@ template <class ELFT> void Writer<ELFT>:
> uintX_t VA = 0x1000; // The first page is kept unmapped.
> uintX_t FileOff = SizeOfHeaders;
>
> - std::stable_sort(OutputSections.begin(), OutputSections.end(),
> compSec<ELFT>);
> + std::stable_sort(OutputSections.begin(), OutputSections.end(),
> + compSec<ELFT::Is64Bits>);
>
> - for (OutputSection<ELFT> *Sec : OutputSections) {
> + for (OutputSection<ELFT::Is64Bits> *Sec : OutputSections) {
> if (Sec->getFlags() & SHF_ALLOC) {
> Sec->setVA(VA);
> VA += RoundUpToAlignment(Sec->getSize(), PageSize);
> @@ -267,9 +283,9 @@ template <class ELFT> void Writer<ELFT>:
> auto SHdrs = reinterpret_cast<Elf_Shdr_Impl<ELFT> *>(Buf +
> EHdr->e_shoff);
> // First entry is null.
> ++SHdrs;
> - for (OutputSection<ELFT> *Sec : OutputSections) {
> + for (OutputSection<ELFT::Is64Bits> *Sec : OutputSections) {
> Sec->setNameOffset(StrTabBuilder.getOffset(Sec->getName()));
> - Sec->writeHeaderTo(SHdrs++);
> + Sec->template writeHeaderTo<ELFT::TargetEndianness>(SHdrs++);
> }
>
> // String table.
> @@ -295,7 +311,7 @@ template <class ELFT> void Writer<ELFT>:
> // Write section contents to a mmap'ed file.
> template <class ELFT> void Writer<ELFT>::writeSections() {
> uint8_t *Buf = Buffer->getBufferStart();
> - for (OutputSection<ELFT> *Sec : OutputSections) {
> + for (OutputSection<ELFT::Is64Bits> *Sec : OutputSections) {
> uint8_t *SecBuf = Buf + Sec->getOffset();
> for (Chunk *C : Sec->getChunks())
> C->writeTo(SecBuf);
>
>
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> llvm-commits at lists.llvm.org
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