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[ELF] Make InputSection smaller 

On LP64/Windows platforms, this decreases sizeof(InputSection) from 208 (larger
on Windows) to 184.

For a large executable (7.6GiB, inputSections.size()=5105122,
make<InputSection> called 4835760 times), this decreases cgroup
memory.max_usage_in_bytes by 0.6%

Reviewed By: grimar

Differential Revision: https://reviews.llvm.org/D91018
This commit is contained in:
Fangrui Song 2020-11-09 09:55:09 -08:00
parent 9c098d37f4
commit 2eccde4a2b
1 changed files with 11 additions and 9 deletions
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20
lld/ELF/InputSection.h
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@ -52,15 +52,15 @@ public:
// this but instead this->Repl. // this but instead this->Repl.
SectionBase *repl; SectionBase *repl;
unsigned sectionKind : 3; uint8_t sectionKind : 3;
// The next two bit fields are only used by InputSectionBase, but we // The next two bit fields are only used by InputSectionBase, but we
// put them here so the struct packs better. // put them here so the struct packs better.
unsigned bss : 1; uint8_t bss : 1;
// Set for sections that should not be folded by ICF. // Set for sections that should not be folded by ICF.
unsigned keepUnique : 1; uint8_t keepUnique : 1;
// The 1-indexed partition that this section is assigned to by the garbage // The 1-indexed partition that this section is assigned to by the garbage
// collector, or 0 if this section is dead. Normally there is only one // collector, or 0 if this section is dead. Normally there is only one
@ -134,6 +134,10 @@ public:
// and shrinking a section. // and shrinking a section.
unsigned bytesDropped = 0; unsigned bytesDropped = 0;
// Whether the section needs to be padded with a NOP filler due to
// deleteFallThruJmpInsn.
bool nopFiller = false;
void drop_back(uint64_t num) { bytesDropped += num; } void drop_back(uint64_t num) { bytesDropped += num; }
void push_back(uint64_t num) { void push_back(uint64_t num) {
@ -210,17 +214,13 @@ public:
// The native ELF reloc data type is not very convenient to handle. // The native ELF reloc data type is not very convenient to handle.
// So we convert ELF reloc records to our own records in Relocations.cpp. // So we convert ELF reloc records to our own records in Relocations.cpp.
// This vector contains such "cooked" relocations. // This vector contains such "cooked" relocations.
std::vector<Relocation> relocations; SmallVector<Relocation, 0> relocations;
// Indicates that this section needs to be padded with a NOP filler if set to
// true.
bool nopFiller = false;
// These are modifiers to jump instructions that are necessary when basic // These are modifiers to jump instructions that are necessary when basic
// block sections are enabled. Basic block sections creates opportunities to // block sections are enabled. Basic block sections creates opportunities to
// relax jump instructions at basic block boundaries after reordering the // relax jump instructions at basic block boundaries after reordering the
// basic blocks. // basic blocks.
std::vector<JumpInstrMod> jumpInstrMods; SmallVector<JumpInstrMod, 0> jumpInstrMods;
// A function compiled with -fsplit-stack calling a function // A function compiled with -fsplit-stack calling a function
// compiled without -fsplit-stack needs its prologue adjusted. Find // compiled without -fsplit-stack needs its prologue adjusted. Find
@ -390,6 +390,8 @@ private:
template <class ELFT> void copyShtGroup(uint8_t *buf); template <class ELFT> void copyShtGroup(uint8_t *buf);
}; };
static_assert(sizeof(InputSection) <= 184, "InputSection is too big");
inline bool isDebugSection(const InputSectionBase &sec) { inline bool isDebugSection(const InputSectionBase &sec) {
return sec.name.startswith(".debug") || sec.name.startswith(".zdebug"); return sec.name.startswith(".debug") || sec.name.startswith(".zdebug");
} }