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Fix quadratic performance during debug compression due to sections x symbols iteration.

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When fixing the symbols in each compressed section we were iterating
over all symbols for each compressed section. In extreme cases this
could snowball severely (5min uncompressed -> 35min compressed) due to
iterating over all symbols for each compressed section (large numbers of
compressed sections can be generated by DWARF type units).

To address this, build a map of the symbols in each section ahead of
time, and access that map if a section is being compressed. This brings
compile time for the aforementioned example down to ~6 minutes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207167 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Blaikie 2014-04-25 00:48:01 +00:00
parent 680311d2d2
commit 6715d6ec2e
1 changed files with 21 additions and 12 deletions
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33
lib/MC/ELFObjectWriter.cpp
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@ -1250,20 +1250,21 @@ getCompressedFragment(MCAsmLayout &Layout,
return CompressedFragment;
}
static void UpdateSymbols(const MCAsmLayout &Layout, const MCSectionData &SD,
MCAssembler::symbol_range Symbols,
MCFragment *NewFragment) {
for (MCSymbolData &Data : Symbols) {
MCFragment *F = Data.getFragment();
if (F && F->getParent() == &SD) {
Data.setOffset(Data.getOffset() +
Layout.getFragmentOffset(Data.Fragment));
Data.setFragment(NewFragment);
}
typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
DefiningSymbolMap;
static void UpdateSymbols(const MCAsmLayout &Layout,
const std::vector<MCSymbolData *> &Symbols,
MCFragment &NewFragment) {
for (MCSymbolData *Sym : Symbols) {
Sym->setOffset(Sym->getOffset() +
Layout.getFragmentOffset(Sym->getFragment()));
Sym->setFragment(&NewFragment);
}
}
static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
const DefiningSymbolMap &DefiningSymbols,
const MCSectionELF &Section,
MCSectionData &SD) {
StringRef SectionName = Section.getSectionName();
@ -1278,7 +1279,9 @@ static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
// Update the fragment+offsets of any symbols referring to fragments in this
// section to refer to the new fragment.
UpdateSymbols(Layout, SD, Asm.symbols(), CompressedFragment.get());
auto I = DefiningSymbols.find(&SD);
if (I != DefiningSymbols.end())
UpdateSymbols(Layout, I->second, *CompressedFragment);
// Invalidate the layout for the whole section since it will have new and
// different fragments now.
@ -1300,6 +1303,12 @@ void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
if (!Asm.getContext().getAsmInfo()->compressDebugSections())
return;
DefiningSymbolMap DefiningSymbols;
for (MCSymbolData &SD : Asm.symbols())
if (MCFragment *F = SD.getFragment())
DefiningSymbols[F->getParent()].push_back(&SD);
for (MCSectionData &SD : Asm) {
const MCSectionELF &Section =
static_cast<const MCSectionELF &>(SD.getSection());
@ -1311,7 +1320,7 @@ void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
continue;
CompressDebugSection(Asm, Layout, Section, SD);
CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
}
}