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PECOFF: Do not add layout-after edges. 

Previously we needed to create atoms as a doubly-linked link, but it's
no longer needed. Also we don't use layout-after edges in PE/COFF.
Creating such edges is just waste.

llvm-svn: 230732
This commit is contained in:
Rui Ueyama 2015-02-27 05:05:38 +00:00
parent 60aa7985cc
commit 584abaee67
2 changed files with 7 additions and 18 deletions
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23
lld/lib/ReaderWriter/PECOFF/Atoms.h
View File

@ -351,27 +351,16 @@ void addLayoutEdge(T *a, U *b, uint32_t which) {
a->addReference(std::unique_ptr<COFFReference>(ref));
}
template <typename T, typename U> void connectWithLayoutEdge(T *a, U *b) {
addLayoutEdge(a, b, lld::Reference::kindLayoutAfter);
addLayoutEdge(b, a, lld::Reference::kindLayoutBefore);
}
/// Connect atoms with layout-{before,after} edges. It usually serves two
/// purposes.
///
/// - To prevent atoms from being GC'ed (aka dead-stripped) if there is a
/// reference to one of the atoms. In that case we want to emit all the
/// atoms appeared in the same section, because the referenced "live" atom
/// may reference other atoms in the same section. If we don't add layout
/// edges between atoms, unreferenced atoms in the same section would be
/// GC'ed.
/// - To preserve the order of atmos. We want to emit the atoms in the
/// same order as they appeared in the input object file.
/// Connect atoms with layout-before edges. It prevents atoms from
/// being GC'ed (aka dead-stripped) if there is a reference to one of
/// the atoms in the same layout-before chain. In such case we want to
/// emit all the atoms appeared in the same chain, because the "live"
/// atom may reference other atoms in the same chain.
template <typename T> void connectAtomsWithLayoutEdge(std::vector<T *> &atoms) {
if (atoms.size() < 2)
return;
for (auto it = atoms.begin(), e = atoms.end(); it + 1 != e; ++it)
connectWithLayoutEdge(*it, *(it + 1));
addLayoutEdge(*(it + 1), *it, lld::Reference::kindLayoutBefore);
}
} // namespace pecoff

2
lld/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp
View File

@ -756,7 +756,7 @@ std::error_code FileCOFF::AtomizeDefinedSymbols(
if (atoms.size() > 0)
atoms[0]->setAlignment(getAlignment(section));
// Connect atoms with layout-before/layout-after edges.
// Connect atoms with layout-before edges.
connectAtomsWithLayoutEdge(atoms);
for (COFFDefinedFileAtom *atom : atoms) {