/// means R_X86_64_32 for x86_64, and R_386_GOTPC for i386. For PE/COFF
/// relocation 10 means IMAGE_REL_AMD64_SECTION.
///
+/// References and atoms form a directed graph. The dead-stripping pass
+/// traverses them starting from dead-strip root atoms to garbage collect
+/// unreachable ones.
+///
+/// References of any kind are considered as directed edges. In addition to
+/// that, references of some kind is considered as bidirected edges.
class Reference {
public:
/// Which universe defines the kindValue().
/// KindValues used with KindNamespace::all and KindArch::all.
enum {
kindInGroup = 1,
+ // kindLayoutAfter is treated as a bidirected edge by the dead-stripping
+ // pass.
kindLayoutAfter = 2,
- // kindLayoutBefore is currently used only by dead-stripping pass in
- // the Resolver. Will be removed soon. To enforce layout, use
- // kindLayoutAfter instead.
+ // kindLayoutBefore is currently used only by PECOFF port, and will
+ // be removed soon. To enforce layout, use kindLayoutAfter instead.
kindLayoutBefore = 3,
kindGroupChild = 4,
kindGroupParent = 5
#include "lld/Core/SharedLibraryFile.h"
#include "lld/Core/SymbolTable.h"
+#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include <set>
std::set<const Atom *> _deadStripRoots;
llvm::DenseSet<const Atom *> _liveAtoms;
std::unique_ptr<MergedFile> _result;
+ llvm::DenseMap<const Atom *, llvm::DenseSet<const Atom *>> _reverseRef;
};
} // namespace lld
return;
// Mark all atoms it references as live
- if (const DefinedAtom *defAtom = dyn_cast<DefinedAtom>(atom))
+ if (const DefinedAtom *defAtom = dyn_cast<DefinedAtom>(atom)) {
for (const Reference *ref : *defAtom)
markLive(ref->target());
+ for (const Atom *target : _reverseRef[defAtom])
+ markLive(target);
+ }
+}
+
+static bool isBackref(const Reference *ref) {
+ return ref->kindNamespace() == lld::Reference::KindNamespace::all &&
+ ref->kindValue() == lld::Reference::kindLayoutBefore;
}
// remove all atoms not actually used
// only do this optimization with -dead_strip
if (!_context.deadStrip())
return;
- assert(_liveAtoms.empty());
+
+ // Some type of references prevent referring atoms to be dead-striped.
+ // Make a reverse map of such references before traversing the graph.
+ for (const Atom *atom : _atoms)
+ if (const DefinedAtom *defAtom = dyn_cast<DefinedAtom>(atom))
+ for (const Reference *ref : *defAtom)
+ if (isBackref(ref))
+ _reverseRef[ref->target()].insert(atom);
// By default, shared libraries are built with all globals as dead strip roots
if (_context.globalsAreDeadStripRoots())
--- /dev/null
+# RUN: lld -core --dead-strip %s | FileCheck -check-prefix=CHECK1 %s
+# RUN: lld -core %s | FileCheck -check-prefix=CHECK2 %s
+
+---
+defined-atoms:
+ - name: entry
+ dead-strip: never
+ scope: global
+ references:
+ - kind: layout-after
+ offset: 0
+ target: def
+ - name: def
+ scope: global
+ - name: dead
+ scope: global
+...
+
+# CHECK1: name: entry
+# CHECK1: name: def
+# CHECK1-NOT: name: dead
+
+# CHECK2: name: entry
+# CHECK2: name: def
+# CHECK2: name: dead