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[DWARF] - Speedup handling of relocations in DWARFContextInMemory.

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I am working on a speedup of building .gdb_index in LLD and 
noticed that relocations that are proccessed in DWARFContextInMemory often uses
the same symbol in a row. This patch introduces caching to reduce the relocations
proccessing time.

For benchmark,
I took debug LLC binary objects configured with -ggnu-pubnames and linked it using LLD.

Link time without --gdb-index is about 4,45s.
Link time with --gdb-index: a) Without patch: 19,16s b) With patch: 15,52s
That means time spent on --gdb-index in this configuration is 
19,16s - 4,45s = 14,71s (without patch) vs 15,52s - 4,45s = 11,07s (with patch).

Differential revision: https://reviews.llvm.org/D31136

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@303051 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
George Rimar 2017-05-15 11:45:28 +00:00
parent eadb58fda7
commit fbe48085e6
1 changed files with 17 additions and 4 deletions
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21
lib/DebugInfo/DWARF/DWARFContext.cpp
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@ -905,16 +905,23 @@ static Error createError(const Twine &Reason, llvm::Error E) {
/// Returns the address of symbol relocation used against. Used for futher
/// relocations computation. Symbol's section load address is taken in account if
/// LoadedObjectInfo interface is provided.
static Expected<uint64_t> getSymbolAddress(const object::ObjectFile &Obj,
const RelocationRef &Reloc,
const LoadedObjectInfo *L) {
static Expected<uint64_t>
getSymbolAddress(const object::ObjectFile &Obj, const RelocationRef &Reloc,
const LoadedObjectInfo *L,
std::map<SymbolRef, uint64_t> &Cache) {
uint64_t Ret = 0;
object::section_iterator RSec = Obj.section_end();
object::symbol_iterator Sym = Reloc.getSymbol();
std::map<SymbolRef, uint64_t>::iterator CacheIt = Cache.end();
// First calculate the address of the symbol or section as it appears
// in the object file
if (Sym != Obj.symbol_end()) {
bool New;
std::tie(CacheIt, New) = Cache.insert({*Sym, 0});
if (!New)
return CacheIt->second;
Expected<uint64_t> SymAddrOrErr = Sym->getAddress();
if (!SymAddrOrErr)
return createError("error: failed to compute symbol address: ",
@ -943,6 +950,10 @@ static Expected<uint64_t> getSymbolAddress(const object::ObjectFile &Obj,
if (L && RSec != Obj.section_end())
if (uint64_t SectionLoadAddress = L->getSectionLoadAddress(*RSec))
Ret += SectionLoadAddress - RSec->getAddress();
if (CacheIt != Cache.end())
CacheIt->second = Ret;
return Ret;
}
@ -1075,6 +1086,7 @@ DWARFContextInMemory::DWARFContextInMemory(const object::ObjectFile &Obj,
continue;
}
std::map<SymbolRef, uint64_t> AddrCache;
if (Section.relocation_begin() != Section.relocation_end()) {
uint64_t SectionSize = RelocatedSection->getSize();
for (const RelocationRef &Reloc : Section.relocations()) {
@ -1083,7 +1095,8 @@ DWARFContextInMemory::DWARFContextInMemory(const object::ObjectFile &Obj,
if (isRelocScattered(Obj, Reloc))
continue;
Expected<uint64_t> SymAddrOrErr = getSymbolAddress(Obj, Reloc, L);
Expected<uint64_t> SymAddrOrErr =
getSymbolAddress(Obj, Reloc, L, AddrCache);
if (!SymAddrOrErr) {
errs() << toString(SymAddrOrErr.takeError()) << '\n';
continue;