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[ELF] maybeCompress: replace vector<uint8_t> with unique_ptr<uint8_t[]>. NFC 

And mention that it is zero-initialized. I do not notice a speed-up if
changed to be uninitialized by forcing the zero filler in writeTo.
This commit is contained in:
Fangrui Song 2022-01-25 22:15:44 -08:00
parent 8597458278
commit 223f9dea3d
1 changed files with 6 additions and 6 deletions
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12
lld/ELF/OutputSections.cpp
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@ -337,9 +337,9 @@ template <class ELFT> void OutputSection::maybeCompress() {
hdr->ch_size = size;
hdr->ch_addralign = alignment;
// Write section contents to a temporary buffer and compress it.
std::vector<uint8_t> buf(size);
writeTo<ELFT>(buf.data());
// Write uncompressed data to a temporary zero-initialized buffer.
auto buf = std::make_unique<uint8_t[]>(size);
writeTo<ELFT>(buf.get());
// We chose 1 as the default compression level because it is the fastest. If
// -O2 is given, we use level 6 to compress debug info more by ~15%. We found
// that level 7 to 9 doesn't make much difference (~1% more compression) while
@ -350,9 +350,9 @@ template <class ELFT> void OutputSection::maybeCompress() {
constexpr size_t shardSize = 1 << 20;
const size_t numShards = (size + shardSize - 1) / shardSize;
auto shardsIn = std::make_unique<ArrayRef<uint8_t>[]>(numShards);
for (size_t i = 0, start = 0, end; start != buf.size(); ++i, start = end) {
end = std::min(start + shardSize, buf.size());
shardsIn[i] = makeArrayRef<uint8_t>(buf.data() + start, end - start);
for (size_t i = 0, start = 0, end; start != size; ++i, start = end) {
end = std::min(start + shardSize, size);
shardsIn[i] = makeArrayRef<uint8_t>(buf.get() + start, end - start);
}
// Compress shards and compute Alder-32 checksums. Use Z_SYNC_FLUSH for all