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[lld-macho] Remove cuIndices indirection in UnwindInfoSection. NFC (#170252)

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cuEntries was sorted indirectly through a separate `cuIndices`.
Eliminate cuIndices for simplicity.

Linking chromium_framework from `#48001` with `-no_uuid` gives identical
executable using this patch.
This commit is contained in:
Fangrui Song
2025-12-02 00:18:09 -08:00
committed by GitHub
parent b5f7058e91
commit 87d37956b3
1 changed files with 32 additions and 43 deletions
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75
lld/MachO/UnwindInfoSection.cpp
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@@ -153,8 +153,6 @@ private:
// The entries here will be in the same order as their originating symbols
// in symbolsVec.
std::vector<CompactUnwindEntry> cuEntries;
// Indices into the cuEntries vector.
std::vector<size_t> cuIndices;
std::vector<Symbol *> personalities;
SmallDenseMap<std::pair<InputSection *, uint64_t /* addend */>, Symbol *>
personalityTable;
@@ -400,8 +398,7 @@ void UnwindInfoSectionImpl::relocateCompactUnwind(
// There should only be a handful of unique personality pointers, so we can
// encode them as 2-bit indices into a small array.
void UnwindInfoSectionImpl::encodePersonalities() {
for (size_t idx : cuIndices) {
CompactUnwindEntry &cu = cuEntries[idx];
for (CompactUnwindEntry &cu : cuEntries) {
if (cu.personality == nullptr)
continue;
// Linear search is fast enough for a small array.
@@ -467,27 +464,24 @@ void UnwindInfoSectionImpl::finalize() {
symbolsVec = symbols.takeVector();
relocateCompactUnwind(cuEntries);
// Rather than sort & fold the 32-byte entries directly, we create a
// vector of indices to entries and sort & fold that instead.
cuIndices.resize(cuEntries.size());
std::iota(cuIndices.begin(), cuIndices.end(), 0);
llvm::sort(cuIndices, [&](size_t a, size_t b) {
return cuEntries[a].functionAddress < cuEntries[b].functionAddress;
// Sort the entries by address.
llvm::sort(cuEntries, [&](auto &a, auto &b) {
return a.functionAddress < b.functionAddress;
});
// Record the ending boundary before we fold the entries.
cueEndBoundary = cuEntries[cuIndices.back()].functionAddress +
cuEntries[cuIndices.back()].functionLength;
cueEndBoundary =
cuEntries.back().functionAddress + cuEntries.back().functionLength;
// Fold adjacent entries with matching encoding+personality and without LSDA
// We use three iterators on the same cuIndices to fold in-situ:
// We use three iterators to fold in-situ:
// (1) `foldBegin` is the first of a potential sequence of matching entries
// (2) `foldEnd` is the first non-matching entry after `foldBegin`.
// The semi-open interval [ foldBegin .. foldEnd ) contains a range
// entries that can be folded into a single entry and written to ...
// (3) `foldWrite`
auto foldWrite = cuIndices.begin();
for (auto foldBegin = cuIndices.begin(); foldBegin < cuIndices.end();) {
auto foldWrite = cuEntries.begin();
for (auto foldBegin = cuEntries.begin(); foldBegin != cuEntries.end();) {
auto foldEnd = foldBegin;
// Common LSDA encodings (e.g. for C++ and Objective-C) contain offsets from
// a base address. The base address is normally not contained directly in
@@ -503,9 +497,9 @@ void UnwindInfoSectionImpl::finalize() {
// directly in the LSDA, two functions at different addresses would
// necessarily have different LSDAs, so their CU entries would not have been
// folded anyway.
while (++foldEnd < cuIndices.end() &&
cuEntries[*foldBegin].encoding == cuEntries[*foldEnd].encoding &&
!cuEntries[*foldBegin].lsda && !cuEntries[*foldEnd].lsda &&
while (++foldEnd != cuEntries.end() &&
foldBegin->encoding == foldEnd->encoding && !foldBegin->lsda &&
!foldEnd->lsda &&
// If we've gotten to this point, we don't have an LSDA, which should
// also imply that we don't have a personality function, since in all
// likelihood a personality function needs the LSDA to do anything
@@ -513,21 +507,20 @@ void UnwindInfoSectionImpl::finalize() {
// and no LSDA though (e.g. the C++ personality __gxx_personality_v0
// is just a no-op without LSDA), so we still check for personality
// function equivalence to handle that case.
cuEntries[*foldBegin].personality ==
cuEntries[*foldEnd].personality &&
canFoldEncoding(cuEntries[*foldEnd].encoding))
foldBegin->personality == foldEnd->personality &&
canFoldEncoding(foldEnd->encoding))
;
*foldWrite++ = *foldBegin;
foldBegin = foldEnd;
}
cuIndices.erase(foldWrite, cuIndices.end());
cuEntries.erase(foldWrite, cuEntries.end());
encodePersonalities();
// Count frequencies of the folded encodings
EncodingMap encodingFrequencies;
for (size_t idx : cuIndices)
encodingFrequencies[cuEntries[idx].encoding]++;
for (const CompactUnwindEntry &cu : cuEntries)
encodingFrequencies[cu.encoding]++;
// Make a vector of encodings, sorted by descending frequency
for (const auto &frequency : encodingFrequencies)
@@ -558,21 +551,19 @@ void UnwindInfoSectionImpl::finalize() {
// and 127..255 references a local per-second-level-page table.
// First we try the compact format and determine how many entries fit.
// If more entries fit in the regular format, we use that.
for (size_t i = 0; i < cuIndices.size();) {
size_t idx = cuIndices[i];
for (size_t i = 0; i < cuEntries.size();) {
secondLevelPages.emplace_back();
SecondLevelPage &page = secondLevelPages.back();
page.entryIndex = i;
uint64_t functionAddressMax =
cuEntries[idx].functionAddress + COMPRESSED_ENTRY_FUNC_OFFSET_MASK;
cuEntries[i].functionAddress + COMPRESSED_ENTRY_FUNC_OFFSET_MASK;
size_t n = commonEncodings.size();
size_t wordsRemaining =
SECOND_LEVEL_PAGE_WORDS -
sizeof(unwind_info_compressed_second_level_page_header) /
sizeof(uint32_t);
while (wordsRemaining >= 1 && i < cuIndices.size()) {
idx = cuIndices[i];
const CompactUnwindEntry *cuPtr = &cuEntries[idx];
while (wordsRemaining >= 1 && i < cuEntries.size()) {
const CompactUnwindEntry *cuPtr = &cuEntries[i];
if (cuPtr->functionAddress >= functionAddressMax)
break;
if (commonEncodingIndexes.count(cuPtr->encoding) ||
@@ -593,21 +584,21 @@ void UnwindInfoSectionImpl::finalize() {
// If this is not the final page, see if it's possible to fit more entries
// by using the regular format. This can happen when there are many unique
// encodings, and we saturated the local encoding table early.
if (i < cuIndices.size() &&
if (i < cuEntries.size() &&
page.entryCount < REGULAR_SECOND_LEVEL_ENTRIES_MAX) {
page.kind = UNWIND_SECOND_LEVEL_REGULAR;
page.entryCount = std::min(REGULAR_SECOND_LEVEL_ENTRIES_MAX,
cuIndices.size() - page.entryIndex);
cuEntries.size() - page.entryIndex);
i = page.entryIndex + page.entryCount;
} else {
page.kind = UNWIND_SECOND_LEVEL_COMPRESSED;
}
}
for (size_t idx : cuIndices) {
lsdaIndex[idx] = entriesWithLsda.size();
if (cuEntries[idx].lsda)
entriesWithLsda.push_back(idx);
for (size_t i = 0; i < cuEntries.size(); ++i) {
lsdaIndex[i] = entriesWithLsda.size();
if (cuEntries[i].lsda)
entriesWithLsda.push_back(i);
}
// compute size of __TEXT,__unwind_info section
@@ -626,7 +617,7 @@ void UnwindInfoSectionImpl::finalize() {
// All inputs are relocated and output addresses are known, so write!
void UnwindInfoSectionImpl::writeTo(uint8_t *buf) const {
assert(!cuIndices.empty() && "call only if there is unwind info");
assert(!cuEntries.empty() && "call only if there is unwind info");
// section header
auto *uip = reinterpret_cast<unwind_info_section_header *>(buf);
@@ -660,7 +651,7 @@ void UnwindInfoSectionImpl::writeTo(uint8_t *buf) const {
uint64_t l2PagesOffset = level2PagesOffset;
auto *iep = reinterpret_cast<unwind_info_section_header_index_entry *>(i32p);
for (const SecondLevelPage &page : secondLevelPages) {
size_t idx = cuIndices[page.entryIndex];
size_t idx = page.entryIndex;
iep->functionOffset = cuEntries[idx].functionAddress - in.header->addr;
iep->secondLevelPagesSectionOffset = l2PagesOffset;
iep->lsdaIndexArraySectionOffset =
@@ -695,7 +686,7 @@ void UnwindInfoSectionImpl::writeTo(uint8_t *buf) const {
for (const SecondLevelPage &page : secondLevelPages) {
if (page.kind == UNWIND_SECOND_LEVEL_COMPRESSED) {
uintptr_t functionAddressBase =
cuEntries[cuIndices[page.entryIndex]].functionAddress;
cuEntries[page.entryIndex].functionAddress;
auto *p2p =
reinterpret_cast<unwind_info_compressed_second_level_page_header *>(
pp);
@@ -708,8 +699,7 @@ void UnwindInfoSectionImpl::writeTo(uint8_t *buf) const {
p2p->encodingsCount = page.localEncodings.size();
auto *ep = reinterpret_cast<uint32_t *>(&p2p[1]);
for (size_t i = 0; i < page.entryCount; i++) {
const CompactUnwindEntry &cue =
cuEntries[cuIndices[page.entryIndex + i]];
const CompactUnwindEntry &cue = cuEntries[page.entryIndex + i];
auto it = commonEncodingIndexes.find(cue.encoding);
if (it == commonEncodingIndexes.end())
it = page.localEncodingIndexes.find(cue.encoding);
@@ -728,8 +718,7 @@ void UnwindInfoSectionImpl::writeTo(uint8_t *buf) const {
p2p->entryCount = page.entryCount;
auto *ep = reinterpret_cast<uint32_t *>(&p2p[1]);
for (size_t i = 0; i < page.entryCount; i++) {
const CompactUnwindEntry &cue =
cuEntries[cuIndices[page.entryIndex + i]];
const CompactUnwindEntry &cue = cuEntries[page.entryIndex + i];
*ep++ = cue.functionAddress;
*ep++ = cue.encoding;
}