[ELF] Move gotIndex/pltIndex/globalDynIndex to SymbolAux

to decrease sizeof(SymbolUnion) by 8 on ELF64 platforms.

Symbols needing such information are typically 1% or fewer (5134 out of 560520
when linking clang, 19898 out of 5550705 when linking chrome). Storing them
elsewhere can decrease memory usage and symbol initialization time.
There is a ~0.8% saving on max RSS when linking a large program.

Future direction:

* Move some of dynsymIndex/verdefIndex/versionId to SymbolAux
* Support mixed TLSDESC and TLS GD without increasing sizeof(SymbolUnion)

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D116281

1 files changed, 25 insertions, 17 deletions

diff --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
index f93c09b..6af1023 100644
--- a/lld/ELF/SyntheticSections.cpp
+++ b/lld/ELF/SyntheticSections.cpp
@@ -650,14 +650,13 @@ GotSection::GotSection()
 }
 
 void GotSection::addEntry(Symbol &sym) {
-  sym.gotIndex = numEntries;
-  ++numEntries;
+  assert(sym.auxIdx == symAux.size() - 1);
+  symAux.back().gotIdx = numEntries++;
 }
 
 bool GotSection::addDynTlsEntry(Symbol &sym) {
-  if (sym.globalDynIndex != -1U)
-    return false;
-  sym.globalDynIndex = numEntries;
+  assert(sym.auxIdx == symAux.size() - 1);
+  symAux.back().tlsGdIdx = numEntries;
   // Global Dynamic TLS entries take two GOT slots.
   numEntries += 2;
   return true;
@@ -674,11 +673,11 @@ bool GotSection::addTlsIndex() {
 }
 
 uint64_t GotSection::getGlobalDynAddr(const Symbol &b) const {
-  return this->getVA() + b.globalDynIndex * config->wordsize;
+  return this->getVA() + b.getTlsGdIdx() * config->wordsize;
 }
 
 uint64_t GotSection::getGlobalDynOffset(const Symbol &b) const {
-  return b.globalDynIndex * config->wordsize;
+  return b.getTlsGdIdx() * config->wordsize;
 }
 
 void GotSection::finalizeContents() {
@@ -972,12 +971,18 @@ void MipsGotSection::build() {
     }
   }
 
-  // Update Symbol::gotIndex field to use this
+  // Update SymbolAux::gotIdx field to use this
   // value later in the `sortMipsSymbols` function.
-  for (auto &p : primGot->global)
-    p.first->gotIndex = p.second;
-  for (auto &p : primGot->relocs)
-    p.first->gotIndex = p.second;
+  for (auto &p : primGot->global) {
+    if (p.first->auxIdx == uint32_t(-1))
+      p.first->allocateAux();
+    symAux.back().gotIdx = p.second;
+  }
+  for (auto &p : primGot->relocs) {
+    if (p.first->auxIdx == uint32_t(-1))
+      p.first->allocateAux();
+    symAux.back().gotIdx = p.second;
+  }
 
   // Create dynamic relocations.
   for (FileGot &got : gots) {
@@ -1145,7 +1150,8 @@ GotPltSection::GotPltSection()
 }
 
 void GotPltSection::addEntry(Symbol &sym) {
-  assert(sym.pltIndex == entries.size());
+  assert(sym.auxIdx == symAux.size() - 1 &&
+         symAux.back().pltIdx == entries.size());
   entries.push_back(&sym);
 }
 
@@ -1190,7 +1196,7 @@ IgotPltSection::IgotPltSection()
                        target->gotEntrySize, getIgotPltName()) {}
 
 void IgotPltSection::addEntry(Symbol &sym) {
-  assert(sym.pltIndex == entries.size());
+  assert(symAux.back().pltIdx == entries.size());
   entries.push_back(&sym);
 }
 
@@ -2069,7 +2075,7 @@ static bool sortMipsSymbols(const SymbolTableEntry &l,
   // Sort entries related to non-local preemptible symbols by GOT indexes.
   // All other entries go to the beginning of a dynsym in arbitrary order.
   if (l.sym->isInGot() && r.sym->isInGot())
-    return l.sym->gotIndex < r.sym->gotIndex;
+    return l.sym->getGotIdx() < r.sym->getGotIdx();
   if (!l.sym->isInGot() && !r.sym->isInGot())
     return false;
   return !l.sym->isInGot();
@@ -2546,7 +2552,8 @@ void PltSection::writeTo(uint8_t *buf) {
 }
 
 void PltSection::addEntry(Symbol &sym) {
-  sym.pltIndex = entries.size();
+  assert(sym.auxIdx == symAux.size() - 1);
+  symAux.back().pltIdx = entries.size();
   entries.push_back(&sym);
 }
 
@@ -2592,7 +2599,8 @@ size_t IpltSection::getSize() const {
 }
 
 void IpltSection::addEntry(Symbol &sym) {
-  sym.pltIndex = entries.size();
+  assert(sym.auxIdx == symAux.size() - 1);
+  symAux.back().pltIdx = entries.size();
   entries.push_back(&sym);
 }