[lld] 417cd2e - [ELF] SymbolTable: change some vector<Symbol *> to SmallVector

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2021-12-23T16:49:38-08:00
New Revision: 417cd2e5c5e0ef0a3c8161298b7690f7911ce7ed

URL: https://github.com/llvm/llvm-project/commit/417cd2e5c5e0ef0a3c8161298b7690f7911ce7ed
DIFF: https://github.com/llvm/llvm-project/commit/417cd2e5c5e0ef0a3c8161298b7690f7911ce7ed.diff

LOG: [ELF] SymbolTable: change some vector<Symbol *> to SmallVector

The generated assembly for Symbol::insert is much shorter (std::vector resize is
inefficient) and enables some inlining.

Added: 
    

Modified: 
    lld/ELF/SymbolTable.cpp
    lld/ELF/SymbolTable.h

Removed: 
    


################################################################################
diff  --git a/lld/ELF/SymbolTable.cpp b/lld/ELF/SymbolTable.cpp
index 5c7b8b00a6eea..a501b270010bf 100644
--- a/lld/ELF/SymbolTable.cpp
+++ b/lld/ELF/SymbolTable.cpp
@@ -133,7 +133,7 @@ static bool canBeVersioned(const Symbol &sym) {
 // other than trying to match a pattern against all demangled symbols.
 // So, if "extern C++" feature is used, we need to demangle all known
 // symbols.
-StringMap<std::vector<Symbol *>> &SymbolTable::getDemangledSyms() {
+StringMap<SmallVector<Symbol *, 0>> &SymbolTable::getDemangledSyms() {
   if (!demangledSyms) {
     demangledSyms.emplace();
     std::string demangled;
@@ -154,7 +154,7 @@ StringMap<std::vector<Symbol *>> &SymbolTable::getDemangledSyms() {
   return *demangledSyms;
 }
 
-std::vector<Symbol *> SymbolTable::findByVersion(SymbolVersion ver) {
+SmallVector<Symbol *, 0> SymbolTable::findByVersion(SymbolVersion ver) {
   if (ver.isExternCpp)
     return getDemangledSyms().lookup(ver.name);
   if (Symbol *sym = find(ver.name))
@@ -163,9 +163,9 @@ std::vector<Symbol *> SymbolTable::findByVersion(SymbolVersion ver) {
   return {};
 }
 
-std::vector<Symbol *> SymbolTable::findAllByVersion(SymbolVersion ver,
-                                                    bool includeNonDefault) {
-  std::vector<Symbol *> res;
+SmallVector<Symbol *, 0> SymbolTable::findAllByVersion(SymbolVersion ver,
+                                                       bool includeNonDefault) {
+  SmallVector<Symbol *, 0> res;
   SingleStringMatcher m(ver.name);
   auto check = [&](StringRef name) {
     size_t pos = name.find('@');
@@ -191,8 +191,8 @@ std::vector<Symbol *> SymbolTable::findAllByVersion(SymbolVersion ver,
 }
 
 void SymbolTable::handleDynamicList() {
+  SmallVector<Symbol *, 0> syms;
   for (SymbolVersion &ver : config->dynamicList) {
-    std::vector<Symbol *> syms;
     if (ver.hasWildcard)
       syms = findAllByVersion(ver, /*includeNonDefault=*/true);
     else
@@ -209,7 +209,7 @@ bool SymbolTable::assignExactVersion(SymbolVersion ver, uint16_t versionId,
                                      StringRef versionName,
                                      bool includeNonDefault) {
   // Get a list of symbols which we need to assign the version to.
-  std::vector<Symbol *> syms = findByVersion(ver);
+  SmallVector<Symbol *, 0> syms = findByVersion(ver);
 
   auto getName = [](uint16_t ver) -> std::string {
     if (ver == VER_NDX_LOCAL)

diff  --git a/lld/ELF/SymbolTable.h b/lld/ELF/SymbolTable.h
index 568e4559ec346..84d93a3dc7863 100644
--- a/lld/ELF/SymbolTable.h
+++ b/lld/ELF/SymbolTable.h
@@ -35,8 +35,9 @@ class SymbolTable {
   struct FilterOutPlaceholder {
     bool operator()(Symbol *S) const { return !S->isPlaceholder(); }
   };
-  using iterator = llvm::filter_iterator<std::vector<Symbol *>::const_iterator,
-                                         FilterOutPlaceholder>;
+  using iterator =
+      llvm::filter_iterator<SmallVector<Symbol *, 0>::const_iterator,
+                            FilterOutPlaceholder>;
 
 public:
   llvm::iterator_range<iterator> symbols() const {
@@ -64,11 +65,11 @@ class SymbolTable {
   llvm::DenseMap<llvm::CachedHashStringRef, const InputFile *> comdatGroups;
 
 private:
-  std::vector<Symbol *> findByVersion(SymbolVersion ver);
-  std::vector<Symbol *> findAllByVersion(SymbolVersion ver,
-                                         bool includeNonDefault);
+  SmallVector<Symbol *, 0> findByVersion(SymbolVersion ver);
+  SmallVector<Symbol *, 0> findAllByVersion(SymbolVersion ver,
+                                            bool includeNonDefault);
 
-  llvm::StringMap<std::vector<Symbol *>> &getDemangledSyms();
+  llvm::StringMap<SmallVector<Symbol *, 0>> &getDemangledSyms();
   bool assignExactVersion(SymbolVersion ver, uint16_t versionId,
                           StringRef versionName, bool includeNonDefault);
   void assignWildcardVersion(SymbolVersion ver, uint16_t versionId,
@@ -82,13 +83,13 @@ class SymbolTable {
   // FIXME: Experiment with passing in a custom hashing or sorting the symbols
   // once symbol resolution is finished.
   llvm::DenseMap<llvm::CachedHashStringRef, int> symMap;
-  std::vector<Symbol *> symVector;
+  SmallVector<Symbol *, 0> symVector;
 
   // A map from demangled symbol names to their symbol objects.
   // This mapping is 1:N because two symbols with 
diff erent versions
   // can have the same name. We use this map to handle "extern C++ {}"
   // directive in version scripts.
-  llvm::Optional<llvm::StringMap<std::vector<Symbol *>>> demangledSyms;
+  llvm::Optional<llvm::StringMap<SmallVector<Symbol *, 0>>> demangledSyms;
 };
 
 extern std::unique_ptr<SymbolTable> symtab;