Object: Shrink the size of irsymtab::Symbol by a word. NFCI.

Instead of storing an UncommonIndex on the Symbol, use a flag bit to store
whether the Symbol has an Uncommon. This shrinks Chromium's .bc files (after
D32061) by about 1%.

Differential Revision: https://reviews.llvm.org/D32070

llvm-svn: 300514

1 files changed, 18 insertions, 14 deletions

diff --git a/llvm/lib/Object/IRSymtab.cpp b/llvm/lib/Object/IRSymtab.cpp
index 43e623a88a4..bb3d1b2cf69 100644
--- a/llvm/lib/Object/IRSymtab.cpp
+++ b/llvm/lib/Object/IRSymtab.cpp
@@ -34,8 +34,6 @@ struct Builder {
   StringSaver Saver{Alloc};
 
   DenseMap<const Comdat *, unsigned> ComdatMap;
-  ModuleSymbolTable Msymtab;
-  SmallPtrSet<GlobalValue *, 8> Used;
   Mangler Mang;
   Triple TT;
 
@@ -60,18 +58,24 @@ struct Builder {
   }
 
   Error addModule(Module *M);
-  Error addSymbol(ModuleSymbolTable::Symbol Sym);
+  Error addSymbol(const ModuleSymbolTable &Msymtab,
+                  const SmallPtrSet<GlobalValue *, 8> &Used,
+                  ModuleSymbolTable::Symbol Sym);
 
   Error build(ArrayRef<Module *> Mods);
 };
 
 Error Builder::addModule(Module *M) {
+  SmallPtrSet<GlobalValue *, 8> Used;
   collectUsedGlobalVariables(*M, Used, /*CompilerUsed*/ false);
 
-  storage::Module Mod;
-  Mod.Begin = Msymtab.symbols().size();
+  ModuleSymbolTable Msymtab;
   Msymtab.addModule(M);
-  Mod.End = Msymtab.symbols().size();
+
+  storage::Module Mod;
+  Mod.Begin = Syms.size();
+  Mod.End = Syms.size() + Msymtab.symbols().size();
+  Mod.UncBegin = Uncommons.size();
   Mods.push_back(Mod);
 
   if (TT.isOSBinFormatCOFF()) {
@@ -85,20 +89,25 @@ Error Builder::addModule(Module *M) {
     }
   }
 
+  for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
+    if (Error Err = addSymbol(Msymtab, Used, Msym))
+      return Err;
+
   return Error::success();
 }
 
-Error Builder::addSymbol(ModuleSymbolTable::Symbol Msym) {
+Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
+                         const SmallPtrSet<GlobalValue *, 8> &Used,
+                         ModuleSymbolTable::Symbol Msym) {
   Syms.emplace_back();
   storage::Symbol &Sym = Syms.back();
   Sym = {};
 
-  Sym.UncommonIndex = -1;
   storage::Uncommon *Unc = nullptr;
   auto Uncommon = [&]() -> storage::Uncommon & {
     if (Unc)
       return *Unc;
-    Sym.UncommonIndex = Uncommons.size();
+    Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;
     Uncommons.emplace_back();
     Unc = &Uncommons.back();
     *Unc = {};
@@ -195,15 +204,10 @@ Error Builder::build(ArrayRef<Module *> IRMods) {
   setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());
   TT = Triple(IRMods[0]->getTargetTriple());
 
-  // This adds the symbols for each module to Msymtab.
   for (auto *M : IRMods)
     if (Error Err = addModule(M))
       return Err;
 
-  for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
-    if (Error Err = addSymbol(Msym))
-      return Err;
-
   COFFLinkerOptsOS.flush();
   setStr(Hdr.COFFLinkerOpts, COFFLinkerOpts);