[gold] Fix common symbols handling.

LLVM Gold plugin decides which instance of a common symbol it wants
based on the symbol size in claim_file_hook. If the file that
contains the chosen instance is later dropped from the link, we end
up with an undefined reference.

This change delays this decision until the set of the included files
is known.

llvm-svn: 263180

1 files changed, 40 insertions, 20 deletions

diff --git a/llvm/tools/gold/gold-plugin.cpp b/llvm/tools/gold/gold-plugin.cpp
index 678e6e6707d..f9ff66a97bf 100644
--- a/llvm/tools/gold/gold-plugin.cpp
+++ b/llvm/tools/gold/gold-plugin.cpp
@@ -101,14 +101,13 @@ struct PluginInputFile {
 };
 
 struct ResolutionInfo {
+  uint64_t CommonSize = 0;
+  unsigned CommonAlign = 0;
   bool IsLinkonceOdr = true;
   bool UnnamedAddr = true;
   GlobalValue::VisibilityTypes Visibility = GlobalValue::DefaultVisibility;
   bool CommonInternal = false;
   bool UseCommon = false;
-  unsigned CommonSize = 0;
-  unsigned CommonAlign = 0;
-  claimed_file *CommonFile = nullptr;
 };
 
 /// Class to own information used by a task or during its cleanup for a
@@ -515,15 +514,6 @@ static ld_plugin_status claim_file_hook(const ld_plugin_input_file *file,
     if (GV) {
       Res.UnnamedAddr &= GV->hasUnnamedAddr();
       Res.IsLinkonceOdr &= GV->hasLinkOnceLinkage();
-      if (GV->hasCommonLinkage()) {
-        Res.CommonAlign = std::max(Res.CommonAlign, GV->getAlignment());
-        const DataLayout &DL = GV->getParent()->getDataLayout();
-        uint64_t Size = DL.getTypeAllocSize(GV->getType()->getElementType());
-        if (Size >= Res.CommonSize) {
-          Res.CommonSize = Size;
-          Res.CommonFile = &cf;
-        }
-      }
       Res.Visibility = getMinVisibility(Res.Visibility, GV->getVisibility());
       switch (GV->getVisibility()) {
       case GlobalValue::DefaultVisibility:
@@ -637,6 +627,8 @@ static const void *getSymbolsAndView(claimed_file &F) {
 static std::unique_ptr<FunctionInfoIndex>
 getFunctionIndexForFile(claimed_file &F, ld_plugin_input_file &Info) {
   const void *View = getSymbolsAndView(F);
+  if (!View)
+    return nullptr;
 
   MemoryBufferRef BufferRef(StringRef((const char *)View, Info.filesize),
                             Info.name);
@@ -663,7 +655,8 @@ static std::unique_ptr<Module>
 getModuleForFile(LLVMContext &Context, claimed_file &F, const void *View,
                  ld_plugin_input_file &Info, raw_fd_ostream *ApiFile,
                  StringSet<> &Internalize, StringSet<> &Maybe,
-                 std::vector<GlobalValue *> &Keep) {
+                 std::vector<GlobalValue *> &Keep,
+                 StringMap<unsigned> &Realign) {
   MemoryBufferRef BufferRef(StringRef((const char *)View, Info.filesize),
                             Info.name);
   ErrorOr<std::unique_ptr<object::IRObjectFile>> ObjOrErr =
@@ -725,7 +718,6 @@ getModuleForFile(LLVMContext &Context, claimed_file &F, const void *View,
     // Override gold's resolution for common symbols. We want the largest
     // one to win.
     if (GV->hasCommonLinkage()) {
-      cast<GlobalVariable>(GV)->setAlignment(Res.CommonAlign);
       if (Resolution == LDPR_PREVAILING_DEF_IRONLY)
         Res.CommonInternal = true;
 
@@ -733,14 +725,29 @@ getModuleForFile(LLVMContext &Context, claimed_file &F, const void *View,
           Resolution == LDPR_PREVAILING_DEF)
         Res.UseCommon = true;
 
-      if (Res.CommonFile == &F && Res.UseCommon) {
+      const DataLayout &DL = GV->getParent()->getDataLayout();
+      uint64_t Size = DL.getTypeAllocSize(GV->getType()->getElementType());
+      unsigned Align = GV->getAlignment();
+
+      if (Res.UseCommon && Size >= Res.CommonSize) {
+        // Take GV.
         if (Res.CommonInternal)
           Resolution = LDPR_PREVAILING_DEF_IRONLY;
         else
           Resolution = LDPR_PREVAILING_DEF;
+        cast<GlobalVariable>(GV)->setAlignment(
+            std::max(Res.CommonAlign, Align));
       } else {
+        // Do not take GV, it's smaller than what we already have in the
+        // combined module.
         Resolution = LDPR_PREEMPTED_IR;
+        if (Align > Res.CommonAlign)
+          // Need to raise the alignment though.
+          Realign[Sym.name] = Align;
       }
+
+      Res.CommonSize = std::max(Res.CommonSize, Size);
+      Res.CommonAlign = std::max(Res.CommonAlign, Align);
     }
 
     switch (Resolution) {
@@ -1058,8 +1065,9 @@ static bool linkInModule(LLVMContext &Context, IRMover &L, claimed_file &F,
                          raw_fd_ostream *ApiFile, StringSet<> &Internalize,
                          StringSet<> &Maybe) {
   std::vector<GlobalValue *> Keep;
-  std::unique_ptr<Module> M = getModuleForFile(Context, F, View, File, ApiFile,
-                                               Internalize, Maybe, Keep);
+  StringMap<unsigned> Realign;
+  std::unique_ptr<Module> M = getModuleForFile(
+      Context, F, View, File, ApiFile, Internalize, Maybe, Keep, Realign);
   if (!M.get())
     return false;
   if (!options::triple.empty())
@@ -1068,9 +1076,17 @@ static bool linkInModule(LLVMContext &Context, IRMover &L, claimed_file &F,
     M->setTargetTriple(DefaultTriple);
   }
 
-  if (L.move(std::move(M), Keep, [](GlobalValue &, IRMover::ValueAdder) {}))
-    return true;
-  return false;
+  if (!L.move(std::move(M), Keep, [](GlobalValue &, IRMover::ValueAdder) {}))
+    return false;
+
+  for (const auto &I : Realign) {
+    GlobalValue *Dst = L.getModule().getNamedValue(I.first());
+    if (!Dst)
+      continue;
+    cast<GlobalVariable>(Dst)->setAlignment(I.second);
+  }
+
+  return true;
 }
 
 /// Perform the ThinLTO backend on a single module, invoking the LTO and codegen
@@ -1116,6 +1132,8 @@ static void thinLTOBackends(raw_fd_ostream *ApiFile,
       // safe by default.
       PluginInputFile InputFile(F.handle);
       const void *View = getSymbolsAndView(F);
+      if (!View)
+        continue;
 
       SmallString<128> Filename;
       if (!options::obj_path.empty())
@@ -1211,6 +1229,8 @@ static ld_plugin_status allSymbolsReadHook(raw_fd_ostream *ApiFile) {
   for (claimed_file &F : Modules) {
     PluginInputFile InputFile(F.handle);
     const void *View = getSymbolsAndView(F);
+    if (!View)
+      continue;
     if (linkInModule(Context, L, F, View, InputFile.file(), ApiFile,
                      Internalize, Maybe))
       message(LDPL_FATAL, "Failed to link module");