From 7e667c56cf7e27ff521ceb86518beab32bfb630d Mon Sep 17 00:00:00 2001
From: Rafael Espindola <rafael.espindola@gmail.com>
Date: Thu, 31 Oct 2013 20:51:58 +0000
Subject: Use LTO_SYMBOL_SCOPE_DEFAULT_CAN_BE_HIDDEN instead of the "dso list".

There are two ways one could implement hiding of linkonce_odr symbols in LTO:
* LLVM tells the linker which symbols can be hidden if not used from native
  files.
* The linker tells LLVM which symbols are not used from other object files,
  but will be put in the dso symbol table if present.

GOLD's API is the second option. It was implemented almost 1:1 in llvm by
passing the list down to internalize.

LLVM already had partial support for the first option. It is also very similar
to how ld64 handles hiding these symbols when *not* doing LTO.

This patch then
* removes the APIs for the DSO list.
* marks LTO_SYMBOL_SCOPE_DEFAULT_CAN_BE_HIDDEN all linkonce_odr unnamed_addr
  global values and other linkonce_odr whose address is not used.
* makes the gold plugin responsible for handling the API mismatch.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193800 91177308-0d34-0410-b5e6-96231b3b80d8
---
 tools/llvm-lto/llvm-lto.cpp | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

(limited to 'tools/llvm-lto')

diff --git a/tools/llvm-lto/llvm-lto.cpp b/tools/llvm-lto/llvm-lto.cpp
index bce903fa16..0fc68ae3ad 100644
--- a/tools/llvm-lto/llvm-lto.cpp
+++ b/tools/llvm-lto/llvm-lto.cpp
@@ -12,6 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/ADT/StringSet.h"
 #include "llvm/CodeGen/CommandFlags.h"
 #include "llvm/LTO/LTOCodeGenerator.h"
 #include "llvm/LTO/LTOModule.h"
@@ -55,6 +56,12 @@ DSOSymbols("dso-symbol",
   cl::desc("Symbol to put in the symtab in the resulting dso"),
   cl::ZeroOrMore);
 
+namespace {
+struct ModuleInfo {
+  std::vector<bool> CanBeHidden;
+};
+}
+
 int main(int argc, char **argv) {
   // Print a stack trace if we signal out.
   sys::PrintStackTraceOnErrorSignal();
@@ -99,6 +106,12 @@ int main(int argc, char **argv) {
   CodeGen.setDebugInfo(LTO_DEBUG_MODEL_DWARF);
   CodeGen.setTargetOptions(Options);
 
+  llvm::StringSet<llvm::MallocAllocator> DSOSymbolsSet;
+  for (unsigned i = 0; i < DSOSymbols.size(); ++i)
+    DSOSymbolsSet.insert(DSOSymbols[i]);
+
+  std::vector<std::string> KeptDSOSyms;
+
   for (unsigned i = BaseArg; i < InputFilenames.size(); ++i) {
     std::string error;
     OwningPtr<LTOModule> Module(LTOModule::makeLTOModule(InputFilenames[i].c_str(),
@@ -115,6 +128,17 @@ int main(int argc, char **argv) {
              << "': " << error << "\n";
       return 1;
     }
+
+    unsigned NumSyms = Module->getSymbolCount();
+    for (unsigned I = 0; I < NumSyms; ++I) {
+      StringRef Name = Module->getSymbolName(I);
+      if (!DSOSymbolsSet.count(Name))
+        continue;
+      lto_symbol_attributes Attrs = Module->getSymbolAttributes(I);
+      unsigned Scope = Attrs & LTO_SYMBOL_SCOPE_MASK;
+      if (Scope != LTO_SYMBOL_SCOPE_DEFAULT_CAN_BE_HIDDEN)
+        KeptDSOSyms.push_back(Name);
+    }
   }
 
   // Add all the exported symbols to the table of symbols to preserve.
@@ -122,8 +146,8 @@ int main(int argc, char **argv) {
     CodeGen.addMustPreserveSymbol(ExportedSymbols[i].c_str());
 
   // Add all the dso symbols to the table of symbols to expose.
-  for (unsigned i = 0; i < DSOSymbols.size(); ++i)
-    CodeGen.addDSOSymbol(DSOSymbols[i].c_str());
+  for (unsigned i = 0; i < KeptDSOSyms.size(); ++i)
+    CodeGen.addMustPreserveSymbol(KeptDSOSyms[i].c_str());
 
   if (!OutputFilename.empty()) {
     size_t len = 0;
-- 
cgit v1.2.3