Optimize linkonce_odr unnamed_addr functions during LTO.

Generalize the API so we can distinguish symbols that are needed just for a DSO
symbol table from those that are used from some native .o.

The symbols that are only wanted for the dso symbol table can be dropped if
llvm can prove every other dso has a copy (linkonce_odr) and the address is not
important (unnamed_addr).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191922 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 29 insertions, 3 deletions

diff --git a/include/llvm/LTO/LTOCodeGenerator.h b/include/llvm/LTO/LTOCodeGenerator.h
index 97a5066..9f50770 100644
--- a/include/llvm/LTO/LTOCodeGenerator.h
+++ b/include/llvm/LTO/LTOCodeGenerator.h
@@ -73,6 +73,10 @@ struct LTOCodeGenerator {
 
   void addMustPreserveSymbol(const char *sym) { MustPreserveSymbols[sym] = 1; }
 
+  void addDSOSymbol(const char* Sym) {
+    DSOSymbols[Sym] = 1;
+  }
+
   // To pass options to the driver and optimization passes. These options are
   // not necessarily for debugging purpose (The function name is misleading).
   // This function should be called before LTOCodeGenerator::compilexxx(),
@@ -126,6 +130,7 @@ private:
   void applyScopeRestrictions();
   void applyRestriction(llvm::GlobalValue &GV,
                         std::vector<const char*> &MustPreserveList,
+                        std::vector<const char*> &SymtabList,
                         llvm::SmallPtrSet<llvm::GlobalValue*, 8> &AsmUsed,
                         llvm::Mangler &Mangler);
   bool determineTarget(std::string &errMsg);
@@ -138,6 +143,7 @@ private:
   bool EmitDwarfDebugInfo;
   bool ScopeRestrictionsDone;
   lto_codegen_model CodeModel;
+  StringSet DSOSymbols;
   StringSet MustPreserveSymbols;
   StringSet AsmUndefinedRefs;
   llvm::MemoryBuffer *NativeObjectFile;
diff --git a/include/llvm/Transforms/IPO.h b/include/llvm/Transforms/IPO.h
index 6ebb6c4..ed28230 100644
--- a/include/llvm/Transforms/IPO.h
+++ b/include/llvm/Transforms/IPO.h
@@ -104,12 +104,32 @@ Pass *createPruneEHPass();
 
 //===----------------------------------------------------------------------===//
 /// createInternalizePass - This pass loops over all of the functions in the
-/// input module, internalizing all globals (functions and variables) not in the
-/// given exportList.
+/// input module, internalizing all globals (functions and variables) it can.
+////
+/// The symbols in \p ExportList are never internalized.
+///
+/// The symbol in DSOList are internalized if it is safe to drop them from
+/// the symbol table.
+///
+/// For example of the difference, consider a dynamic library being built from
+/// two translation units. The first one compiled to a native object
+/// (ELF/MachO/COFF) and second one compiled to IL. Translation unit A has a
+/// copy of linkonce_odr unnamed_addr function F. The translation unit B has a
+/// copy of the linkonce_odr unnamed_addr functions F and G.
+///
+/// Assume the linker decides to keep the copy of F in B. This means that LLVM
+/// must produce F in the object file it passes to the linker, otherwise we
+/// will have an undefined reference. For G the situation is different. The
+/// linker puts the function in the DSOList, since it is only wanted for the
+/// symbol table. With this information internalize can now reason that since
+/// the function is a linkonce_odr and its address is not important, it can be
+/// omitted. Any other shared library needing this function will have a copy of
+/// it.
 ///
 /// Note that commandline options that are used with the above function are not
 /// used now!
-ModulePass *createInternalizePass(ArrayRef<const char *> ExportList);
+ModulePass *createInternalizePass(ArrayRef<const char *> ExportList,
+                                  ArrayRef<const char *> DSOList);
 /// createInternalizePass - Same as above, but with an empty exportList.
 ModulePass *createInternalizePass();