1 files changed, 101 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/IPO/StripSymbols.cpp b/llvm/lib/Transforms/IPO/StripSymbols.cpp
index 08ad4de429a..12e8db8b4a5 100644
--- a/llvm/lib/Transforms/IPO/StripSymbols.cpp
+++ b/llvm/lib/Transforms/IPO/StripSymbols.cpp
@@ -73,6 +73,19 @@ namespace {
       AU.setPreservesAll();
     }
   };
+
+  class StripDeadDebugInfo : public ModulePass {
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    explicit StripDeadDebugInfo()
+      : ModulePass(&ID) {}
+
+    virtual bool runOnModule(Module &M);
+
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.setPreservesAll();
+    }
+  };
 }
 
 char StripSymbols::ID = 0;
@@ -99,6 +112,14 @@ ModulePass *llvm::createStripDebugDeclarePass() {
   return new StripDebugDeclare();
 }
 
+char StripDeadDebugInfo::ID = 0;
+static RegisterPass<StripDeadDebugInfo>
+A("strip-dead-debug-info", "Strip debug info for unused symbols");
+
+ModulePass *llvm::createStripDeadDebugInfoPass() {
+  return new StripDeadDebugInfo();
+}
+
 /// OnlyUsedBy - Return true if V is only used by Usr.
 static bool OnlyUsedBy(Value *V, Value *Usr) {
   for(Value::use_iterator I = V->use_begin(), E = V->use_end(); I != E; ++I) {
@@ -295,3 +316,83 @@ bool StripDebugDeclare::runOnModule(Module &M) {
 
   return true;
 }
+
+/// getRealLinkageName - If special LLVM prefix that is used to inform the asm 
+/// printer to not emit usual symbol prefix before the symbol name is used then
+/// return linkage name after skipping this special LLVM prefix.
+static StringRef getRealLinkageName(StringRef LinkageName) {
+  char One = '\1';
+  if (LinkageName.startswith(StringRef(&One, 1)))
+    return LinkageName.substr(1);
+  return LinkageName;
+}
+
+bool StripDeadDebugInfo::runOnModule(Module &M) {
+  bool Changed = false;
+
+  // Debugging infomration is encoded in llvm IR using metadata. This is designed
+  // such a way that debug info for symbols preserved even if symbols are
+  // optimized away by the optimizer. This special pass removes debug info for 
+  // such symbols.
+
+  // llvm.dbg.gv keeps track of debug info for global variables.
+  if (NamedMDNode *NMD = M.getNamedMetadata("llvm.dbg.gv")) {
+    SmallVector<MDNode *, 8> MDs;
+    for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
+      if (DIGlobalVariable(NMD->getOperand(i)).Verify())
+        MDs.push_back(NMD->getOperand(i));
+      else
+        Changed = true;
+    NMD->eraseFromParent();
+    NMD = NULL;
+
+    for (SmallVector<MDNode *, 8>::iterator I = MDs.begin(),
+           E = MDs.end(); I != E; ++I) {
+      if (M.getGlobalVariable(DIGlobalVariable(*I).getGlobal()->getName(), 
+                              true)) {
+        if (!NMD)
+          NMD = M.getOrInsertNamedMetadata("llvm.dbg.gv");
+        NMD->addOperand(*I);
+      }
+      else
+        Changed = true;
+    }
+  }
+
+  // llvm.dbg.sp keeps track of debug info for subprograms.
+  if (NamedMDNode *NMD = M.getNamedMetadata("llvm.dbg.sp")) {
+    SmallVector<MDNode *, 8> MDs;
+    for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
+      if (DISubprogram(NMD->getOperand(i)).Verify())
+        MDs.push_back(NMD->getOperand(i));
+      else
+        Changed = true;
+    NMD->eraseFromParent();
+    NMD = NULL;
+
+    for (SmallVector<MDNode *, 8>::iterator I = MDs.begin(),
+           E = MDs.end(); I != E; ++I) {
+      bool FnIsLive = false;
+      if (Function *F = DISubprogram(*I).getFunction())
+        if (M.getFunction(F->getName()))
+          FnIsLive = true;
+      if (FnIsLive) {
+          if (!NMD)
+            NMD = M.getOrInsertNamedMetadata("llvm.dbg.sp");
+          NMD->addOperand(*I);
+      } else {
+        // Remove llvm.dbg.lv.fnname named mdnode which may have been used
+        // to hold debug info for dead function's local variables.
+        StringRef FName = DISubprogram(*I).getLinkageName();
+        if (FName.empty())
+          FName = DISubprogram(*I).getName();
+        if (NamedMDNode *LVNMD = 
+            M.getNamedMetadata(Twine("llvm.dbg.lv.", 
+                                     getRealLinkageName(FName)))) 
+          LVNMD->eraseFromParent();
+      }
+    }
+  }
+
+  return Changed;
+}