+
+/// 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) {
+ GlobalVariable *GV = DIGlobalVariable(*I).getGlobal();
+ if (GV && M.getGlobalVariable(GV->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;
+}