1 //===-- GlobalDCE.cpp - DCE unreachable internal functions ----------------===//
3 // This transform is designed to eliminate unreachable internal globals
4 // FIXME: GlobalDCE should update the callgraph, not destroy it!
6 //===----------------------------------------------------------------------===//
8 #include "llvm/Transforms/IPO/GlobalDCE.h"
9 #include "llvm/Analysis/CallGraph.h"
10 #include "llvm/Module.h"
11 #include "llvm/Function.h"
12 #include "Support/DepthFirstIterator.h"
14 static bool RemoveUnreachableFunctions(Module *M, CallGraph &CallGraph) {
15 // Calculate which functions are reachable from the external functions in the
18 std::set<CallGraphNode*> ReachableNodes(df_begin(&CallGraph),
21 // Loop over the functions in the module twice. The first time is used to
22 // drop references that functions have to each other before they are deleted.
23 // The second pass removes the functions that need to be removed.
25 std::vector<CallGraphNode*> FunctionsToDelete; // Track unused functions
26 for (Module::iterator I = M->begin(), E = M->end(); I != E; ++I) {
27 CallGraphNode *N = CallGraph[*I];
28 if (!ReachableNodes.count(N)) { // Not reachable??
29 (*I)->dropAllReferences();
30 N->removeAllCalledMethods();
31 FunctionsToDelete.push_back(N);
35 // Nothing to do if no unreachable functions have been found...
36 if (FunctionsToDelete.empty()) return false;
38 // Unreachables functions have been found and should have no references to
39 // them, delete them now.
41 for (std::vector<CallGraphNode*>::iterator I = FunctionsToDelete.begin(),
42 E = FunctionsToDelete.end(); I != E; ++I)
43 delete CallGraph.removeMethodFromModule(*I);
49 struct GlobalDCE : public Pass {
50 const char *getPassName() const { return "Dead Global Elimination"; }
52 // run - Do the GlobalDCE pass on the specified module, optionally updating
53 // the specified callgraph to reflect the changes.
56 return RemoveUnreachableFunctions(M, getAnalysis<CallGraph>());
59 // getAnalysisUsage - This function works on the call graph of a module.
60 // It is capable of updating the call graph to reflect the new state of the
63 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
64 AU.addRequired(CallGraph::ID);
69 Pass *createGlobalDCEPass() { return new GlobalDCE(); }