1 //===-- GlobalDCE.cpp - DCE unreachable internal functions ----------------===//
3 // This transform is designed to eliminate unreachable internal globals
5 //===----------------------------------------------------------------------===//
7 #include "llvm/Transforms/IPO/GlobalDCE.h"
8 #include "llvm/Analysis/CallGraph.h"
9 #include "llvm/Module.h"
10 #include "llvm/Function.h"
11 #include "llvm/Pass.h"
12 #include "Support/DepthFirstIterator.h"
15 static bool RemoveUnreachableFunctions(Module *M, CallGraph &CallGraph) {
16 // Calculate which functions are reachable from the external functions in the
19 std::set<CallGraphNode*> ReachableNodes(df_begin(&CallGraph),
22 // Loop over the functions in the module twice. The first time is used to
23 // drop references that functions have to each other before they are deleted.
24 // The second pass removes the functions that need to be removed.
26 std::vector<CallGraphNode*> FunctionsToDelete; // Track unused functions
27 for (Module::iterator I = M->begin(), E = M->end(); I != E; ++I) {
28 CallGraphNode *N = CallGraph[*I];
29 if (!ReachableNodes.count(N)) { // Not reachable??
30 (*I)->dropAllReferences();
31 N->removeAllCalledMethods();
32 FunctionsToDelete.push_back(N);
36 // Nothing to do if no unreachable functions have been found...
37 if (FunctionsToDelete.empty()) return false;
39 // Unreachables functions have been found and should have no references to
40 // them, delete them now.
42 for (std::vector<CallGraphNode*>::iterator I = FunctionsToDelete.begin(),
43 E = FunctionsToDelete.end(); I != E; ++I)
44 delete CallGraph.removeMethodFromModule(*I);
50 struct GlobalDCE : public Pass {
51 // run - Do the GlobalDCE pass on the specified module, optionally updating
52 // the specified callgraph to reflect the changes.
55 return RemoveUnreachableFunctions(M, getAnalysis<CallGraph>());
58 // getAnalysisUsageInfo - This function works on the call graph of a module.
59 // It is capable of updating the call graph to reflect the new state of the
62 virtual void getAnalysisUsageInfo(Pass::AnalysisSet &Required,
63 Pass::AnalysisSet &Destroyed,
64 Pass::AnalysisSet &Provided) {
65 Required.push_back(CallGraph::ID);
66 // FIXME: This should update the callgraph, not destroy it!
67 Destroyed.push_back(CallGraph::ID);
72 Pass *createGlobalDCEPass() { return new GlobalDCE(); }