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 "llvm/Pass.h"
13 #include "Support/DepthFirstIterator.h"
16 static bool RemoveUnreachableFunctions(Module *M, CallGraph &CallGraph) {
17 // Calculate which functions are reachable from the external functions in the
20 std::set<CallGraphNode*> ReachableNodes(df_begin(&CallGraph),
23 // Loop over the functions in the module twice. The first time is used to
24 // drop references that functions have to each other before they are deleted.
25 // The second pass removes the functions that need to be removed.
27 std::vector<CallGraphNode*> FunctionsToDelete; // Track unused functions
28 for (Module::iterator I = M->begin(), E = M->end(); I != E; ++I) {
29 CallGraphNode *N = CallGraph[*I];
30 if (!ReachableNodes.count(N)) { // Not reachable??
31 (*I)->dropAllReferences();
32 N->removeAllCalledMethods();
33 FunctionsToDelete.push_back(N);
37 // Nothing to do if no unreachable functions have been found...
38 if (FunctionsToDelete.empty()) return false;
40 // Unreachables functions have been found and should have no references to
41 // them, delete them now.
43 for (std::vector<CallGraphNode*>::iterator I = FunctionsToDelete.begin(),
44 E = FunctionsToDelete.end(); I != E; ++I)
45 delete CallGraph.removeMethodFromModule(*I);
51 struct GlobalDCE : public Pass {
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(); }