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/Module.h"
10 #include "llvm/Function.h"
11 #include "llvm/GlobalVariable.h"
12 #include "llvm/Analysis/CallGraph.h"
13 #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);
49 static bool RemoveUnreachableGlobalVariables(Module *M) {
51 // Eliminate all global variables that are unused, and that are internal, or
52 // do not have an initializer.
54 for (Module::giterator I = M->gbegin(); I != M->gend(); )
55 if (!(*I)->use_empty() ||
56 ((*I)->hasExternalLinkage() && (*I)->hasInitializer()))
57 ++I; // Cannot eliminate global variable
59 delete M->getGlobalList().remove(I);
66 struct GlobalDCE : public Pass {
67 const char *getPassName() const { return "Dead Global Elimination"; }
69 // run - Do the GlobalDCE pass on the specified module, optionally updating
70 // the specified callgraph to reflect the changes.
73 return RemoveUnreachableFunctions(M, getAnalysis<CallGraph>()) |
74 RemoveUnreachableGlobalVariables(M);
77 // getAnalysisUsage - This function works on the call graph of a module.
78 // It is capable of updating the call graph to reflect the new state of the
81 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
82 AU.addRequired(CallGraph::ID);
87 Pass *createGlobalDCEPass() { return new GlobalDCE(); }