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"
14 #include "Support/StatisticReporter.h"
16 static Statistic<> NumRemoved("globaldce\t- Number of global values removed");
18 static bool RemoveUnreachableFunctions(Module &M, CallGraph &CallGraph) {
19 // Calculate which functions are reachable from the external functions in the
22 std::set<CallGraphNode*> ReachableNodes(df_begin(&CallGraph),
25 // Loop over the functions in the module twice. The first time is used to
26 // drop references that functions have to each other before they are deleted.
27 // The second pass removes the functions that need to be removed.
29 std::vector<CallGraphNode*> FunctionsToDelete; // Track unused functions
30 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
31 CallGraphNode *N = CallGraph[I];
33 if (!ReachableNodes.count(N)) { // Not reachable??
34 I->dropAllReferences();
35 N->removeAllCalledFunctions();
36 FunctionsToDelete.push_back(N);
41 // Nothing to do if no unreachable functions have been found...
42 if (FunctionsToDelete.empty()) return false;
44 // Unreachables functions have been found and should have no references to
45 // them, delete them now.
47 for (std::vector<CallGraphNode*>::iterator I = FunctionsToDelete.begin(),
48 E = FunctionsToDelete.end(); I != E; ++I)
49 delete CallGraph.removeFunctionFromModule(*I);
54 static bool RemoveUnreachableGlobalVariables(Module &M) {
56 // Eliminate all global variables that are unused, and that are internal, or
57 // do not have an initializer.
59 for (Module::giterator I = M.gbegin(); I != M.gend(); )
60 if (!I->use_empty() || (I->hasExternalLinkage() && I->hasInitializer()))
61 ++I; // Cannot eliminate global variable
63 I = M.getGlobalList().erase(I);
71 struct GlobalDCE : public Pass {
72 const char *getPassName() const { return "Dead Global Elimination"; }
74 // run - Do the GlobalDCE pass on the specified module, optionally updating
75 // the specified callgraph to reflect the changes.
78 return RemoveUnreachableFunctions(M, getAnalysis<CallGraph>()) |
79 RemoveUnreachableGlobalVariables(M);
82 // getAnalysisUsage - This function works on the call graph of a module.
83 // It is capable of updating the call graph to reflect the new state of the
86 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
87 AU.addRequired(CallGraph::ID);
92 Pass *createGlobalDCEPass() { return new GlobalDCE(); }