1 //===- ConstantMerge.cpp - Merge duplicate global constants -----------------=//
3 // This file defines the interface to a pass that merges duplicate global
4 // constants together into a single constant that is shared. This is useful
5 // because some passes (ie TraceValues) insert a lot of string constants into
6 // the program, regardless of whether or not they duplicate an existing string.
8 // Algorithm: ConstantMerge is designed to build up a map of available constants
9 // and elminate duplicates when it is initialized.
11 // The DynamicConstantMerge method is a superset of the ConstantMerge algorithm
12 // that checks for each method to see if constants have been added to the
13 // constant pool since it was last run... if so, it processes them.
15 //===----------------------------------------------------------------------===//
17 #include "llvm/Transforms/ConstantMerge.h"
18 #include "llvm/GlobalVariable.h"
20 // mergeDuplicateConstants - Workhorse for the pass. This eliminates duplicate
21 // constants, starting at global ConstantNo, and adds vars to the map if they
22 // are new and unique.
25 bool mergeDuplicateConstants(Module *M, unsigned &ConstantNo,
26 std::map<Constant*, GlobalVariable*> &CMap) {
27 Module::GlobalListType &GList = M->getGlobalList();
28 if (GList.size() <= ConstantNo) return false; // No new constants
29 bool MadeChanges = false;
31 for (; ConstantNo < GList.size(); ++ConstantNo) {
32 GlobalVariable *GV = GList[ConstantNo];
33 if (GV->isConstant()) { // Only process constants
34 assert(GV->hasInitializer() && "Globals constants must have inits!");
35 Constant *Init = GV->getInitializer();
37 // Check to see if the initializer is already known...
38 std::map<Constant*, GlobalVariable*>::iterator I = CMap.find(Init);
40 if (I == CMap.end()) { // Nope, add it to the map
41 CMap.insert(std::make_pair(Init, GV));
42 } else { // Yup, this is a duplicate!
43 // Make all uses of the duplicate constant use the cannonical version...
44 GV->replaceAllUsesWith(I->second);
46 // Remove and delete the global value from the module...
47 delete GList.remove(GList.begin()+ConstantNo);
49 --ConstantNo; // Don't skip the next constant.
58 // mergeDuplicateConstants - Static accessor for clients that don't want to
61 bool ConstantMerge::mergeDuplicateConstants(Module *M) {
62 std::map<Constant*, GlobalVariable*> Constants;
63 unsigned LastConstantSeen = 0;
64 return ::mergeDuplicateConstants(M, LastConstantSeen, Constants);
68 // doInitialization - For this pass, process all of the globals in the
69 // module, eliminating duplicate constants.
71 bool ConstantMerge::doInitialization(Module *M) {
72 return ::mergeDuplicateConstants(M, LastConstantSeen, Constants);
75 // doPerMethodWork - Check to see if any globals have been added to the
76 // global list for the module. If so, eliminate them.
78 bool DynamicConstantMerge::runOnMethod(Method *M) {
79 return ::mergeDuplicateConstants(M->getParent(), LastConstantSeen, Constants);