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 function 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/IPO.h"
18 #include "llvm/Module.h"
19 #include "llvm/Pass.h"
20 #include "Support/StatisticReporter.h"
23 struct ConstantMerge : public Pass {
24 // run - For this pass, process all of the globals in the module,
25 // eliminating duplicate constants.
29 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
34 Statistic<> NumMerged("constmerge\t\t- Number of global constants merged");
35 RegisterPass<ConstantMerge> X("constmerge", "Merge Duplicate Global Constants");
38 Pass *createConstantMergePass() { return new ConstantMerge(); }
41 // ConstantMerge::run - Workhorse for the pass. This eliminates duplicate
42 // constants, starting at global ConstantNo, and adds vars to the map if they
43 // are new and unique.
45 bool ConstantMerge::run(Module &M) {
46 std::map<Constant*, GlobalVariable*> CMap;
47 bool MadeChanges = false;
49 for (Module::giterator GV = M.gbegin(), E = M.gend(); GV != E; ++GV)
50 if (GV->isConstant()) { // Only process constants
51 assert(GV->hasInitializer() && "Globals constants must have inits!");
52 Constant *Init = GV->getInitializer();
54 // Check to see if the initializer is already known...
55 std::map<Constant*, GlobalVariable*>::iterator I = CMap.find(Init);
57 if (I == CMap.end()) { // Nope, add it to the map
58 CMap.insert(I, std::make_pair(Init, GV));
59 } else { // Yup, this is a duplicate!
60 // Make all uses of the duplicate constant use the cannonical version...
61 GV->replaceAllUsesWith(I->second);
63 // Delete the global value from the module... and back up iterator to
64 // not skip the next global...
65 GV = --M.getGlobalList().erase(GV);