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Merging constants can cause further room for improvement. Iterate until
we converge git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10618 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -44,44 +44,54 @@ bool ConstantMerge::run(Module &M) {
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// Replacements - This vector contains a list of replacements to perform.
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std::vector<std::pair<GlobalVariable*, GlobalVariable*> > Replacements;
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// First pass: identify all globals that can be merged together, filling in
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// the Replacements vector. We cannot do the replacement in this pass because
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// doing so may cause initializers of other globals to be rewritten,
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// invalidating the Constant* pointers in CMap.
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//
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for (Module::giterator GV = M.gbegin(), E = M.gend(); GV != E; ++GV)
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// Only process constants with initializers
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if (GV->isConstant() && GV->hasInitializer()) {
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Constant *Init = GV->getInitializer();
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bool MadeChange = false;
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// Check to see if the initializer is already known...
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std::map<Constant*, GlobalVariable*>::iterator I = CMap.find(Init);
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if (I == CMap.end()) { // Nope, add it to the map
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CMap.insert(I, std::make_pair(Init, GV));
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} else if (GV->hasInternalLinkage()) { // Yup, this is a duplicate!
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// Make all uses of the duplicate constant use the canonical version...
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Replacements.push_back(std::make_pair(GV, I->second));
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} else if (I->second->hasInternalLinkage()) {
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// Make all uses of the duplicate constant use the canonical version...
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Replacements.push_back(std::make_pair(I->second, GV));
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I->second = GV;
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// Iterate constant merging while we are still making progress. Merging two
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// constants together may allow us to merge other constants together if the
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// second level constants have initializers which point to the globals that
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// were just merged.
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while (1) {
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// First pass: identify all globals that can be merged together, filling in
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// the Replacements vector. We cannot do the replacement in this pass
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// because doing so may cause initializers of other globals to be rewritten,
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// invalidating the Constant* pointers in CMap.
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//
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for (Module::giterator GV = M.gbegin(), E = M.gend(); GV != E; ++GV)
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// Only process constants with initializers
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if (GV->isConstant() && GV->hasInitializer()) {
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Constant *Init = GV->getInitializer();
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// Check to see if the initializer is already known...
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std::map<Constant*, GlobalVariable*>::iterator I = CMap.find(Init);
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if (I == CMap.end()) { // Nope, add it to the map
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CMap.insert(I, std::make_pair(Init, GV));
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} else if (GV->hasInternalLinkage()) { // Yup, this is a duplicate!
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// Make all uses of the duplicate constant use the canonical version.
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Replacements.push_back(std::make_pair(GV, I->second));
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} else if (I->second->hasInternalLinkage()) {
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// Make all uses of the duplicate constant use the canonical version.
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Replacements.push_back(std::make_pair(I->second, GV));
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I->second = GV;
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}
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}
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}
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if (Replacements.empty()) return false;
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CMap.clear();
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// Now that we have figured out which replacements must be made, do them all
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// now. This avoid invalidating the pointers in CMap, which are unneeded now.
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for (unsigned i = 0, e = Replacements.size(); i != e; ++i) {
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// Eliminate any uses of the dead global...
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Replacements[i].first->replaceAllUsesWith(Replacements[i].second);
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// Delete the global value from the module...
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M.getGlobalList().erase(Replacements[i].first);
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if (Replacements.empty())
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return MadeChange;
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CMap.clear();
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// Now that we have figured out which replacements must be made, do them all
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// now. This avoid invalidating the pointers in CMap, which are unneeded
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// now.
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for (unsigned i = 0, e = Replacements.size(); i != e; ++i) {
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// Eliminate any uses of the dead global...
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Replacements[i].first->replaceAllUsesWith(Replacements[i].second);
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// Delete the global value from the module...
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M.getGlobalList().erase(Replacements[i].first);
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}
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NumMerged += Replacements.size();
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Replacements.clear();
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}
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NumMerged += Replacements.size();
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return true;
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}
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