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Merging constants can cause further room for improvement. Iterate until

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we converge


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10618 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2003-12-28 07:19:08 +00:00
parent 6cdc42b3d1
commit 0898c78a52
1 changed files with 46 additions and 36 deletions
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82
lib/Transforms/IPO/ConstantMerge.cpp
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@ -44,44 +44,54 @@ bool ConstantMerge::run(Module &M) {
// Replacements - This vector contains a list of replacements to perform.
std::vector<std::pair<GlobalVariable*, GlobalVariable*> > Replacements;
// First pass: identify all globals that can be merged together, filling in
// the Replacements vector. We cannot do the replacement in this pass because
// doing so may cause initializers of other globals to be rewritten,
// invalidating the Constant* pointers in CMap.
//
for (Module::giterator GV = M.gbegin(), E = M.gend(); GV != E; ++GV)
// Only process constants with initializers
if (GV->isConstant() && GV->hasInitializer()) {
Constant *Init = GV->getInitializer();
bool MadeChange = false;
// Check to see if the initializer is already known...
std::map<Constant*, GlobalVariable*>::iterator I = CMap.find(Init);
if (I == CMap.end()) { // Nope, add it to the map
CMap.insert(I, std::make_pair(Init, GV));
} else if (GV->hasInternalLinkage()) { // Yup, this is a duplicate!
// Make all uses of the duplicate constant use the canonical version...
Replacements.push_back(std::make_pair(GV, I->second));
} else if (I->second->hasInternalLinkage()) {
// Make all uses of the duplicate constant use the canonical version...
Replacements.push_back(std::make_pair(I->second, GV));
I->second = GV;
// Iterate constant merging while we are still making progress. Merging two
// constants together may allow us to merge other constants together if the
// second level constants have initializers which point to the globals that
// were just merged.
while (1) {
// First pass: identify all globals that can be merged together, filling in
// the Replacements vector. We cannot do the replacement in this pass
// because doing so may cause initializers of other globals to be rewritten,
// invalidating the Constant* pointers in CMap.
//
for (Module::giterator GV = M.gbegin(), E = M.gend(); GV != E; ++GV)
// Only process constants with initializers
if (GV->isConstant() && GV->hasInitializer()) {
Constant *Init = GV->getInitializer();
// Check to see if the initializer is already known...
std::map<Constant*, GlobalVariable*>::iterator I = CMap.find(Init);
if (I == CMap.end()) { // Nope, add it to the map
CMap.insert(I, std::make_pair(Init, GV));
} else if (GV->hasInternalLinkage()) { // Yup, this is a duplicate!
// Make all uses of the duplicate constant use the canonical version.
Replacements.push_back(std::make_pair(GV, I->second));
} else if (I->second->hasInternalLinkage()) {
// Make all uses of the duplicate constant use the canonical version.
Replacements.push_back(std::make_pair(I->second, GV));
I->second = GV;
}
}
}
if (Replacements.empty()) return false;
CMap.clear();
// Now that we have figured out which replacements must be made, do them all
// now. This avoid invalidating the pointers in CMap, which are unneeded now.
for (unsigned i = 0, e = Replacements.size(); i != e; ++i) {
// Eliminate any uses of the dead global...
Replacements[i].first->replaceAllUsesWith(Replacements[i].second);
// Delete the global value from the module...
M.getGlobalList().erase(Replacements[i].first);
if (Replacements.empty())
return MadeChange;
CMap.clear();
// Now that we have figured out which replacements must be made, do them all
// now. This avoid invalidating the pointers in CMap, which are unneeded
// now.
for (unsigned i = 0, e = Replacements.size(); i != e; ++i) {
// Eliminate any uses of the dead global...
Replacements[i].first->replaceAllUsesWith(Replacements[i].second);
// Delete the global value from the module...
M.getGlobalList().erase(Replacements[i].first);
}
NumMerged += Replacements.size();
Replacements.clear();
}
NumMerged += Replacements.size();
return true;
}