llvm-6502/lib/Transforms/IPO/ConstantMerge.cpp
Chris Lattner b12914bfc0 'Pass' should now not be derived from by clients. Instead, they should derive
from ModulePass.  Instead of implementing Pass::run, then should implement
ModulePass::runOnModule.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16436 91177308-0d34-0410-b5e6-96231b3b80d8
2004-09-20 04:48:05 +00:00

98 lines
3.8 KiB
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//===- ConstantMerge.cpp - Merge duplicate global constants ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the interface to a pass that merges duplicate global
// constants together into a single constant that is shared. This is useful
// because some passes (ie TraceValues) insert a lot of string constants into
// the program, regardless of whether or not an existing string is available.
//
// Algorithm: ConstantMerge is designed to build up a map of available constants
// and eliminate duplicates when it is initialized.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/IPO.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
namespace {
Statistic<> NumMerged("constmerge", "Number of global constants merged");
struct ConstantMerge : public ModulePass {
// run - For this pass, process all of the globals in the module,
// eliminating duplicate constants.
//
bool runOnModule(Module &M);
};
RegisterOpt<ConstantMerge> X("constmerge","Merge Duplicate Global Constants");
}
ModulePass *llvm::createConstantMergePass() { return new ConstantMerge(); }
bool ConstantMerge::runOnModule(Module &M) {
std::map<Constant*, GlobalVariable*> CMap;
// Replacements - This vector contains a list of replacements to perform.
std::vector<std::pair<GlobalVariable*, GlobalVariable*> > Replacements;
bool MadeChange = false;
// 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 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();
}
}