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70 lines
2.4 KiB
C++
70 lines
2.4 KiB
C++
//===- ConstantMerge.cpp - Merge duplicate global constants ---------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the interface to a pass that merges duplicate global
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// constants together into a single constant that is shared. This is useful
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// because some passes (ie TraceValues) insert a lot of string constants into
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// the program, regardless of whether or not an existing string is available.
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//
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// Algorithm: ConstantMerge is designed to build up a map of available constants
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// and eliminate duplicates when it is initialized.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/IPO.h"
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#include "llvm/Module.h"
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#include "llvm/Pass.h"
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#include "Support/Statistic.h"
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namespace {
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Statistic<> NumMerged("constmerge", "Number of global constants merged");
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struct ConstantMerge : public Pass {
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// run - For this pass, process all of the globals in the module,
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// eliminating duplicate constants.
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//
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bool run(Module &M);
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};
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RegisterOpt<ConstantMerge> X("constmerge","Merge Duplicate Global Constants");
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}
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Pass *createConstantMergePass() { return new ConstantMerge(); }
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bool ConstantMerge::run(Module &M) {
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std::map<Constant*, GlobalVariable*> CMap;
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bool MadeChanges = false;
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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 { // Yup, this is a duplicate!
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// Make all uses of the duplicate constant use the canonical version...
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GV->replaceAllUsesWith(I->second);
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// Delete the global value from the module... and back up iterator to
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// not skip the next global...
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GV = --M.getGlobalList().erase(GV);
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++NumMerged;
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MadeChanges = true;
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}
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}
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return MadeChanges;
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}
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