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//===- ConstantMerge.cpp - Merge duplicate global constants -----------------=//
//
// 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 they duplicate an existing string.
//
// Algorithm: ConstantMerge is designed to build up a map of available constants
// and elminate duplicates when it is initialized.
//
// The DynamicConstantMerge method is a superset of the ConstantMerge algorithm
// that checks for each function to see if constants have been added to the
// constant pool since it was last run... if so, it processes them.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/ConstantMerge.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "Support/StatisticReporter.h"
static Statistic<> NumMerged("constmerge\t\t- Number of global constants merged");
namespace {
struct ConstantMerge : public Pass {
const char *getPassName() const {return "Merge Duplicate Global Constants";}
// run - For this pass, process all of the globals in the module,
// eliminating duplicate constants.
//
bool run(Module &M);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.preservesCFG();
}
};
}
Pass *createConstantMergePass() { return new ConstantMerge(); }
// ConstantMerge::run - Workhorse for the pass. This eliminates duplicate
// constants, starting at global ConstantNo, and adds vars to the map if they
// are new and unique.
//
bool ConstantMerge::run(Module &M) {
std::map<Constant*, GlobalVariable*> CMap;
bool MadeChanges = false;
for (Module::giterator GV = M.gbegin(), E = M.gend(); GV != E; ++GV)
if (GV->isConstant()) { // Only process constants
assert(GV->hasInitializer() && "Globals constants must have inits!");
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 { // Yup, this is a duplicate!
// Make all uses of the duplicate constant use the cannonical version...
GV->replaceAllUsesWith(I->second);
// Delete the global value from the module... and back up iterator to
// not skip the next global...
GV = --M.getGlobalList().erase(GV);
++NumMerged;
MadeChanges = true;
}
}
return MadeChanges;
}
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