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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 method 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/GlobalVariable.h"
// mergeDuplicateConstants - Workhorse for the pass. This eliminates duplicate
// constants, starting at global ConstantNo, and adds vars to the map if they
// are new and unique.
//
static inline
bool mergeDuplicateConstants(Module *M, unsigned &ConstantNo,
map<ConstPoolVal*, GlobalVariable*> &CMap) {
Module::GlobalListType &GList = M->getGlobalList();
if (GList.size() <= ConstantNo) return false; // No new constants
bool MadeChanges = false;
for (; ConstantNo < GList.size(); ++ConstantNo) {
GlobalVariable *GV = GList[ConstantNo];
if (GV->isConstant()) { // Only process constants
assert(GV->hasInitializer() && "Globals constants must have inits!");
ConstPoolVal *Init = GV->getInitializer();
// Check to see if the initializer is already known...
map<ConstPoolVal*, GlobalVariable*>::iterator I = CMap.find(Init);
if (I == CMap.end()) { // Nope, add it to the map
CMap.insert(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);
// Remove and delete the global value from the module...
delete GList.remove(GList.begin()+ConstantNo);
--ConstantNo; // Don't skip the next constant.
MadeChanges = true;
}
}
}
return MadeChanges;
}
// mergeDuplicateConstants - Static accessor for clients that don't want to
// deal with passes.
//
bool ConstantMerge::mergeDuplicateConstants(Module *M) {
map<ConstPoolVal*, GlobalVariable*> Constants;
unsigned LastConstantSeen = 0;
return ::mergeDuplicateConstants(M, LastConstantSeen, Constants);
}
// doPassInitialization - For this pass, process all of the globals in the
// module, eliminating duplicate constants.
//
bool ConstantMerge::doPassInitialization(Module *M) {
return ::mergeDuplicateConstants(M, LastConstantSeen, Constants);
}
// doPerMethodWork - Check to see if any globals have been added to the
// global list for the module. If so, eliminate them.
//
bool DynamicConstantMerge::doPerMethodWork(Method *M) {
return ::mergeDuplicateConstants(M->getParent(), LastConstantSeen, Constants);
}
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