-//===- ConstantMerge.cpp - Merge duplicate global constants -----------------=//
+//===- ConstantMerge.cpp - Merge duplicate global constants ---------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file 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 they duplicate an existing string.
+// 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 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.
+// and eliminate duplicates when it is initialized.
//
//===----------------------------------------------------------------------===//
-#include "llvm/Transforms/ConstantMerge.h"
-#include "llvm/GlobalVariable.h"
+#define DEBUG_TYPE "constmerge"
+#include "llvm/Transforms/IPO.h"
#include "llvm/Module.h"
-#include "llvm/Function.h"
#include "llvm/Pass.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Support/Compiler.h"
+using namespace llvm;
-// 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,
- std::map<Constant*, 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!");
- 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(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);
-
- // 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;
-}
+STATISTIC(NumMerged, "Number of global constants merged");
namespace {
- // FIXME: ConstantMerge should not be a FunctionPass!!!
- class ConstantMerge : public FunctionPass {
- protected:
- std::map<Constant*, GlobalVariable*> Constants;
- unsigned LastConstantSeen;
- public:
- inline ConstantMerge() : LastConstantSeen(0) {}
-
- // doInitialization - For this pass, process all of the globals in the
- // module, eliminating duplicate constants.
+ struct VISIBILITY_HIDDEN ConstantMerge : public ModulePass {
+ static char ID; // Pass identification, replacement for typeid
+ ConstantMerge() : ModulePass((intptr_t)&ID) {}
+
+ // run - For this pass, process all of the globals in the module,
+ // eliminating duplicate constants.
//
- bool doInitialization(Module *M) {
- return ::mergeDuplicateConstants(M, LastConstantSeen, Constants);
- }
-
- bool runOnFunction(Function *) { return false; }
-
- // doFinalization - Clean up internal state for this module
+ bool runOnModule(Module &M);
+ };
+
+ char ConstantMerge::ID = 0;
+ RegisterPass<ConstantMerge>X("constmerge","Merge Duplicate Global Constants");
+}
+
+ModulePass *llvm::createConstantMergePass() { return new ConstantMerge(); }
+
+bool ConstantMerge::runOnModule(Module &M) {
+ // Map unique constant/section pairs to globals. We don't want to merge
+ // globals in different sections.
+ std::map<std::pair<Constant*, std::string>, 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.
//
- bool doFinalization(Module *M) {
- LastConstantSeen = 0;
- Constants.clear();
- return false;
- }
+ for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
+ GVI != E; ) {
+ GlobalVariable *GV = GVI++;
+
+ // If this GV is dead, remove it.
+ GV->removeDeadConstantUsers();
+ if (GV->use_empty() && GV->hasInternalLinkage()) {
+ GV->eraseFromParent();
+ continue;
+ }
+
+ // Only process constants with initializers.
+ if (GV->isConstant() && GV->hasInitializer()) {
+ Constant *Init = GV->getInitializer();
+
+ // Check to see if the initializer is already known.
+ GlobalVariable *&Slot = CMap[std::make_pair(Init, GV->getSection())];
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.setPreservesAll();
+ if (Slot == 0) { // Nope, add it to the map.
+ Slot = 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, Slot));
+ } else if (GV->hasInternalLinkage()) {
+ // Make all uses of the duplicate constant use the canonical version.
+ Replacements.push_back(std::make_pair(Slot, GV));
+ Slot = GV;
+ }
+ }
}
- };
-
- struct DynamicConstantMerge : public ConstantMerge {
- // runOnFunction - Check to see if any globals have been added to the
- // global list for the module. If so, eliminate them.
- //
- bool runOnFunction(Function *F) {
- return ::mergeDuplicateConstants(F->getParent(), LastConstantSeen,
- Constants);
+
+ 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);
}
- };
-}
-Pass *createConstantMergePass() { return new ConstantMerge(); }
-Pass *createDynamicConstantMergePass() { return new DynamicConstantMerge(); }
+ NumMerged += Replacements.size();
+ Replacements.clear();
+ }
+}
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