-//===- 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 method 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/DerivedTypes.h"
+#include "llvm/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/Statistic.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();
+STATISTIC(NumMerged, "Number of global constants merged");
- // Check to see if the initializer is already known...
- std::map<Constant*, GlobalVariable*>::iterator I = CMap.find(Init);
+namespace {
+ struct ConstantMerge : public ModulePass {
+ static char ID; // Pass identification, replacement for typeid
+ ConstantMerge() : ModulePass(ID) {}
- 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);
+ // run - For this pass, process all of the globals in the module,
+ // eliminating duplicate constants.
+ //
+ bool runOnModule(Module &M);
+ };
+}
+
+char ConstantMerge::ID = 0;
+INITIALIZE_PASS(ConstantMerge, "constmerge",
+ "Merge Duplicate Global Constants", false, false);
+
+ModulePass *llvm::createConstantMergePass() { return new ConstantMerge(); }
- // Remove and delete the global value from the module...
- delete GList.remove(GList.begin()+ConstantNo);
+bool ConstantMerge::runOnModule(Module &M) {
+ // Map unique constant/section pairs to globals. We don't want to merge
+ // globals in different sections.
+ DenseMap<Constant*, GlobalVariable*> CMap;
- --ConstantNo; // Don't skip the next constant.
- MadeChanges = true;
+ // Replacements - This vector contains a list of replacements to perform.
+ SmallVector<std::pair<GlobalVariable*, GlobalVariable*>, 32> 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::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->hasLocalLinkage()) {
+ GV->eraseFromParent();
+ continue;
}
- }
- }
- return MadeChanges;
-}
+
+ // Only process constants with initializers in the default addres space.
+ if (!GV->isConstant() ||!GV->hasDefinitiveInitializer() ||
+ GV->getType()->getAddressSpace() != 0 || !GV->getSection().empty())
+ continue;
+
+ Constant *Init = GV->getInitializer();
+ // Check to see if the initializer is already known.
+ GlobalVariable *&Slot = CMap[Init];
-// mergeDuplicateConstants - Static accessor for clients that don't want to
-// deal with passes.
-//
-bool ConstantMerge::mergeDuplicateConstants(Module *M) {
- std::map<Constant*, GlobalVariable*> Constants;
- unsigned LastConstantSeen = 0;
- return ::mergeDuplicateConstants(M, LastConstantSeen, Constants);
-}
+ if (Slot == 0) { // Nope, add it to the map.
+ Slot = GV;
+ } else if (GV->hasLocalLinkage()) { // Yup, this is a duplicate!
+ // Make all uses of the duplicate constant use the canonical version.
+ Replacements.push_back(std::make_pair(GV, Slot));
+ }
+ }
+ if (Replacements.empty())
+ return MadeChange;
+ CMap.clear();
-// doInitialization - For this pass, process all of the globals in the
-// module, eliminating duplicate constants.
-//
-bool ConstantMerge::doInitialization(Module *M) {
- return ::mergeDuplicateConstants(M, LastConstantSeen, Constants);
-}
+ // 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);
-// doPerMethodWork - Check to see if any globals have been added to the
-// global list for the module. If so, eliminate them.
-//
-bool DynamicConstantMerge::runOnMethod(Method *M) {
- return ::mergeDuplicateConstants(M->getParent(), LastConstantSeen, Constants);
+ // Delete the global value from the module.
+ Replacements[i].first->eraseFromParent();
+ }
+
+ NumMerged += Replacements.size();
+ Replacements.clear();
+ }
}
projects / oota-llvm.git / blobdiff