-//===- 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/ADT/DenseMap.h"
+#include "llvm/ADT/PointerIntPair.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.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,
- 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;
- }
+STATISTIC(NumMerged, "Number of global constants merged");
+
+namespace {
+ struct ConstantMerge : public ModulePass {
+ static char ID; // Pass identification, replacement for typeid
+ ConstantMerge() : ModulePass(ID) {
+ initializeConstantMergePass(*PassRegistry::getPassRegistry());
}
- }
- return MadeChanges;
+
+ // For this pass, process all of the globals in the module, eliminating
+ // duplicate constants.
+ bool runOnModule(Module &M);
+
+ // Return true iff we can determine the alignment of this global variable.
+ bool hasKnownAlignment(GlobalVariable *GV) const;
+
+ // Return the alignment of the global, including converting the default
+ // alignment to a concrete value.
+ unsigned getAlignment(GlobalVariable *GV) const;
+
+ const DataLayout *TD;
+ };
}
+char ConstantMerge::ID = 0;
+INITIALIZE_PASS(ConstantMerge, "constmerge",
+ "Merge Duplicate Global Constants", false, false)
-// 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);
+ModulePass *llvm::createConstantMergePass() { return new ConstantMerge(); }
+
+
+
+/// Find values that are marked as llvm.used.
+static void FindUsedValues(GlobalVariable *LLVMUsed,
+ SmallPtrSet<const GlobalValue*, 8> &UsedValues) {
+ if (LLVMUsed == 0) return;
+ ConstantArray *Inits = dyn_cast<ConstantArray>(LLVMUsed->getInitializer());
+ if (Inits == 0) return;
+
+ for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
+ if (GlobalValue *GV =
+ dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))
+ UsedValues.insert(GV);
}
+// True if A is better than B.
+static bool IsBetterCannonical(const GlobalVariable &A,
+ const GlobalVariable &B) {
+ if (!A.hasLocalLinkage() && B.hasLocalLinkage())
+ return true;
-// 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);
+ if (A.hasLocalLinkage() && !B.hasLocalLinkage())
+ return false;
+
+ return A.hasUnnamedAddr();
}
-// 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);
+bool ConstantMerge::hasKnownAlignment(GlobalVariable *GV) const {
+ return TD || GV->getAlignment() != 0;
+}
+
+unsigned ConstantMerge::getAlignment(GlobalVariable *GV) const {
+ if (TD)
+ return TD->getPreferredAlignment(GV);
+ return GV->getAlignment();
+}
+
+bool ConstantMerge::runOnModule(Module &M) {
+ TD = getAnalysisIfAvailable<DataLayout>();
+
+ // Find all the globals that are marked "used". These cannot be merged.
+ SmallPtrSet<const GlobalValue*, 8> UsedGlobals;
+ FindUsedValues(M.getGlobalVariable("llvm.used"), UsedGlobals);
+ FindUsedValues(M.getGlobalVariable("llvm.compiler.used"), UsedGlobals);
+
+ // Map unique <constants, has-unknown-alignment> pairs to globals. We don't
+ // want to merge globals of unknown alignment with those of explicit
+ // alignment. If we have DataLayout, we always know the alignment.
+ DenseMap<PointerIntPair<Constant*, 1, bool>, GlobalVariable*> CMap;
+
+ // 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: Find the canonical constants others will be merged with.
+ 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;
+ }
+
+ // Only process constants with initializers in the default address space.
+ if (!GV->isConstant() || !GV->hasDefinitiveInitializer() ||
+ GV->getType()->getAddressSpace() != 0 || GV->hasSection() ||
+ // Don't touch values marked with attribute(used).
+ UsedGlobals.count(GV))
+ continue;
+
+ // This transformation is legal for weak ODR globals in the sense it
+ // doesn't change semantics, but we really don't want to perform it
+ // anyway; it's likely to pessimize code generation, and some tools
+ // (like the Darwin linker in cases involving CFString) don't expect it.
+ if (GV->isWeakForLinker())
+ continue;
+
+ Constant *Init = GV->getInitializer();
+
+ // Check to see if the initializer is already known.
+ PointerIntPair<Constant*, 1, bool> Pair(Init, hasKnownAlignment(GV));
+ GlobalVariable *&Slot = CMap[Pair];
+
+ // If this is the first constant we find or if the old one is local,
+ // replace with the current one. If the current is externally visible
+ // it cannot be replace, but can be the canonical constant we merge with.
+ if (Slot == 0 || IsBetterCannonical(*GV, *Slot))
+ Slot = GV;
+ }
+
+ // Second: 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++;
+
+ // Only process constants with initializers in the default address space.
+ if (!GV->isConstant() || !GV->hasDefinitiveInitializer() ||
+ GV->getType()->getAddressSpace() != 0 || GV->hasSection() ||
+ // Don't touch values marked with attribute(used).
+ UsedGlobals.count(GV))
+ continue;
+
+ // We can only replace constant with local linkage.
+ if (!GV->hasLocalLinkage())
+ continue;
+
+ Constant *Init = GV->getInitializer();
+
+ // Check to see if the initializer is already known.
+ PointerIntPair<Constant*, 1, bool> Pair(Init, hasKnownAlignment(GV));
+ GlobalVariable *Slot = CMap[Pair];
+
+ if (!Slot || Slot == GV)
+ continue;
+
+ if (!Slot->hasUnnamedAddr() && !GV->hasUnnamedAddr())
+ continue;
+
+ if (!GV->hasUnnamedAddr())
+ Slot->setUnnamedAddr(false);
+
+ // 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();
+
+ // 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) {
+ // Bump the alignment if necessary.
+ if (Replacements[i].first->getAlignment() ||
+ Replacements[i].second->getAlignment()) {
+ Replacements[i].second->setAlignment(std::max(
+ Replacements[i].first->getAlignment(),
+ Replacements[i].second->getAlignment()));
+ }
+
+ // Eliminate any uses of the dead global.
+ Replacements[i].first->replaceAllUsesWith(Replacements[i].second);
+
+ // Delete the global value from the module.
+ assert(Replacements[i].first->hasLocalLinkage() &&
+ "Refusing to delete an externally visible global variable.");
+ Replacements[i].first->eraseFromParent();
+ }
+
+ NumMerged += Replacements.size();
+ Replacements.clear();
+ }
}
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