| //===- DataStructureOpt.cpp - Data Structure Analysis Based Optimizations -===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file was developed by the LLVM research group and is distributed under |
| // the University of Illinois Open Source License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass uses DSA to a series of simple optimizations, like marking |
| // unwritten global variables 'constant'. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Analysis/DataStructure.h" |
| #include "llvm/Analysis/DSGraph.h" |
| #include "llvm/Module.h" |
| #include "llvm/Constant.h" |
| #include "Support/Statistic.h" |
| |
| namespace llvm { |
| |
| namespace { |
| Statistic<> |
| NumGlobalsConstanted("ds-opt", "Number of globals marked constant"); |
| Statistic<> |
| NumGlobalsIsolated("ds-opt", "Number of globals with references dropped"); |
| |
| class DSOpt : public Pass { |
| TDDataStructures *TD; |
| public: |
| bool run(Module &M) { |
| TD = &getAnalysis<TDDataStructures>(); |
| bool Changed = OptimizeGlobals(M); |
| return Changed; |
| } |
| |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addRequired<TDDataStructures>(); // Uses TD Datastructures |
| AU.addPreserved<LocalDataStructures>(); // Preserves local... |
| AU.addPreserved<TDDataStructures>(); // Preserves bu... |
| AU.addPreserved<BUDataStructures>(); // Preserves td... |
| } |
| |
| private: |
| bool OptimizeGlobals(Module &M); |
| }; |
| |
| RegisterOpt<DSOpt> X("ds-opt", "DSA-based simple optimizations"); |
| } |
| |
| /// OptimizeGlobals - This method uses information taken from DSA to optimize |
| /// global variables. |
| /// |
| bool DSOpt::OptimizeGlobals(Module &M) { |
| DSGraph &GG = TD->getGlobalsGraph(); |
| const DSGraph::ScalarMapTy &SM = GG.getScalarMap(); |
| bool Changed = false; |
| |
| for (Module::giterator I = M.gbegin(), E = M.gend(); I != E; ++I) |
| if (!I->isExternal()) { // Loop over all of the non-external globals... |
| // Look up the node corresponding to this global, if it exists. |
| DSNode *GNode = 0; |
| DSGraph::ScalarMapTy::const_iterator SMI = SM.find(I); |
| if (SMI != SM.end()) GNode = SMI->second.getNode(); |
| |
| if (GNode == 0 && I->hasInternalLinkage()) { |
| // If there is no entry in the scalar map for this global, it was never |
| // referenced in the program. If it has internal linkage, that means we |
| // can delete it. We don't ACTUALLY want to delete the global, just |
| // remove anything that references the global: later passes will take |
| // care of nuking it. |
| if (!I->use_empty()) { |
| I->replaceAllUsesWith(Constant::getNullValue((Type*)I->getType())); |
| ++NumGlobalsIsolated; |
| } |
| } else if (GNode && GNode->isComplete()) { |
| |
| // If the node has not been read or written, and it is not externally |
| // visible, kill any references to it so it can be DCE'd. |
| if (!GNode->isModified() && !GNode->isRead() &&I->hasInternalLinkage()){ |
| if (!I->use_empty()) { |
| I->replaceAllUsesWith(Constant::getNullValue((Type*)I->getType())); |
| ++NumGlobalsIsolated; |
| } |
| } |
| |
| // We expect that there will almost always be a node for this global. |
| // If there is, and the node doesn't have the M bit set, we can set the |
| // 'constant' bit on the global. |
| if (!GNode->isModified() && !I->isConstant()) { |
| I->setConstant(true); |
| ++NumGlobalsConstanted; |
| Changed = true; |
| } |
| } |
| } |
| return Changed; |
| } |
| |
| } // End llvm namespace |