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801e22514d
read or written to. Keep track of how many times this happens. This should be good for deleting things like references to type information in C++ classes llvm-svn: 6946
92 lines
3.2 KiB
C++
92 lines
3.2 KiB
C++
//===- DataStructureOpt.cpp - Data Structure Analysis Based Optimizations -===//
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//
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// This pass uses DSA to a series of simple optimizations, like marking
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// unwritten global variables 'constant'.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/DataStructure.h"
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#include "llvm/Analysis/DSGraph.h"
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#include "llvm/Module.h"
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#include "llvm/Constant.h"
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#include "Support/Statistic.h"
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namespace {
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Statistic<>
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NumGlobalsConstanted("ds-opt", "Number of globals marked constant");
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Statistic<>
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NumGlobalsIsolated("ds-opt", "Number of globals with references dropped");
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class DSOpt : public Pass {
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TDDataStructures *TD;
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public:
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bool run(Module &M) {
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TD = &getAnalysis<TDDataStructures>();
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bool Changed = OptimizeGlobals(M);
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return Changed;
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}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<TDDataStructures>(); // Uses TD Datastructures
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AU.addPreserved<LocalDataStructures>(); // Preserves local...
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AU.addPreserved<TDDataStructures>(); // Preserves bu...
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AU.addPreserved<BUDataStructures>(); // Preserves td...
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}
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private:
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bool OptimizeGlobals(Module &M);
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};
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RegisterOpt<DSOpt> X("ds-opt", "DSA-based simple optimizations");
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}
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/// OptimizeGlobals - This method uses information taken from DSA to optimize
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/// global variables.
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///
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bool DSOpt::OptimizeGlobals(Module &M) {
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DSGraph &GG = TD->getGlobalsGraph();
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const DSGraph::ScalarMapTy &SM = GG.getScalarMap();
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bool Changed = false;
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for (Module::giterator I = M.gbegin(), E = M.gend(); I != E; ++I)
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if (!I->isExternal()) { // Loop over all of the non-external globals...
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// Look up the node corresponding to this global, if it exists.
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DSNode *GNode = 0;
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DSGraph::ScalarMapTy::const_iterator SMI = SM.find(I);
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if (SMI != SM.end()) GNode = SMI->second.getNode();
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if (GNode == 0 && I->hasInternalLinkage()) {
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// If there is no entry in the scalar map for this global, it was never
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// referenced in the program. If it has internal linkage, that means we
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// can delete it. We don't ACTUALLY want to delete the global, just
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// remove anything that references the global: later passes will take
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// care of nuking it.
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if (!I->use_empty()) {
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I->replaceAllUsesWith(Constant::getNullValue((Type*)I->getType()));
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++NumGlobalsIsolated;
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}
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} else if (GNode && GNode->isComplete()) {
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// If the node has not been read or written, and it is not externally
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// visible, kill any references to it so it can be DCE'd.
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if (!GNode->isModified() && !GNode->isRead() &&I->hasInternalLinkage()){
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if (!I->use_empty()) {
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I->replaceAllUsesWith(Constant::getNullValue((Type*)I->getType()));
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++NumGlobalsIsolated;
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}
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}
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// We expect that there will almost always be a node for this global.
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// If there is, and the node doesn't have the M bit set, we can set the
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// 'constant' bit on the global.
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if (!GNode->isModified() && !I->isConstant()) {
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I->setConstant(true);
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++NumGlobalsConstanted;
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Changed = true;
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}
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}
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}
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return Changed;
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}
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