Initial checkin of Steensgaards context insensitive flow insensitive

alias analysis


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@3997 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 224 insertions, 0 deletions

diff --git a/lib/Analysis/DataStructure/Steensgaard.cpp b/lib/Analysis/DataStructure/Steensgaard.cpp
new file mode 100644
index 0000000000..c6728b58dd
--- /dev/null
+++ b/lib/Analysis/DataStructure/Steensgaard.cpp
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+//===- Steensgaard.cpp - Context Insensitive Alias Analysis ---------------===//
+//
+// This pass uses the data structure graphs to implement a simple context
+// insensitive alias analysis.  It does this by computing the local analysis
+// graphs for all of the functions, then merging them together into a single big
+// graph without cloning.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/DataStructure.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Module.h"
+#include "Support/Statistic.h"
+
+namespace {
+  class Steens : public Pass, public AliasAnalysis {
+    DSGraph *ResultGraph;
+  public:
+    Steens() : ResultGraph(0) {}
+    ~Steens() { assert(ResultGraph == 0 && "releaseMemory not called?"); }
+
+    //------------------------------------------------
+    // Implement the Pass API
+    //
+
+    // run - Build up the result graph, representing the pointer graph for the
+    // program.
+    //
+    bool run(Module &M);
+
+    virtual void releaseMemory() { delete ResultGraph; ResultGraph = 0; }
+
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.setPreservesAll();                    // Does not transform code...
+      AU.addRequired<LocalDataStructures>();   // Uses local dsgraph
+      AU.addRequired<AliasAnalysis>();         // Chains to another AA impl...
+    }
+
+    // print - Implement the Pass::print method...
+    void print(std::ostream &O, const Module *M) const {
+      assert(ResultGraph && "Result graph has not yet been computed!");
+      ResultGraph->writeGraphToFile(O, "steensgaards");
+    }
+
+    //------------------------------------------------
+    // Implement the AliasAnalysis API
+    //  
+
+    // alias - This is the only method here that does anything interesting...
+    Result alias(const Value *V1, const Value *V2) const;
+    
+    /// canCallModify - We are not interprocedural, so we do nothing exciting.
+    ///
+    Result canCallModify(const CallInst &CI, const Value *Ptr) const {
+      return MayAlias;
+    }
+    
+    /// canInvokeModify - We are not interprocedural, so we do nothing exciting.
+    ///
+    Result canInvokeModify(const InvokeInst &I, const Value *Ptr) const {
+      return MayAlias;  // We are not interprocedural
+    }
+
+  private:
+    void ResolveFunctionCall(Function *F, const std::vector<DSNodeHandle> &Call,
+                             DSNodeHandle &RetVal);
+  };
+
+  // Register the pass...
+  RegisterOpt<Steens> X("steens-aa",
+                        "Steensgaard's FlowInsensitive/ConIns alias analysis");
+
+  // Register as an implementation of AliasAnalysis
+  RegisterAnalysisGroup<AliasAnalysis, Steens> Y;
+}
+
+
+/// ResolveFunctionCall - Resolve the actual arguments of a call to function F
+/// with the specified call site descriptor.  This function links the arguments
+/// and the return value for the call site context-insensitively.
+///
+void Steens::ResolveFunctionCall(Function *F,
+                                 const std::vector<DSNodeHandle> &Call,
+                                 DSNodeHandle &RetVal) {
+  assert(ResultGraph != 0 && "Result graph not allocated!");
+  std::map<Value*, DSNodeHandle> &ValMap = ResultGraph->getValueMap();
+
+  // Handle the return value of the function... which is Call[0]
+  if (Call[0].getNode() && RetVal.getNode())
+    RetVal.mergeWith(Call[0]);
+
+  // Loop over all pointer arguments, resolving them to their provided pointers
+  unsigned ArgIdx = 2; // Skip retval and function to call...
+  for (Function::aiterator AI = F->abegin(), AE = F->aend(); AI != AE; ++AI) {
+    std::map<Value*, DSNodeHandle>::iterator I = ValMap.find(AI);
+    if (I != ValMap.end())    // If its a pointer argument...
+      I->second.addEdgeTo(Call[ArgIdx++]);
+  }
+
+  assert(ArgIdx == Call.size() && "Argument resolution mismatch!");
+}
+
+
+/// run - Build up the result graph, representing the pointer graph for the
+/// program.
+///
+bool Steens::run(Module &M) {
+  assert(ResultGraph == 0 && "Result graph already allocated!");
+  LocalDataStructures &LDS = getAnalysis<LocalDataStructures>();
+
+  // Create a new, empty, graph...
+  ResultGraph = new DSGraph();
+
+  // RetValMap - Keep track of the return values for all functions that return
+  // valid pointers.
+  //
+  std::map<Function*, DSNodeHandle> RetValMap;
+
+  // Loop over the rest of the module, merging graphs for non-external functions
+  // into this graph.
+  //
+  for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
+    if (!I->isExternal()) {
+      std::map<Value*, DSNodeHandle> ValMap;
+      {  // Scope to free NodeMap memory ASAP
+        std::map<const DSNode*, DSNode*> NodeMap;
+        const DSGraph &FDSG = LDS.getDSGraph(*I);
+        DSNodeHandle RetNode = ResultGraph->cloneInto(FDSG, ValMap, NodeMap);
+
+        // Keep track of the return node of the function's graph if it returns a
+        // value...
+        //
+        if (RetNode.getNode())
+          RetValMap[I] = RetNode;
+      }
+
+      // Incorporate the inlined Function's ValueMap into the global ValueMap...
+      std::map<Value*, DSNodeHandle> &GVM = ResultGraph->getValueMap();
+
+      while (!ValMap.empty()) { // Loop over value map, moving entries over...
+        const std::pair<Value*, DSNodeHandle> &DSN = *ValMap.begin();
+        std::map<Value*, DSNodeHandle>::iterator I = GVM.find(DSN.first);
+        if (I == GVM.end())
+          GVM[DSN.first] = DSN.second;
+        else
+          I->second.mergeWith(DSN.second);
+        ValMap.erase(ValMap.begin());
+      }
+    }
+
+  // FIXME: Must recalculate and use the Incomplete markers!!
+
+  // Now that we have all of the graphs inlined, we can go about eliminating
+  // call nodes...
+  //
+  std::vector<std::vector<DSNodeHandle> > &Calls =
+    ResultGraph->getFunctionCalls();
+  for (unsigned i = 0; i != Calls.size(); ) {
+    std::vector<DSNodeHandle> &CurCall = Calls[i];
+    
+    // Loop over the called functions, eliminating as many as possible...
+    std::vector<GlobalValue*> CallTargets = CurCall[1].getNode()->getGlobals();
+    for (unsigned c = 0; c != CallTargets.size(); ) {
+      // If we can eliminate this function call, do so!
+      bool Eliminated = false;
+      if (Function *F = dyn_cast<Function>(CallTargets[c]))
+        if (!F->isExternal()) {
+          ResolveFunctionCall(F, CurCall, RetValMap[F]);
+          Eliminated = true;
+        }
+      if (Eliminated)
+        CallTargets.erase(CallTargets.begin()+c);
+      else
+        ++c;  // Cannot eliminate this call, skip over it...
+    }
+
+    if (CallTargets.empty())          // Eliminated all calls?
+      Calls.erase(Calls.begin()+i);   // Remove from call list...
+    else
+      ++i;                            // Skip this call site...
+  }
+
+  // Update the "incomplete" markers on the nodes, ignoring unknownness due to
+  // incoming arguments...
+  ResultGraph->maskIncompleteMarkers();
+  ResultGraph->markIncompleteNodes(false);
+
+  // Remove any nodes that are dead after all of the merging we have done...
+  ResultGraph->removeTriviallyDeadNodes();
+
+  DEBUG(print(std::cerr, &M));
+  return false;
+}
+
+// alias - This is the only method here that does anything interesting...
+AliasAnalysis::Result Steens::alias(const Value *V1, const Value *V2) const {
+  assert(ResultGraph && "Result grcaph has not yet been computed!");
+
+  std::map<Value*, DSNodeHandle> &GVM = ResultGraph->getValueMap();
+
+  std::map<Value*, DSNodeHandle>::iterator I = GVM.find(const_cast<Value*>(V1));
+  if (I != GVM.end() && I->second.getNode()) {
+    DSNodeHandle &V1H = I->second;
+    std::map<Value*, DSNodeHandle>::iterator J=GVM.find(const_cast<Value*>(V2));
+    if (J != GVM.end() && J->second.getNode()) {
+      DSNodeHandle &V2H = J->second;
+      // If the two pointers point to different data structure graph nodes, they
+      // cannot alias!
+      if (V1H.getNode() != V2H.getNode())
+        return NoAlias;
+
+      // FIXME: If the two pointers point to the same node, and the offsets are
+      // different, and the LinkIndex vector doesn't alias the section, then the
+      // two pointers do not alias.  We need access size information for the two
+      // accesses though!
+      //
+    }
+  }
+
+  // If we cannot determine alias properties based on our graph, fall back on
+  // some other AA implementation.
+  //
+  return getAnalysis<AliasAnalysis>().alias(V1, V2);
+}