Initial implementation of ds-aa

llvm-svn: 5484

lib/Analysis/DataStructure/DataStructureAA.cpp

@@ -0,0 +1,128 @@
+//===- DataStructureAA.cpp - Data Structure Based Alias Analysis ----------===//
+//
+// This pass uses the top-down data structure graphs to implement a simple
+// context sensitive alias analysis.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/DataStructure.h"
+#include "llvm/Analysis/DSGraph.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Module.h"
+#include "Support/Statistic.h"
+
+namespace {
+  Statistic<> NumNoAlias  ("ds-aa", "Number of 'no alias' replies");
+  Statistic<> NumMayAlias ("ds-aa", "Number of 'may alias' replies");
+};
+
+namespace {
+  class DSAA : public Pass, public AliasAnalysis {
+    TDDataStructures *TD;
+  public:
+    DSAA() : TD(0) {}
+
+    //------------------------------------------------
+    // Implement the Pass API
+    //
+
+    // run - Build up the result graph, representing the pointer graph for the
+    // program.
+    //
+    bool run(Module &M) {
+      TD = &getAnalysis<TDDataStructures>();
+      return false;
+    }
+
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.setPreservesAll();                    // Does not transform code...
+      AU.addRequired<TDDataStructures>();      // Uses TD Datastructures
+      AU.addRequired<AliasAnalysis>();         // Chains to another AA impl...
+    }
+
+    //------------------------------------------------
+    // Implement the AliasAnalysis API
+    //  
+
+    // alias - This is the only method here that does anything interesting...
+    Result alias(const Value *V1, const Value *V2);
+    
+    /// canCallModify - Not implemented yet: FIXME
+    ///
+    Result canCallModify(const CallInst &CI, const Value *Ptr) {
+      return MayAlias;
+    }
+    
+    /// canInvokeModify - Not implemented yet: FIXME
+    ///
+    Result canInvokeModify(const InvokeInst &I, const Value *Ptr) {
+      return MayAlias;
+    }
+  };
+
+  // Register the pass...
+  RegisterOpt<DSAA> X("ds-aa", "Data Structure Graph Based Alias Analysis");
+
+  // Register as an implementation of AliasAnalysis
+  RegisterAnalysisGroup<AliasAnalysis, DSAA> Y;
+}
+
+// getValueFunction - return the function containing the specified value if
+// available, or null otherwise.
+//
+static const Function *getValueFunction(const Value *V) {
+  if (const Instruction *I = dyn_cast<Instruction>(V))
+    return I->getParent()->getParent();
+  else if (const Argument *A = dyn_cast<Argument>(V))
+    return A->getParent();
+  else if (const BasicBlock *BB = dyn_cast<BasicBlock>(V))
+    return BB->getParent();
+  return 0;
+}
+
+// alias - This is the only method here that does anything interesting...
+AliasAnalysis::Result DSAA::alias(const Value *V1, const Value *V2) {
+  const Function *F1 = getValueFunction(V1);
+  const Function *F2 = getValueFunction(V2);
+  assert((!F1 || !F2 || F1 == F2) && "Alias query for 2 different functions?");
+  
+
+  // FIXME: This can return must alias if querying a DSNode for a global value
+  // where the node has only the G composition bit set, and only one entry in
+  // the globals list...
+  if (F2) F1 = F2;
+  if (F1) {
+    // Get the graph for a function...
+    DSGraph &G = TD->getDSGraph(*F1);
+    hash_map<Value*, DSNodeHandle> &GSM = G.getScalarMap();
+    hash_map<Value*, DSNodeHandle>::iterator I = GSM.find((Value*)V1);
+    if (I != GSM.end()) {
+      assert(I->second.getNode() && "Scalar map points to null node?");
+      hash_map<Value*, DSNodeHandle>::iterator J = GSM.find((Value*)V2);
+      if (J != GSM.end()) {
+        assert(J->second.getNode() && "Scalar map points to null node?");
+        if (I->second.getNode() != J->second.getNode()) {
+          // Return noalias if one of the nodes is complete...
+          if ((~I->second.getNode()->NodeType | ~J->second.getNode()->NodeType)
+              & DSNode::Incomplete) {
+            ++NumNoAlias;
+            return NoAlias;
+          }
+          // both are incomplete, they may alias...
+        } else {
+          // Both point to the same node, see if they point to different
+          // offsets...  FIXME: This needs to know the size of the alias query
+          if (I->second.getOffset() != J->second.getOffset()) {
+            ++NumNoAlias;
+            return NoAlias;
+          }
+        }
+      }
+    }
+  }
+
+  // FIXME: we could improve on this by checking the globals graph for aliased
+  // global queries...
+  ++NumMayAlias;
+  return getAnalysis<AliasAnalysis>().alias(V1, V2);
+}