3 files changed, 132 insertions, 128 deletions

diff --git a/include/llvm/Analysis/CaptureTracking.h b/include/llvm/Analysis/CaptureTracking.h
index b033f14cec..b49646b2a2 100644
--- a/include/llvm/Analysis/CaptureTracking.h
+++ b/include/llvm/Analysis/CaptureTracking.h
@@ -33,132 +33,31 @@ namespace llvm {
                             bool ReturnCaptures,
                             bool StoreCaptures);
 
+  /// This callback is used in conjunction with PointerMayBeCaptured. In
+  /// addition to the interface here, you'll need to provide your own getters
+  /// to see whether anything was captured.
+  struct CaptureTracker {
+    /// tooManyUses - The depth of traversal has breached a limit. There may be
+    /// capturing instructions that will not be passed into captured().
+    virtual void tooManyUses() = 0;
+
+    /// shouldExplore - This is the use of a value derived from the pointer.
+    /// To prune the search (ie., assume that none of its users could possibly
+    /// capture) return false. To search it, return true.
+    ///
+    /// U->getUser() is always an Instruction.
+    virtual bool shouldExplore(Use *U) = 0;
+
+    /// captured - The instruction I captured the pointer. Return true to
+    /// stop the traversal or false to continue looking for more capturing
+    /// instructions.
+    virtual bool captured(Instruction *I) = 0;
+  };
+
   /// PointerMayBeCaptured - Visit the value and the values derived from it and
   /// find values which appear to be capturing the pointer value. This feeds
-  /// results into and is controlled by the templated CaptureTracker object:
-  ///
-  /// struct YourCaptureTracker {
-  ///   /// tooManyUses - The depth of traversal has breached a limit.
-  ///   /// The tracker should conservatively assume that the value is captured.
-  ///   void tooManyUses();
-  ///
-  ///   /// shouldExplore - This is the use of a value derived from the pointer.
-  ///   /// Return false to prune the search (ie., assume that none of its users
-  ///   /// could possibly capture) return false. To search it, return true.
-  ///   ///
-  ///   /// Also, U->getUser() is guaranteed to be an Instruction.
-  ///   bool shouldExplore(Use *U);
-  ///
-  ///   /// captured - The instruction I captured the pointer. Return true to
-  ///   /// stop the traversal or false to continue looking for more capturing
-  ///   /// instructions.
-  ///   bool captured(Instruction *I);
-  ///
-  ///   /// Provide your own getters for the state.
-  /// };
-  template<typename CaptureTracker>
-  void PointerMayBeCaptured(const Value *V, CaptureTracker &Tracker);
+  /// results into and is controlled by the CaptureTracker object.
+  void PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker);
 } // end namespace llvm
 
-template<typename CaptureTracker>
-void llvm::PointerMayBeCaptured(const llvm::Value *V, CaptureTracker &Tracker) {
-  assert(V->getType()->isPointerTy() && "Capture is for pointers only!");
-  SmallVector<Use*, 20> Worklist;
-  SmallSet<Use*, 20> Visited;
-  int Count = 0;
-
-  for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end();
-       UI != UE; ++UI) {
-    // If there are lots of uses, conservatively say that the value
-    // is captured to avoid taking too much compile time.
-    if (Count++ >= 20)
-      return Tracker.tooManyUses();
-
-    Use *U = &UI.getUse();
-    if (!Tracker.shouldExplore(U)) continue;
-    Visited.insert(U);
-    Worklist.push_back(U);
-  }
-
-  while (!Worklist.empty()) {
-    Use *U = Worklist.pop_back_val();
-    Instruction *I = cast<Instruction>(U->getUser());
-    V = U->get();
-
-    switch (I->getOpcode()) {
-    case Instruction::Call:
-    case Instruction::Invoke: {
-      CallSite CS(I);
-      // Not captured if the callee is readonly, doesn't return a copy through
-      // its return value and doesn't unwind (a readonly function can leak bits
-      // by throwing an exception or not depending on the input value).
-      if (CS.onlyReadsMemory() && CS.doesNotThrow() && I->getType()->isVoidTy())
-        break;
-
-      // Not captured if only passed via 'nocapture' arguments.  Note that
-      // calling a function pointer does not in itself cause the pointer to
-      // be captured.  This is a subtle point considering that (for example)
-      // the callee might return its own address.  It is analogous to saying
-      // that loading a value from a pointer does not cause the pointer to be
-      // captured, even though the loaded value might be the pointer itself
-      // (think of self-referential objects).
-      CallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end();
-      for (CallSite::arg_iterator A = B; A != E; ++A)
-        if (A->get() == V && !CS.doesNotCapture(A - B))
-          // The parameter is not marked 'nocapture' - captured.
-          if (Tracker.captured(I))
-            return;
-      break;
-    }
-    case Instruction::Load:
-      // Loading from a pointer does not cause it to be captured.
-      break;
-    case Instruction::VAArg:
-      // "va-arg" from a pointer does not cause it to be captured.
-      break;
-    case Instruction::Store:
-      if (V == I->getOperand(0))
-        // Stored the pointer - conservatively assume it may be captured.
-        if (Tracker.captured(I))
-          return;
-      // Storing to the pointee does not cause the pointer to be captured.
-      break;
-    case Instruction::BitCast:
-    case Instruction::GetElementPtr:
-    case Instruction::PHI:
-    case Instruction::Select:
-      // The original value is not captured via this if the new value isn't.
-      for (Instruction::use_iterator UI = I->use_begin(), UE = I->use_end();
-           UI != UE; ++UI) {
-        Use *U = &UI.getUse();
-        if (Visited.insert(U))
-          if (Tracker.shouldExplore(U))
-            Worklist.push_back(U);
-      }
-      break;
-    case Instruction::ICmp:
-      // Don't count comparisons of a no-alias return value against null as
-      // captures. This allows us to ignore comparisons of malloc results
-      // with null, for example.
-      if (isNoAliasCall(V->stripPointerCasts()))
-        if (ConstantPointerNull *CPN =
-              dyn_cast<ConstantPointerNull>(I->getOperand(1)))
-          if (CPN->getType()->getAddressSpace() == 0)
-            break;
-      // Otherwise, be conservative. There are crazy ways to capture pointers
-      // using comparisons.
-      if (Tracker.captured(I))
-        return;
-      break;
-    default:
-      // Something else - be conservative and say it is captured.
-      if (Tracker.captured(I))
-        return;
-      break;
-    }
-  }
-
-  // All uses examined.
-}
-
 #endif
diff --git a/lib/Analysis/CaptureTracking.cpp b/lib/Analysis/CaptureTracking.cpp
index a84dafb5fb..9be00971dc 100644
--- a/lib/Analysis/CaptureTracking.cpp
+++ b/lib/Analysis/CaptureTracking.cpp
@@ -20,7 +20,7 @@
 using namespace llvm;
 
 namespace {
-  struct SimpleCaptureTracker {
+  struct SimpleCaptureTracker : public CaptureTracker {
     explicit SimpleCaptureTracker(bool ReturnCaptures)
       : ReturnCaptures(ReturnCaptures), Captured(false) {}
 
@@ -58,6 +58,111 @@ bool llvm::PointerMayBeCaptured(const Value *V,
   (void)StoreCaptures;
 
   SimpleCaptureTracker SCT(ReturnCaptures);
-  PointerMayBeCaptured(V, SCT);
+  PointerMayBeCaptured(V, &SCT);
   return SCT.Captured;
 }
+
+/// TODO: Write a new FunctionPass AliasAnalysis so that it can keep
+/// a cache. Then we can move the code from BasicAliasAnalysis into
+/// that path, and remove this threshold.
+static int const Threshold = 20;
+
+void llvm::PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker) {
+  assert(V->getType()->isPointerTy() && "Capture is for pointers only!");
+  SmallVector<Use*, Threshold> Worklist;
+  SmallSet<Use*, Threshold> Visited;
+  int Count = 0;
+
+  for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end();
+       UI != UE; ++UI) {
+    // If there are lots of uses, conservatively say that the value
+    // is captured to avoid taking too much compile time.
+    if (Count++ >= Threshold)
+      return Tracker->tooManyUses();
+
+    Use *U = &UI.getUse();
+    if (!Tracker->shouldExplore(U)) continue;
+    Visited.insert(U);
+    Worklist.push_back(U);
+  }
+
+  while (!Worklist.empty()) {
+    Use *U = Worklist.pop_back_val();
+    Instruction *I = cast<Instruction>(U->getUser());
+    V = U->get();
+
+    switch (I->getOpcode()) {
+    case Instruction::Call:
+    case Instruction::Invoke: {
+      CallSite CS(I);
+      // Not captured if the callee is readonly, doesn't return a copy through
+      // its return value and doesn't unwind (a readonly function can leak bits
+      // by throwing an exception or not depending on the input value).
+      if (CS.onlyReadsMemory() && CS.doesNotThrow() && I->getType()->isVoidTy())
+        break;
+
+      // Not captured if only passed via 'nocapture' arguments.  Note that
+      // calling a function pointer does not in itself cause the pointer to
+      // be captured.  This is a subtle point considering that (for example)
+      // the callee might return its own address.  It is analogous to saying
+      // that loading a value from a pointer does not cause the pointer to be
+      // captured, even though the loaded value might be the pointer itself
+      // (think of self-referential objects).
+      CallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end();
+      for (CallSite::arg_iterator A = B; A != E; ++A)
+        if (A->get() == V && !CS.doesNotCapture(A - B))
+          // The parameter is not marked 'nocapture' - captured.
+          if (Tracker->captured(I))
+            return;
+      break;
+    }
+    case Instruction::Load:
+      // Loading from a pointer does not cause it to be captured.
+      break;
+    case Instruction::VAArg:
+      // "va-arg" from a pointer does not cause it to be captured.
+      break;
+    case Instruction::Store:
+      if (V == I->getOperand(0))
+        // Stored the pointer - conservatively assume it may be captured.
+        if (Tracker->captured(I))
+          return;
+      // Storing to the pointee does not cause the pointer to be captured.
+      break;
+    case Instruction::BitCast:
+    case Instruction::GetElementPtr:
+    case Instruction::PHI:
+    case Instruction::Select:
+      // The original value is not captured via this if the new value isn't.
+      for (Instruction::use_iterator UI = I->use_begin(), UE = I->use_end();
+           UI != UE; ++UI) {
+        Use *U = &UI.getUse();
+        if (Visited.insert(U))
+          if (Tracker->shouldExplore(U))
+            Worklist.push_back(U);
+      }
+      break;
+    case Instruction::ICmp:
+      // Don't count comparisons of a no-alias return value against null as
+      // captures. This allows us to ignore comparisons of malloc results
+      // with null, for example.
+      if (isNoAliasCall(V->stripPointerCasts()))
+        if (ConstantPointerNull *CPN =
+              dyn_cast<ConstantPointerNull>(I->getOperand(1)))
+          if (CPN->getType()->getAddressSpace() == 0)
+            break;
+      // Otherwise, be conservative. There are crazy ways to capture pointers
+      // using comparisons.
+      if (Tracker->captured(I))
+        return;
+      break;
+    default:
+      // Something else - be conservative and say it is captured.
+      if (Tracker->captured(I))
+        return;
+      break;
+    }
+  }
+
+  // All uses examined.
+}
diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp
index e779bf2b99..128c7f93a4 100644
--- a/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -336,7 +336,7 @@ getLoadLoadClobberFullWidthSize(const Value *MemLocBase, int64_t MemLocOffs,
 namespace {
   /// Only find pointer captures which happen before the given instruction. Uses
   /// the dominator tree to determine whether one instruction is before another.
-  struct CapturesBefore {
+  struct CapturesBefore : public CaptureTracker {
     CapturesBefore(const Instruction *I, DominatorTree *DT)
       : BeforeHere(I), DT(DT), Captured(false) {}
 
@@ -381,7 +381,7 @@ MemoryDependenceAnalysis::getModRefInfo(const Instruction *Inst,
   if (!CS.getInstruction()) return AliasAnalysis::ModRef;
 
   CapturesBefore CB(Inst, DT);
-  llvm::PointerMayBeCaptured(Object, CB);
+  llvm::PointerMayBeCaptured(Object, &CB);
 
   if (isa<Constant>(Object) || CS.getInstruction() == Object || CB.Captured)
     return AliasAnalysis::ModRef;