3 files changed, 30 insertions, 14 deletions

diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index b8d69f41c2a..66bb4397c3a 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -79,7 +79,12 @@ static bool isKnownNonNull(const Value *V) {
 static bool isNonEscapingLocalObject(const Value *V) {
   // If this is a local allocation, check to see if it escapes.
   if (isa<AllocaInst>(V) || isNoAliasCall(V))
-    return !PointerMayBeCaptured(V, false);
+    // Set StoreCaptures to True so that we can assume in our callers that the
+    // pointer is not the result of a load instruction. Currently
+    // PointerMayBeCaptured doesn't have any special analysis for the
+    // StoreCaptures=false case; if it did, our callers could be refined to be
+    // more precise.
+    return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
 
   // If this is an argument that corresponds to a byval or noalias argument,
   // then it has not escaped before entering the function.  Check if it escapes
@@ -89,7 +94,7 @@ static bool isNonEscapingLocalObject(const Value *V) {
       // Don't bother analyzing arguments already known not to escape.
       if (A->hasNoCaptureAttr())
         return true;
-      return !PointerMayBeCaptured(V, false);
+      return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
     }
   return false;
 }
@@ -683,15 +688,19 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size,
         (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, *TD)))
       return NoAlias;
   
-  // If one pointer is the result of a call/invoke and the other is a
+  // If one pointer is the result of a call/invoke or load and the other is a
   // non-escaping local object, then we know the object couldn't escape to a
-  // point where the call could return it.
-  if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
-      isNonEscapingLocalObject(O2) && O1 != O2)
-    return NoAlias;
-  if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
-      isNonEscapingLocalObject(O1) && O1 != O2)
-    return NoAlias;
+  // point where the call could return it. The load case works because
+  // isNonEscapingLocalObject considers all stores to be escapes (it
+  // passes true for the StoreCaptures argument to PointerMayBeCaptured).
+  if (O1 != O2) {
+    if ((isa<CallInst>(O1) || isa<InvokeInst>(O1) || isa<LoadInst>(O1)) &&
+        isNonEscapingLocalObject(O2))
+      return NoAlias;
+    if ((isa<CallInst>(O2) || isa<InvokeInst>(O2) || isa<LoadInst>(O2)) &&
+        isNonEscapingLocalObject(O1))
+      return NoAlias;
+  }
 
   if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
     std::swap(V1, V2);
diff --git a/llvm/lib/Analysis/CaptureTracking.cpp b/llvm/lib/Analysis/CaptureTracking.cpp
index 7cd055dcd89..ae0766b237c 100644
--- a/llvm/lib/Analysis/CaptureTracking.cpp
+++ b/llvm/lib/Analysis/CaptureTracking.cpp
@@ -28,8 +28,11 @@ using namespace llvm;
 /// by the enclosing function (which is required to exist).  This routine can
 /// be expensive, so consider caching the results.  The boolean ReturnCaptures
 /// specifies whether returning the value (or part of it) from the function
+/// counts as capturing it or not.  The boolean StoreCaptures specified whether
+/// storing the value (or part of it) into memory anywhere automatically
 /// counts as capturing it or not.
-bool llvm::PointerMayBeCaptured(const Value *V, bool ReturnCaptures) {
+bool llvm::PointerMayBeCaptured(const Value *V,
+                                bool ReturnCaptures, bool StoreCaptures) {
   assert(isa<PointerType>(V->getType()) && "Capture is for pointers only!");
   SmallVector<Use*, 16> Worklist;
   SmallSet<Use*, 16> Visited;
@@ -82,7 +85,11 @@ bool llvm::PointerMayBeCaptured(const Value *V, bool ReturnCaptures) {
       break;
     case Instruction::Store:
       if (V == I->getOperand(0))
-        // Stored the pointer - it may be captured.
+        // Stored the pointer - conservatively assume it may be captured.
+        // TODO: If StoreCaptures is not true, we could do Fancy analysis
+        // to determine whether this store is not actually an escape point.
+        // In that case, BasicAliasAnalysis should be updated as well to
+        // take advantage of this.
         return true;
       // Storing to the pointee does not cause the pointer to be captured.
       break;
diff --git a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
index b3a832f12d0..a16d335ef50 100644
--- a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -212,7 +212,7 @@ bool FunctionAttrs::AddNoCaptureAttrs(const std::vector<CallGraphNode *> &SCC) {
 
     for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A!=E; ++A)
       if (isa<PointerType>(A->getType()) && !A->hasNoCaptureAttr() &&
-          !PointerMayBeCaptured(A, true)) {
+          !PointerMayBeCaptured(A, true, /*StoreCaptures=*/false)) {
         A->addAttr(Attribute::NoCapture);
         ++NumNoCapture;
         Changed = true;
@@ -280,7 +280,7 @@ bool FunctionAttrs::IsFunctionMallocLike(Function *F,
           return false;  // Did not come from an allocation.
       }
 
-    if (PointerMayBeCaptured(RetVal, false))
+    if (PointerMayBeCaptured(RetVal, false, /*StoreCaptures=*/false))
       return false;
   }