Extend CaptureTracking to indicate when a value is never stored, even
if it is not ultimately captured. Teach BasicAliasAnalysis that a
local object address which does not escape and is never stored does
not alias with a value resulting from a load.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89398 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/CaptureTracking.cpp b/lib/Analysis/CaptureTracking.cpp
index 7cd055dcd..ae0766b 100644
--- a/lib/Analysis/CaptureTracking.cpp
+++ b/lib/Analysis/CaptureTracking.cpp
@@ -28,8 +28,11 @@
/// 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 @@
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;