Restore minor deletion.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@70892 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 47 insertions, 28 deletions

diff --git a/lib/Analysis/CaptureTracking.cpp b/lib/Analysis/CaptureTracking.cpp
index ceb964619c..773f53d2cd 100644
--- a/lib/Analysis/CaptureTracking.cpp
+++ b/lib/Analysis/CaptureTracking.cpp
@@ -49,11 +49,7 @@ bool llvm::PointerMayBeCaptured(const Value *V, bool ReturnCaptures) {
     switch (I->getOpcode()) {
     case Instruction::Call:
     case Instruction::Invoke: {
-      CallSite CS = CallSite::get(I);
-      // Not captured if the callee is readonly and doesn't return a copy
-      // through its return value.
-      if (CS.onlyReadsMemory() && I->getType() == Type::VoidTy)
-        break;
+      CallSite CS(I);
 
       // Not captured if only passed via 'nocapture' arguments.  Note that
       // calling a function pointer does not in itself cause the pointer to
@@ -62,46 +58,69 @@ bool llvm::PointerMayBeCaptured(const Value *V, bool ReturnCaptures) {
       // 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).
+      bool MayBeCaptured = false;
       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.paramHasAttr(A - B + 1, Attribute::NoCapture))
-          // The parameter is not marked 'nocapture' - captured.
-          return true;
-      // Only passed via 'nocapture' arguments, or is the called function - not
-      // captured.
+        if (A->get() == V && !CS.paramHasAttr(A-B+1, Attribute::NoCapture)) {
+          // The parameter is not marked 'nocapture' - handled by generic code
+          // below.
+          MayBeCaptured = true;
+          break;
+        }
+      if (!MayBeCaptured)
+        // Only passed via 'nocapture' arguments, or is the called function -
+        // not captured.
+        continue;
+      if (!CS.doesNotThrow())
+        // Even a readonly function can leak bits by throwing an exception or
+        // not depending on the input value.
+        return true;
+      // Fall through to the generic code.
       break;
     }
     case Instruction::Free:
       // Freeing a pointer does not cause it to be captured.
-      break;
+      continue;
     case Instruction::Load:
       // Loading from a pointer does not cause it to be captured.
-      break;
+      continue;
     case Instruction::Ret:
       if (ReturnCaptures)
         return true;
-      break;
+      continue;
     case Instruction::Store:
       if (V == I->getOperand(0))
         // Stored the pointer - it may be captured.
         return true;
       // 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))
-          Worklist.push_back(U);
-      }
-      break;
-    default:
-      // Something else - be conservative and say it is captured.
+      continue;
+    }
+
+    // If it may write to memory and isn't one of the special cases above,
+    // be conservative and assume the pointer is captured.
+    if (I->mayWriteToMemory())
       return true;
+
+    // If the instruction doesn't write memory, it can only capture by
+    // having its own value depend on the input value.
+    const Type* Ty = I->getType();
+    if (Ty == Type::VoidTy)
+      // The value of an instruction can't be a copy if it can't contain any
+      // information.
+      continue;
+    if (!isa<PointerType>(Ty))
+      // At the moment, we don't track non-pointer values, so be conservative
+      // and assume the pointer is captured.
+      // FIXME: Track these too.  This would need to be done very carefully as
+      // it is easy to leak bits via control flow if integer values are allowed.
+      return true;
+
+    // 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))
+        Worklist.push_back(U);
     }
   }