#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/AliasAnalysis.h"
-#include "llvm/ADT/SmallSet.h"
-#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/CallSite.h"
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 {
+ virtual ~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);
+
+ /// captured - Information about the pointer was captured by the user of
+ /// use U. Return true to stop the traversal or false to continue looking
+ /// for more capturing instructions.
+ virtual bool captured(Use *U) = 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
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