//
//===----------------------------------------------------------------------===//
-#include "llvm/Analysis/CaptureTracking.h"
-#include "llvm/Analysis/MallocFreeHelper.h"
-#include "llvm/Instructions.h"
-#include "llvm/Value.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
-#include "llvm/Support/CallSite.h"
+#include "llvm/Analysis/CaptureTracking.h"
using namespace llvm;
+CaptureTracker::~CaptureTracker() {}
+
+namespace {
+ struct SimpleCaptureTracker : public CaptureTracker {
+ explicit SimpleCaptureTracker(bool ReturnCaptures)
+ : ReturnCaptures(ReturnCaptures), Captured(false) {}
+
+ void tooManyUses() { Captured = true; }
+
+ bool shouldExplore(Use *U) { return true; }
+
+ bool captured(Use *U) {
+ if (isa<ReturnInst>(U->getUser()) && !ReturnCaptures)
+ return false;
+
+ Captured = true;
+ return true;
+ }
+
+ bool ReturnCaptures;
+
+ bool Captured;
+ };
+}
+
/// PointerMayBeCaptured - Return true if this pointer value may be captured
/// 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) {
- assert(isa<PointerType>(V->getType()) && "Capture is for pointers only!");
- SmallVector<Use*, 16> Worklist;
- SmallSet<Use*, 16> Visited;
+bool llvm::PointerMayBeCaptured(const Value *V,
+ bool ReturnCaptures, bool StoreCaptures) {
+ assert(!isa<GlobalValue>(V) &&
+ "It doesn't make sense to ask whether a global is 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.
+ (void)StoreCaptures;
+
+ SimpleCaptureTracker SCT(ReturnCaptures);
+ 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::use_const_iterator UI = V->use_begin(), UE = V->use_end();
+ 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);
}
switch (I->getOpcode()) {
case Instruction::Call:
- if (isFreeCall(I))
- // Freeing a pointer does not cause it to be captured.
- break;
case Instruction::Invoke: {
- CallSite CS = CallSite::get(I);
+ 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() == Type::getVoidTy(V->getContext()))
+ if (CS.onlyReadsMemory() && CS.doesNotThrow() && I->getType()->isVoidTy())
break;
// Not captured if only passed via 'nocapture' arguments. Note that
// (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.paramHasAttr(A - B + 1, Attribute::NoCapture))
+ if (A->get() == V && !CS.doesNotCapture(A - B))
// The parameter is not marked 'nocapture' - captured.
- return true;
- // Only passed via 'nocapture' arguments, or is the called function - not
- // captured.
+ if (Tracker->captured(U))
+ return;
break;
}
case Instruction::Load:
// Loading from a pointer does not cause it to be captured.
break;
- case Instruction::Ret:
- if (ReturnCaptures)
- return true;
+ 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 - it may be captured.
- return true;
+ // Stored the pointer - conservatively assume it may be captured.
+ if (Tracker->captured(U))
+ return;
// Storing to the pointee does not cause the pointer to be captured.
break;
case Instruction::BitCast:
UI != UE; ++UI) {
Use *U = &UI.getUse();
if (Visited.insert(U))
- Worklist.push_back(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(U))
+ return;
+ break;
default:
// Something else - be conservative and say it is captured.
- return true;
+ if (Tracker->captured(U))
+ return;
+ break;
}
}
- // All uses examined - not captured.
- return false;
+ // All uses examined.
}
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