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//===--- CaptureTracking.cpp - Determine whether a pointer is captured ----===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains routines that help determine which pointers are captured.
// A pointer value is captured if the function makes a copy of any part of the
// pointer that outlives the call. Not being captured means, more or less, that
// the pointer is only dereferenced and not stored in a global. Returning part
// of the pointer as the function return value may or may not count as capturing
// the pointer, depending on the context.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/CaptureTracking.h"
using namespace llvm;
namespace {
struct SimpleCaptureTracker {
explicit SimpleCaptureTracker(bool ReturnCaptures)
: ReturnCaptures(ReturnCaptures), Captured(false) {}
void tooManyUses() { Captured = true; }
bool shouldExplore(Use *U) { return true; }
bool captured(Instruction *I) {
if (isa<ReturnInst>(I) && !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, bool StoreCaptures) {
// 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;
}
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