forked from OSchip/llvm-project
113 lines
4.4 KiB
C++
113 lines
4.4 KiB
C++
//===--- 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"
|
|
#include "llvm/Instructions.h"
|
|
#include "llvm/Value.h"
|
|
#include "llvm/ADT/SmallSet.h"
|
|
#include "llvm/ADT/SmallVector.h"
|
|
#include "llvm/Support/CallSite.h"
|
|
using namespace llvm;
|
|
|
|
/// 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.
|
|
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;
|
|
|
|
for (Value::use_const_iterator UI = V->use_begin(), UE = V->use_end();
|
|
UI != UE; ++UI) {
|
|
Use *U = &UI.getUse();
|
|
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 = CallSite::get(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()))
|
|
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.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.
|
|
break;
|
|
}
|
|
case Instruction::Free:
|
|
// Freeing a pointer does not cause it to be captured.
|
|
break;
|
|
case Instruction::Load:
|
|
// Loading from a pointer does not cause it to be captured.
|
|
break;
|
|
case Instruction::Ret:
|
|
if (ReturnCaptures)
|
|
return true;
|
|
break;
|
|
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.
|
|
return true;
|
|
}
|
|
}
|
|
|
|
// All uses examined - not captured.
|
|
return false;
|
|
}
|