#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/CaptureTracking.h"
+#include "llvm/Analysis/OrderedBasicBlock.h"
+#include "llvm/IR/CallSite.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Instructions.h"
+
using namespace llvm;
CaptureTracker::~CaptureTracker() {}
-bool CaptureTracker::shouldExplore(Use *U) { return true; }
+bool CaptureTracker::shouldExplore(const Use *U) { return true; }
namespace {
struct SimpleCaptureTracker : public CaptureTracker {
explicit SimpleCaptureTracker(bool ReturnCaptures)
: ReturnCaptures(ReturnCaptures), Captured(false) {}
- void tooManyUses() { Captured = true; }
+ void tooManyUses() override { Captured = true; }
+
+ bool captured(const Use *U) override {
+ if (isa<ReturnInst>(U->getUser()) && !ReturnCaptures)
+ return false;
+
+ Captured = true;
+ return true;
+ }
+
+ bool ReturnCaptures;
+
+ bool Captured;
+ };
+
+ /// Only find pointer captures which happen before the given instruction. Uses
+ /// the dominator tree to determine whether one instruction is before another.
+ /// Only support the case where the Value is defined in the same basic block
+ /// as the given instruction and the use.
+ struct CapturesBefore : public CaptureTracker {
+
+ CapturesBefore(bool ReturnCaptures, const Instruction *I, DominatorTree *DT,
+ bool IncludeI, OrderedBasicBlock *IC)
+ : OrderedBB(IC), BeforeHere(I), DT(DT),
+ ReturnCaptures(ReturnCaptures), IncludeI(IncludeI), Captured(false) {}
+
+ void tooManyUses() override { Captured = true; }
+
+ bool isSafeToPrune(Instruction *I) {
+ BasicBlock *BB = I->getParent();
+ // We explore this usage only if the usage can reach "BeforeHere".
+ // If use is not reachable from entry, there is no need to explore.
+ if (BeforeHere != I && !DT->isReachableFromEntry(BB))
+ return true;
+
+ // Compute the case where both instructions are inside the same basic
+ // block. Since instructions in the same BB as BeforeHere are numbered in
+ // 'OrderedBB', avoid using 'dominates' and 'isPotentiallyReachable'
+ // which are very expensive for large basic blocks.
+ if (BB == BeforeHere->getParent()) {
+ // 'I' dominates 'BeforeHere' => not safe to prune.
+ //
+ // The value defined by an invoke dominates an instruction only if it
+ // dominates every instruction in UseBB. A PHI is dominated only if
+ // the instruction dominates every possible use in the UseBB. Since
+ // UseBB == BB, avoid pruning.
+ if (isa<InvokeInst>(BeforeHere) || isa<PHINode>(I) || I == BeforeHere)
+ return false;
+ if (!OrderedBB->dominates(BeforeHere, I))
+ return false;
+
+ // 'BeforeHere' comes before 'I', it's safe to prune if we also
+ // guarantee that 'I' never reaches 'BeforeHere' through a back-edge or
+ // by its successors, i.e, prune if:
+ //
+ // (1) BB is an entry block or have no sucessors.
+ // (2) There's no path coming back through BB sucessors.
+ if (BB == &BB->getParent()->getEntryBlock() ||
+ !BB->getTerminator()->getNumSuccessors())
+ return true;
+
+ SmallVector<BasicBlock*, 32> Worklist;
+ Worklist.append(succ_begin(BB), succ_end(BB));
+ if (!isPotentiallyReachableFromMany(Worklist, BB, DT))
+ return true;
+
+ return false;
+ }
+
+ // If the value is defined in the same basic block as use and BeforeHere,
+ // there is no need to explore the use if BeforeHere dominates use.
+ // Check whether there is a path from I to BeforeHere.
+ if (BeforeHere != I && DT->dominates(BeforeHere, I) &&
+ !isPotentiallyReachable(I, BeforeHere, DT))
+ return true;
+
+ return false;
+ }
+
+ bool shouldExplore(const Use *U) override {
+ Instruction *I = cast<Instruction>(U->getUser());
+
+ if (BeforeHere == I && !IncludeI)
+ return false;
+
+ if (isSafeToPrune(I))
+ return false;
+
+ return true;
+ }
- bool captured(Use *U) {
+ bool captured(const Use *U) override {
if (isa<ReturnInst>(U->getUser()) && !ReturnCaptures)
return false;
+ if (!shouldExplore(U))
+ return false;
+
Captured = true;
return true;
}
+ OrderedBasicBlock *OrderedBB;
+ const Instruction *BeforeHere;
+ DominatorTree *DT;
+
bool ReturnCaptures;
+ bool IncludeI;
bool Captured;
};
return SCT.Captured;
}
+/// PointerMayBeCapturedBefore - Return true if this pointer value may be
+/// captured by the enclosing function (which is required to exist). If a
+/// DominatorTree is provided, only captures which happen before the given
+/// instruction are considered. 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. A ordered basic block \p OBB can be used in order to speed up
+/// queries about relative order among instructions in the same basic block.
+bool llvm::PointerMayBeCapturedBefore(const Value *V, bool ReturnCaptures,
+ bool StoreCaptures, const Instruction *I,
+ DominatorTree *DT, bool IncludeI,
+ OrderedBasicBlock *OBB) {
+ assert(!isa<GlobalValue>(V) &&
+ "It doesn't make sense to ask whether a global is captured.");
+ bool UseNewOBB = OBB == nullptr;
+
+ if (!DT)
+ return PointerMayBeCaptured(V, ReturnCaptures, StoreCaptures);
+ if (UseNewOBB)
+ OBB = new OrderedBasicBlock(I->getParent());
+
+ // TODO: See comment in PointerMayBeCaptured regarding what could be done
+ // with StoreCaptures.
+
+ CapturesBefore CB(ReturnCaptures, I, DT, IncludeI, OBB);
+ PointerMayBeCaptured(V, &CB);
+
+ if (UseNewOBB)
+ delete OBB;
+ return CB.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.
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;
+ SmallVector<const Use *, Threshold> Worklist;
+ SmallSet<const Use *, Threshold> Visited;
int Count = 0;
- for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end();
- UI != UE; ++UI) {
+ for (const Use &U : V->uses()) {
// 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);
+ if (!Tracker->shouldExplore(&U)) continue;
+ Visited.insert(&U);
+ Worklist.push_back(&U);
}
while (!Worklist.empty()) {
- Use *U = Worklist.pop_back_val();
+ const Use *U = Worklist.pop_back_val();
Instruction *I = cast<Instruction>(U->getUser());
V = U->get();
case Instruction::GetElementPtr:
case Instruction::PHI:
case Instruction::Select:
+ case Instruction::AddrSpaceCast:
// 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);
+ Count = 0;
+ for (Use &UU : I->uses()) {
+ // 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();
+
+ if (Visited.insert(&UU).second)
+ if (Tracker->shouldExplore(&UU))
+ Worklist.push_back(&UU);
}
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)
+ if (ConstantPointerNull *CPN =
+ dyn_cast<ConstantPointerNull>(I->getOperand(1)))
+ if (CPN->getType()->getAddressSpace() == 0)
+ if (isNoAliasCall(V->stripPointerCasts()))
break;
// Otherwise, be conservative. There are crazy ways to capture pointers
// using comparisons.
projects / oota-llvm.git / blobdiff