-namespace {
- // Conservatively return true. Return false, if there is a single path
- // starting from "From" and the path does not reach "To".
- static bool hasPath(const BasicBlock *From, const BasicBlock *To) {
- const unsigned MaxCheck = 5;
- const BasicBlock *Current = From;
- for (unsigned I = 0; I < MaxCheck; I++) {
- unsigned NumSuccs = Current->getTerminator()->getNumSuccessors();
- if (NumSuccs > 1)
- return true;
- if (NumSuccs == 0)
- return false;
- Current = Current->getTerminator()->getSuccessor(0);
- if (Current == To)
- return true;
- }
- return true;
- }
-
- /// 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(const Instruction *I, DominatorTree *DT)
- : BeforeHere(I), DT(DT), Captured(false) {}
-
- void tooManyUses() { Captured = true; }
-
- bool shouldExplore(Use *U) {
- Instruction *I = cast<Instruction>(U->getUser());
- 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 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) &&
- !hasPath(BB, BeforeHere->getParent()))
- return false;
- return true;
- }
-
- bool captured(Use *U) {
- Instruction *I = cast<Instruction>(U->getUser());
- BasicBlock *BB = I->getParent();
- // Same logic as in shouldExplore.
- if (BeforeHere != I && !DT->isReachableFromEntry(BB))
- return false;
- if (BeforeHere != I && DT->dominates(BeforeHere, I) &&
- !hasPath(BB, BeforeHere->getParent()))
- return false;
- Captured = true;
- return true;
- }
-
- const Instruction *BeforeHere;
- DominatorTree *DT;
-
- bool Captured;
- };
-}
-