Move the CapturesBefore tracker from AA into CaptureTracking

There were two generally-useful CaptureTracker classes defined in LLVM: the
simple tracker defined in CaptureTracking (and made available via the
PointerMayBeCaptured utility function), and the CapturesBefore tracker
available only inside of AA. This change moves the CapturesBefore tracker into
CaptureTracking, generalizes it slightly (by adding a ReturnCaptures
parameter), and makes it generally available via a PointerMayBeCapturedBefore
utility function.

This logic will be needed, for example, to perform noalias function parameter
attribute inference.

No functionality change intended.

llvm-svn: 213519

1 files changed, 2 insertions, 50 deletions

diff --git a/llvm/lib/Analysis/AliasAnalysis.cpp b/llvm/lib/Analysis/AliasAnalysis.cpp
index fa1484d57de..3f1cf6aa3f8 100644
--- a/llvm/lib/Analysis/AliasAnalysis.cpp
+++ b/llvm/lib/Analysis/AliasAnalysis.cpp
@@ -388,53 +388,6 @@ AliasAnalysis::getModRefInfo(const AtomicRMWInst *RMW, const Location &Loc) {
   return ModRef;
 }
 
-namespace {
-  /// 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() override { Captured = true; }
-
-    bool shouldExplore(const Use *U) override {
-      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) &&
-          !isPotentiallyReachable(I, BeforeHere, DT))
-        return false;
-      return true;
-    }
-
-    bool captured(const Use *U) override {
-      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) &&
-          !isPotentiallyReachable(I, BeforeHere, DT))
-        return false;
-      Captured = true;
-      return true;
-    }
-
-    const Instruction *BeforeHere;
-    DominatorTree *DT;
-
-    bool Captured;
-  };
-}
-
 // FIXME: this is really just shoring-up a deficiency in alias analysis.
 // BasicAA isn't willing to spend linear time determining whether an alloca
 // was captured before or after this particular call, while we are. However,
@@ -454,9 +407,8 @@ AliasAnalysis::callCapturesBefore(const Instruction *I,
   if (!CS.getInstruction() || CS.getInstruction() == Object)
     return AliasAnalysis::ModRef;
 
-  CapturesBefore CB(I, DT);
-  llvm::PointerMayBeCaptured(Object, &CB);
-  if (CB.Captured)
+  if (llvm::PointerMayBeCapturedBefore(Object, /* ReturnCaptures */ true,
+                                       /* StoreCaptures */ true, I, DT))
     return AliasAnalysis::ModRef;
 
   unsigned ArgNo = 0;