[CaptureTracking] Allow passing LI to PointerMayBeCapturedBefore (NFC).

[fhahn]

Summary

isPotentiallyReachable can use LoopInfo to return earlier. This patch
allows passing an optional LI to PointerMayBeCapturedBefore. Used in
D109844.

[nikic]

LGTM, though I think I tried that in the past, and didn't see any significant impact on compile-time.

llvm/include/llvm/Analysis/CaptureTracking.h

 
 namespace llvm {
 
   class Value;
   class Use;
   class DataLayout;
   class Instruction;
   class DominatorTree;
+  class LoopInfo;
 
   /// getDefaultMaxUsesToExploreForCaptureTracking - Return default value of
   /// the maximal number of uses to explore before giving up. It is used by
   /// PointerMayBeCaptured family analysis.
   unsigned getDefaultMaxUsesToExploreForCaptureTracking();
 
   /// PointerMayBeCaptured - Return true if this pointer value may be captured
   /// by the enclosing function (which is required to exist).  This routine can
namespace llvm {
   /// 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. Captures by the provided instruction are considered if the
   /// final parameter is true.
   /// MaxUsesToExplore specifies how many uses the analysis should explore for
   /// one value before giving up due too "too many uses". If MaxUsesToExplore
   /// is zero, a default value is assumed.
-  bool PointerMayBeCapturedBefore(
-      const Value *V, bool ReturnCaptures, bool StoreCaptures,
-      const Instruction *I, const DominatorTree *DT, bool IncludeI = false,
-      unsigned MaxUsesToExplore = 0);
+  bool PointerMayBeCapturedBefore(const Value *V, bool ReturnCaptures,
+                                  bool StoreCaptures, const Instruction *I,
+                                  const DominatorTree *DT,
+                                  bool IncludeI = false,
+                                  unsigned MaxUsesToExplore = 0,
+                                  const LoopInfo *LI = nullptr);
 
   /// This callback is used in conjunction with PointerMayBeCaptured. In
   /// addition to the interface here, you'll need to provide your own getters
   /// to see whether anything was captured.
   struct CaptureTracker {
     virtual ~CaptureTracker();
 
     /// tooManyUses - The depth of traversal has breached a limit. There may be

llvm/lib/Analysis/CaptureTracking.cpp

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(bool ReturnCaptures, const Instruction *I, const DominatorTree *DT,
-                   bool IncludeI)
-      : BeforeHere(I), DT(DT),
-        ReturnCaptures(ReturnCaptures), IncludeI(IncludeI), Captured(false) {}
+    CapturesBefore(bool ReturnCaptures, const Instruction *I,
+                   const DominatorTree *DT, bool IncludeI, const LoopInfo *LI)
+        : BeforeHere(I), DT(DT), ReturnCaptures(ReturnCaptures),
+          IncludeI(IncludeI), Captured(false), LI(LI) {}
 
     void tooManyUses() override { Captured = true; }
 
     bool isSafeToPrune(Instruction *I) {
       if (BeforeHere == I)
         return !IncludeI;
 
       // 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 (!DT->isReachableFromEntry(I->getParent()))
         return true;
 
       // Check whether there is a path from I to BeforeHere.
-      return !isPotentiallyReachable(I, BeforeHere, nullptr, DT);
+      return !isPotentiallyReachable(I, BeforeHere, nullptr, DT, LI);
     }
 
     bool captured(const Use *U) override {
       Instruction *I = cast<Instruction>(U->getUser());
       if (isa<ReturnInst>(I) && !ReturnCaptures)
         return false;
 
       // Check isSafeToPrune() here rather than in shouldExplore() to avoid
       // an expensive reachability query for every instruction we look at.
       // Instead we only do one for actual capturing candidates.
       if (isSafeToPrune(I))
         return false;
 
       Captured = true;
       return true;
     }
 
     const Instruction *BeforeHere;
     const DominatorTree *DT;
 
     bool ReturnCaptures;
     bool IncludeI;
 
     bool Captured;
+
+    const LoopInfo *LI;
   };
 }
 
 /// 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

 /// 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::PointerMayBeCapturedBefore(const Value *V, bool ReturnCaptures,
                                       bool StoreCaptures, const Instruction *I,
                                       const DominatorTree *DT, bool IncludeI,
-                                      unsigned MaxUsesToExplore) {
+                                      unsigned MaxUsesToExplore,
+                                      const LoopInfo *LI) {
   assert(!isa<GlobalValue>(V) &&
          "It doesn't make sense to ask whether a global is captured.");
 
   if (!DT)
     return PointerMayBeCaptured(V, ReturnCaptures, StoreCaptures,
                                 MaxUsesToExplore);
 
   // TODO: See comment in PointerMayBeCaptured regarding what could be done
   // with StoreCaptures.
 
-  CapturesBefore CB(ReturnCaptures, I, DT, IncludeI);
+  CapturesBefore CB(ReturnCaptures, I, DT, IncludeI, LI);
   PointerMayBeCaptured(V, &CB, MaxUsesToExplore);
   if (CB.Captured)
     ++NumCapturedBefore;
   else
     ++NumNotCapturedBefore;
   return CB.Captured;
 }