[erel-matcher] Do not throw away the list of releases if we do not have a joint post-dominating release set. Instead, use a flag.

I am tuning a new argument explosion heuristic to reduce code-size. One part of
the heuristic I am playing with is the part of the algorithm that attempts to
figure out if we could eliminate additonal arguments after performing
owned->guaranteed an additional release when we run FSO a second time. Today we
do this unconditionally. I am trying to do it in a more conservative way where
we only do it if we know that we aren't going to increase the number of
arguments too much.

rdar://41146023

Author: gottesmm

include/swift/SILOptimizer/Analysis/ARCAnalysis.h

@@ -204,11 +204,47 @@ class ConsumedArgToEpilogueReleaseMatcher {
   ExitKind Kind;
   ArrayRef<SILArgumentConvention> ArgumentConventions;
 
-  using InstListTy = TinyPtrVector<SILInstruction *>;
-  llvm::SmallMapVector<SILArgument *, InstListTy, 8> ArgInstMap;
+  class ArgumentState {
+    /// The list of releases associated with this argument.
+    TinyPtrVector<SILInstruction *> releases;
 
-  /// Set to true if we found some releases but not all for the argument.
-  llvm::DenseSet<SILArgument *> FoundSomeReleases;
+    /// If this is set to true, then we know that we were able to find
+    /// a set of releases.
+    bool jointPostDominatingReleaseSet;
+
+  public:
+    ArgumentState(ArrayRef<SILInstruction *> releases)
+        : releases(releases), jointPostDominatingReleaseSet(false) {}
+
+    void addRelease(SILInstruction *release) { releases.push_back(release); }
+    void setHasJointPostDominatingReleaseSet() {
+      jointPostDominatingReleaseSet = true;
+    }
+
+    bool foundSomeButNotAllReleases() const {
+      return releases.size() && !jointPostDominatingReleaseSet;
+    }
+
+    /// If we were able to find a set of releases for this argument that joint
+    /// post-dominate the argument, return our release set.
+    Optional<ArrayRef<SILInstruction *>> getFullyPostDomReleases() const {
+      if (releases.empty() || foundSomeButNotAllReleases())
+        return None;
+      return {releases};
+    }
+
+    /// If we were able to find a set of releases for this argument, but those
+    /// releases do not joint post-dominate the argument, return our release
+    /// set.
+    ///
+    /// *NOTE* This returns none if we did not find any releases.
+    Optional<ArrayRef<SILInstruction *>> getPartiallyPostDomReleases() const {
+      if (releases.empty() || !foundSomeButNotAllReleases())
+        return None;
+      return ArrayRef<SILInstruction *>(releases);
+    }
+  };
+  llvm::SmallMapVector<SILArgument *, ArgumentState, 8> ArgInstMap;
 
   /// Eventually this will be used in place of HasBlock.
   SILBasicBlock *ProcessedBlock;
@@ -227,95 +263,97 @@ class ConsumedArgToEpilogueReleaseMatcher {
 
   bool hasBlock() const { return ProcessedBlock != nullptr; }
 
-  bool isEpilogueRelease(SILInstruction *I) const {
+  bool isEpilogueRelease(SILInstruction *i) const {
     // This is not a release instruction in the epilogue block.
-    if (I->getParent() != ProcessedBlock)
+    if (i->getParent() != ProcessedBlock)
       return false;
-    for (auto &X : ArgInstMap) {
-      // Either did not find epilogue release or found exploded epilogue
-      // releases.
-      if (X.second.size() != 1)
-        continue;
-      if (*X.second.begin() == I) 
-        return true;
-    }
-    return false;
+
+    using PairTy = const std::pair<SILArgument *, ArgumentState>;
+    return llvm::any_of(ArgInstMap, [&i](PairTy &p) {
+      auto completeList = p.second.getFullyPostDomReleases();
+      // If we did not have a complete post dominating release set, then we do
+      // not want to treat any releases from p as epilogue releases.
+      if (!completeList)
+        return false;
+
+      // Then make sure that we either found an epilogue release or found
+      // exploded epilogue releases. We rely on our callers to split up exploded
+      // parameters.
+      return completeList->size() == 1 && *completeList->begin() == i;
+    });
   }
 
   /// Return true if we've found some epilogue releases for the argument
   /// but not all.
-  bool hasSomeReleasesForArgument(SILArgument *Arg) {
-    return FoundSomeReleases.find(Arg) != FoundSomeReleases.end();
+  bool hasSomeReleasesForArgument(SILArgument *arg) const {
+    auto iter = ArgInstMap.find(arg);
+    if (iter == ArgInstMap.end())
+      return false;
+    return iter->second.foundSomeButNotAllReleases();
   }
 
-  bool isSingleRelease(SILArgument *Arg) const {
-    auto Iter = ArgInstMap.find(Arg);
-    assert(Iter != ArgInstMap.end() && "Failed to get release list for argument");
-    return Iter->second.size() == 1;
+  bool isSingleRelease(SILArgument *arg) const {
+    auto iter = ArgInstMap.find(arg);
+    assert(iter != ArgInstMap.end() &&
+           "Failed to get release list for argument");
+
+    // If we do not have a fully post dominating release set bail.
+    auto completeList = iter->second.getFullyPostDomReleases();
+    if (!completeList)
+      return false;
+
+    return completeList->size() == 1;
   }
 
-  SILInstruction *getSingleReleaseForArgument(SILArgument *Arg) {
-    auto I = ArgInstMap.find(Arg);
-    if (I == ArgInstMap.end())
+  SILInstruction *getSingleReleaseForArgument(SILArgument *arg) const {
+    auto iter = ArgInstMap.find(arg);
+    if (iter == ArgInstMap.end())
+      return nullptr;
+    if (!isSingleRelease(arg))
       return nullptr;
-    if (!isSingleRelease(Arg))
+    auto completeList = iter->second.getFullyPostDomReleases();
+    if (!completeList)
       return nullptr;
-    return *I->second.begin();
+    return *completeList->begin();
   }
 
-  SILInstruction *getSingleReleaseForArgument(SILValue V) {
-    auto *Arg = dyn_cast<SILArgument>(V);
-    if (!Arg)
+  SILInstruction *getSingleReleaseForArgument(SILValue value) const {
+    auto *arg = dyn_cast<SILArgument>(value);
+    if (!arg)
       return nullptr;
-    return getSingleReleaseForArgument(Arg);
+    return getSingleReleaseForArgument(arg);
   }
 
-  ArrayRef<SILInstruction *> getReleasesForArgument(SILArgument *Arg) {
-    auto I = ArgInstMap.find(Arg);
-    if (I == ArgInstMap.end())
+  ArrayRef<SILInstruction *> getReleasesForArgument(SILArgument *arg) const {
+    auto iter = ArgInstMap.find(arg);
+    if (iter == ArgInstMap.end())
+      return {};
+    auto completeList = iter->second.getFullyPostDomReleases();
+    if (!completeList)
       return {};
-    return I->second;
+    return completeList.getValue();
   }
 
-  ArrayRef<SILInstruction *> getReleasesForArgument(SILValue V) {
-    auto *Arg = dyn_cast<SILArgument>(V);
-    if (!Arg)
+  ArrayRef<SILInstruction *> getReleasesForArgument(SILValue value) const {
+    auto *arg = dyn_cast<SILArgument>(value);
+    if (!arg)
       return {};
-    return getReleasesForArgument(Arg);
+    return getReleasesForArgument(arg);
   }
 
   /// Recompute the mapping from argument to consumed arg.
   void recompute();
 
-  bool isSingleReleaseMatchedToArgument(SILInstruction *Inst) {
-    return count_if(
-        ArgInstMap,
-        [&Inst](const std::pair<SILArgument *, ArrayRef<SILInstruction *>> &P)
-            -> bool {
-          if (P.second.size() > 1)
-            return false;
-          return *P.second.begin() == Inst;
-        });
+  bool isSingleReleaseMatchedToArgument(SILInstruction *inst) {
+    using PairTy = const std::pair<SILArgument *, ArgumentState>;
+    return count_if(ArgInstMap, [&inst](PairTy &p) {
+      auto completeList = p.second.getFullyPostDomReleases();
+      if (!completeList || completeList->size() > 1)
+        return false;
+      return *completeList->begin() == inst;
+    });
   }
 
-  using iterator = decltype(ArgInstMap)::iterator;
-  using const_iterator = decltype(ArgInstMap)::const_iterator;
-  iterator begin() { return ArgInstMap.begin(); }
-  iterator end() { return ArgInstMap.end(); }
-  const_iterator begin() const { return ArgInstMap.begin(); }
-  const_iterator end() const { return ArgInstMap.end(); }
-
-  using reverse_iterator = decltype(ArgInstMap)::reverse_iterator;
-  using const_reverse_iterator = decltype(ArgInstMap)::const_reverse_iterator;
-  reverse_iterator rbegin() { return ArgInstMap.rbegin(); }
-  reverse_iterator rend() { return ArgInstMap.rend(); }
-  const_reverse_iterator rbegin() const { return ArgInstMap.rbegin(); }
-  const_reverse_iterator rend() const { return ArgInstMap.rend(); }
-
-  unsigned size() const { return ArgInstMap.size(); }
-
-  iterator_range<iterator> getRange() { return swift::make_range(begin(), end()); }
-
 private:
   /// Return true if we have seen releases to part or all of \p Derived in
   /// \p Insts.