Reapply r135121 with a fixed copy constructor.

Original commit message:

Count references to interference cache entries.

Each InterferenceCache::Cursor instance references a cache entry. A
non-zero reference count guarantees that the entry won't be reused for a
new register.

This makes it possible to have multiple live cursors examining
interference for different physregs.

The total number of live cursors into a cache must be kept below
InterferenceCache::getMaxCursors().

Code generation should be unaffected by this change, and it doesn't seem
to affect the cache replacement strategy either.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@135130 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 40 insertions, 3 deletions

diff --git a/lib/CodeGen/InterferenceCache.h b/lib/CodeGen/InterferenceCache.h
index 6434b3a788..7f0a27a41b 100644
--- a/lib/CodeGen/InterferenceCache.h
+++ b/lib/CodeGen/InterferenceCache.h
@@ -43,6 +43,9 @@ class InterferenceCache {
     /// change.
     unsigned Tag;
 
+    /// RefCount - The total number of Cursor instances referring to this Entry.
+    unsigned RefCount;
+
     /// MF - The current function.
     MachineFunction *MF;
 
@@ -68,9 +71,10 @@ class InterferenceCache {
     void update(unsigned MBBNum);
 
   public:
-    Entry() : PhysReg(0), Tag(0), Indexes(0) {}
+    Entry() : PhysReg(0), Tag(0), RefCount(0), Indexes(0) {}
 
     void clear(MachineFunction *mf, SlotIndexes *indexes) {
+      assert(!hasRefs() && "Cannot clear cache entry with references");
       PhysReg = 0;
       MF = mf;
       Indexes = indexes;
@@ -78,6 +82,10 @@ class InterferenceCache {
 
     unsigned getPhysReg() const { return PhysReg; }
 
+    void addRef(int Delta) { RefCount += Delta; }
+
+    bool hasRefs() const { return RefCount > 0; }
+
     void revalidate();
 
     /// valid - Return true if this is a valid entry for physReg.
@@ -122,18 +130,47 @@ public:
   void init(MachineFunction*, LiveIntervalUnion*, SlotIndexes*,
             const TargetRegisterInfo *);
 
+  /// getMaxCursors - Return the maximum number of concurrent cursors that can
+  /// be supported.
+  unsigned getMaxCursors() const { return CacheEntries; }
+
   /// Cursor - The primary query interface for the block interference cache.
   class Cursor {
     Entry *CacheEntry;
     BlockInterference *Current;
+
+    void setEntry(Entry *E) {
+      Current = 0;
+      // Update reference counts. Nothing happens when RefCount reaches 0, so
+      // we don't have to check for E == CacheEntry etc.
+      if (CacheEntry)
+        CacheEntry->addRef(-1);
+      CacheEntry = E;
+      if (CacheEntry)
+        CacheEntry->addRef(+1);
+    }
+
   public:
     /// Cursor - Create a dangling cursor.
     Cursor() : CacheEntry(0), Current(0) {}
+    ~Cursor() { setEntry(0); }
+
+    Cursor(const Cursor &O) : CacheEntry(0), Current(0) {
+      setEntry(O.CacheEntry);
+    }
+
+    Cursor &operator=(const Cursor &O) {
+      setEntry(O.CacheEntry);
+      return *this;
+    }
 
     /// setPhysReg - Point this cursor to PhysReg's interference.
     void setPhysReg(InterferenceCache &Cache, unsigned PhysReg) {
-      CacheEntry = Cache.get(PhysReg);
-      Current = 0;
+      // Release reference before getting a new one. That guarantees we can
+      // actually have CacheEntries live cursors.
+      setEntry(0);
+      if (PhysReg)
+        setEntry(Cache.get(PhysReg));
     }
 
     /// moveTo - Move cursor to basic block MBBNum.