[NFC] FSPrunedLiveness: Deduplicated isDef impls.

The version for Value and Instruction are identical except for the type
of the source of the cast to SILNode.  Add an overload for SILNode
through which the other two call.

Author: nate-chandler

include/swift/SIL/FieldSensitivePrunedLiveness.h

@@ -1362,27 +1362,26 @@ class FieldSensitiveMultiDefPrunedLiveRange
     }
   }
 
-  bool isDef(SILInstruction *inst, unsigned bit) const {
+  bool isDef(SILNode *node, unsigned bit) const {
     assert(isInitialized());
-    auto iter = defs.find(cast<SILNode>(inst));
+    auto iter = defs.find(node);
     if (!iter)
       return false;
     return llvm::any_of(
         *iter, [&](TypeTreeLeafTypeRange span) { return span.contains(bit); });
   }
 
+  bool isDef(SILInstruction *inst, unsigned bit) const {
+    return isDef(cast<SILNode>(inst), bit);
+  }
+
   bool isDef(SILValue value, unsigned bit) const {
-    assert(isInitialized());
-    auto iter = defs.find(cast<SILNode>(value));
-    if (!iter)
-      return false;
-    return llvm::any_of(
-        *iter, [&](TypeTreeLeafTypeRange span) { return span.contains(bit); });
+    return isDef(cast<SILNode>(value), bit);
   }
 
-  bool isDef(SILValue value, SmallBitVector const &bits) const {
+  bool isDef(SILNode *node, SmallBitVector const &bits) const {
     assert(isInitialized());
-    auto iter = defs.find(cast<SILNode>(value));
+    auto iter = defs.find(node);
     if (!iter)
       return false;
     SmallBitVector allBits(bits.size());
@@ -1392,36 +1391,30 @@ class FieldSensitiveMultiDefPrunedLiveRange
     return (bits & allBits) == bits;
   }
 
+  bool isDef(SILValue value, SmallBitVector const &bits) const {
+    return isDef(cast<SILNode>(value), bits);
+  }
+
   bool isDef(SILInstruction *inst, SmallBitVector const &bits) const {
-    assert(isInitialized());
-    auto iter = defs.find(cast<SILNode>(inst));
-    if (!iter)
-      return false;
-    SmallBitVector allBits(bits.size());
-    for (auto range : *iter) {
-      range.setBits(allBits);
-    }
-    return (bits & allBits) == bits;
+    return isDef(cast<SILNode>(inst), bits);
   }
 
-  bool isDef(SILInstruction *inst, TypeTreeLeafTypeRange span) const {
+  bool isDef(SILNode *node, TypeTreeLeafTypeRange span) const {
     assert(isInitialized());
-    auto iter = defs.find(cast<SILNode>(inst));
+    auto iter = defs.find(node);
     if (!iter)
       return false;
     return llvm::any_of(*iter, [&](TypeTreeLeafTypeRange storedSpan) {
       return span.setIntersection(storedSpan).has_value();
     });
   }
 
+  bool isDef(SILInstruction *inst, TypeTreeLeafTypeRange span) const {
+    return isDef(cast<SILNode>(inst), span);
+  }
+
   bool isDef(SILValue value, TypeTreeLeafTypeRange span) const {
-    assert(isInitialized());
-    auto iter = defs.find(cast<SILNode>(value));
-    if (!iter)
-      return false;
-    return llvm::any_of(*iter, [&](TypeTreeLeafTypeRange storedSpan) {
-      return span.setIntersection(storedSpan).has_value();
-    });
+    return isDef(cast<SILNode>(value), span);
   }
 
   void