SIL: change way how a SILInstruction is marked as deleted

Instead of setting the parent pointer to null, set the `lastInitializedBitfieldID` to -1.
This allows to keep the parent block information, even when an instruction is removed from it's list.

Author: eeckstein

include/swift/SIL/SILBasicBlock.h

@@ -85,7 +85,7 @@ public SwiftObjectHeader {
   ///    DD and EEE are uninitialized
   ///
   /// See also: SILBitfield::bitfieldID, SILFunction::currentBitfieldID.
-  uint64_t lastInitializedBitfieldID = 0;
+  int64_t lastInitializedBitfieldID = 0;
 
   // Used by `BasicBlockBitfield`.
   unsigned getCustomBits() const { return customBits; }

include/swift/SIL/SILBitfield.h

@@ -30,7 +30,7 @@ template <class Impl, class T> class SILBitfield {
   /// that the bits of that block are not initialized yet.
   /// See also: SILBasicBlock::lastInitializedBitfieldID,
   ///           SILFunction::currentBitfieldID
-  uint64_t bitfieldID;
+  int64_t bitfieldID;
 
   short startBit;
   short endBit;

include/swift/SIL/SILFunction.h

@@ -266,7 +266,7 @@ class SILFunction
   /// A monotonically increasing ID which is incremented whenever a
   /// BasicBlockBitfield or NodeBitfield is constructed.
   /// For details see SILBitfield::bitfieldID;
-  uint64_t currentBitfieldID = 1;
+  int64_t currentBitfieldID = 1;
 
   /// Unique identifier for vector indexing and deterministic sorting.
   /// May be reused when zombie functions are recovered.

include/swift/SIL/SILInstruction.h

@@ -391,7 +391,7 @@ class SILInstruction : public llvm::ilist_node<SILInstruction> {
 
   /// Returns true if this instruction is removed from its function and
   /// scheduled to be deleted.
-  bool isDeleted() const { return !ParentBB; }
+  bool isDeleted() const { return asSILNode()->isMarkedAsDeleted(); }
 
   enum class MemoryBehavior {
     None,
@@ -10138,7 +10138,6 @@ struct ilist_traits<::swift::SILInstruction> :
   }
 
   void addNodeToList(SILInstruction *I);
-  void removeNodeFromList(SILInstruction *I);
   void transferNodesFromList(ilist_traits<SILInstruction> &L2,
                              instr_iterator first, instr_iterator last);
 

include/swift/SIL/SILNode.h

@@ -330,8 +330,13 @@ class alignas(8) SILNode :
   /// -> AAA, BB and C are initialized,
   ///    DD and EEE are uninitialized
   ///
+  /// If the ID is negative, it means that the node (in case it's an instruction)
+  /// is deleted, i.e. it does not belong to the function anymore. Conceptually
+  /// this results in setting all bitfields to zero, which e.g. "removes" the
+  /// node from all NodeSets.
+  ///
   /// See also: SILBitfield::bitfieldID, SILFunction::currentBitfieldID.
-  uint64_t lastInitializedBitfieldID = 0;
+  int64_t lastInitializedBitfieldID = 0;
 
 private:
   SwiftMetatype getSILNodeMetatype(SILNodeKind kind);
@@ -389,6 +394,12 @@ class alignas(8) SILNode :
     lastInitializedBitfieldID = 0;
   }
 
+  void markAsDeleted() {
+    lastInitializedBitfieldID = -1;
+  }
+
+  bool isMarkedAsDeleted() const { return lastInitializedBitfieldID < 0; }
+
   static SILNode *instAsNode(SILInstruction *inst);
   static const SILNode *instAsNode(const SILInstruction *inst);
 

lib/SIL/IR/SILBasicBlock.cpp

@@ -103,8 +103,10 @@ void SILBasicBlock::erase(SILInstruction *I) {
 }
 
 void SILBasicBlock::erase(SILInstruction *I, SILModule &module) {
+  assert(!I->isDeleted() && "double delete of instruction");
   module.willDeleteInstruction(I);
   InstList.remove(I);
+  I->asSILNode()->markAsDeleted();
   module.scheduleForDeletion(I);
 }
 
@@ -113,13 +115,11 @@ void SILBasicBlock::moveInstruction(SILInstruction *inst,
   if (inst == beforeInst)
     return;
   inst->getParent()->InstList.remove(inst);
-  inst->ParentBB = nullptr;
   beforeInst->getParent()->insert(beforeInst->getIterator(), inst);
 }
 
 void SILBasicBlock::moveInstructionToFront(SILInstruction *inst) {
   inst->getParent()->InstList.remove(inst);
-  inst->ParentBB = nullptr;
   push_front(inst);
 }
 

lib/SIL/IR/SILInstruction.cpp

@@ -61,15 +61,9 @@ SILBasicBlock *llvm::ilist_traits<SILInstruction>::getContainingBlock() {
 
 
 void llvm::ilist_traits<SILInstruction>::addNodeToList(SILInstruction *I) {
-  assert(I->ParentBB == nullptr && "Already in a list!");
   I->ParentBB = getContainingBlock();
 }
 
-void llvm::ilist_traits<SILInstruction>::removeNodeFromList(SILInstruction *I) {
-  // When an instruction is removed from a BB, clear the parent pointer.
-  I->ParentBB = nullptr;
-}
-
 void llvm::ilist_traits<SILInstruction>::
 transferNodesFromList(llvm::ilist_traits<SILInstruction> &L2,
                       instr_iterator first, instr_iterator last) {

lib/SIL/IR/SILModule.cpp

@@ -276,7 +276,6 @@ void SILModule::willDeleteInstruction(SILInstruction *I) {
 void SILModule::scheduleForDeletion(SILInstruction *I) {
   I->dropAllReferences();
   scheduledForDeletion.push_back(I);
-  I->ParentBB = nullptr;
 }
 
 void SILModule::flushDeletedInsts() {

unittests/SIL/SILBitfieldTest.cpp

@@ -21,13 +21,13 @@ class BasicBlockBitfield;
 
 struct SILFunction {
   BasicBlockBitfield *newestAliveBlockBitfield = nullptr;
-  uint64_t currentBitfieldID = 1;
+  int64_t currentBitfieldID = 1;
 };
 
 struct SILBasicBlock {
   SILFunction *function;
   uint32_t customBits = 0;
-  uint64_t lastInitializedBitfieldID = 0;
+  int64_t lastInitializedBitfieldID = 0;
 
   enum { numCustomBits = 32 };