[semantic-arc-opts] Create an explicit composition type for "ownership phi operands".

This is letting me refactor the implementation of every place that I work with
branches as "ownership phi operands" to instead work with
OwnershipPhiOperand. In a future commit, I am going to use this to add support
for optimizing structs and tuples that have multiple owned incoming values.

<rdar://problem/63950481>

Author: gottesmm

include/swift/SIL/OwnershipUtils.h

@@ -598,8 +598,12 @@ struct OwnedValueIntroducer {
   }
 
   /// Returns true if this owned introducer is able to be converted into a
-  /// guaranteed form if none of its uses are consuming uses (looking through
-  /// forwarding uses).
+  /// guaranteed form if none of its direct uses are consuming uses (looking
+  /// through forwarding uses).
+  ///
+  /// NOTE: Since the direct uses must be non-consuming, this means that any
+  /// "ownership phis" (e.x. branch, struct) must return false here since we can
+  /// not analyze them without analyzing their operands/incoming values.
   bool isConvertableToGuaranteed() const {
     switch (kind) {
     case OwnedValueIntroducerKind::Copy:
@@ -619,6 +623,28 @@ struct OwnedValueIntroducer {
     llvm_unreachable("Covered switch isn't covered?!");
   }
 
+  /// Returns true if this introducer when converted to guaranteed is expected
+  /// to have guaranteed operands that are consumed by the instruction.
+  ///
+  /// E.x.: phi, struct.
+  bool hasConsumingGuaranteedOperands() const {
+    switch (kind) {
+    case OwnedValueIntroducerKind::Phi:
+      return true;
+    case OwnedValueIntroducerKind::Copy:
+    case OwnedValueIntroducerKind::LoadCopy:
+    case OwnedValueIntroducerKind::Apply:
+    case OwnedValueIntroducerKind::BeginApply:
+    case OwnedValueIntroducerKind::TryApply:
+    case OwnedValueIntroducerKind::LoadTake:
+    case OwnedValueIntroducerKind::FunctionArgument:
+    case OwnedValueIntroducerKind::PartialApplyInit:
+    case OwnedValueIntroducerKind::AllocBoxInit:
+    case OwnedValueIntroducerKind::AllocRefInit:
+      return false;
+    }
+  }
+
   bool operator==(const OwnedValueIntroducer &other) const {
     return value == other.value;
   }

include/swift/SIL/SILArgument.h

@@ -148,6 +148,14 @@ class SILArgument : public ValueBase {
   bool
   getIncomingPhiOperands(SmallVectorImpl<Operand *> &returnedPhiOperands) const;
 
+  /// If this argument is a true phi, for each operand in each predecessor block
+  /// associated with an incoming value, call visitor(op). Visitor must return
+  /// true for iteration to continue. False to stop it.
+  ///
+  /// Returns false if this is not a true phi or that a visitor signaled error
+  /// by returning false.
+  bool visitIncomingPhiOperands(function_ref<bool(Operand *)> visitor) const;
+
   /// Returns true if we were able to find a single terminator operand value for
   /// each predecessor of this arguments basic block. The found values are
   /// stored in OutArray.
@@ -248,6 +256,13 @@ class SILPhiArgument : public SILArgument {
   bool
   getIncomingPhiOperands(SmallVectorImpl<Operand *> &returnedPhiOperands) const;
 
+  /// If this argument is a phi, call visitor for each passing the operand for
+  /// each incoming phi values for each predecessor BB. If this argument is not
+  /// a phi, return false.
+  ///
+  /// If visitor returns false, iteration is stopped and we return false.
+  bool visitIncomingPhiOperands(function_ref<bool(Operand *)> visitor) const;
+
   /// Returns true if we were able to find a single terminator operand value for
   /// each predecessor of this arguments basic block. The found values are
   /// stored in OutArray.
@@ -442,6 +457,17 @@ inline bool SILArgument::getIncomingPhiOperands(
   llvm_unreachable("Covered switch is not covered?!");
 }
 
+inline bool SILArgument::visitIncomingPhiOperands(
+    function_ref<bool(Operand *)> visitor) const {
+  switch (getKind()) {
+  case SILArgumentKind::SILPhiArgument:
+    return cast<SILPhiArgument>(this)->visitIncomingPhiOperands(visitor);
+  case SILArgumentKind::SILFunctionArgument:
+    return false;
+  }
+  llvm_unreachable("Covered switch is not covered?!");
+}
+
 } // end swift namespace
 
 #endif

lib/SIL/IR/SILArgument.cpp

@@ -169,6 +169,28 @@ bool SILPhiArgument::getIncomingPhiOperands(
   return true;
 }
 
+bool SILPhiArgument::visitIncomingPhiOperands(
+    function_ref<bool(Operand *)> visitor) const {
+  if (!isPhiArgument())
+    return false;
+
+  const auto *parentBlock = getParent();
+  assert(!parentBlock->pred_empty());
+
+  unsigned argIndex = getIndex();
+  for (auto *predBlock : getParent()->getPredecessorBlocks()) {
+    Operand *incomingOperand =
+        getIncomingPhiOperandForPred(parentBlock, predBlock, argIndex);
+    assert(incomingOperand);
+
+    // Call the visitor, bailing if the callee signals error.
+    if (!visitor(incomingOperand)) {
+      return false;
+    }
+  }
+  return true;
+}
+
 bool SILPhiArgument::getIncomingPhiValues(
     SmallVectorImpl<std::pair<SILBasicBlock *, SILValue>>
         &returnedPredBBAndPhiValuePairs) const {