Add SILValue::isFromVarDecl utility.

Author: atrick

include/swift/SIL/SILInstruction.h

@@ -1978,6 +1978,7 @@ enum HasPointerEscape_t : bool {
   HasPointerEscape = true,
 };
 
+// See SILValue::isFromVarDecl()
 enum IsFromVarDecl_t : bool {
   IsNotFromVarDecl = false,
   IsFromVarDecl = true,

include/swift/SIL/SILValue.h

@@ -609,6 +609,12 @@ class ValueBase : public SILNode, public SILAllocated<ValueBase> {
   /// (it has a debug_value [trace] user).
   bool hasDebugTrace() const;
 
+  /// Does this SILValue begin a VarDecl scope? Only true in OSSA.
+  ///
+  /// If this is true, the value must be a SingleValueInstruction whose first
+  /// operand is the variable's initial value.
+  bool isFromVarDecl();
+
   static bool classof(SILNodePointer node) {
     return node->getKind() >= SILNodeKind::First_ValueBase &&
            node->getKind() <= SILNodeKind::Last_ValueBase;

lib/SIL/IR/SILValue.cpp

@@ -209,6 +209,16 @@ bool ValueBase::hasDebugTrace() const {
   return false;
 }
 
+bool ValueBase::isFromVarDecl() {
+  if (auto *mvi = dyn_cast<MoveValueInst>(this)) {
+    return mvi->isFromVarDecl();
+  }
+  if (auto *bbi = dyn_cast<BeginBorrowInst>(this)) {
+    return bbi->isFromVarDecl();
+  }
+  return false;
+}
+
 SILBasicBlock *SILNode::getParentBlock() const {
   if (auto *Inst = dyn_cast<SILInstruction>(this))
     return Inst->getParent();