SILGen: Emit implicit constructors.

Teach SILGen how to emit the implicit elementwise constructor for structs and the implicit default constructor for classes, and eliminate the now dead IRGen code for them. Add a StructInst SIL instruction to represent constructing a loadable struct value from elements, analogous to TupleInst for tuples.

Swift SVN r4778

include/swift/SIL/SILInstruction.h

@@ -379,7 +379,7 @@ public:
 /// a StringLiteralExpr.
 class StringLiteralInst : public SILInstruction {
 public:
-  StringLiteralInst(StringLiteralExpr *E);
+  StringLiteralInst(StringLiteralExpr *E, SILType ty);
 
   StringLiteralExpr *getExpr() const;
 
@@ -694,7 +694,44 @@ public:
     return V->getKind() == ValueKind::SuperToArchetypeInst;
   }
 };
-  
+
+/// StructInst - Represents a constructed tuple.
+class StructInst : public SILInstruction {
+  TailAllocatedOperandList<0> Operands;
+
+  /// Private constructor.  Because of the storage requirements of
+  /// StructInst, object creation goes through 'create()'.
+  StructInst(SILLocation Loc, SILType Ty, ArrayRef<SILValue> Elements);
+  static StructInst *createImpl(SILLocation Loc, SILType Ty,
+                                ArrayRef<SILValue> Elements, SILFunction &F);
+
+public:
+  /// The elements referenced by this TupleInst.
+  MutableArrayRef<Operand> getElementOperands() {
+    return Operands.getDynamicAsArray();
+  }
+
+  /// The elements referenced by this TupleInst.
+  OperandValueArrayRef getElements() const {
+    return Operands.getDynamicValuesAsArray();
+  }
+
+  /// Construct a StructInst.
+  static StructInst *create(SILLocation Loc, SILType Ty,
+                            ArrayRef<SILValue> Elements, SILFunction &F) {
+    return createImpl(Loc, Ty, Elements, F);
+  }
+
+  /// getType() is ok since this is known to only have one type.
+  SILType getType(unsigned i = 0) const { return ValueBase::getType(i); }
+
+  ArrayRef<Operand> getAllOperands() const { return Operands.asArray(); }
+
+  static bool classof(const ValueBase *V) {
+    return V->getKind() == ValueKind::StructInst;
+  }
+};
+
 /// TupleInst - Represents a constructed tuple.
 class TupleInst : public SILInstruction {
   TailAllocatedOperandList<0> Operands;