[sil] Add a forwarding cast called unchecked_value_cast.

Today unchecked_bitwise_cast returns a value with ObjCUnowned ownership. This is
important to do since the instruction can truncate memory meaning we want to
treat it as a new object that must be copied before use.

This means that in OSSA we do not have a purely ossa forwarding unchecked
layout-compatible assuming cast. This role is filled by unchecked_value_cast.

Author: gottesmm

docs/SIL.rst

@@ -5148,6 +5148,21 @@ unchecked_bitwise_cast
 Bitwise copies an object of type ``A`` into a new object of type ``B``
 of the same size or smaller.
 
+unchecked_value_cast
+````````````````````
+::
+
+   sil-instruction ::= 'unchecked_value_cast' sil-operand 'to' sil-type
+
+   %1 = unchecked_value_cast %0 : $A to $B
+
+Bitwise copies an object of type ``A`` into a new layout-compatible object of
+type ``B`` of the same size.
+
+This instruction is assumed to forward a fixed ownership (set upon its
+construction) and lowers to 'unchecked_bitwise_cast' in non-ossa code. This
+causes the cast to lose its guarantee of layout-compatibility.
+
 ref_to_raw_pointer
 ``````````````````
 ::

include/swift/SIL/SILBuilder.h

@@ -1102,6 +1102,12 @@ class SILBuilder {
         getSILDebugLocation(Loc), Op, Ty, getFunction(), C.OpenedArchetypes));
   }
 
+  UncheckedValueCastInst *createUncheckedValueCast(SILLocation Loc, SILValue Op,
+                                                   SILType Ty) {
+    return insert(UncheckedValueCastInst::create(
+        getSILDebugLocation(Loc), Op, Ty, getFunction(), C.OpenedArchetypes));
+  }
+
   RefToBridgeObjectInst *createRefToBridgeObject(SILLocation Loc, SILValue Ref,
                                                  SILValue Bits) {
     auto Ty = SILType::getBridgeObjectType(getASTContext());

include/swift/SIL/SILCloner.h

@@ -1538,6 +1538,16 @@ visitUncheckedBitwiseCastInst(UncheckedBitwiseCastInst *Inst) {
                                     getOpType(Inst->getType())));
 }
 
+template <typename ImplClass>
+void SILCloner<ImplClass>::visitUncheckedValueCastInst(
+    UncheckedValueCastInst *Inst) {
+  getBuilder().setCurrentDebugScope(getOpScope(Inst->getDebugScope()));
+  recordClonedInstruction(Inst, getBuilder().createUncheckedValueCast(
+                                    getOpLocation(Inst->getLoc()),
+                                    getOpValue(Inst->getOperand()),
+                                    getOpType(Inst->getType())));
+}
+
 template<typename ImplClass>
 void
 SILCloner<ImplClass>::

include/swift/SIL/SILInstruction.h

@@ -4576,6 +4576,23 @@ class UncheckedBitwiseCastInst final
          SILFunction &F, SILOpenedArchetypesState &OpenedArchetypes);
 };
 
+/// Bitwise copy a value into another value of the same size.
+class UncheckedValueCastInst final
+    : public UnaryInstructionWithTypeDependentOperandsBase<
+          SILInstructionKind::UncheckedValueCastInst, UncheckedValueCastInst,
+          OwnershipForwardingConversionInst> {
+  friend SILBuilder;
+
+  UncheckedValueCastInst(SILDebugLocation DebugLoc, SILValue Operand,
+                         ArrayRef<SILValue> TypeDependentOperands, SILType Ty)
+      : UnaryInstructionWithTypeDependentOperandsBase(
+            DebugLoc, Operand, TypeDependentOperands, Ty,
+            Operand.getOwnershipKind()) {}
+  static UncheckedValueCastInst *
+  create(SILDebugLocation DebugLoc, SILValue Operand, SILType Ty,
+         SILFunction &F, SILOpenedArchetypesState &OpenedArchetypes);
+};
+
 /// Build a Builtin.BridgeObject from a heap object reference by bitwise-or-ing
 /// in bits from a word.
 class RefToBridgeObjectInst

include/swift/SIL/SILNodes.def

@@ -500,6 +500,8 @@ ABSTRACT_VALUE_AND_INST(SingleValueInstruction, ValueBase, SILInstruction)
                       ConversionInst, None, DoesNotRelease)
     SINGLE_VALUE_INST(UncheckedBitwiseCastInst, unchecked_bitwise_cast,
                       ConversionInst, None, DoesNotRelease)
+    SINGLE_VALUE_INST(UncheckedValueCastInst, unchecked_value_cast,
+                      ConversionInst, None, DoesNotRelease)
     SINGLE_VALUE_INST(RefToRawPointerInst, ref_to_raw_pointer,
                       ConversionInst, None, DoesNotRelease)
     SINGLE_VALUE_INST(RawPointerToRefInst, raw_pointer_to_ref,

lib/IRGen/IRGenSIL.cpp

@@ -1026,6 +1026,9 @@ class IRGenSILFunction :
   void visitUncheckedAddrCastInst(UncheckedAddrCastInst *i);
   void visitUncheckedTrivialBitCastInst(UncheckedTrivialBitCastInst *i);
   void visitUncheckedBitwiseCastInst(UncheckedBitwiseCastInst *i);
+  void visitUncheckedValueCastInst(UncheckedValueCastInst *i) {
+    llvm_unreachable("Should never be seen in Lowered SIL");
+  }
   void visitRefToRawPointerInst(RefToRawPointerInst *i);
   void visitRawPointerToRefInst(RawPointerToRefInst *i);
   void visitThinToThickFunctionInst(ThinToThickFunctionInst *i);

lib/SIL/IR/OperandOwnership.cpp

@@ -350,6 +350,7 @@ FORWARD_ANY_OWNERSHIP_INST(DestructureTuple)
 FORWARD_ANY_OWNERSHIP_INST(InitExistentialRef)
 FORWARD_ANY_OWNERSHIP_INST(DifferentiableFunction)
 FORWARD_ANY_OWNERSHIP_INST(LinearFunction)
+FORWARD_ANY_OWNERSHIP_INST(UncheckedValueCast)
 #undef FORWARD_ANY_OWNERSHIP_INST
 
 // An instruction that forwards a constant ownership or trivial ownership.

lib/SIL/IR/SILInstructions.cpp

@@ -2217,6 +2217,21 @@ UncheckedRefCastInst::create(SILDebugLocation DebugLoc, SILValue Operand,
                                              TypeDependentOperands, Ty);
 }
 
+UncheckedValueCastInst *
+UncheckedValueCastInst::create(SILDebugLocation DebugLoc, SILValue Operand,
+                               SILType Ty, SILFunction &F,
+                               SILOpenedArchetypesState &OpenedArchetypes) {
+  SILModule &Mod = F.getModule();
+  SmallVector<SILValue, 8> TypeDependentOperands;
+  collectTypeDependentOperands(TypeDependentOperands, OpenedArchetypes, F,
+                               Ty.getASTType());
+  unsigned size =
+      totalSizeToAlloc<swift::Operand>(1 + TypeDependentOperands.size());
+  void *Buffer = Mod.allocateInst(size, alignof(UncheckedValueCastInst));
+  return ::new (Buffer)
+      UncheckedValueCastInst(DebugLoc, Operand, TypeDependentOperands, Ty);
+}
+
 UncheckedAddrCastInst *
 UncheckedAddrCastInst::create(SILDebugLocation DebugLoc, SILValue Operand,
                               SILType Ty, SILFunction &F,

lib/SIL/IR/SILPrinter.cpp

@@ -1620,6 +1620,9 @@ class SILPrinter : public SILInstructionVisitor<SILPrinter> {
   void visitUncheckedBitwiseCastInst(UncheckedBitwiseCastInst *CI) {
     printUncheckedConversionInst(CI, CI->getOperand());
   }
+  void visitUncheckedValueCastInst(UncheckedValueCastInst *CI) {
+    printUncheckedConversionInst(CI, CI->getOperand());
+  }
   void visitRefToRawPointerInst(RefToRawPointerInst *CI) {
     printUncheckedConversionInst(CI, CI->getOperand());
   }

lib/SIL/IR/ValueOwnership.cpp

@@ -254,6 +254,7 @@ FORWARDING_OWNERSHIP_INST(Tuple)
 FORWARDING_OWNERSHIP_INST(UncheckedRefCast)
 FORWARDING_OWNERSHIP_INST(UnconditionalCheckedCast)
 FORWARDING_OWNERSHIP_INST(Upcast)
+FORWARDING_OWNERSHIP_INST(UncheckedValueCast)
 FORWARDING_OWNERSHIP_INST(UncheckedEnumData)
 FORWARDING_OWNERSHIP_INST(SelectEnum)
 FORWARDING_OWNERSHIP_INST(Enum)