[sil] Catch if we are creating ABI incompatible convert_function instructions when constructing the inst.

I ran into this earlier today. It is a pretty annoying error to track down in
SILGen since the verifier doesn't run until the full function is emitted. With
this change, we get a check immediately when the value is constructed by
SILBuilder making it a very easy problem to track down.

Author: gottesmm

lib/SIL/SILInstructions.cpp

@@ -2107,8 +2107,18 @@ ConvertFunctionInst::create(SILDebugLocation DebugLoc, SILValue Operand,
   unsigned size =
     totalSizeToAlloc<swift::Operand>(1 + TypeDependentOperands.size());
   void *Buffer = Mod.allocateInst(size, alignof(ConvertFunctionInst));
-  return ::new (Buffer) ConvertFunctionInst(DebugLoc, Operand,
-                                            TypeDependentOperands, Ty);
+  auto *CFI = ::new (Buffer)
+      ConvertFunctionInst(DebugLoc, Operand, TypeDependentOperands, Ty);
+  // Make sure we are not performing ABI-incompatible conversions.
+  CanSILFunctionType opTI =
+      CFI->getOperand()->getType().castTo<SILFunctionType>();
+  (void)opTI;
+  CanSILFunctionType resTI =
+      CFI->getOperand()->getType().castTo<SILFunctionType>();
+  (void)resTI;
+  assert(opTI->isABICompatibleWith(resTI).isCompatible() &&
+         "Can not convert in between ABI incompatible function types");
+  return CFI;
 }
 
 bool KeyPathPatternComponent::isComputedSettablePropertyMutating() const {