When checking for ABI compatibility of a convert_function, don't compare the operand against itself, compare the operand against the convert_function result.

This was a thinko on my part.

rdar://34222540

Author: gottesmm

lib/SIL/SILInstructions.cpp

@@ -2108,15 +2108,21 @@ ConvertFunctionInst::create(SILDebugLocation DebugLoc, SILValue Operand,
   void *Buffer = Mod.allocateInst(size, alignof(ConvertFunctionInst));
   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");
+  // If we do not have lowered SIL, make sure that are not performing
+  // ABI-incompatible conversions.
+  //
+  // *NOTE* We purposely do not use an early return here to ensure that in
+  // builds without assertions this whole if statement is optimized out.
+  if (F.getModule().getStage() != SILStage::Lowered) {
+    // Make sure we are not performing ABI-incompatible conversions.
+    CanSILFunctionType opTI =
+        CFI->getOperand()->getType().castTo<SILFunctionType>();
+    (void)opTI;
+    CanSILFunctionType resTI = CFI->getType().castTo<SILFunctionType>();
+    (void)resTI;
+    assert(opTI->isABICompatibleWith(resTI).isCompatible() &&
+           "Can not convert in between ABI incompatible function types");
+  }
   return CFI;
 }