[move-only] Fix SILCombine to preserve value deinit

Fix a special case in visitReleaseValueInst for enum-with-deinit.

Author: atrick

lib/SILOptimizer/SILCombiner/SILCombinerMiscVisitors.cpp

@@ -858,6 +858,10 @@ SILInstruction *SILCombiner::visitReleaseValueInst(ReleaseValueInst *RVI) {
   SILValue Operand = RVI->getOperand();
   SILType OperandTy = Operand->getType();
 
+  // Do not remove a release that calls a value deinit.
+  if (hasValueDeinit(OperandTy))
+    return nullptr;
+
   // Destroy value of an enum with a trivial payload or no-payload is a no-op.
   if (auto *EI = dyn_cast<EnumInst>(Operand)) {
     if (!EI->hasOperand() ||

test/SILOptimizer/sil_combine_moveonly.sil

@@ -57,3 +57,17 @@ bb0:
   %42 = tuple ()
   return %42 : $()
 }
+
+// Test that a release of a trivial payload is not removed.
+//
+// CHECK-LABEL: sil hidden [noinline] @testEnumDeinitTrivialPayload : $@convention(thin) () -> () {
+// CHECK:   release_value %{{.*}} : $MaybeFileDescriptor
+// CHECK-LABEL: } // end sil function 'testEnumDeinitTrivialPayload'
+sil hidden [noinline] @testEnumDeinitTrivialPayload : $@convention(thin) () -> () {
+bb0:
+  %0 = enum $MaybeFileDescriptor, #MaybeFileDescriptor.nothing!enumelt // users: %2, %1
+  debug_value %0 : $MaybeFileDescriptor, var, name "maybe" // id: %1
+  release_value %0 : $MaybeFileDescriptor
+  %9 = tuple ()
+  return %9 : $()
+}