[AST] Paren'd reference to an IUO function crashes the compiler in SILGen

lib/Sema/CSGen.cpp

@@ -2507,6 +2507,17 @@ namespace {
           CS.getConstraintLocator(expr, ConstraintLocator::FunctionResult),
           TVO_CanBindToNoEscape);
 
+      // If we have something like '(s.foo)()', where 's.foo()' returns an IUO,
+      // then we need to change the return type to be an optional, so if the
+      // user is assigning the value to a variable of type T, then we can
+      // inform the user that it needs to be T? instead.
+      if (auto overload = CS.findSelectedOverloadFor(expr->getSemanticFn())) {
+        if (overload->Choice.isImplicitlyUnwrappedValueOrReturnValue() &&
+            expr->getSemanticFn() != expr->getFn()) {
+          resultType = OptionalType::get(resultType);
+        }
+      }
+
       // A direct call to a ClosureExpr makes it noescape.
       FunctionType::ExtInfo extInfo;
       if (isa<ClosureExpr>(fnExpr->getSemanticsProvidingExpr()))

test/Constraints/iuo.swift

@@ -223,3 +223,15 @@ var y: Int = 2
 
 let r = sr6988(x: x, y: y)
 let _: Int = r
+
+// SR-10492
+
+struct SR_10492_S {
+  func foo() -> Int! { return 0 }
+}
+
+let sr_10492_s = SR_10492_S()
+let sr_10492_int1: Int = (sr_10492_s.foo)() // expected-error {{value of optional type 'Int?' must be unwrapped to a value of type 'Int'}}
+// expected-note@-1 {{coalesce}}{{44-44= ?? <#default value#>}}
+// expected-note@-2 {{force-unwrap}}{{44-44=!}}
+let sr_10492_int2: Int? = (sr_10492_s.foo)() // Okay

validation-test/compiler_crashers_2_fixed/sr10492.swift

@@ -0,0 +1,8 @@
+// RUN: not %target-swift-frontend -emit-silgen %s
+
+struct S {
+  func foo() -> Int! { return 0 }
+}
+
+let s = S()
+let x: Int = (s.foo)()