Fix `specializeRTTIObject` to use non-zero RTTI value to work with `Optional<T>`. (#8677)

Closes #8673.

The issue is that we use the RTTI field of an existential to check if it
is null. We have the logic to help the user to fill in a non-zero value
for the RTTI field when such an object is filled from the host. However,
when there is slang code creating an existential value, we still have
old logic in the compiler that just fills in 0 for the RTTI field,
causing an `Optional<IFoo>.hasValue` to always return false in such
cases.

1 files changed, 3 insertions, 3 deletions

diff --git a/source/slang/slang-ir-lower-generics.cpp b/source/slang/slang-ir-lower-generics.cpp
index be21a66ba..8677973f5 100644
--- a/source/slang/slang-ir-lower-generics.cpp
+++ b/source/slang/slang-ir-lower-generics.cpp
@@ -23,11 +23,11 @@
 namespace Slang
 {
 // Replace all uses of RTTI objects with its sequential ID.
-// Currently we don't use RTTI objects at all, so all of them
-// are 0.
+// Currently we don't use RTTI objects other than check for null/invalid value,
+// so all of them are 0xFFFFFFFF.
 void specializeRTTIObjectReferences(SharedGenericsLoweringContext* sharedContext)
 {
-    uint32_t id = 0;
+    uint32_t id = 0xFFFFFFFF;
     for (auto rtti : sharedContext->mapTypeToRTTIObject)
     {
         IRBuilder builder(sharedContext->module);