Support initializing an existential value from a generic value. (#1503)

* Support initializing an existential value from a generic value.

* Remove trailing spaces and clean up debugging code.

1 files changed, 14 insertions, 3 deletions

diff --git a/source/slang/slang-ir-lower-generics.cpp b/source/slang/slang-ir-lower-generics.cpp
index b00e36ef1..63e1fdc49 100644
--- a/source/slang/slang-ir-lower-generics.cpp
+++ b/source/slang/slang-ir-lower-generics.cpp
@@ -2,6 +2,7 @@
 #include "slang-ir-lower-generics.h"
 
 #include "slang-ir-any-value-marshalling.h"
+#include "slang-ir-augment-make-existential.h"
 #include "slang-ir-generics-lowering-context.h"
 #include "slang-ir-lower-existential.h"
 #include "slang-ir-lower-generic-function.h"
@@ -21,9 +22,15 @@ namespace Slang
         sharedContext.module = module;
         sharedContext.sink = sink;
 
-        lowerExistentials(&sharedContext);
-        if (sink->getErrorCount() != 0)
-            return;
+        // Replace all `makeExistential` insts with `makeExistentialWithRTTI`
+        // before making any other changes. This is necessary because a parameter of
+        // generic type will be lowered into `AnyValueType`, and after that we can no longer
+        // access the original generic type parameter from the lowered parameter value.
+        // This steps ensures that the generic type parameter is available via an
+        // explicit operand in `makeExistentialWithRTTI`, so that type parameter
+        // can be translated into an RTTI object during `lower-generic-type`,
+        // and used to create a tuple representing the existential value.
+        augmentMakeExistentialInsts(module);
 
         lowerGenericFunctions(&sharedContext);
         if (sink->getErrorCount() != 0)
@@ -33,6 +40,10 @@ namespace Slang
         if (sink->getErrorCount() != 0)
             return;
 
+        lowerExistentials(&sharedContext);
+        if (sink->getErrorCount() != 0)
+            return;
+
         lowerGenericCalls(&sharedContext);
         if (sink->getErrorCount() != 0)
             return;