Eliminate empty struct on metal target (#6603)

* Eliminate empty struct on metal target

Close 6573.

We previously disabled the type legalization for ParameterBlock on
Metal, but Metal doesn't allow empty struct in the argument buffer
which is mapped from ParameterBlock, so we will need legalizeEmptyTypes
on Metal target.

* update test

* update function name

1 files changed, 10 insertions, 0 deletions

diff --git a/source/slang/slang-ir-legalize-types.cpp b/source/slang/slang-ir-legalize-types.cpp
index 197cd93c5..837193abc 100644
--- a/source/slang/slang-ir-legalize-types.cpp
+++ b/source/slang/slang-ir-legalize-types.cpp
@@ -4123,6 +4123,11 @@ struct IREmptyTypeLegalizationContext : IRTypeLegalizationContext
 
     bool isSimpleType(IRType* type) override
     {
+        if (isMetalTarget(targetProgram->getTargetReq()))
+        {
+            return false;
+        }
+
         // If type is used as public interface, then treat it as simple.
         for (auto decor : type->getDecorations())
         {
@@ -4145,6 +4150,11 @@ struct IREmptyTypeLegalizationContext : IRTypeLegalizationContext
     {
         return LegalType();
     }
+
+    virtual bool shouldLegalizeParameterBlockElementType() override
+    {
+        return isMetalTarget(targetProgram->getTargetReq());
+    }
 };
 
 // The main entry points that are used when transforming IR code