Specialize interfaces in DebugFunction (#8617)

E.g. in
[generic-extension-2.slang](https://github.com/shader-slang/slang/blob/master/tests/language-feature/extensions/generic-extension-2.slang),
incorrect DebugFunctions are generated for `getFirstOuter`:

```
let  %33        : Void  = DebugFunction("getFirstOuter", 18 : UInt, 3 : UInt, %26, Func(Int, 0 : Int))
```

This happens because specialization passes are leaving a `%IFoo` in the
function type, instead of replacing with a concrete type:
```
let  %34        : Void  = DebugFunction("getFirstOuter", 18 : UInt, 3 : UInt, %26, Func(Int, %IFoo))
```
and later, `cleanUpInterfaceTypes()` just replaces all interfaces with
the literal zero. So now we have a parameter type which isn't actually a
type at all, but an IntLit instead.

I'm not sure if the approach I picked is good, though. Some other
options that crossed my mind were:
* Make `fixUpFuncType` also update related DebugFunctions
- But is there a reason why DebugFunctions separately carry a function
type in the first place?
* Make `cleanUpInterfaceTypes` less aggressive or at least replace types
with a type instead of a value
    - But this will still make the debug info incorrect :(

1 files changed, 31 insertions, 0 deletions

diff --git a/source/slang/slang-ir.cpp b/source/slang/slang-ir.cpp
index ba8864684..7b7d5ec17 100644
--- a/source/slang/slang-ir.cpp
+++ b/source/slang/slang-ir.cpp
@@ -815,6 +815,37 @@ IRType* IRFunc::getParamType(UInt index)
     return getDataType()->getParamType(index);
 }
 
+void fixUpDebugFuncType(IRFunc* func)
+{
+    SLANG_ASSERT(func);
+
+    if (auto debugFuncDecor = func->findDecoration<IRDebugFuncDecoration>())
+    {
+        auto funcType = func->getDataType();
+        auto oldDebugFunc = cast<IRDebugFunction>(debugFuncDecor->getDebugFunc());
+
+        // If the existing debug func type is already the same, there's no need
+        // to do anything.
+        if (isTypeEqual(funcType, as<IRType>(oldDebugFunc->getDebugType())))
+            return;
+
+        auto irModule = func->getModule();
+        SLANG_ASSERT(irModule);
+
+        IRBuilder builder(irModule);
+        builder.setInsertInto(irModule->getModuleInst());
+
+        auto newDebugFunc = builder.emitDebugFunction(
+            oldDebugFunc->getName(),
+            oldDebugFunc->getLine(),
+            oldDebugFunc->getCol(),
+            oldDebugFunc->getFile(),
+            funcType);
+        debugFuncDecor->removeAndDeallocate();
+        builder.addDecoration(funcType, kIROp_DebugFuncDecoration, newDebugFunc);
+    }
+}
+
 void fixUpFuncType(IRFunc* func, IRType* resultType)
 {
     SLANG_ASSERT(func);