[llvm] [SPIRV] Emit NonSemantic DebugTypedef (PR #211883)

[Juan Manuel Martinez Caamaño via llvm-commits]

================
@@ -712,6 +717,47 @@ std::optional<MCRegister> SPIRVNonSemanticDebugHandler::emitDebugTypeVector(
                      ExtInstSetReg, {BTIt->second, CountReg}, MAI);
 }
 
+std::optional<MCRegister> SPIRVNonSemanticDebugHandler::emitDebugTypedef(
+    const DIDerivedType *TD, MCRegister VoidTypeReg, MCRegister I32TypeReg,
+    MCRegister ExtInstSetReg, SPIRV::ModuleAnalysisInfo &MAI) {
+  // The underlying (base) type must already be in DebugTypeRegs.
+  auto BaseRegOpt = lookupOptReg(DebugTypeRegs, TD->getBaseType());
+  if (!BaseRegOpt)
+    return std::nullopt;
+
+  MCRegister NameReg = getCachedOpStringReg(TD->getName());
+  MCRegister FileStrReg = getCachedScopePathOpStringReg(
+      TD->getFile(), /*UseEmptyPathIfNullScope=*/true);
+  MCRegister SrcReg = getOrEmitDebugSourceForFileStrReg(FileStrReg, VoidTypeReg,
+                                                        ExtInstSetReg, MAI);
+  MCRegister LineReg =
+      emitOpConstantI32(static_cast<uint32_t>(TD->getLine()), I32TypeReg, MAI);
+  // DIDerivedType typedefs carry no column, so emit 0.
+  MCRegister ColReg = emitOpConstantI32(0, I32TypeReg, MAI);
+
+  // Parent: the enclosing type when the scope is an emitted DIType (a typedef
+  // nested in another type), otherwise the compile unit. Fall back to the
+  // compile unit rather than dropping the typedef when the scope type is not
+  // emitted.
+  MCRegister ParentReg;
+  if (const auto *Ty = dyn_cast_or_null<DIType>(TD->getScope()))
----------------
jmmartinez wrote:

It can also be a `DISubprogram`, for example in:

```cpp
int foo() {
    using A = int;
    A a = 0;
    return a;
}
```

we get:

```
!9 = distinct !DISubprogram(name: "foo", linkageName: "_Z3foov", scope: !10, file: !10, line: 1, type: !11, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !14)
...
!15 = !DIDerivedType(tag: DW_TAG_typedef, name: "A", scope: !9, file: !10, line: 2, baseType: !13)
```

---

Or is this a restriction coming from the SPIRV spec ? Does it make sense to simply go through `lookupOptReg` for whatever the scope is, and then fallback to the `CompileUnit` ?

https://github.com/llvm/llvm-project/pull/211883