[clang] [CIR] Implement 'referenced-by-subobject' static-local lowering (PR #194070)

[Andy Kaylor via cfe-commits]

================
@@ -1008,10 +1008,20 @@ LValue CIRGenFunction::emitDeclRefLValue(const DeclRefExpr *e) {
     auto iter = localDeclMap.find(vd);
     if (iter != localDeclMap.end()) {
       addr = iter->second;
-    } else {
+
+    } else if (vd->isStaticLocal()) {
       // Otherwise, it might be static local we haven't emitted yet for some
       // reason; most likely, because it's in an outer function.
-      cgm.errorNYI(e->getSourceRange(), "emitDeclRefLValue: static local");
+      cir::GlobalOp var =
+          cgm.getOrCreateStaticVarDecl(*vd, cgm.getCIRLinkageVarDefinition(vd));
+      mlir::Value getGlobVal = builder.createGetGlobal(var);
+      auto getGlob = getGlobVal.getDefiningOp<cir::GetGlobalOp>();
+      getGlob.setStaticLocal(true);
----------------
andykaylor wrote:

This isn't quite right because the `static_local` attribute on GetGlobalOp isn't as general as it sounds like it would be. Per the definition (and this is enforced by the verifier) it means "this global is a function-local static variable that requires guarded initialization." So, if we get here with a static local that doesn't require a guard variable, we get a verifier error.

This example demonstrates the verifier error with this PR:

```
int referenced_inside_const() {
  static int static_local = 42;          // no guard
  auto lam = []() { return static_local; };  // setStaticLocal(true) -> verifier error
  return lam();
}
```

https://github.com/llvm/llvm-project/pull/194070