Auto merge of #68828 - oli-obk:inline_cycle, r=wesleywiser

Prevent query cycles in the MIR inliner

r? `@eddyb` `@wesleywiser`

cc `@rust-lang/wg-mir-opt`

The general design is that we have a new query that is run on the `validated_mir` instead of on the `optimized_mir`. That query is forced before going into the optimization pipeline, so as to not try to read from a stolen MIR.

The query should not be cached cross crate, as you should never call it for items from other crates. By its very design calls into other crates can never cause query cycles.

This is a pessimistic approach to inlining, since we strictly have more calls in the `validated_mir` than we have in `optimized_mir`, but that's not a problem imo.

compiler/rustc_middle/src/query/mod.rs

@@ -782,6 +782,27 @@ rustc_queries! {
     }
 
     Other {
+        /// Check whether the function has any recursion that could cause the inliner to trigger
+        /// a cycle. Returns the call stack causing the cycle. The call stack does not contain the
+        /// current function, just all intermediate functions.
+        query mir_callgraph_reachable(key: (ty::Instance<'tcx>, LocalDefId)) -> bool {
+            fatal_cycle
+            desc { |tcx|
+                "computing if `{}` (transitively) calls `{}`",
+                key.0,
+                tcx.def_path_str(key.1.to_def_id()),
+            }
+        }
+
+        /// Obtain all the calls into other local functions
+        query mir_inliner_callees(key: ty::InstanceDef<'tcx>) -> &'tcx [(DefId, SubstsRef<'tcx>)] {
+            fatal_cycle
+            desc { |tcx|
+                "computing all local function calls in `{}`",
+                tcx.def_path_str(key.def_id()),
+            }
+        }
+
         /// Evaluates a constant and returns the computed allocation.
         ///
         /// **Do not use this** directly, use the `tcx.eval_static_initializer` wrapper.