Rollup merge of rust-lang#66726 - CAD97:miri-recursion-limit, r=RalfJung

Use recursion_limit for const eval stack limit

cc rust-lang/miri#643 @orium @RalfJung

I'm really not certain how exactly to handle this change, but it looks like it's that simple.

Reuse `recursion_limit` ("The maximum recursion limit for potentially infinitely recursive operations such as auto-dereference and monomorphization") which is configurable by the user for the const evaluation stack frame limit.

The other option is to make `const_eval_stack_frame_limit` configurable in the same way as `recursion_limit` (but I'm not sure how to do that and it'd be a bigger change).

Fixes rust-lang/miri#643.

Author: Centril

src/librustc/session/mod.rs

@@ -94,9 +94,6 @@ pub struct Session {
     /// The maximum length of types during monomorphization.
     pub type_length_limit: Once<usize>,
 
-    /// The maximum number of stackframes allowed in const eval.
-    pub const_eval_stack_frame_limit: usize,
-
     /// Map from imported macro spans (which consist of
     /// the localized span for the macro body) to the
     /// macro name and definition span in the source crate.
@@ -1158,7 +1155,6 @@ fn build_session_(
         features: Once::new(),
         recursion_limit: Once::new(),
         type_length_limit: Once::new(),
-        const_eval_stack_frame_limit: 100,
         imported_macro_spans: OneThread::new(RefCell::new(FxHashMap::default())),
         incr_comp_session: OneThread::new(RefCell::new(IncrCompSession::NotInitialized)),
         cgu_reuse_tracker,

src/librustc_mir/interpret/eval_context.rs

@@ -548,7 +548,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
         info!("ENTERING({}) {}", self.cur_frame(), self.frame().instance);
 
-        if self.stack.len() > self.tcx.sess.const_eval_stack_frame_limit {
+        if self.stack.len() > *self.tcx.sess.recursion_limit.get() {
             throw_exhaust!(StackFrameLimitReached)
         } else {
             Ok(())