Auto merge of #103877 - oli-obk:const_eval_step_limit, r=fee1-dead

Replace const eval limit by a lint and add an exponential backoff warning

The lint triggers at the first power of 2 that comes after 1 million function calls or traversed back-edges (takes less than a second on usual programs). After the first emission, an unsilenceable warning is repeated at every following power of 2 terminators, causing it to get reported less and less the longer the evaluation runs.

cc `@rust-lang/wg-const-eval`

fixes #93481
closes #67217

3 files changed, 2 insertions, 26 deletions

diff --git a/compiler/rustc_middle/src/middle/limits.rs b/compiler/rustc_middle/src/middle/limits.rs
index bd859d4d61b..d4f023958d6 100644
--- a/compiler/rustc_middle/src/middle/limits.rs
+++ b/compiler/rustc_middle/src/middle/limits.rs
@@ -1,8 +1,7 @@
 //! Registering limits:
 //! * recursion_limit,
-//! * move_size_limit,
-//! * type_length_limit, and
-//! * const_eval_limit
+//! * move_size_limit, and
+//! * type_length_limit
 //!
 //! There are various parts of the compiler that must impose arbitrary limits
 //! on how deeply they recurse to prevent stack overflow. Users can override
@@ -34,12 +33,6 @@ pub fn provide(providers: &mut Providers) {
             sym::type_length_limit,
             1048576,
         ),
-        const_eval_limit: get_limit(
-            tcx.hir().krate_attrs(),
-            tcx.sess,
-            sym::const_eval_limit,
-            2_000_000,
-        ),
     }
 }
 
diff --git a/compiler/rustc_middle/src/mir/interpret/error.rs b/compiler/rustc_middle/src/mir/interpret/error.rs
index 055d8e9a352..357bcca4419 100644
--- a/compiler/rustc_middle/src/mir/interpret/error.rs
+++ b/compiler/rustc_middle/src/mir/interpret/error.rs
@@ -465,10 +465,6 @@ impl fmt::Display for UnsupportedOpInfo {
 pub enum ResourceExhaustionInfo {
     /// The stack grew too big.
     StackFrameLimitReached,
-    /// The program ran for too long.
-    ///
-    /// The exact limit is set by the `const_eval_limit` attribute.
-    StepLimitReached,
     /// There is not enough memory (on the host) to perform an allocation.
     MemoryExhausted,
     /// The address space (of the target) is full.
@@ -482,9 +478,6 @@ impl fmt::Display for ResourceExhaustionInfo {
             StackFrameLimitReached => {
                 write!(f, "reached the configured maximum number of stack frames")
             }
-            StepLimitReached => {
-                write!(f, "exceeded interpreter step limit (see `#[const_eval_limit]`)")
-            }
             MemoryExhausted => {
                 write!(f, "tried to allocate more memory than available to compiler")
             }
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 77725f0b3b6..b05e791211d 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -82,8 +82,6 @@ use std::iter;
 use std::mem;
 use std::ops::{Bound, Deref};
 
-const TINY_CONST_EVAL_LIMIT: Limit = Limit(20);
-
 #[allow(rustc::usage_of_ty_tykind)]
 impl<'tcx> Interner for TyCtxt<'tcx> {
     type AdtDef = ty::AdtDef<'tcx>;
@@ -1178,14 +1176,6 @@ impl<'tcx> TyCtxt<'tcx> {
         self.limits(()).move_size_limit
     }
 
-    pub fn const_eval_limit(self) -> Limit {
-        if self.sess.opts.unstable_opts.tiny_const_eval_limit {
-            TINY_CONST_EVAL_LIMIT
-        } else {
-            self.limits(()).const_eval_limit
-        }
-    }
-
     pub fn all_traits(self) -> impl Iterator<Item = DefId> + 'tcx {
         iter::once(LOCAL_CRATE)
             .chain(self.crates(()).iter().copied())