Suppress errors in const eval during trait selection v2

compiler/rustc_codegen_cranelift/src/constant.rs

@@ -64,6 +64,12 @@ pub(crate) fn check_constants(fx: &mut FunctionCx<'_, '_, '_>) -> bool {
                                 err
                             );
                         }
+                        ErrorHandled::Silent => {
+                            span_bug!(
+                                constant.span,
+                                "codegen encountered silent error",
+                            );
+                        }
                     }
                 }
             }

compiler/rustc_codegen_ssa/src/mir/mod.rs

@@ -189,7 +189,10 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
                 // errored or at least linted
                 ErrorHandled::Reported(ErrorReported) | ErrorHandled::Linted => {}
                 ErrorHandled::TooGeneric => {
-                    span_bug!(const_.span, "codgen encountered polymorphic constant: {:?}", err)
+                    span_bug!(const_.span, "codegen encountered polymorphic constant: {:?}", err)
+                }
+                ErrorHandled::Silent => {
+                    span_bug!(const_.span, "silent error during codegen")
                 }
             }
         }

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -13,7 +13,7 @@ use rustc_middle::mir;
 use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::mir::pretty::display_allocation;
 use rustc_middle::traits::Reveal;
-use rustc_middle::ty::layout::LayoutOf;
+use rustc_middle::ty::layout::{LayoutError, LayoutOf};
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, subst::Subst, TyCtxt};
 use rustc_span::source_map::Span;
@@ -28,6 +28,7 @@ pub fn note_on_undefined_behavior_error() -> &'static str {
 }
 
 // Returns a pointer to where the result lives
+#[instrument(skip(ecx, body), level = "debug")]
 fn eval_body_using_ecx<'mir, 'tcx>(
     ecx: &mut CompileTimeEvalContext<'mir, 'tcx>,
     cid: GlobalId<'tcx>,
@@ -160,6 +161,7 @@ pub(super) fn op_to_const<'tcx>(
             ConstValue::Scalar(Scalar::ZST)
         }
     };
+
     match immediate {
         Ok(ref mplace) => to_const_value(mplace),
         // see comment on `let try_as_immediate` above
@@ -212,77 +214,65 @@ fn turn_into_const_value<'tcx>(
     op_to_const(&ecx, &mplace.into())
 }
 
+#[instrument(skip(tcx), level = "debug")]
 pub fn eval_to_const_value_raw_provider<'tcx>(
     tcx: TyCtxt<'tcx>,
     key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
 ) -> ::rustc_middle::mir::interpret::EvalToConstValueResult<'tcx> {
     assert!(key.param_env.constness() == hir::Constness::Const);
-    // see comment in eval_to_allocation_raw_provider for what we're doing here
-    if key.param_env.reveal() == Reveal::All {
-        let mut key = key;
-        key.param_env = key.param_env.with_user_facing();
-        match tcx.eval_to_const_value_raw(key) {
-            // try again with reveal all as requested
-            Err(ErrorHandled::TooGeneric) => {}
-            // deduplicate calls
-            other => return other,
-        }
-    }
+    let (param_env, id) = key.into_parts();
+    let reveal = param_env.reveal();
 
     // We call `const_eval` for zero arg intrinsics, too, in order to cache their value.
     // Catch such calls and evaluate them instead of trying to load a constant's MIR.
     if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
-        let ty = key.value.instance.ty(tcx, key.param_env);
+        let ty = key.value.instance.ty(tcx, param_env);
         let substs = match ty.kind() {
             ty::FnDef(_, substs) => substs,
             _ => bug!("intrinsic with type {:?}", ty),
         };
-        return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
-            let span = tcx.def_span(def_id);
-            let error = ConstEvalErr { error: error.into_kind(), stacktrace: vec![], span };
-            error.report_as_error(tcx.at(span), "could not evaluate nullary intrinsic")
-        });
+
+        match eval_nullary_intrinsic(tcx, param_env, def_id, substs) {
+            Ok(val) => {
+                // store result for deduplication
+                tcx.save_const_value_for_dedup(id, reveal);
+
+                return Ok(val);
+            }
+            Err(e) => {
+                let span = tcx.def_span(def_id);
+                let error = ConstEvalErr { error: e.into_kind(), stacktrace: vec![], span };
+
+                return Err(
+                    error.report_as_error(tcx.at(span), "could not evaluate nullary intrinsic")
+                );
+            }
+        }
     }
 
-    tcx.eval_to_allocation_raw(key).map(|val| turn_into_const_value(tcx, val, key))
+    tcx.dedup_eval_alloc_raw(key, None).map(|val| turn_into_const_value(tcx, val, key))
 }
 
+#[instrument(skip(tcx), level = "debug")]
 pub fn eval_to_allocation_raw_provider<'tcx>(
     tcx: TyCtxt<'tcx>,
     key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
 ) -> ::rustc_middle::mir::interpret::EvalToAllocationRawResult<'tcx> {
     assert!(key.param_env.constness() == hir::Constness::Const);
-    // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
-    // reporting the same error twice here. To resolve this, we check whether we can evaluate the
-    // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
-    // computed. For a large percentage of constants that will already have succeeded. Only
-    // associated constants of generic functions will fail due to not enough monomorphization
-    // information being available.
-
-    // In case we fail in the `UserFacing` variant, we just do the real computation.
-    if key.param_env.reveal() == Reveal::All {
-        let mut key = key;
-        key.param_env = key.param_env.with_user_facing();
-        match tcx.eval_to_allocation_raw(key) {
-            // try again with reveal all as requested
-            Err(ErrorHandled::TooGeneric) => {}
-            // deduplicate calls
-            other => return other,
-        }
-    }
+    let (param_env, cid) = key.into_parts();
+    let reveal = param_env.reveal();
+    let def = cid.instance.def.with_opt_param();
+
     if cfg!(debug_assertions) {
         // Make sure we format the instance even if we do not print it.
         // This serves as a regression test against an ICE on printing.
         // The next two lines concatenated contain some discussion:
         // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
         // subject/anon_const_instance_printing/near/135980032
-        let instance = with_no_trimmed_paths(|| key.value.instance.to_string());
+        let instance = with_no_trimmed_paths(|| cid.instance.to_string());
         trace!("const eval: {:?} ({})", key, instance);
     }
 
-    let cid = key.value;
-    let def = cid.instance.def.with_opt_param();
-
     if let Some(def) = def.as_local() {
         if tcx.has_typeck_results(def.did) {
             if let Some(error_reported) = tcx.typeck_opt_const_arg(def).tainted_by_errors {
@@ -316,6 +306,20 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
     let res = ecx.load_mir(cid.instance.def, cid.promoted);
     match res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, &body)) {
         Err(error) => {
+            debug!("error from eval_body_using_ecx: {:?}", error);
+            if reveal == Reveal::Selection {
+                match error.kind() {
+                    err_inval!(Layout(LayoutError::Unknown(_)))
+                    | err_inval!(TooGeneric)
+                    | err_inval!(AlreadyReported(_)) => {
+                        // We do want to report these errors
+                    }
+                    _ => {
+                        return Err(ErrorHandled::Silent);
+                    }
+                }
+            }
+
             let err = ConstEvalErr::new(&ecx, error, None);
             // Some CTFE errors raise just a lint, not a hard error; see
             // <https://github.com/rust-lang/rust/issues/71800>.
@@ -328,7 +332,6 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
                 // use of broken constant from other crate: always an error
                 true
             };
-
             if is_hard_err {
                 let msg = if is_static {
                     Cow::from("could not evaluate static initializer")
@@ -345,7 +348,6 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
                         Cow::from("evaluation of constant value failed")
                     }
                 };
-
                 Err(err.report_as_error(ecx.tcx.at(ecx.cur_span()), &msg))
             } else {
                 let hir_id = tcx.hir().local_def_id_to_hir_id(def.as_local().unwrap().did);
@@ -377,10 +379,26 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
                 }
             };
             let alloc_id = mplace.ptr.provenance.unwrap();
+
             if let Err(error) = validation {
                 // Validation failed, report an error. This is always a hard error.
                 let err = ConstEvalErr::new(&ecx, error, None);
-                Err(err.struct_error(
+
+                // FIXME Do we also want to keep these silent with Reveal::Selection?
+                if reveal == Reveal::Selection {
+                    match err.error {
+                        err_inval!(Layout(LayoutError::Unknown(_)))
+                        | err_inval!(TooGeneric)
+                        | err_inval!(AlreadyReported(_)) => {
+                            // We do want to report these errors
+                        }
+                        _ => {
+                            return Err(ErrorHandled::Silent);
+                        }
+                    }
+                }
+
+                let error = Err(err.struct_error(
                     ecx.tcx,
                     "it is undefined behavior to use this value",
                     |mut diag| {
@@ -394,10 +412,19 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
                         ));
                         diag.emit();
                     },
-                ))
+                ));
+
+                debug!(?error);
+
+                error
             } else {
                 // Convert to raw constant
-                Ok(ConstAlloc { alloc_id, ty: mplace.layout.ty })
+                let const_alloc = ConstAlloc { alloc_id, ty: mplace.layout.ty };
+
+                // store information that allows deduplication
+                tcx.save_alloc_for_dedup(cid, reveal);
+
+                Ok(const_alloc)
             }
         }
     }

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -18,7 +18,8 @@ use rustc_middle::ty::{
 use rustc_mir_dataflow::storage::AlwaysLiveLocals;
 use rustc_query_system::ich::StableHashingContext;
 use rustc_session::Limit;
-use rustc_span::{Pos, Span};
+use rustc_span::Pos;
+use rustc_span::Span;
 use rustc_target::abi::{call::FnAbi, Align, HasDataLayout, Size, TargetDataLayout};
 
 use super::{
@@ -809,7 +810,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     /// cause us to continue unwinding.
     pub(super) fn pop_stack_frame(&mut self, unwinding: bool) -> InterpResult<'tcx> {
         info!(
-            "popping stack frame ({})",
+            "popping following stack frame ({})",
             if unwinding { "during unwinding" } else { "returning from function" }
         );
 
@@ -926,6 +927,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         Ok(())
     }
 
+    #[instrument(skip(self), level = "debug")]
     pub fn eval_to_allocation(
         &self,
         gid: GlobalId<'tcx>,
@@ -941,8 +943,10 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             self.param_env
         };
         let param_env = param_env.with_const();
-        let val = self.tcx.eval_to_allocation_raw(param_env.and(gid))?;
-        self.raw_const_to_mplace(val)
+        let val = self.tcx.dedup_eval_alloc_raw(param_env.and(gid), None);
+        debug!(?val);
+
+        self.raw_const_to_mplace(val?)
     }
 
     #[must_use]

compiler/rustc_middle/src/mir/interpret/error.rs

@@ -18,6 +18,9 @@ pub enum ErrorHandled {
     Reported(ErrorReported),
     /// Already emitted a lint for this evaluation.
     Linted,
+    /// Encountered an error without emitting anything. Only returned
+    /// with `Reveal::Selection`.
+    Silent,
     /// Don't emit an error, the evaluation failed because the MIR was generic
     /// and the substs didn't fully monomorphize it.
     TooGeneric,
@@ -88,7 +91,7 @@ fn print_backtrace(backtrace: &Backtrace) {
 impl From<ErrorHandled> for InterpErrorInfo<'_> {
     fn from(err: ErrorHandled) -> Self {
         match err {
-            ErrorHandled::Reported(ErrorReported) | ErrorHandled::Linted => {
+            ErrorHandled::Reported(ErrorReported) | ErrorHandled::Linted | ErrorHandled::Silent => {
                 err_inval!(ReferencedConstant)
             }
             ErrorHandled::TooGeneric => err_inval!(TooGeneric),