Remove cur_span hook.

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -445,7 +445,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
     #[inline(always)]
     pub fn cur_span(&self) -> Span {
-        M::cur_span(self)
+        // This deliberately does *not* honor `requires_caller_location` since it is used for much
+        // more than just panics.
+        self.stack().last().map_or(self.tcx.span, |f| f.current_span())
     }
 
     #[inline(always)]

compiler/rustc_const_eval/src/interpret/machine.rs

@@ -11,7 +11,6 @@ use rustc_middle::mir;
 use rustc_middle::ty::layout::TyAndLayout;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::def_id::DefId;
-use rustc_span::Span;
 use rustc_target::abi::{Align, Size};
 use rustc_target::spec::abi::Abi as CallAbi;
 
@@ -441,16 +440,6 @@ pub trait Machine<'mir, 'tcx: 'mir>: Sized {
         frame: Frame<'mir, 'tcx, Self::Provenance>,
     ) -> InterpResult<'tcx, Frame<'mir, 'tcx, Self::Provenance, Self::FrameExtra>>;
 
-    #[inline(always)]
-    fn cur_span(ecx: &InterpCx<'mir, 'tcx, Self>) -> Span
-    where
-        'tcx: 'mir,
-    {
-        // This deliberately does *not* honor `requires_caller_location` since it is used for much
-        // more than just panics.
-        Self::stack(ecx).last().map_or(ecx.tcx.span, |f| f.current_span())
-    }
-
     /// Borrow the current thread's stack.
     fn stack<'a>(
         ecx: &'a InterpCx<'mir, 'tcx, Self>,

compiler/rustc_mir_transform/src/dataflow_const_prop.rs

@@ -16,7 +16,7 @@ use rustc_mir_dataflow::value_analysis::{
 };
 use rustc_mir_dataflow::{lattice::FlatSet, Analysis, Results, ResultsVisitor};
 use rustc_span::def_id::DefId;
-use rustc_span::{Span, DUMMY_SP};
+use rustc_span::DUMMY_SP;
 use rustc_target::abi::{Align, FieldIdx, VariantIdx};
 
 use crate::MirPass;
@@ -689,11 +689,6 @@ impl<'mir, 'tcx: 'mir> rustc_const_eval::interpret::Machine<'mir, 'tcx> for Dumm
     type MemoryKind = !;
     const PANIC_ON_ALLOC_FAIL: bool = true;
 
-    #[inline(always)]
-    fn cur_span(_ecx: &InterpCx<'mir, 'tcx, Self>) -> Span {
-        DUMMY_SP
-    }
-
     #[inline(always)]
     fn enforce_alignment(_ecx: &InterpCx<'mir, 'tcx, Self>) -> CheckAlignment {
         // We do not check for alignment to avoid having to carry an `Align`
@@ -802,7 +797,8 @@ impl<'mir, 'tcx: 'mir> rustc_const_eval::interpret::Machine<'mir, 'tcx> for Dumm
         _ecx: &'a InterpCx<'mir, 'tcx, Self>,
     ) -> &'a [rustc_const_eval::interpret::Frame<'mir, 'tcx, Self::Provenance, Self::FrameExtra>]
     {
-        unimplemented!()
+        // Return an empty stack instead of panicking, as `cur_span` uses it to evaluate constants.
+        &[]
     }
 
     fn stack_mut<'a>(