panic when an interpreter error gets unintentionally discarded

Author: RalfJung

src/concurrency/data_race.rs

@@ -641,7 +641,7 @@ pub trait EvalContextExt<'tcx>: MiriInterpCxExt<'tcx> {
         // The program didn't actually do a read, so suppress the memory access hooks.
         // This is also a very special exception where we just ignore an error -- if this read
         // was UB e.g. because the memory is uninitialized, we don't want to know!
-        let old_val = this.run_for_validation(|this| this.read_scalar(dest)).ok();
+        let old_val = this.run_for_validation(|this| this.read_scalar(dest)).discard_interp_err();
         this.allow_data_races_mut(move |this| this.write_scalar(val, dest))?;
         this.validate_atomic_store(dest, atomic)?;
         this.buffered_atomic_write(val, dest, atomic, old_val)

src/diagnostics.rs

@@ -223,7 +223,10 @@ pub fn report_error<'tcx>(
         let info = info.downcast_ref::<TerminationInfo>().expect("invalid MachineStop payload");
         use TerminationInfo::*;
         let title = match info {
-            Exit { code, leak_check } => return Some((*code, *leak_check)),
+            &Exit { code, leak_check } => {
+                e.discard_interp_err();
+                return Some((code, leak_check));
+            }
             Abort(_) => Some("abnormal termination"),
             UnsupportedInIsolation(_) | Int2PtrWithStrictProvenance | UnsupportedForeignItem(_) =>
                 Some("unsupported operation"),
@@ -375,6 +378,7 @@ pub fn report_error<'tcx>(
                 InvalidProgramInfo::AlreadyReported(_)
             ) => {
                 // This got already reported. No point in reporting it again.
+                e.discard_interp_err();
                 return None;
             }
             _ =>

src/intrinsics/simd.rs

@@ -247,7 +247,8 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                             // This does NaN adjustments.
                             let val = this.binary_op(mir_op, &left, &right).map_err(|err| {
                                 match err.kind() {
-                                    InterpError::UndefinedBehavior(UndefinedBehaviorInfo::ShiftOverflow { shift_amount, .. }) => {
+                                    &InterpError::UndefinedBehavior(UndefinedBehaviorInfo::ShiftOverflow { shift_amount, .. }) => {
+                                        err.discard_interp_err();
                                         // This resets the interpreter backtrace, but it's not worth avoiding that.
                                         let shift_amount = match shift_amount {
                                             Either::Left(v) => v.to_string(),