From 4f25c91a0530d2337bff2b27c938e458a95e943b Mon Sep 17 00:00:00 2001
From: Aaron Hill <aa1ronham@gmail.com>
Date: Mon, 28 Oct 2019 21:37:58 -0400
Subject: [PATCH] Fix unwinding logic

---
 src/librustc_mir/interpret/eval_context.rs |  9 +++++++--
 src/librustc_mir/interpret/machine.rs      |  1 +
 src/librustc_mir/transform/const_prop.rs   | 11 +----------
 3 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/src/librustc_mir/interpret/eval_context.rs b/src/librustc_mir/interpret/eval_context.rs
index 6598b0f99f2..fb3f4f21a97 100644
--- a/src/librustc_mir/interpret/eval_context.rs
+++ b/src/librustc_mir/interpret/eval_context.rs
@@ -584,7 +584,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         let frame = self.stack.pop().expect(
             "tried to pop a stack frame, but there were none",
         );
-        let stack_pop_info = M::stack_pop(self, frame.extra)?;
+        let stack_pop_info = M::stack_pop(self, frame.extra, unwinding)?;
         match (unwinding, stack_pop_info) {
             (true, StackPopInfo::StartUnwinding) =>
                 bug!("Attempted to start unwinding while already unwinding!"),
@@ -616,7 +616,12 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         // Now where do we jump next?
 
         // Determine if we leave this function normally or via unwinding.
-        let cur_unwinding = unwinding && stack_pop_info != StackPopInfo::StopUnwinding;
+        let cur_unwinding = match stack_pop_info {
+            StackPopInfo::StartUnwinding => true,
+            StackPopInfo::StopUnwinding => false,
+            _ => unwinding
+        };
+
         trace!("StackPopCleanup: {:?} StackPopInfo: {:?} cur_unwinding = {:?}",
                frame.return_to_block, stack_pop_info, cur_unwinding);
         if cur_unwinding {
diff --git a/src/librustc_mir/interpret/machine.rs b/src/librustc_mir/interpret/machine.rs
index 18f831f8257..bed6c0b67eb 100644
--- a/src/librustc_mir/interpret/machine.rs
+++ b/src/librustc_mir/interpret/machine.rs
@@ -270,6 +270,7 @@ pub trait Machine<'mir, 'tcx>: Sized {
     fn stack_pop(
         _ecx: &mut InterpCx<'mir, 'tcx, Self>,
         _extra: Self::FrameExtra,
+        _unwinding: bool
     ) -> InterpResult<'tcx, StackPopInfo> {
         // By default, we do not support unwinding from panics
         Ok(StackPopInfo::Normal)
diff --git a/src/librustc_mir/transform/const_prop.rs b/src/librustc_mir/transform/const_prop.rs
index 5c83fb8c821..3ee9445f9c0 100644
--- a/src/librustc_mir/transform/const_prop.rs
+++ b/src/librustc_mir/transform/const_prop.rs
@@ -30,7 +30,7 @@ use crate::interpret::{
     self, InterpCx, ScalarMaybeUndef, Immediate, OpTy,
     StackPopCleanup, LocalValue, LocalState, AllocId, Frame,
     Allocation, MemoryKind, ImmTy, Pointer, Memory, PlaceTy,
-    StackPopInfo, Operand as InterpOperand,
+    Operand as InterpOperand,
 };
 use crate::const_eval::error_to_const_error;
 use crate::transform::{MirPass, MirSource};
@@ -252,15 +252,6 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine {
     fn stack_push(_ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
         Ok(())
     }
-
-    /// Called immediately before a stack frame gets popped.
-    #[inline(always)]
-    fn stack_pop(
-        _ecx: &mut InterpCx<'mir, 'tcx, Self>,
-        _extra: ()
-    ) -> InterpResult<'tcx, StackPopInfo> {
-        Ok(StackPopInfo::Normal)
-    }
 }
 
 type Const<'tcx> = OpTy<'tcx>;