Add UnwindAction::Unreachable

This also makes eval machine's `StackPopUnwind`
redundant so that is replaced.

Author: nbdd0121

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1612,47 +1612,27 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             TerminatorKind::Drop { target, unwind, .. }
             | TerminatorKind::Assert { target, unwind, .. } => {
                 self.assert_iscleanup(body, block_data, target, is_cleanup);
-                if let UnwindAction::Cleanup(unwind) = unwind {
-                    if is_cleanup {
-                        span_mirbug!(self, block_data, "unwind on cleanup block")
-                    }
-                    self.assert_iscleanup(body, block_data, unwind, true);
-                }
+                self.assert_iscleanup_unwind(body, block_data, unwind, is_cleanup);
             }
             TerminatorKind::Call { ref target, unwind, .. } => {
                 if let &Some(target) = target {
                     self.assert_iscleanup(body, block_data, target, is_cleanup);
                 }
-                if let UnwindAction::Cleanup(cleanup) = unwind {
-                    if is_cleanup {
-                        span_mirbug!(self, block_data, "cleanup on cleanup block")
-                    }
-                    self.assert_iscleanup(body, block_data, cleanup, true);
-                }
+                self.assert_iscleanup_unwind(body, block_data, unwind, is_cleanup);
             }
             TerminatorKind::FalseEdge { real_target, imaginary_target } => {
                 self.assert_iscleanup(body, block_data, real_target, is_cleanup);
                 self.assert_iscleanup(body, block_data, imaginary_target, is_cleanup);
             }
             TerminatorKind::FalseUnwind { real_target, unwind } => {
                 self.assert_iscleanup(body, block_data, real_target, is_cleanup);
-                if let UnwindAction::Cleanup(unwind) = unwind {
-                    if is_cleanup {
-                        span_mirbug!(self, block_data, "cleanup in cleanup block via false unwind");
-                    }
-                    self.assert_iscleanup(body, block_data, unwind, true);
-                }
+                self.assert_iscleanup_unwind(body, block_data, unwind, is_cleanup);
             }
             TerminatorKind::InlineAsm { destination, unwind, .. } => {
                 if let Some(target) = destination {
                     self.assert_iscleanup(body, block_data, target, is_cleanup);
                 }
-                if let UnwindAction::Cleanup(cleanup) = unwind {
-                    if is_cleanup {
-                        span_mirbug!(self, block_data, "cleanup on cleanup block")
-                    }
-                    self.assert_iscleanup(body, block_data, cleanup, true);
-                }
+                self.assert_iscleanup_unwind(body, block_data, unwind, is_cleanup);
             }
         }
     }
@@ -1669,6 +1649,25 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         }
     }
 
+    fn assert_iscleanup_unwind(
+        &mut self,
+        body: &Body<'tcx>,
+        ctxt: &dyn fmt::Debug,
+        unwind: UnwindAction,
+        is_cleanup: bool,
+    ) {
+        match unwind {
+            UnwindAction::Cleanup(unwind) => {
+                if is_cleanup {
+                    span_mirbug!(self, ctxt, "unwind on cleanup block")
+                }
+                self.assert_iscleanup(body, ctxt, unwind, true);
+            }
+            UnwindAction::Continue => (),
+            UnwindAction::Unreachable => (),
+        }
+    }
+
     fn check_local(&mut self, body: &Body<'tcx>, local: Local, local_decl: &LocalDecl<'tcx>) {
         match body.local_kind(local) {
             LocalKind::ReturnPointer | LocalKind::Arg => {

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -156,35 +156,36 @@ impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
         fn_ptr: Bx::Value,
         llargs: &[Bx::Value],
         destination: Option<(ReturnDest<'tcx, Bx::Value>, mir::BasicBlock)>,
-        unwind: mir::UnwindAction,
+        mut unwind: mir::UnwindAction,
         copied_constant_arguments: &[PlaceRef<'tcx, <Bx as BackendTypes>::Value>],
         mergeable_succ: bool,
     ) -> MergingSucc {
         // If there is a cleanup block and the function we're calling can unwind, then
         // do an invoke, otherwise do a call.
         let fn_ty = bx.fn_decl_backend_type(&fn_abi);
 
-        let cleanup = match unwind {
-            mir::UnwindAction::Cleanup(cleanup) => Some(cleanup),
+        if !fn_abi.can_unwind {
+            unwind = mir::UnwindAction::Unreachable;
+        }
+
+        let unwind_block = match unwind {
+            mir::UnwindAction::Cleanup(cleanup) => Some(self.llbb_with_cleanup(fx, cleanup)),
+            _ if fx.mir[self.bb].is_cleanup
+                && fn_abi.can_unwind
+                && !base::wants_msvc_seh(fx.cx.tcx().sess) =>
+            {
+                // Exception must not propagate out of the execution of a cleanup (doing so
+                // can cause undefined behaviour). We insert a double unwind guard for
+                // functions that can potentially unwind to protect against this.
+                //
+                // This is not necessary for SEH which does not use successive unwinding
+                // like Itanium EH. EH frames in SEH are different from normal function
+                // frames and SEH will abort automatically if an exception tries to
+                // propagate out from cleanup.
+                Some(fx.double_unwind_guard())
+            }
             mir::UnwindAction::Continue => None,
-        };
-        let unwind_block = if let Some(cleanup) = cleanup.filter(|_| fn_abi.can_unwind) {
-            Some(self.llbb_with_cleanup(fx, cleanup))
-        } else if fx.mir[self.bb].is_cleanup
-            && fn_abi.can_unwind
-            && !base::wants_msvc_seh(fx.cx.tcx().sess)
-        {
-            // Exception must not propagate out of the execution of a cleanup (doing so
-            // can cause undefined behaviour). We insert a double unwind guard for
-            // functions that can potentially unwind to protect against this.
-            //
-            // This is not necessary for SEH which does not use successive unwinding
-            // like Itanium EH. EH frames in SEH are different from normal function
-            // frames and SEH will abort automatically if an exception tries to
-            // propagate out from cleanup.
-            Some(fx.double_unwind_guard())
-        } else {
-            None
+            mir::UnwindAction::Unreachable => None,
         };
 
         if let Some(unwind_block) = unwind_block {
@@ -640,7 +641,17 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         let (fn_abi, llfn) = common::build_langcall(bx, Some(span), LangItem::PanicCannotUnwind);
 
         // Codegen the actual panic invoke/call.
-        let merging_succ = helper.do_call(self, bx, fn_abi, llfn, &[], None, mir::UnwindAction::Continue, &[], false);
+        let merging_succ = helper.do_call(
+            self,
+            bx,
+            fn_abi,
+            llfn,
+            &[],
+            None,
+            mir::UnwindAction::Unreachable,
+            &[],
+            false,
+        );
         assert_eq!(merging_succ, MergingSucc::False);
     }
 

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -23,7 +23,7 @@ use rustc_target::spec::abi::Abi as CallAbi;
 
 use crate::interpret::{
     self, compile_time_machine, AllocId, ConstAllocation, FnVal, Frame, ImmTy, InterpCx,
-    InterpResult, OpTy, PlaceTy, Pointer, Scalar, StackPopUnwind,
+    InterpResult, OpTy, PlaceTy, Pointer, Scalar,
 };
 
 use super::error::*;
@@ -271,7 +271,7 @@ impl<'mir, 'tcx: 'mir> CompileTimeEvalContext<'mir, 'tcx> {
                         /* with_caller_location = */ false,
                         dest,
                         ret,
-                        StackPopUnwind::NotAllowed,
+                        mir::UnwindAction::Unreachable,
                     )?;
                     Ok(ControlFlow::Break(()))
                 } else {
@@ -401,7 +401,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         args: &[OpTy<'tcx>],
         dest: &PlaceTy<'tcx>,
         ret: Option<mir::BasicBlock>,
-        _unwind: StackPopUnwind, // unwinding is not supported in consts
+        _unwind: mir::UnwindAction, // unwinding is not supported in consts
     ) -> InterpResult<'tcx, Option<(&'mir mir::Body<'tcx>, ty::Instance<'tcx>)>> {
         debug!("find_mir_or_eval_fn: {:?}", instance);
 
@@ -450,7 +450,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         args: &[OpTy<'tcx>],
         dest: &PlaceTy<'tcx, Self::Provenance>,
         target: Option<mir::BasicBlock>,
-        _unwind: StackPopUnwind,
+        _unwind: mir::UnwindAction,
     ) -> InterpResult<'tcx> {
         // Shared intrinsics.
         if ecx.emulate_intrinsic(instance, args, dest, target)? {

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -139,25 +139,14 @@ pub struct FrameInfo<'tcx> {
     pub lint_root: Option<hir::HirId>,
 }
 
-/// Unwind information.
-#[derive(Clone, Copy, Eq, PartialEq, Debug)]
-pub enum StackPopUnwind {
-    /// The cleanup block.
-    Cleanup(mir::BasicBlock),
-    /// No cleanup needs to be done.
-    Skip,
-    /// Unwinding is not allowed (UB).
-    NotAllowed,
-}
-
 #[derive(Clone, Copy, Eq, PartialEq, Debug)] // Miri debug-prints these
 pub enum StackPopCleanup {
     /// Jump to the next block in the caller, or cause UB if None (that's a function
     /// that may never return). Also store layout of return place so
     /// we can validate it at that layout.
     /// `ret` stores the block we jump to on a normal return, while `unwind`
     /// stores the block used for cleanup during unwinding.
-    Goto { ret: Option<mir::BasicBlock>, unwind: StackPopUnwind },
+    Goto { ret: Option<mir::BasicBlock>, unwind: mir::UnwindAction },
     /// The root frame of the stack: nowhere else to jump to.
     /// `cleanup` says whether locals are deallocated. Static computation
     /// wants them leaked to intern what they need (and just throw away
@@ -735,16 +724,16 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     /// *Unwind* to the given `target` basic block.
     /// Do *not* use for returning! Use `return_to_block` instead.
     ///
-    /// If `target` is `StackPopUnwind::Skip`, that indicates the function does not need cleanup
+    /// If `target` is `UnwindAction::Continue`, that indicates the function does not need cleanup
     /// during unwinding, and we will just keep propagating that upwards.
     ///
-    /// If `target` is `StackPopUnwind::NotAllowed`, that indicates the function does not allow
+    /// If `target` is `UnwindAction::Unreachable`, that indicates the function does not allow
     /// unwinding, and doing so is UB.
-    pub fn unwind_to_block(&mut self, target: StackPopUnwind) -> InterpResult<'tcx> {
+    pub fn unwind_to_block(&mut self, target: mir::UnwindAction) -> InterpResult<'tcx> {
         self.frame_mut().loc = match target {
-            StackPopUnwind::Cleanup(block) => Left(mir::Location { block, statement_index: 0 }),
-            StackPopUnwind::Skip => Right(self.frame_mut().body.span),
-            StackPopUnwind::NotAllowed => {
+            mir::UnwindAction::Cleanup(block) => Left(mir::Location { block, statement_index: 0 }),
+            mir::UnwindAction::Continue => Right(self.frame_mut().body.span),
+            mir::UnwindAction::Unreachable => {
                 throw_ub_format!("unwinding past a stack frame that does not allow unwinding")
             }
         };

compiler/rustc_const_eval/src/interpret/machine.rs

@@ -18,7 +18,7 @@ use crate::const_eval::CheckAlignment;
 
 use super::{
     AllocBytes, AllocId, AllocRange, Allocation, ConstAllocation, Frame, ImmTy, InterpCx,
-    InterpResult, MemoryKind, OpTy, Operand, PlaceTy, Pointer, Provenance, Scalar, StackPopUnwind,
+    InterpResult, MemoryKind, OpTy, Operand, PlaceTy, Pointer, Provenance, Scalar,
 };
 
 /// Data returned by Machine::stack_pop,
@@ -185,7 +185,7 @@ pub trait Machine<'mir, 'tcx>: Sized {
         args: &[OpTy<'tcx, Self::Provenance>],
         destination: &PlaceTy<'tcx, Self::Provenance>,
         target: Option<mir::BasicBlock>,
-        unwind: StackPopUnwind,
+        unwind: mir::UnwindAction,
     ) -> InterpResult<'tcx, Option<(&'mir mir::Body<'tcx>, ty::Instance<'tcx>)>>;
 
     /// Execute `fn_val`. It is the hook's responsibility to advance the instruction
@@ -197,7 +197,7 @@ pub trait Machine<'mir, 'tcx>: Sized {
         args: &[OpTy<'tcx, Self::Provenance>],
         destination: &PlaceTy<'tcx, Self::Provenance>,
         target: Option<mir::BasicBlock>,
-        unwind: StackPopUnwind,
+        unwind: mir::UnwindAction,
     ) -> InterpResult<'tcx>;
 
     /// Directly process an intrinsic without pushing a stack frame. It is the hook's
@@ -208,7 +208,7 @@ pub trait Machine<'mir, 'tcx>: Sized {
         args: &[OpTy<'tcx, Self::Provenance>],
         destination: &PlaceTy<'tcx, Self::Provenance>,
         target: Option<mir::BasicBlock>,
-        unwind: StackPopUnwind,
+        unwind: mir::UnwindAction,
     ) -> InterpResult<'tcx>;
 
     /// Called to evaluate `Assert` MIR terminators that trigger a panic.
@@ -487,7 +487,7 @@ pub macro compile_time_machine(<$mir: lifetime, $tcx: lifetime>) {
         _args: &[OpTy<$tcx>],
         _destination: &PlaceTy<$tcx, Self::Provenance>,
         _target: Option<mir::BasicBlock>,
-        _unwind: StackPopUnwind,
+        _unwind: mir::UnwindAction,
     ) -> InterpResult<$tcx> {
         match fn_val {}
     }

compiler/rustc_const_eval/src/interpret/mod.rs

@@ -20,9 +20,7 @@ mod visitor;
 
 pub use rustc_middle::mir::interpret::*; // have all the `interpret` symbols in one place: here
 
-pub use self::eval_context::{
-    Frame, FrameInfo, InterpCx, LocalState, LocalValue, StackPopCleanup, StackPopUnwind,
-};
+pub use self::eval_context::{Frame, FrameInfo, InterpCx, LocalState, LocalValue, StackPopCleanup};
 pub use self::intern::{intern_const_alloc_recursive, InternKind};
 pub use self::machine::{compile_time_machine, AllocMap, Machine, MayLeak, StackPopJump};
 pub use self::memory::{AllocKind, AllocRef, AllocRefMut, FnVal, Memory, MemoryKind};

compiler/rustc_const_eval/src/interpret/terminator.rs

@@ -13,7 +13,7 @@ use rustc_target::spec::abi::Abi;
 
 use super::{
     FnVal, ImmTy, Immediate, InterpCx, InterpResult, MPlaceTy, Machine, MemoryKind, OpTy, Operand,
-    PlaceTy, Scalar, StackPopCleanup, StackPopUnwind,
+    PlaceTy, Scalar, StackPopCleanup,
 };
 
 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
@@ -60,7 +60,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 ref args,
                 destination,
                 target,
-                ref unwind,
+                unwind,
                 from_hir_call: _,
                 fn_span: _,
             } => {
@@ -106,13 +106,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     with_caller_location,
                     &destination,
                     target,
-                    match (unwind, fn_abi.can_unwind) {
-                        (mir::UnwindAction::Cleanup(cleanup), true) => {
-                            StackPopUnwind::Cleanup(*cleanup)
-                        }
-                        (mir::UnwindAction::Continue, true) => StackPopUnwind::Skip,
-                        (_, false) => StackPopUnwind::NotAllowed,
-                    },
+                    if fn_abi.can_unwind { unwind } else { mir::UnwindAction::Unreachable },
                 )?;
                 // Sanity-check that `eval_fn_call` either pushed a new frame or
                 // did a jump to another block.
@@ -353,7 +347,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         with_caller_location: bool,
         destination: &PlaceTy<'tcx, M::Provenance>,
         target: Option<mir::BasicBlock>,
-        mut unwind: StackPopUnwind,
+        mut unwind: mir::UnwindAction,
     ) -> InterpResult<'tcx> {
         trace!("eval_fn_call: {:#?}", fn_val);
 
@@ -412,9 +406,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     }
                 }
 
-                if !matches!(unwind, StackPopUnwind::NotAllowed) && !callee_fn_abi.can_unwind {
-                    // The callee cannot unwind.
-                    unwind = StackPopUnwind::NotAllowed;
+                if !callee_fn_abi.can_unwind {
+                    // The callee cannot unwind, so force the `Unreachable` unwind handling.
+                    unwind = mir::UnwindAction::Unreachable;
                 }
 
                 self.push_stack_frame(
@@ -719,10 +713,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             false,
             &ret.into(),
             Some(target),
-            match unwind {
-                mir::UnwindAction::Cleanup(cleanup) => StackPopUnwind::Cleanup(cleanup),
-                mir::UnwindAction::Continue => StackPopUnwind::Skip,
-            },
+            unwind,
         )
     }
 }

compiler/rustc_middle/src/mir/patch.rs

@@ -12,6 +12,8 @@ pub struct MirPatch<'tcx> {
     new_statements: Vec<(Location, StatementKind<'tcx>)>,
     new_locals: Vec<LocalDecl<'tcx>>,
     resume_block: Option<BasicBlock>,
+    // Only for unreachable in cleanup path.
+    unreachable_block: Option<BasicBlock>,
     body_span: Span,
     next_local: usize,
 }
@@ -25,11 +27,12 @@ impl<'tcx> MirPatch<'tcx> {
             new_locals: vec![],
             next_local: body.local_decls.len(),
             resume_block: None,
+            unreachable_block: None,
             body_span: body.span,
         };
 
-        // Check if we already have a resume block
         for (bb, block) in body.basic_blocks.iter_enumerated() {
+            // Check if we already have a resume block
             if let TerminatorKind::Resume = block.terminator().kind && block.statements.is_empty() {
                 result.resume_block = Some(bb);
                 break;