Auto merge of #121985 - RalfJung:interpret-return-place, r=oli-obk

interpret: avoid a long-lived PlaceTy in stack frames

`PlaceTy` uses a representation that's not very stable under changes to the stack. I'd feel better if we didn't have one in the long-term machine state.

r? `@oli-obk`

6 files changed, 27 insertions, 31 deletions

diff --git a/compiler/rustc_const_eval/src/const_eval/machine.rs b/compiler/rustc_const_eval/src/const_eval/machine.rs
index 946ffc05cc1..864241fbd4a 100644
--- a/compiler/rustc_const_eval/src/const_eval/machine.rs
+++ b/compiler/rustc_const_eval/src/const_eval/machine.rs
@@ -24,7 +24,7 @@ use crate::errors::{LongRunning, LongRunningWarn};
 use crate::fluent_generated as fluent;
 use crate::interpret::{
     self, compile_time_machine, AllocId, AllocRange, ConstAllocation, CtfeProvenance, FnArg, FnVal,
-    Frame, ImmTy, InterpCx, InterpResult, OpTy, PlaceTy, Pointer, PointerArithmetic, Scalar,
+    Frame, ImmTy, InterpCx, InterpResult, MPlaceTy, OpTy, Pointer, PointerArithmetic, Scalar,
 };
 
 use super::error::*;
@@ -219,7 +219,7 @@ impl<'mir, 'tcx: 'mir> CompileTimeEvalContext<'mir, 'tcx> {
         &mut self,
         instance: ty::Instance<'tcx>,
         args: &[FnArg<'tcx>],
-        dest: &PlaceTy<'tcx>,
+        dest: &MPlaceTy<'tcx>,
         ret: Option<mir::BasicBlock>,
     ) -> InterpResult<'tcx, Option<ty::Instance<'tcx>>> {
         let def_id = instance.def_id();
@@ -280,7 +280,7 @@ impl<'mir, 'tcx: 'mir> CompileTimeEvalContext<'mir, 'tcx> {
         &mut self,
         instance: ty::Instance<'tcx>,
         args: &[OpTy<'tcx>],
-        dest: &PlaceTy<'tcx>,
+        dest: &MPlaceTy<'tcx>,
         ret: Option<mir::BasicBlock>,
     ) -> InterpResult<'tcx, ControlFlow<()>> {
         assert_eq!(args.len(), 2);
@@ -410,7 +410,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         orig_instance: ty::Instance<'tcx>,
         _abi: CallAbi,
         args: &[FnArg<'tcx>],
-        dest: &PlaceTy<'tcx>,
+        dest: &MPlaceTy<'tcx>,
         ret: Option<mir::BasicBlock>,
         _unwind: mir::UnwindAction, // unwinding is not supported in consts
     ) -> InterpResult<'tcx, Option<(&'mir mir::Body<'tcx>, ty::Instance<'tcx>)>> {
@@ -455,7 +455,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         ecx: &mut InterpCx<'mir, 'tcx, Self>,
         instance: ty::Instance<'tcx>,
         args: &[OpTy<'tcx>],
-        dest: &PlaceTy<'tcx, Self::Provenance>,
+        dest: &MPlaceTy<'tcx, Self::Provenance>,
         target: Option<mir::BasicBlock>,
         _unwind: mir::UnwindAction,
     ) -> InterpResult<'tcx> {
diff --git a/compiler/rustc_const_eval/src/interpret/eval_context.rs b/compiler/rustc_const_eval/src/interpret/eval_context.rs
index cb308ab53ec..a484fbd892c 100644
--- a/compiler/rustc_const_eval/src/interpret/eval_context.rs
+++ b/compiler/rustc_const_eval/src/interpret/eval_context.rs
@@ -108,7 +108,7 @@ pub struct Frame<'mir, 'tcx, Prov: Provenance = CtfeProvenance, Extra = ()> {
 
     /// The location where the result of the current stack frame should be written to,
     /// and its layout in the caller.
-    pub return_place: PlaceTy<'tcx, Prov>,
+    pub return_place: MPlaceTy<'tcx, Prov>,
 
     /// The list of locals for this stack frame, stored in order as
     /// `[return_ptr, arguments..., variables..., temporaries...]`.
@@ -771,7 +771,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         &mut self,
         instance: ty::Instance<'tcx>,
         body: &'mir mir::Body<'tcx>,
-        return_place: &PlaceTy<'tcx, M::Provenance>,
+        return_place: &MPlaceTy<'tcx, M::Provenance>,
         return_to_block: StackPopCleanup,
     ) -> InterpResult<'tcx> {
         trace!("body: {:#?}", body);
@@ -912,7 +912,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             } else {
                 self.copy_op_allow_transmute(&op, &dest)
             };
-            trace!("return value: {:?}", self.dump_place(&dest));
+            trace!("return value: {:?}", self.dump_place(&dest.into()));
             // We delay actually short-circuiting on this error until *after* the stack frame is
             // popped, since we want this error to be attributed to the caller, whose type defines
             // this transmute.
diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics.rs b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
index 1cb991b38f7..b68bfb4211d 100644
--- a/compiler/rustc_const_eval/src/interpret/intrinsics.rs
+++ b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
@@ -21,7 +21,7 @@ use rustc_span::symbol::{sym, Symbol};
 use rustc_target::abi::Size;
 
 use super::{
-    util::ensure_monomorphic_enough, CheckInAllocMsg, ImmTy, InterpCx, Machine, OpTy, PlaceTy,
+    util::ensure_monomorphic_enough, CheckInAllocMsg, ImmTy, InterpCx, MPlaceTy, Machine, OpTy,
     Pointer,
 };
 
@@ -104,7 +104,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         &mut self,
         instance: ty::Instance<'tcx>,
         args: &[OpTy<'tcx, M::Provenance>],
-        dest: &PlaceTy<'tcx, M::Provenance>,
+        dest: &MPlaceTy<'tcx, M::Provenance>,
         ret: Option<mir::BasicBlock>,
     ) -> InterpResult<'tcx, bool> {
         let instance_args = instance.args;
@@ -377,7 +377,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
                 let elem = &args[2];
                 let (input, input_len) = self.operand_to_simd(&args[0])?;
-                let (dest, dest_len) = self.place_to_simd(dest)?;
+                let (dest, dest_len) = self.mplace_to_simd(dest)?;
                 assert_eq!(input_len, dest_len, "Return vector length must match input length");
                 // Bounds are not checked by typeck so we have to do it ourselves.
                 if index >= input_len {
@@ -430,7 +430,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             _ => return Ok(false),
         }
 
-        trace!("{:?}", self.dump_place(dest));
+        trace!("{:?}", self.dump_place(&dest.clone().into()));
         self.go_to_block(ret);
         Ok(true)
     }
@@ -488,7 +488,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         &mut self,
         a: &ImmTy<'tcx, M::Provenance>,
         b: &ImmTy<'tcx, M::Provenance>,
-        dest: &PlaceTy<'tcx, M::Provenance>,
+        dest: &MPlaceTy<'tcx, M::Provenance>,
     ) -> InterpResult<'tcx> {
         assert_eq!(a.layout.ty, b.layout.ty);
         assert!(matches!(a.layout.ty.kind(), ty::Int(..) | ty::Uint(..)));
@@ -506,7 +506,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             )
         }
         // `Rem` says this is all right, so we can let `Div` do its job.
-        self.binop_ignore_overflow(BinOp::Div, a, b, dest)
+        self.binop_ignore_overflow(BinOp::Div, a, b, &dest.clone().into())
     }
 
     pub fn saturating_arith(
diff --git a/compiler/rustc_const_eval/src/interpret/machine.rs b/compiler/rustc_const_eval/src/interpret/machine.rs
index 0106ec425bc..ee5de44a651 100644
--- a/compiler/rustc_const_eval/src/interpret/machine.rs
+++ b/compiler/rustc_const_eval/src/interpret/machine.rs
@@ -196,7 +196,7 @@ pub trait Machine<'mir, 'tcx: 'mir>: Sized {
         instance: ty::Instance<'tcx>,
         abi: CallAbi,
         args: &[FnArg<'tcx, Self::Provenance>],
-        destination: &PlaceTy<'tcx, Self::Provenance>,
+        destination: &MPlaceTy<'tcx, Self::Provenance>,
         target: Option<mir::BasicBlock>,
         unwind: mir::UnwindAction,
     ) -> InterpResult<'tcx, Option<(&'mir mir::Body<'tcx>, ty::Instance<'tcx>)>>;
@@ -208,7 +208,7 @@ pub trait Machine<'mir, 'tcx: 'mir>: Sized {
         fn_val: Self::ExtraFnVal,
         abi: CallAbi,
         args: &[FnArg<'tcx, Self::Provenance>],
-        destination: &PlaceTy<'tcx, Self::Provenance>,
+        destination: &MPlaceTy<'tcx, Self::Provenance>,
         target: Option<mir::BasicBlock>,
         unwind: mir::UnwindAction,
     ) -> InterpResult<'tcx>;
@@ -219,7 +219,7 @@ pub trait Machine<'mir, 'tcx: 'mir>: Sized {
         ecx: &mut InterpCx<'mir, 'tcx, Self>,
         instance: ty::Instance<'tcx>,
         args: &[OpTy<'tcx, Self::Provenance>],
-        destination: &PlaceTy<'tcx, Self::Provenance>,
+        destination: &MPlaceTy<'tcx, Self::Provenance>,
         target: Option<mir::BasicBlock>,
         unwind: mir::UnwindAction,
     ) -> InterpResult<'tcx>;
@@ -584,7 +584,7 @@ pub macro compile_time_machine(<$mir: lifetime, $tcx: lifetime>) {
         fn_val: !,
         _abi: CallAbi,
         _args: &[FnArg<$tcx>],
-        _destination: &PlaceTy<$tcx, Self::Provenance>,
+        _destination: &MPlaceTy<$tcx, Self::Provenance>,
         _target: Option<mir::BasicBlock>,
         _unwind: mir::UnwindAction,
     ) -> InterpResult<$tcx> {
diff --git a/compiler/rustc_const_eval/src/interpret/place.rs b/compiler/rustc_const_eval/src/interpret/place.rs
index 672008edfd3..60f7710c11d 100644
--- a/compiler/rustc_const_eval/src/interpret/place.rs
+++ b/compiler/rustc_const_eval/src/interpret/place.rs
@@ -194,6 +194,12 @@ pub(super) enum Place<Prov: Provenance = CtfeProvenance> {
     Local { frame: usize, local: mir::Local, offset: Option<Size> },
 }
 
+/// An evaluated place, together with its type.
+///
+/// This may reference a stack frame by its index, so `PlaceTy` should generally not be kept around
+/// for longer than a single operation. Popping and then pushing a stack frame can make `PlaceTy`
+/// point to the wrong destination. If the interpreter has multiple stacks, stack switching will
+/// also invalidate a `PlaceTy`.
 #[derive(Clone)]
 pub struct PlaceTy<'tcx, Prov: Provenance = CtfeProvenance> {
     place: Place<Prov>, // Keep this private; it helps enforce invariants.
@@ -495,16 +501,6 @@ where
         Ok((mplace, len))
     }
 
-    /// Converts a repr(simd) place into a place where `place_index` accesses the SIMD elements.
-    /// Also returns the number of elements.
-    pub fn place_to_simd(
-        &mut self,
-        place: &PlaceTy<'tcx, M::Provenance>,
-    ) -> InterpResult<'tcx, (MPlaceTy<'tcx, M::Provenance>, u64)> {
-        let mplace = self.force_allocation(place)?;
-        self.mplace_to_simd(&mplace)
-    }
-
     pub fn local_to_place(
         &self,
         frame: usize,
diff --git a/compiler/rustc_const_eval/src/interpret/terminator.rs b/compiler/rustc_const_eval/src/interpret/terminator.rs
index d29e69d753e..55f85573f38 100644
--- a/compiler/rustc_const_eval/src/interpret/terminator.rs
+++ b/compiler/rustc_const_eval/src/interpret/terminator.rs
@@ -153,7 +153,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     ),
                 };
 
-                let destination = self.eval_place(destination)?;
+                let destination = self.force_allocation(&self.eval_place(destination)?)?;
                 self.eval_fn_call(
                     fn_val,
                     (fn_sig.abi, fn_abi),
@@ -497,7 +497,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         (caller_abi, caller_fn_abi): (Abi, &FnAbi<'tcx, Ty<'tcx>>),
         args: &[FnArg<'tcx, M::Provenance>],
         with_caller_location: bool,
-        destination: &PlaceTy<'tcx, M::Provenance>,
+        destination: &MPlaceTy<'tcx, M::Provenance>,
         target: Option<mir::BasicBlock>,
         mut unwind: mir::UnwindAction,
     ) -> InterpResult<'tcx> {
@@ -726,7 +726,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                         });
                     }
                     // Protect return place for in-place return value passing.
-                    M::protect_in_place_function_argument(self, destination)?;
+                    M::protect_in_place_function_argument(self, &destination.clone().into())?;
 
                     // Don't forget to mark "initially live" locals as live.
                     self.storage_live_for_always_live_locals()?;