Auto merge of #114483 - RalfJung:unsized-fields, r=oli-obk

interpret: fix projecting into an unsized field of a local

See the new Miri testcase that didn't work before.

r? `@oli-obk`

Author: bors

src/diagnostics.rs

@@ -283,7 +283,7 @@ pub fn report_error<'tcx, 'mir>(
                 "resource exhaustion",
             Unsupported(
                 // We list only the ones that can actually happen.
-                UnsupportedOpInfo::Unsupported(_)
+                UnsupportedOpInfo::Unsupported(_) | UnsupportedOpInfo::UnsizedLocal
             ) =>
                 "unsupported operation",
             InvalidProgram(

src/helpers.rs

@@ -14,7 +14,7 @@ use rustc_middle::mir;
 use rustc_middle::ty::{
     self,
     layout::{IntegerExt as _, LayoutOf, TyAndLayout},
-    List, Ty, TyCtxt,
+    Ty, TyCtxt,
 };
 use rustc_span::{def_id::CrateNum, sym, Span, Symbol};
 use rustc_target::abi::{Align, FieldIdx, FieldsShape, Integer, Size, Variants};
@@ -282,13 +282,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         Ok(ptr.addr().bytes() == 0)
     }
 
-    /// Get the `Place` for a local
-    fn local_place(&self, local: mir::Local) -> InterpResult<'tcx, PlaceTy<'tcx, Provenance>> {
-        let this = self.eval_context_ref();
-        let place = mir::Place { local, projection: List::empty() };
-        this.eval_place(place)
-    }
-
     /// Generate some random bytes, and write them to `dest`.
     fn gen_random(&mut self, ptr: Pointer<Option<Provenance>>, len: u64) -> InterpResult<'tcx> {
         // Some programs pass in a null pointer and a length of 0
@@ -350,17 +343,21 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         // Initialize arguments.
         let mut callee_args = this.frame().body.args_iter();
         for arg in args {
-            let callee_arg = this.local_place(
-                callee_args
-                    .next()
-                    .ok_or_else(|| err_ub_format!("callee has fewer arguments than expected"))?,
-            )?;
+            let local = callee_args
+                .next()
+                .ok_or_else(|| err_ub_format!("callee has fewer arguments than expected"))?;
+            // Make the local live, and insert the initial value.
+            this.storage_live(local)?;
+            let callee_arg = this.local_to_place(this.frame_idx(), local)?;
             this.write_immediate(*arg, &callee_arg)?;
         }
         if callee_args.next().is_some() {
             throw_ub_format!("callee has more arguments than expected");
         }
 
+        // Initialize remaining locals.
+        this.storage_live_for_always_live_locals()?;
+
         Ok(())
     }
 

tests/fail/type-too-large.rs

@@ -1,6 +1,6 @@
 //@ignore-32bit
 
 fn main() {
-    let _fat: [u8; (1 << 61) + (1 << 31)];
+    let _fat: [u8; (1 << 61) + (1 << 31)]; // ideally we'd error here, but we avoid computing the layout until absolutely necessary
     _fat = [0; (1u64 << 61) as usize + (1u64 << 31) as usize]; //~ ERROR: post-monomorphization error
 }

tests/fail/unsized-local.stderr

@@ -2,7 +2,7 @@ error: unsupported operation: unsized locals are not supported
   --> $DIR/unsized-local.rs:LL:CC
    |
 LL |     let x = *(Box::new(A) as Box<dyn Foo>);
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unsized locals are not supported
+   |         ^ unsized locals are not supported
    |
    = help: this is likely not a bug in the program; it indicates that the program performed an operation that the interpreter does not support
    = note: BACKTRACE:

tests/pass/unsized.rs

@@ -2,6 +2,7 @@
 //@[tree]compile-flags: -Zmiri-tree-borrows
 #![feature(unsized_tuple_coercion)]
 #![feature(unsized_fn_params)]
+#![feature(custom_mir, core_intrinsics)]
 
 use std::mem;
 
@@ -32,7 +33,30 @@ fn unsized_params() {
     f3(*p);
 }
 
+fn unsized_field_projection() {
+    use std::intrinsics::mir::*;
+
+    pub struct S<T: ?Sized>(T);
+
+    #[custom_mir(dialect = "runtime", phase = "optimized")]
+    fn f(x: S<[u8]>) {
+        mir! {
+            {
+                let idx = 0;
+                // Project to an unsized field of an unsized local.
+                x.0[idx] = 0;
+                let _val = x.0[idx];
+                Return()
+            }
+        }
+    }
+
+    let x: Box<S<[u8]>> = Box::new(S([0]));
+    f(*x);
+}
+
 fn main() {
     unsized_tuple();
     unsized_params();
+    unsized_field_projection();
 }