Correctly access ScalarPair fields during const eval

2 files changed, 34 insertions, 60 deletions

diff --git a/src/librustc_mir/interpret/place.rs b/src/librustc_mir/interpret/place.rs
index c1bcffe7e9a..d1f3b8b86de 100644
--- a/src/librustc_mir/interpret/place.rs
+++ b/src/librustc_mir/interpret/place.rs
@@ -136,8 +136,8 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
             Value::ScalarPair(..) |
             Value::Scalar(_) if offset.bytes() == 0 && field.size == base_layout.size => Ok(Some((base, field.ty))),
             // split fat pointers, 2 element tuples, ...
-            Value::ScalarPair(a, b) if base_layout.fields.count() == 2 => {
-                let val = [a, b][field_index];
+            Value::ScalarPair(a, b) => {
+                let val = if offset.bytes() == 0 { a } else { b };
                 Ok(Some((Value::Scalar(val), field.ty)))
             },
             // FIXME(oli-obk): figure out whether we should be calling `try_read_value` here
diff --git a/src/librustc_mir/interpret/terminator/mod.rs b/src/librustc_mir/interpret/terminator/mod.rs
index 9151bfbdd1b..8ed60b2325a 100644
--- a/src/librustc_mir/interpret/terminator/mod.rs
+++ b/src/librustc_mir/interpret/terminator/mod.rs
@@ -4,7 +4,7 @@ use rustc::ty::layout::LayoutOf;
 use syntax::codemap::Span;
 use rustc_target::spec::abi::Abi;
 
-use rustc::mir::interpret::{EvalResult, Scalar, Value};
+use rustc::mir::interpret::{EvalResult, Value};
 use super::{EvalContext, Place, Machine, ValTy};
 
 use rustc_data_structures::indexed_vec::Idx;
@@ -338,65 +338,39 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
 
                         // unpack and write all other args
                         let layout = self.layout_of(args[1].ty)?;
-                        if let ty::TyTuple(..) = args[1].ty.sty {
+                        if let ty::TyTuple(_) = args[1].ty.sty {
+                            if layout.is_zst() {
+                                // Nothing to do, no need to unpack zsts
+                                return Ok(());
+                            }
                             if self.frame().mir.args_iter().count() == layout.fields.count() + 1 {
-                                match args[1].value {
-                                    Value::ByRef(ptr, align) => {
-                                        for (i, arg_local) in arg_locals.enumerate() {
-                                            let field = layout.field(&self, i)?;
-                                            let offset = layout.fields.offset(i);
-                                            let arg = Value::ByRef(ptr.ptr_offset(offset, &self)?,
-                                                                   align.min(field.align));
-                                            let dest =
-                                                self.eval_place(&mir::Place::Local(arg_local))?;
-                                            trace!(
-                                                "writing arg {:?} to {:?} (type: {})",
-                                                arg,
-                                                dest,
-                                                field.ty
-                                            );
-                                            let valty = ValTy {
-                                                value: arg,
-                                                ty: field.ty,
-                                            };
-                                            self.write_value(valty, dest)?;
-                                        }
-                                    }
-                                    Value::Scalar(Scalar::Bits { defined: 0, .. }) => {}
-                                    other => {
-                                        trace!("{:#?}, {:#?}", other, layout);
-                                        let mut layout = layout;
-                                        'outer: loop {
-                                            for i in 0..layout.fields.count() {
-                                                let field = layout.field(&self, i)?;
-                                                if layout.fields.offset(i).bytes() == 0 && layout.size == field.size {
-                                                    layout = field;
-                                                    continue 'outer;
-                                                }
-                                            }
-                                            break;
-                                        }
-                                        {
-                                            let mut write_next = |value| {
-                                                let dest = self.eval_place(&mir::Place::Local(
-                                                    arg_locals.next().unwrap(),
-                                                ))?;
-                                                let valty = ValTy {
-                                                    value: Value::Scalar(value),
-                                                    ty: layout.ty,
-                                                };
-                                                self.write_value(valty, dest)
-                                            };
-                                            match other {
-                                                Value::Scalar(value) | Value::ScalarPair(value, _) => write_next(value)?,
-                                                _ => unreachable!(),
-                                            }
-                                            if let Value::ScalarPair(_, value) = other {
-                                                write_next(value)?;
-                                            }
-                                        }
-                                        assert!(arg_locals.next().is_none());
+                                for (i, arg_local) in arg_locals.enumerate() {
+                                    let field = layout.field(&self, i)?;
+                                    if field.is_zst() {
+                                        continue;
                                     }
+                                    let offset = layout.fields.offset(i);
+                                    let value = match args[1].value {
+                                        Value::ByRef(ptr, align) => Value::ByRef(
+                                            ptr.ptr_offset(offset, &self)?,
+                                            align.min(field.align),
+                                        ),
+                                        other if field.size == layout.size => {
+                                            // this is the case where the field covers the entire type
+                                            assert_eq!(offset.bytes(), 0);
+                                            other
+                                        },
+                                        Value::ScalarPair(a, _) if offset.bytes() == 0 => Value::Scalar(a),
+                                        Value::ScalarPair(_, b) => Value::Scalar(b),
+                                        Value::Scalar(_) => bug!("Scalar does not cover entire type"),
+                                    };
+                                    let dest =
+                                        self.eval_place(&mir::Place::Local(arg_local))?;
+                                    let valty = ValTy {
+                                        value,
+                                        ty: field.ty,
+                                    };
+                                    self.write_value(valty, dest)?;
                                 }
                             } else {
                                 trace!("manual impl of rust-call ABI");