diff options
| -rw-r--r-- | src/librustc_mir/transform/const_prop.rs | 25 |
1 files changed, 14 insertions, 11 deletions
diff --git a/src/librustc_mir/transform/const_prop.rs b/src/librustc_mir/transform/const_prop.rs index f0c0e573443..780b49cd9db 100644 --- a/src/librustc_mir/transform/const_prop.rs +++ b/src/librustc_mir/transform/const_prop.rs @@ -518,27 +518,30 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { } } - // Work around: avoid ICE in miri. - // FIXME(wesleywiser) we don't currently handle the case where we try to make a ref - // from a function argument that hasn't been assigned to in this function. The main - // issue is if an arg is a fat-pointer, miri `expects()` to be able to read the value - // of that pointer to get size info. However, since this is `ConstProp`, that argument - // doesn't actually have a backing value and so this causes an ICE. + // Work around: avoid ICE in miri. FIXME(wesleywiser) + // The Miri engine ICEs when taking a reference to an uninitialized unsized + // local. There's nothing it can do here: taking a reference needs an allocation + // which needs to know the size. Normally that's okay as during execution + // (e.g. for CTFE) it can never happen. But here in const_prop + // unknown data is uninitialized, so if e.g. a function argument is unsized + // and has a reference taken, we get an ICE. Rvalue::Ref(_, _, Place { base: PlaceBase::Local(local), projection: box [] }) => { trace!("checking Ref({:?})", place); let alive = if let LocalValue::Live(_) = self.ecx.frame().locals[*local].value { true - } else { false }; + } else { + false + }; - if local.as_usize() <= self.ecx.frame().body.arg_count && !alive { - trace!("skipping Ref({:?})", place); + if !alive { + trace!("skipping Ref({:?}) to uninitialized local", place); return None; } } - // Work around: avoid extra unnecessary locals. - // FIXME(wesleywiser): const eval will turn this into a `const Scalar(<ZST>)` that + // Work around: avoid extra unnecessary locals. FIXME(wesleywiser) + // Const eval will turn this into a `const Scalar(<ZST>)` that // `SimplifyLocals` doesn't know it can remove. Rvalue::Aggregate(_, operands) if operands.len() == 0 => { return None; |