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author | Ryan Cumming <etaoins@gmail.com> | 2018-01-27 12:14:12 +1100 |
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committer | Ryan Cumming <etaoins@gmail.com> | 2018-01-27 12:57:01 +1100 |
commit | 75c79bdb0204271e09220c4c59239bb85772ee93 (patch) | |
tree | 79da2b9cc5e24d3e99c96015c173c709106be51c | |
parent | bacb5c58dfdde7c35e99b2b0d8171238cc33cf6c (diff) | |
download | rust-75c79bdb0204271e09220c4c59239bb85772ee93.tar.gz |
Fix ICE on const eval of union field
MIR's `Const::get_field()` attempts to retrieve the value for a given
field in a constant. In the case of a union constant it was falling
through to a generic `const_get_elt` based on the field index. As union
fields don't have an index this caused an ICE in `llvm_field_index`.
Fix by simply returning the current value when accessing any field in a
union. This works because all union fields start at byte offset 0.
The added test uses `const_fn` it ensure the field is extracted using
MIR's const evaluation. The crash is reproducible without it, however.
Fixes #47788
-rw-r--r-- | src/librustc_trans/mir/constant.rs | 5 | ||||
-rw-r--r-- | src/test/run-pass/union/union-const-eval-field.rs | 26 |
2 files changed, 30 insertions, 1 deletions
diff --git a/src/librustc_trans/mir/constant.rs b/src/librustc_trans/mir/constant.rs index 71ce0aa3da9..f519e27dce9 100644 --- a/src/librustc_trans/mir/constant.rs +++ b/src/librustc_trans/mir/constant.rs @@ -140,7 +140,10 @@ impl<'a, 'tcx> Const<'tcx> { } } _ => { - const_get_elt(self.llval, layout.llvm_field_index(i)) + match layout.fields { + layout::FieldPlacement::Union(_) => self.llval, + _ => const_get_elt(self.llval, layout.llvm_field_index(i)), + } } } } diff --git a/src/test/run-pass/union/union-const-eval-field.rs b/src/test/run-pass/union/union-const-eval-field.rs new file mode 100644 index 00000000000..a58b8bc34cd --- /dev/null +++ b/src/test/run-pass/union/union-const-eval-field.rs @@ -0,0 +1,26 @@ +// Copyright 2018 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or +// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license +// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +#![feature(const_fn)] + +union DummyUnion { + field1: i32, + field2: i32, +} + +const fn read_field() -> i32 { + const UNION: DummyUnion = DummyUnion { field1: 5 }; + const FIELD: i32 = unsafe { UNION.field2 }; + FIELD +} + +fn main() { + assert_eq!(read_field(), 5); +} |