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Allow Abort terminators in all const-contexts #77512

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merged 6 commits into from
Oct 5, 2020
Merged

Allow Abort terminators in all const-contexts #77512

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98a2292
Allow `Abort` terminators in a const-context
ecstatic-morse Oct 3, 2020
a5f0831
Add check-pass test for `#[unwind(aborts)]` on a `const fn`
ecstatic-morse Oct 3, 2020
14c3705
Ensure that the const-eval engine handles `#[unwind(aborts)]`
ecstatic-morse Oct 3, 2020
25fdbaf
Discuss cleanup blocks and `span_bug` on `Abort`
ecstatic-morse Oct 4, 2020
fe97990
Add comment to `Abort` match arm
ecstatic-morse Oct 4, 2020
6ae1da3
But whatever
ecstatic-morse Oct 4, 2020
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17 changes: 11 additions & 6 deletions compiler/rustc_mir/src/transform/check_consts/validation.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -434,11 +434,13 @@ impl Visitor<'tcx> for Validator<'mir, 'tcx> {
fn visit_basic_block_data(&mut self, bb: BasicBlock, block: &BasicBlockData<'tcx>) {
trace!("visit_basic_block_data: bb={:?} is_cleanup={:?}", bb, block.is_cleanup);

// Just as the old checker did, we skip const-checking basic blocks on the unwind path.
// These blocks often drop locals that would otherwise be returned from the function.
// We don't const-check basic blocks on the cleanup path since we never unwind during
// const-eval: a panic causes an immediate compile error. In other words, cleanup blocks
// are unreachable during const-eval.
//
// FIXME: This shouldn't be unsound since a panic at compile time will cause a compiler
// error anyway, but maybe we should do more here?
// We can't be more conservative (e.g., by const-checking cleanup blocks anyways) because
// locals that would never be dropped during normal execution are sometimes dropped during
// unwinding, which means backwards-incompatible live-drop errors.
if block.is_cleanup {
return;
}
Expand Down Expand Up @@ -879,8 +881,11 @@ impl Visitor<'tcx> for Validator<'mir, 'tcx> {
self.check_op(ops::Generator(hir::GeneratorKind::Gen))
}

TerminatorKind::Abort
| TerminatorKind::Assert { .. }
TerminatorKind::Abort => {
span_bug!(self.span, "`Abort` terminator outside of cleanup block")
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}

TerminatorKind::Assert { .. }
| TerminatorKind::FalseEdge { .. }
| TerminatorKind::FalseUnwind { .. }
| TerminatorKind::Goto { .. }
Expand Down