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Auto merge of #82738 - estebank:tail-expr-check-is-too-slow, r=oli-obk

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Move check only relevant in error case out of critical path

Move the check for potentially forgotten `return` in a tail expression
of arbitrary expressions into the coercion error branch to avoid
computing unncessary coercion checks on successful code.

Follow up to #81458.
This commit is contained in:
bors 2021-03-06 21:02:53 +00:00
commit dfe519b344
1 changed files with 11 additions and 11 deletions
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22
compiler/rustc_typeck/src/check/_match.rs
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@ -207,17 +207,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
), ),
}; };
let cause = self.cause(span, code); let cause = self.cause(span, code);
let can_coerce_to_return_ty = match self.ret_coercion.as_ref() {
Some(ret_coercion) if self.in_tail_expr => {
let ret_ty = ret_coercion.borrow().expected_ty();
let ret_ty = self.inh.infcx.shallow_resolve(ret_ty);
self.can_coerce(arm_ty, ret_ty)
&& prior_arm_ty.map_or(true, |t| self.can_coerce(t, ret_ty))
// The match arms need to unify for the case of `impl Trait`.
&& !matches!(ret_ty.kind(), ty::Opaque(..))
}
_ => false,
};
// This is the moral equivalent of `coercion.coerce(self, cause, arm.body, arm_ty)`. // This is the moral equivalent of `coercion.coerce(self, cause, arm.body, arm_ty)`.
// We use it this way to be able to expand on the potential error and detect when a // We use it this way to be able to expand on the potential error and detect when a
@ -229,6 +218,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
Some(&arm.body), Some(&arm.body),
arm_ty, arm_ty,
Some(&mut |err: &mut DiagnosticBuilder<'_>| { Some(&mut |err: &mut DiagnosticBuilder<'_>| {
let can_coerce_to_return_ty = match self.ret_coercion.as_ref() {
Some(ret_coercion) if self.in_tail_expr => {
let ret_ty = ret_coercion.borrow().expected_ty();
let ret_ty = self.inh.infcx.shallow_resolve(ret_ty);
self.can_coerce(arm_ty, ret_ty)
&& prior_arm_ty.map_or(true, |t| self.can_coerce(t, ret_ty))
// The match arms need to unify for the case of `impl Trait`.
&& !matches!(ret_ty.kind(), ty::Opaque(..))
}
_ => false,
};
if let (Expectation::IsLast(stmt), Some(ret), true) = if let (Expectation::IsLast(stmt), Some(ret), true) =
(orig_expected, self.ret_type_span, can_coerce_to_return_ty) (orig_expected, self.ret_type_span, can_coerce_to_return_ty)
{ {