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Move the no-variants handling code earlier in expand_enum_method_body.

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To avoid computing a bunch of stuff that it doesn't need.
This commit is contained in:
Nicholas Nethercote 2022-07-08 15:31:09 +10:00
parent f1d9e2b50c
commit 4bcbd76bc9
1 changed files with 6 additions and 5 deletions
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11
compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
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@ -1173,6 +1173,12 @@ impl<'a> MethodDef<'a> {
let span = trait_.span;
let variants = &enum_def.variants;
// There is no sensible code to be generated for *any* deriving on a
// zero-variant enum. So we just generate a failing expression.
if variants.is_empty() {
return BlockOrExpr(vec![], Some(deriving::call_unreachable(cx, span)));
}
let prefixes = iter::once("__self".to_string())
.chain(
selflike_args
@ -1365,11 +1371,6 @@ impl<'a> MethodDef<'a> {
let all_match = cx.expr_match(span, match_arg, match_arms);
let arm_expr = cx.expr_if(span, discriminant_test, all_match, Some(arm_expr));
BlockOrExpr(index_let_stmts, Some(arm_expr))
} else if variants.is_empty() {
// There is no sensible code to be generated for *any* deriving on
// a zero-variant enum. So we just generate a failing expression
// for the zero variant case.
BlockOrExpr(vec![], Some(deriving::call_unreachable(cx, span)))
} else {
let match_arg = if selflike_args.len() == 1 {
selflike_args.pop().unwrap()