bjoernager/rust
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Improve derived discriminant testing.

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Currently the generated code for methods like `eq`, `ne`, and `partial_cmp`
includes stuff like this:
```
let __self_vi = ::core::intrinsics::discriminant_value(&*self);
let __arg_1_vi = ::core::intrinsics::discriminant_value(&*other);
if true && __self_vi == __arg_1_vi {
    ...
}
```
This commit removes the unnecessary `true &&`, and makes the generating
code a little easier to read in the process. It also fixes some errors
in comments.
This commit is contained in:
Nicholas Nethercote 2022-06-22 15:00:53 +10:00
parent ea74997c41
commit 00207ead61
2 changed files with 27 additions and 32 deletions
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37
compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
View file

@ -1392,37 +1392,32 @@ impl<'a> MethodDef<'a> {
//
// i.e., for `enum E<T> { A, B(1), C(T, T) }`, and a deriving
// with three Self args, builds three statements:
//
// ```
// let __self0_vi = std::intrinsics::discriminant_value(&self);
// let __self1_vi = std::intrinsics::discriminant_value(&arg1);
// let __self2_vi = std::intrinsics::discriminant_value(&arg2);
// let __self_vi = std::intrinsics::discriminant_value(&self);
// let __arg_1_vi = std::intrinsics::discriminant_value(&arg1);
// let __arg_2_vi = std::intrinsics::discriminant_value(&arg2);
// ```
let mut index_let_stmts: Vec<ast::Stmt> = Vec::with_capacity(vi_idents.len() + 1);
// We also build an expression which checks whether all discriminants are equal
// discriminant_test = __self0_vi == __self1_vi && __self0_vi == __self2_vi && ...
// We also build an expression which checks whether all discriminants are equal:
// `__self_vi == __arg_1_vi && __self_vi == __arg_2_vi && ...`
let mut discriminant_test = cx.expr_bool(span, true);
let mut first_ident = None;
for (&ident, self_arg) in iter::zip(&vi_idents, &self_args) {
for (i, (&ident, self_arg)) in iter::zip(&vi_idents, &self_args).enumerate() {
let self_addr = cx.expr_addr_of(span, self_arg.clone());
let variant_value =
deriving::call_intrinsic(cx, span, sym::discriminant_value, vec![self_addr]);
let let_stmt = cx.stmt_let(span, false, ident, variant_value);
index_let_stmts.push(let_stmt);
match first_ident {
Some(first) => {
let first_expr = cx.expr_ident(span, first);
let id = cx.expr_ident(span, ident);
let test = cx.expr_binary(span, BinOpKind::Eq, first_expr, id);
discriminant_test =
cx.expr_binary(span, BinOpKind::And, discriminant_test, test)
}
None => {
first_ident = Some(ident);
}
if i > 0 {
let id0 = cx.expr_ident(span, vi_idents[0]);
let id = cx.expr_ident(span, ident);
let test = cx.expr_binary(span, BinOpKind::Eq, id0, id);
discriminant_test = if i == 1 {
test
} else {
cx.expr_binary(span, BinOpKind::And, discriminant_test, test)
};
}
}
@ -1453,7 +1448,7 @@ impl<'a> MethodDef<'a> {
// }
// }
// else {
// <delegated expression referring to __self0_vi, et al.>
// <delegated expression referring to __self_vi, et al.>
// }
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));