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Replaced linear token counting macros with optimized implementation #59600

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Merged
merged 1 commit into from
Jun 10, 2019
Merged

Replaced linear token counting macros with optimized implementation #59600

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12 changes: 10 additions & 2 deletions src/librustc/hir/map/definitions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -696,9 +696,17 @@ impl DefPathData {
}
}

/// Evaluates to the number of tokens passed to it.
///
/// Logarithmic counting: every one or two recursive expansions, the number of
/// tokens to count is divided by two, instead of being reduced by one.
/// Therefore, the recursion depth is the binary logarithm of the number of
/// tokens to count, and the expanded tree is likewise very small.
macro_rules! count {
() => (0usize);
( $x:tt $($xs:tt)* ) => (1usize + count!($($xs)*));
() => (0usize);
($one:tt) => (1usize);
($($pairs:tt $_p:tt)*) => (count!($($pairs)*) << 1usize);
($odd:tt $($rest:tt)*) => (count!($($rest)*) | 1usize);
}

// We define the GlobalMetaDataKind enum with this macro because we want to
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17 changes: 12 additions & 5 deletions src/libserialize/serialize.rs
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Expand Up @@ -723,10 +723,17 @@ macro_rules! peel {
($name:ident, $($other:ident,)*) => (tuple! { $($other,)* })
}

/// Evaluates to the number of identifiers passed to it, for example: `count_idents!(a, b, c) == 3
macro_rules! count_idents {
() => { 0 };
($_i:ident, $($rest:ident,)*) => { 1 + count_idents!($($rest,)*) }
/// Evaluates to the number of tokens passed to it.
///
/// Logarithmic counting: every one or two recursive expansions, the number of
/// tokens to count is divided by two, instead of being reduced by one.
/// Therefore, the recursion depth is the binary logarithm of the number of
/// tokens to count, and the expanded tree is likewise very small.
macro_rules! count {
() => (0usize);
($one:tt) => (1usize);
($($pairs:tt $_p:tt)*) => (count!($($pairs)*) << 1usize);
($odd:tt $($rest:tt)*) => (count!($($rest)*) | 1usize);
}

macro_rules! tuple {
Expand All @@ -735,7 +742,7 @@ macro_rules! tuple {
impl<$($name:Decodable),*> Decodable for ($($name,)*) {
#[allow(non_snake_case)]
fn decode<D: Decoder>(d: &mut D) -> Result<($($name,)*), D::Error> {
let len: usize = count_idents!($($name,)*);
let len: usize = count!($($name)*);
d.read_tuple(len, |d| {
let mut i = 0;
let ret = ($(d.read_tuple_arg({ i+=1; i-1 }, |d| -> Result<$name, D::Error> {
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