diff options
Diffstat (limited to 'compiler/rustc_serialize/src')
| -rw-r--r-- | compiler/rustc_serialize/src/int_overflow.rs | 65 | ||||
| -rw-r--r-- | compiler/rustc_serialize/src/leb128.rs | 14 | ||||
| -rw-r--r-- | compiler/rustc_serialize/src/lib.rs | 1 | ||||
| -rw-r--r-- | compiler/rustc_serialize/src/opaque.rs | 10 |
4 files changed, 82 insertions, 8 deletions
diff --git a/compiler/rustc_serialize/src/int_overflow.rs b/compiler/rustc_serialize/src/int_overflow.rs new file mode 100644 index 00000000000..f2aac2ef711 --- /dev/null +++ b/compiler/rustc_serialize/src/int_overflow.rs @@ -0,0 +1,65 @@ +// This would belong to `rustc_data_structures`, but `rustc_serialize` needs it too. + +/// Addition, but only overflow checked when `cfg(debug_assertions)` is set +/// instead of respecting `-Coverflow-checks`. +/// +/// This exists for performance reasons, as we ship rustc with overflow checks. +/// While overflow checks are perf neutral in almost all of the compiler, there +/// are a few particularly hot areas where we don't want overflow checks in our +/// dist builds. Overflow is still a bug there, so we want overflow check for +/// builds with debug assertions. +/// +/// That's a long way to say that this should be used in areas where overflow +/// is a bug but overflow checking is too slow. +pub trait DebugStrictAdd { + /// See [`DebugStrictAdd`]. + fn debug_strict_add(self, other: Self) -> Self; +} + +macro_rules! impl_debug_strict_add { + ($( $ty:ty )*) => { + $( + impl DebugStrictAdd for $ty { + fn debug_strict_add(self, other: Self) -> Self { + if cfg!(debug_assertions) { + self + other + } else { + self.wrapping_add(other) + } + } + } + )* + }; +} + +/// See [`DebugStrictAdd`]. +pub trait DebugStrictSub { + /// See [`DebugStrictAdd`]. + fn debug_strict_sub(self, other: Self) -> Self; +} + +macro_rules! impl_debug_strict_sub { + ($( $ty:ty )*) => { + $( + impl DebugStrictSub for $ty { + fn debug_strict_sub(self, other: Self) -> Self { + if cfg!(debug_assertions) { + self - other + } else { + self.wrapping_sub(other) + } + } + } + )* + }; +} + +impl_debug_strict_add! { + u8 u16 u32 u64 u128 usize + i8 i16 i32 i64 i128 isize +} + +impl_debug_strict_sub! { + u8 u16 u32 u64 u128 usize + i8 i16 i32 i64 i128 isize +} diff --git a/compiler/rustc_serialize/src/leb128.rs b/compiler/rustc_serialize/src/leb128.rs index ca661bac78c..44324804468 100644 --- a/compiler/rustc_serialize/src/leb128.rs +++ b/compiler/rustc_serialize/src/leb128.rs @@ -1,6 +1,10 @@ use crate::opaque::MemDecoder; use crate::serialize::Decoder; +// This code is very hot and uses lots of arithmetic, avoid overflow checks for performance. +// See https://github.com/rust-lang/rust/pull/119440#issuecomment-1874255727 +use crate::int_overflow::DebugStrictAdd; + /// Returns the length of the longest LEB128 encoding for `T`, assuming `T` is an integer type pub const fn max_leb128_len<T>() -> usize { // The longest LEB128 encoding for an integer uses 7 bits per byte. @@ -24,7 +28,7 @@ macro_rules! impl_write_unsigned_leb128 { *out.get_unchecked_mut(i) = value as u8; } - i += 1; + i = i.debug_strict_add(1); break; } else { unsafe { @@ -32,7 +36,7 @@ macro_rules! impl_write_unsigned_leb128 { } value >>= 7; - i += 1; + i = i.debug_strict_add(1); } } @@ -69,7 +73,7 @@ macro_rules! impl_read_unsigned_leb128 { } else { result |= ((byte & 0x7F) as $int_ty) << shift; } - shift += 7; + shift = shift.debug_strict_add(7); } } }; @@ -101,7 +105,7 @@ macro_rules! impl_write_signed_leb128 { *out.get_unchecked_mut(i) = byte; } - i += 1; + i = i.debug_strict_add(1); if !more { break; @@ -130,7 +134,7 @@ macro_rules! impl_read_signed_leb128 { loop { byte = decoder.read_u8(); result |= <$int_ty>::from(byte & 0x7F) << shift; - shift += 7; + shift = shift.debug_strict_add(7); if (byte & 0x80) == 0 { break; diff --git a/compiler/rustc_serialize/src/lib.rs b/compiler/rustc_serialize/src/lib.rs index b67b7d79d97..5a9403e0a85 100644 --- a/compiler/rustc_serialize/src/lib.rs +++ b/compiler/rustc_serialize/src/lib.rs @@ -23,5 +23,6 @@ pub use self::serialize::{Decodable, Decoder, Encodable, Encoder}; mod serialize; +pub mod int_overflow; pub mod leb128; pub mod opaque; diff --git a/compiler/rustc_serialize/src/opaque.rs b/compiler/rustc_serialize/src/opaque.rs index cc8d1c25092..eec83c02d35 100644 --- a/compiler/rustc_serialize/src/opaque.rs +++ b/compiler/rustc_serialize/src/opaque.rs @@ -7,6 +7,10 @@ use std::ops::Range; use std::path::Path; use std::path::PathBuf; +// This code is very hot and uses lots of arithmetic, avoid overflow checks for performance. +// See https://github.com/rust-lang/rust/pull/119440#issuecomment-1874255727 +use crate::int_overflow::DebugStrictAdd; + // ----------------------------------------------------------------------------- // Encoder // ----------------------------------------------------------------------------- @@ -65,7 +69,7 @@ impl FileEncoder { // Tracking position this way instead of having a `self.position` field // means that we only need to update `self.buffered` on a write call, // as opposed to updating `self.position` and `self.buffered`. - self.flushed + self.buffered + self.flushed.debug_strict_add(self.buffered) } #[cold] @@ -119,7 +123,7 @@ impl FileEncoder { } if let Some(dest) = self.buffer_empty().get_mut(..buf.len()) { dest.copy_from_slice(buf); - self.buffered += buf.len(); + self.buffered = self.buffered.debug_strict_add(buf.len()); } else { self.write_all_cold_path(buf); } @@ -158,7 +162,7 @@ impl FileEncoder { if written > N { Self::panic_invalid_write::<N>(written); } - self.buffered += written; + self.buffered = self.buffered.debug_strict_add(written); } #[cold] |