Merge pull request #11 from HadrienG2/slices

Finally implement Pessimize for slices on stable

Author: HadrienG2

.github/workflows/ci.yml

@@ -21,7 +21,7 @@ concurrency:
 env:
   RUSTFLAGS: -D warnings
   RUSTDOCFLAGS: -D warnings
-  MINIMAL_RUST: 1.63.0  # Minimal Supported Rust Version
+  MINIMAL_RUST: 1.79.0  # Minimal Supported Rust Version
 
 jobs:
   # Workaround for github CI dropping env var expansion in matrix strategy

CHANGELOG.md

@@ -11,6 +11,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 _There are no unreleased changes in the pipeline at the moment._
 
 
+## [2.0.0] - 2024-06-14
+
+### Added
+
+- Implement Pessimize for slices.
+
+### Changed
+
+- Bumped MSRV to 1.79.0.
+
+
 ## [1.0.1] - 2024-02-12
 
 ### Fixed

Cargo.toml

@@ -11,14 +11,14 @@ name = "pessimize"
 # - Roll an annotated git tag
 # - Add a github release
 #
-version = "1.0.1"
+version = "2.0.0"
 authors = ["Hadrien G. <[email protected]>"]
 description = "More efficient Rust compiler optimization barriers"
 keywords = [ "optimization", "barrier", "black-box", "efficient", "benchmarking" ]
 categories = [ "development-tools", "hardware-support", "no-std", "rust-patterns" ]
 license = "MPL-2.0"
 edition = "2021"
-rust-version = "1.63.0"
+rust-version = "1.79.0"
 
 [features]
 default = ["std"]

README.md

@@ -6,7 +6,7 @@
 [![Continuous
 Integration](https://img.shields.io/github/actions/workflow/status/HadrienG2/pessimize/ci.yml?branch=master)](https://github.com/HadrienG2/pessimize/actions?query=workflow%3A%22Continuous+Integration%22)
 ![Requires rustc
-1.63.0+](https://img.shields.io/badge/rustc-1.63.0+-lightgray.svg)
+1.79.0+](https://img.shields.io/badge/rustc-1.79.0+-lightgray.svg)
 
 Microbenchmarking is a subtle exercise to begin with, and the lack of
 lightweight optimization barriers on stable Rust makes it even more difficult.

src/ptr.rs

@@ -32,10 +32,11 @@ fn assume_accessed_thin_ptr<T: Sized>(x: *mut T) {
     unsafe { core::arch::asm!("/* {0} */", in(reg) x, options(preserves_flags, nostack)) }
 }
 
-// Implementation of Pessimize for thin *const T
+// Implementation of Pessimize for thin *const T and *const [T]
 #[cfg(not(feature = "nightly"))]
 mod thin_pointers {
     use super::*;
+    use core::ptr;
 
     // Safe because the functions above are implemented as expected
     //
@@ -62,6 +63,44 @@ mod thin_pointers {
             assume_accessed_thin_ptr(*self as *mut T);
         }
     }
+
+    // Safe because the functions above are implemented as expected
+    //
+    // This is one of the primitive Pessimize impls on which the
+    // PessimizeCast/BorrowPessimize stack is built
+    unsafe impl<T: Sized> Pessimize for *const [T] {
+        #[inline]
+        fn hide(self) -> Self {
+            let (data, len) = slice_to_raw_parts(self);
+            ptr::slice_from_raw_parts(hide_thin_ptr(data), crate::hide(len))
+        }
+
+        #[inline]
+        fn assume_read(&self) {
+            let (data, len) = slice_to_raw_parts(*self);
+            assume_read_thin_ptr(data.cast::<()>());
+            crate::consume(len)
+        }
+
+        #[inline]
+        fn assume_accessed(&mut self) {
+            let (data, mut len) = slice_to_raw_parts(*self);
+            assume_accessed_thin_ptr(data.cast::<()>().cast_mut());
+            assume_accessed(&mut len);
+            // Correct because hide is identity and assume_accessed doesn't modify
+            *self = ptr::slice_from_raw_parts(data, len)
+        }
+
+        #[inline]
+        fn assume_accessed_imut(&self) {
+            assume_accessed_thin_ptr(self.cast::<()>().cast_mut());
+            // NOTE: It's not legal to change the length of a slice from &self
+        }
+    }
+
+    fn slice_to_raw_parts<T>(slice: *const [T]) -> (*const T, usize) {
+        (slice.cast::<T>(), slice.len())
+    }
 }
 //
 #[cfg(feature = "nightly")]