Handle a non-Fallback baseline

.github/workflows/ci.yml

@@ -8,7 +8,7 @@ env:
   # If the compilation fails, then the version specified here needs to be bumped up to reality.
   # Be sure to also update the rust-version property in the workspace Cargo.toml file,
   # plus all the README.md files of the affected packages.
-  RUST_MIN_VER: "1.86"
+  RUST_MIN_VER: "1.88"
   # List of packages that will be checked with the minimum supported Rust version.
   # This should be limited to packages that are intended for publishing.
   RUST_MIN_VER_PKGS: "-p fearless_simd"

CHANGELOG.md

@@ -13,7 +13,20 @@ You can find its changes [documented below](#020-2025-10-10).
 
 ## [Unreleased]
 
-This release has an [MSRV][] of 1.86.
+This release has an [MSRV][] of 1.88.
+
+### Changed
+
+- Breaking change: `Level::fallback` has been removed, replaced with `Level::baseline`. ([#105][] by [@DJMcNab][])
+  This corresponds with a change to avoid compiling in support for the fallback level on compilation targets which don't
+  require it; this is most impactful for binary size on WASM, Apple Silicon Macs or Android.
+  A consequence of this is that the available variants on `Level` are now dependent on the target features you are compiling with.
+  The fallback level can be restored with the `force_support_fallback` cargo feature. We don't expect this to be necessary outside
+  of tests.
+
+### Removed
+
+- Breaking change: The (deprecated) `simd_dispatch!` macro. ([#105][] by [@DJMcNab][])
 
 ## [0.3.0][] (2025-10-10)
 
@@ -85,6 +98,7 @@ No changelog was kept for this release.
 [#93]: https://github.com/linebender/fearless_simd/pull/93
 [#96]: https://github.com/linebender/fearless_simd/pull/96
 [#99]: https://github.com/linebender/fearless_simd/pull/99
+[#105]: https://github.com/linebender/fearless_simd/pull/105
 
 [Unreleased]: https://github.com/linebender/fearless_simd/compare/v0.3.0...HEAD
 [0.3.0]: https://github.com/linebender/fearless_simd/compare/v0.3.0...v0.2.0

Cargo.toml

@@ -13,7 +13,7 @@ license = "Apache-2.0 OR MIT"
 repository = "https://github.com/linebender/fearless_simd"
 # Keep in sync with RUST_MIN_VER in .github/workflows/ci.yml, with the relevant README.md files
 # and with the MSRV in the `Unreleased` section of CHANGELOG.md.
-rust-version = "1.86"
+rust-version = "1.88"
 
 [workspace.lints]
 

README.md

@@ -59,7 +59,7 @@ It benefited from conversations with Luca Versari, though he is not responsible
 
 ## Minimum supported Rust Version (MSRV)
 
-This version of Fearless SIMD has been verified to compile with **Rust 1.86** and later.
+This version of Fearless SIMD has been verified to compile with **Rust 1.88** and later.
 
 Future versions of Fearless SIMD might increase the Rust version requirement.
 It will not be treated as a breaking change and as such can even happen with small patch releases.

check_targets.sh

@@ -0,0 +1,41 @@
+# A script to run cargo check for fearless_simd on each supported platform.
+# We currently don't run this in CI, as we expect it would take too long.
+# Before using, you must run:
+# rustup target add aarch64-linux-android x86_64-unknown-linux-gnu i686-pc-windows-msvc wasm32-unknown-unknown riscv64gc-unknown-linux-gnu
+
+# Run using `sh ./check_targets.sh`
+# TODO: Make into an xtask like thing so that windows users can use easily.
+
+# aarch64, both with and without neon support.
+# Note that doing `-neon` is not sound due to the standard library's ABI, but the
+# binary is never executed (nor indeed is it even created), and it's still a useful sanity check.
+RUSTFLAGS=-Ctarget-feature=-neon cargo check -p fearless_simd --target aarch64-linux-android
+RUSTFLAGS=-Ctarget-feature=-neon cargo check -p fearless_simd --target aarch64-linux-android --features force_support_fallback
+cargo check -p fearless_simd --target aarch64-linux-android  --features force_support_fallback
+cargo check -p fearless_simd --target aarch64-linux-android
+
+# x86_64, at all supported static SIMD levels.
+RUSTFLAGS=-Ctarget-feature=+avx2,+fma cargo check -p fearless_simd --target x86_64-unknown-linux-gnu
+RUSTFLAGS=-Ctarget-feature=+avx2,+fma cargo check -p fearless_simd --target x86_64-unknown-linux-gnu --features force_support_fallback
+RUSTFLAGS=-Ctarget-feature=+sse4.2 cargo check -p fearless_simd --target x86_64-unknown-linux-gnu
+RUSTFLAGS=-Ctarget-feature=+sse4.2 cargo check -p fearless_simd --target x86_64-unknown-linux-gnu  --features force_support_fallback
+cargo check -p fearless_simd --target x86_64-unknown-linux-gnu
+cargo check -p fearless_simd --target x86_64-unknown-linux-gnu  --features force_support_fallback
+
+# x86 (i.e. 32 bit) at all supported static SIMD levels.
+RUSTFLAGS=-Ctarget-feature=+avx2,+fma cargo check -p fearless_simd --target i686-pc-windows-msvc
+RUSTFLAGS=-Ctarget-feature=+avx2,+fma cargo check -p fearless_simd --target i686-pc-windows-msvc --features force_support_fallback
+RUSTFLAGS=-Ctarget-feature=+sse4.2 cargo check -p fearless_simd --target i686-pc-windows-msvc
+RUSTFLAGS=-Ctarget-feature=+sse4.2 cargo check -p fearless_simd --target i686-pc-windows-msvc  --features force_support_fallback
+cargo check -p fearless_simd --target i686-pc-windows-msvc
+cargo check -p fearless_simd --target i686-pc-windows-msvc  --features force_support_fallback
+
+# Wasm, both with and without SIMD.
+cargo check -p fearless_simd --target wasm32-unknown-unknown
+cargo check -p fearless_simd --target wasm32-unknown-unknown --features force_support_fallback
+RUSTFLAGS=-Ctarget-feature=+simd128 cargo check -p fearless_simd --target wasm32-unknown-unknown
+RUSTFLAGS=-Ctarget-feature=+simd128 cargo check -p fearless_simd --target wasm32-unknown-unknown --features force_support_fallback
+
+# riscv64, which is importantly a target we don't support any SIMD levels for.
+cargo check -p fearless_simd --target riscv64gc-unknown-linux-gnu
+cargo check -p fearless_simd --target riscv64gc-unknown-linux-gnu --features force_support_fallback

fearless_simd/Cargo.toml

@@ -30,6 +30,10 @@ libm = ["dep:libm"]
 # beyond the basic SIMD operations abstracted on all platforms
 safe_wrappers = []
 
+# Force the "fallback" SIMD level to be supported
+# This is primarily used for tests
+force_support_fallback = []
+
 [lints]
 workspace = true
 

fearless_simd/README.md

@@ -115,6 +115,7 @@ The following crate [feature flags](https://doc.rust-lang.org/cargo/reference/fe
 - `libm`: Use floating point implementations from [libm].
 - `safe_wrappers`: Include safe wrappers for (some) target feature specific intrinsics,
   beyond the basic SIMD operations abstracted on all platforms.
+- `force_support_fallback`: Force scalar fallback, to be supported, even if your compilation target has a better baseline.
 
 At least one of `std` and `libm` is required; `std` overrides `libm`.
 
@@ -124,7 +125,7 @@ At least one of `std` and `libm` is required; `std` overrides `libm`.
 
 ## Minimum supported Rust Version (MSRV)
 
-This version of Fearless SIMD has been verified to compile with **Rust 1.86** and later.
+This version of Fearless SIMD has been verified to compile with **Rust 1.88** and later.
 
 Future versions of Fearless SIMD might increase the Rust version requirement.
 It will not be treated as a breaking change and as such can even happen with small patch releases.

fearless_simd/src/generated/fallback.rs

@@ -83,7 +83,10 @@ impl Simd for Fallback {
     type mask32s = mask32x4<Self>;
     #[inline(always)]
     fn level(self) -> Level {
-        Level::Fallback(self)
+        #[cfg(feature = "force_support_fallback")]
+        return Level::Fallback(self);
+        #[cfg(not(feature = "force_support_fallback"))]
+        Level::baseline()
     }
     #[inline]
     fn vectorize<F: FnOnce() -> R, R>(self, f: F) -> R {

fearless_simd/src/generated/sse4_2.rs

@@ -52,7 +52,12 @@ impl Simd for Sse4_2 {
     type mask32s = mask32x4<Self>;
     #[inline(always)]
     fn level(self) -> Level {
-        Level::Sse4_2(self)
+        #[cfg(not(all(target_feature = "avx2", target_feature = "fma")))]
+        return Level::Sse4_2(self);
+        #[cfg(all(target_feature = "avx2", target_feature = "fma"))]
+        {
+            Level::baseline()
+        }
     }
     #[inline]
     fn vectorize<F: FnOnce() -> R, R>(self, f: F) -> R {