impl: add wasm simd support

This commit adds simd acceleration support to the `memmem` module. This
is added with the freshly-stabilized support from rust-lang/rust#86204.
This mostly just cribs off the generic simd support for 128-bit types
built for sse, copying bits and pieces of code here and there. Some
refactoring happened internally to help reduce duplication where
possible.

I ran some initial benchmarks with the `memmem/krate/*` regex and a
hacked up single-threaded version of criterion. Some [initial
comparisons][compare] using Wasmtime as a runtime do indeed show a lot
of improvements, but there are indeed some slowdowns as well.

[compare]: https://gist.github.com/alexcrichton/6a72e682e7b6d505ade605359fbe3f2d

PR #84

Author: alexcrichton

.github/workflows/ci.yml

@@ -27,6 +27,7 @@ jobs:
         - stable
         - stable-32
         - stable-mips
+        - wasm
         - beta
         - nightly
         - macos
@@ -62,6 +63,10 @@ jobs:
         - build: win-gnu
           os: windows-2019
           rust: stable-x86_64-gnu
+        - build: wasm
+          os: ubuntu-18.04
+          rust: stable-x86_64-gnu
+          wasm: true
     steps:
     - name: Checkout repository
       uses: actions/checkout@v1
@@ -81,6 +86,16 @@ jobs:
         cargo install --git https://github.com/rust-embedded/cross
         echo "CARGO=cross" >> $GITHUB_ENV
         echo "TARGET=--target ${{ matrix.target }}" >> $GITHUB_ENV
+    - name: Download Wasmtime
+      if: matrix.wasm
+      run: |
+        rustup target add wasm32-wasi
+        echo "CARGO_BUILD_TARGET=wasm32-wasi" >> $GITHUB_ENV
+        echo "RUSTFLAGS=-Ctarget-feature=+simd128" >> $GITHUB_ENV
+        curl -LO https://github.com/bytecodealliance/wasmtime/releases/download/v0.32.0/wasmtime-v0.32.0-x86_64-linux.tar.xz
+        tar xvf wasmtime-v0.32.0-x86_64-linux.tar.xz
+        echo `pwd`/wasmtime-v0.32.0-x86_64-linux >> $GITHUB_PATH
+        echo "CARGO_TARGET_WASM32_WASI_RUNNER=wasmtime run --wasm-features simd --" >> $GITHUB_ENV
     - name: Show command used for Cargo
       run: |
         echo "cargo command is: ${{ env.CARGO }}"

bench/src/memmem/imp.rs

@@ -640,44 +640,47 @@ pub(crate) mod sliceslice {
         }
 
         pub(crate) fn prebuilt(_: &str) -> impl Fn(&str) -> bool + 'static {
-            unimplemented!("sliceslice only runs on x86")
+            if true {
+                unimplemented!("sliceslice only runs on x86")
+            }
+            |_| false
         }
 
         pub(crate) fn oneshotiter<'a>(
-            haystack: &'a str,
-            needle: &'a str,
+            _haystack: &'a str,
+            _needle: &'a str,
         ) -> impl Iterator<Item = usize> + 'static {
             std::iter::from_fn(move || {
                 unimplemented!("sliceslice only runs on x86")
             })
         }
 
-        pub(crate) fn prebuiltiter(needle: &str) -> super::super::NoIter {
+        pub(crate) fn prebuiltiter(_needle: &str) -> super::super::NoIter {
             unimplemented!("sliceslice only runs on x86")
         }
     }
 
     pub(crate) mod rev {
-        pub(crate) fn oneshot(haystack: &str, needle: &str) -> bool {
+        pub(crate) fn oneshot(_haystack: &str, _needle: &str) -> bool {
             unimplemented!("sliceslice does not support reverse searches")
         }
 
         pub(crate) fn prebuilt(
-            needle: &str,
+            _needle: &str,
         ) -> impl Fn(&str) -> bool + 'static {
             |_| unimplemented!("sliceslice does not support reverse searches")
         }
 
         pub(crate) fn oneshotiter(
-            haystack: &str,
-            needle: &str,
+            _haystack: &str,
+            _needle: &str,
         ) -> impl Iterator<Item = usize> + 'static {
             std::iter::from_fn(move || {
                 unimplemented!("sliceslice does not support reverse searches")
             })
         }
 
-        pub(crate) fn prebuiltiter(needle: &str) -> super::super::NoIter {
+        pub(crate) fn prebuiltiter(_needle: &str) -> super::super::NoIter {
             unimplemented!("sliceslice does not support reverse searches")
         }
     }
@@ -693,9 +696,21 @@ pub(crate) mod libc {
     }
 
     pub(crate) mod fwd {
+        #[cfg(target_arch = "wasm32")]
+        extern "C" {
+            fn memmem(
+                haystack: *const libc::c_void,
+                haystack_len: usize,
+                needle: *const libc::c_void,
+                needle_len: usize,
+            ) -> *const libc::c_void;
+        }
+        #[cfg(not(target_arch = "wasm32"))]
+        use libc::memmem;
+
         fn find(haystack: &[u8], needle: &[u8]) -> Option<usize> {
             let p = unsafe {
-                libc::memmem(
+                memmem(
                     haystack.as_ptr() as *const libc::c_void,
                     haystack.len(),
                     needle.as_ptr() as *const libc::c_void,

build.rs

@@ -15,15 +15,29 @@ fn main() {
 // is not a problem. In that case, the fastest option will be chosen at
 // runtime.
 fn enable_simd_optimizations() {
-    if is_env_set("CARGO_CFG_MEMCHR_DISABLE_AUTO_SIMD")
-        || !target_has_feature("sse2")
-    {
+    if is_env_set("CARGO_CFG_MEMCHR_DISABLE_AUTO_SIMD") {
         return;
     }
-    println!("cargo:rustc-cfg=memchr_runtime_simd");
-    println!("cargo:rustc-cfg=memchr_runtime_sse2");
-    println!("cargo:rustc-cfg=memchr_runtime_sse42");
-    println!("cargo:rustc-cfg=memchr_runtime_avx");
+    let arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
+    match &arch[..] {
+        "x86_64" => {
+            if !target_has_feature("sse2") {
+                return;
+            }
+            println!("cargo:rustc-cfg=memchr_runtime_simd");
+            println!("cargo:rustc-cfg=memchr_runtime_sse2");
+            println!("cargo:rustc-cfg=memchr_runtime_sse42");
+            println!("cargo:rustc-cfg=memchr_runtime_avx");
+        }
+        "wasm32" | "wasm64" => {
+            if !target_has_feature("simd128") {
+                return;
+            }
+            println!("cargo:rustc-cfg=memchr_runtime_simd");
+            println!("cargo:rustc-cfg=memchr_runtime_wasm128");
+        }
+        _ => {}
+    }
 }
 
 // This adds a `memchr_libc` cfg if and only if libc can be used, if no other

src/memmem/mod.rs

@@ -146,16 +146,17 @@ macro_rules! define_memmem_simple_tests {
 }
 
 mod byte_frequencies;
-#[cfg(all(target_arch = "x86_64", memchr_runtime_simd))]
+#[cfg(memchr_runtime_simd)]
 mod genericsimd;
 mod prefilter;
 mod rabinkarp;
 mod rarebytes;
 mod twoway;
 mod util;
-// SIMD is only supported on x86_64 currently.
-#[cfg(target_arch = "x86_64")]
+#[cfg(memchr_runtime_simd)]
 mod vector;
+#[cfg(all(memchr_runtime_wasm128))]
+mod wasm;
 #[cfg(all(not(miri), target_arch = "x86_64", memchr_runtime_simd))]
 mod x86;
 
@@ -773,47 +774,47 @@ enum SearcherKind {
     TwoWay(twoway::Forward),
     #[cfg(all(not(miri), target_arch = "x86_64", memchr_runtime_simd))]
     GenericSIMD128(x86::sse::Forward),
+    #[cfg(memchr_runtime_wasm128)]
+    GenericSIMD128(wasm::Forward),
     #[cfg(all(not(miri), target_arch = "x86_64", memchr_runtime_simd))]
     GenericSIMD256(x86::avx::Forward),
 }
 
 impl<'n> Searcher<'n> {
-    #[cfg(all(not(miri), target_arch = "x86_64", memchr_runtime_simd))]
     fn new(config: SearcherConfig, needle: &'n [u8]) -> Searcher<'n> {
         use self::SearcherKind::*;
 
         let ninfo = NeedleInfo::new(needle);
-        let prefn =
-            prefilter::forward(&config.prefilter, &ninfo.rarebytes, needle);
-        let kind = if needle.len() == 0 {
-            Empty
-        } else if needle.len() == 1 {
-            OneByte(needle[0])
-        } else if let Some(fwd) = x86::avx::Forward::new(&ninfo, needle) {
-            GenericSIMD256(fwd)
-        } else if let Some(fwd) = x86::sse::Forward::new(&ninfo, needle) {
-            GenericSIMD128(fwd)
-        } else {
-            TwoWay(twoway::Forward::new(needle))
+        let mk = |kind: SearcherKind| {
+            let prefn = prefilter::forward(
+                &config.prefilter,
+                &ninfo.rarebytes,
+                needle,
+            );
+            Searcher { needle: CowBytes::new(needle), ninfo, prefn, kind }
         };
-        Searcher { needle: CowBytes::new(needle), ninfo, prefn, kind }
-    }
-
-    #[cfg(not(all(not(miri), target_arch = "x86_64", memchr_runtime_simd)))]
-    fn new(config: SearcherConfig, needle: &'n [u8]) -> Searcher<'n> {
-        use self::SearcherKind::*;
+        if needle.len() == 0 {
+            return mk(Empty);
+        }
+        if needle.len() == 1 {
+            return mk(OneByte(needle[0]));
+        }
+        #[cfg(all(not(miri), target_arch = "x86_64", memchr_runtime_simd))]
+        {
+            if let Some(fwd) = x86::avx::Forward::new(&ninfo, needle) {
+                return mk(GenericSIMD256(fwd));
+            } else if let Some(fwd) = x86::sse::Forward::new(&ninfo, needle) {
+                return mk(GenericSIMD128(fwd));
+            }
+        }
+        #[cfg(all(target_arch = "wasm32", memchr_runtime_simd))]
+        {
+            if let Some(fwd) = wasm::Forward::new(&ninfo, needle) {
+                return mk(GenericSIMD128(fwd));
+            }
+        }
 
-        let ninfo = NeedleInfo::new(needle);
-        let prefn =
-            prefilter::forward(&config.prefilter, &ninfo.rarebytes, needle);
-        let kind = if needle.len() == 0 {
-            Empty
-        } else if needle.len() == 1 {
-            OneByte(needle[0])
-        } else {
-            TwoWay(twoway::Forward::new(needle))
-        };
-        Searcher { needle: CowBytes::new(needle), ninfo, prefn, kind }
+        mk(TwoWay(twoway::Forward::new(needle)))
     }
 
     /// Return a fresh prefilter state that can be used with this searcher.
@@ -844,11 +845,7 @@ impl<'n> Searcher<'n> {
             Empty => Empty,
             OneByte(b) => OneByte(b),
             TwoWay(tw) => TwoWay(tw),
-            #[cfg(all(
-                not(miri),
-                target_arch = "x86_64",
-                memchr_runtime_simd
-            ))]
+            #[cfg(all(not(miri), memchr_runtime_simd))]
             GenericSIMD128(gs) => GenericSIMD128(gs),
             #[cfg(all(
                 not(miri),
@@ -873,11 +870,7 @@ impl<'n> Searcher<'n> {
             Empty => Empty,
             OneByte(b) => OneByte(b),
             TwoWay(tw) => TwoWay(tw),
-            #[cfg(all(
-                not(miri),
-                target_arch = "x86_64",
-                memchr_runtime_simd
-            ))]
+            #[cfg(all(not(miri), memchr_runtime_simd))]
             GenericSIMD128(gs) => GenericSIMD128(gs),
             #[cfg(all(
                 not(miri),
@@ -921,11 +914,7 @@ impl<'n> Searcher<'n> {
                     self.find_tw(tw, state, haystack, needle)
                 }
             }
-            #[cfg(all(
-                not(miri),
-                target_arch = "x86_64",
-                memchr_runtime_simd
-            ))]
+            #[cfg(all(not(miri), memchr_runtime_simd))]
             GenericSIMD128(ref gs) => {
                 // The SIMD matcher can't handle particularly short haystacks,
                 // so we fall back to RK in these cases.