Auto merge of rust-lang#111475 - workingjubilee:sync-simd-2023-may-10…

…, r=workingjubilee

 Sync portable-simd to 2023 May 10

Take 2.

r? `@ghost`

library/portable-simd/.github/workflows/ci.yml

@@ -241,6 +241,10 @@ jobs:
           - "--features std"
           - "--features generic_const_exprs"
           - "--features std --features generic_const_exprs"
+          - "--features all_lane_counts"
+          - "--features all_lane_counts --features std"
+          - "--features all_lane_counts --features generic_const_exprs"
+          - "--features all_lane_counts --features std --features generic_const_exprs"
 
     steps:
       - uses: actions/checkout@v2

library/portable-simd/README.md

@@ -24,44 +24,34 @@ or by setting up `rustup default nightly` or else with `cargo +nightly {build,te
 ```bash
 cargo new hellosimd
 ```
-to create a new crate. Edit `hellosimd/Cargo.toml` to be 
-```toml
-[package]
-name = "hellosimd"
-version = "0.1.0"
-edition = "2018"
-[dependencies]
-core_simd = { git = "https://github.com/rust-lang/portable-simd" }
-```
-
-and finally write this in `src/main.rs`:
+to create a new crate. Finally write this in `src/main.rs`:
 ```rust
-use core_simd::*;
+#![feature(portable_simd)]
+use std::simd::f32x4;
 fn main() {
     let a = f32x4::splat(10.0);
     let b = f32x4::from_array([1.0, 2.0, 3.0, 4.0]);
     println!("{:?}", a + b);
 }
 ```
 
-Explanation: We import all the bindings from the crate with the first line. Then, we construct our SIMD vectors with methods like `splat` or `from_array`. Finally, we can use operators on them like `+` and the appropriate SIMD instructions will be carried out. When we run `cargo run` you should get `[11.0, 12.0, 13.0, 14.0]`.
-
-## Code Organization
+Explanation: We construct our SIMD vectors with methods like `splat` or `from_array`. Next, we can use operators like `+` on them, and the appropriate SIMD instructions will be carried out. When we run `cargo run` you should get `[11.0, 12.0, 13.0, 14.0]`.
 
-Currently the crate is organized so that each element type is a file, and then the 64-bit, 128-bit, 256-bit, and 512-bit vectors using those types are contained in said file.
+## Supported vectors
 
-All types are then exported as a single, flat module.
+Currently, vectors may have up to 64 elements, but aliases are provided only up to 512-bit vectors.
 
 Depending on the size of the primitive type, the number of lanes the vector will have varies. For example, 128-bit vectors have four `f32` lanes and two `f64` lanes.
 
 The supported element types are as follows:
 * **Floating Point:** `f32`, `f64`
-* **Signed Integers:** `i8`, `i16`, `i32`, `i64`, `i128`, `isize`
-* **Unsigned Integers:** `u8`, `u16`, `u32`, `u64`, `u128`, `usize`
-* **Masks:** `mask8`, `mask16`, `mask32`, `mask64`, `mask128`, `masksize`
+* **Signed Integers:** `i8`, `i16`, `i32`, `i64`, `isize` (`i128` excluded)
+* **Unsigned Integers:** `u8`, `u16`, `u32`, `u64`, `usize` (`u128` excluded)
+* **Pointers:** `*const T` and `*mut T` (zero-sized metadata only)
+* **Masks:** 8-bit, 16-bit, 32-bit, 64-bit, and `usize`-sized masks
 
-Floating point, signed integers, and unsigned integers are the [primitive types](https://doc.rust-lang.org/core/primitive/index.html) you're already used to.
-The `mask` types are "truthy" values, but they use the number of bits in their name instead of just 1 bit like a normal `bool` uses.
+Floating point, signed integers, unsigned integers, and pointers are the [primitive types](https://doc.rust-lang.org/core/primitive/index.html) you're already used to.
+The mask types have elements that are "truthy" values, like `bool`, but have an unspecified layout because different architectures prefer different layouts for mask types.
 
 [simd-guide]: ./beginners-guide.md
 [zulip-project-portable-simd]: https://rust-lang.zulipchat.com/#narrow/stream/257879-project-portable-simd

library/portable-simd/crates/core_simd/Cargo.toml

@@ -13,12 +13,11 @@ default = ["as_crate"]
 as_crate = []
 std = []
 generic_const_exprs = []
+all_lane_counts = []
 
-[target.'cfg(target_arch = "wasm32")'.dev-dependencies.wasm-bindgen]
-version = "0.2"
-
-[dev-dependencies.wasm-bindgen-test]
-version = "0.3"
+[target.'cfg(target_arch = "wasm32")'.dev-dependencies]
+wasm-bindgen = "0.2"
+wasm-bindgen-test = "0.3"
 
 [dev-dependencies.proptest]
 version = "0.10"

library/portable-simd/crates/core_simd/examples/README.md

@@ -0,0 +1,13 @@
+### `stdsimd` examples
+
+This crate is a port of example uses of `stdsimd`, mostly taken from the `packed_simd` crate.
+
+The examples contain, as in the case of `dot_product.rs`, multiple ways of solving the problem, in order to show idiomatic uses of SIMD and iteration of performance designs.
+
+Run the tests with the command 
+
+```
+cargo run --example dot_product
+```
+
+and verify the code for `dot_product.rs` on your machine.

library/portable-simd/crates/core_simd/examples/dot_product.rs

@@ -0,0 +1,169 @@
+// Code taken from the `packed_simd` crate
+// Run this code with `cargo test --example dot_product`
+//use std::iter::zip;
+
+#![feature(array_chunks)]
+#![feature(slice_as_chunks)]
+// Add these imports to use the stdsimd library
+#![feature(portable_simd)]
+use core_simd::simd::*;
+
+// This is your barebones dot product implementation:
+// Take 2 vectors, multiply them element wise and *then*
+// go along the resulting array and add up the result.
+// In the next example we will see if there
+//  is any difference to adding and multiplying in tandem.
+pub fn dot_prod_scalar_0(a: &[f32], b: &[f32]) -> f32 {
+    assert_eq!(a.len(), b.len());
+
+    a.iter().zip(b.iter()).map(|(a, b)| a * b).sum()
+}
+
+// When dealing with SIMD, it is very important to think about the amount
+// of data movement and when it happens. We're going over simple computation examples here, and yet
+// it is not trivial to understand what may or may not contribute to performance
+// changes. Eventually, you will need tools to inspect the generated assembly and confirm your
+// hypothesis and benchmarks - we will mention them later on.
+// With the use of `fold`, we're doing a multiplication,
+// and then adding it to the sum, one element from both vectors at a time.
+pub fn dot_prod_scalar_1(a: &[f32], b: &[f32]) -> f32 {
+    assert_eq!(a.len(), b.len());
+    a.iter()
+        .zip(b.iter())
+        .fold(0.0, |a, zipped| a + zipped.0 * zipped.1)
+}
+
+// We now move on to the SIMD implementations: notice the following constructs:
+// `array_chunks::<4>`: mapping this over the vector will let use construct SIMD vectors
+// `f32x4::from_array`: construct the SIMD vector from a slice
+// `(a * b).reduce_sum()`: Multiply both f32x4 vectors together, and then reduce them.
+// This approach essentially uses SIMD to produce a vector of length N/4 of all the products,
+// and then add those with `sum()`. This is suboptimal.
+// TODO: ASCII diagrams
+pub fn dot_prod_simd_0(a: &[f32], b: &[f32]) -> f32 {
+    assert_eq!(a.len(), b.len());
+    // TODO handle remainder when a.len() % 4 != 0
+    a.array_chunks::<4>()
+        .map(|&a| f32x4::from_array(a))
+        .zip(b.array_chunks::<4>().map(|&b| f32x4::from_array(b)))
+        .map(|(a, b)| (a * b).reduce_sum())
+        .sum()
+}
+
+// There's some simple ways to improve the previous code:
+// 1. Make a `zero` `f32x4` SIMD vector that we will be accumulating into
+// So that there is only one `sum()` reduction when the last `f32x4` has been processed
+// 2. Exploit Fused Multiply Add so that the multiplication, addition and sinking into the reduciton
+// happen in the same step.
+// If the arrays are large, minimizing the data shuffling will lead to great perf.
+// If the arrays are small, handling the remainder elements when the length isn't a multiple of 4
+// Can become a problem.
+pub fn dot_prod_simd_1(a: &[f32], b: &[f32]) -> f32 {
+    assert_eq!(a.len(), b.len());
+    // TODO handle remainder when a.len() % 4 != 0
+    a.array_chunks::<4>()
+        .map(|&a| f32x4::from_array(a))
+        .zip(b.array_chunks::<4>().map(|&b| f32x4::from_array(b)))
+        .fold(f32x4::splat(0.0), |acc, zipped| acc + zipped.0 * zipped.1)
+        .reduce_sum()
+}
+
+// A lot of knowledgeable use of SIMD comes from knowing specific instructions that are
+// available - let's try to use the `mul_add` instruction, which is the fused-multiply-add we were looking for.
+use std_float::StdFloat;
+pub fn dot_prod_simd_2(a: &[f32], b: &[f32]) -> f32 {
+    assert_eq!(a.len(), b.len());
+    // TODO handle remainder when a.len() % 4 != 0
+    let mut res = f32x4::splat(0.0);
+    a.array_chunks::<4>()
+        .map(|&a| f32x4::from_array(a))
+        .zip(b.array_chunks::<4>().map(|&b| f32x4::from_array(b)))
+        .for_each(|(a, b)| {
+            res = a.mul_add(b, res);
+        });
+    res.reduce_sum()
+}
+
+// Finally, we will write the same operation but handling the loop remainder.
+const LANES: usize = 4;
+pub fn dot_prod_simd_3(a: &[f32], b: &[f32]) -> f32 {
+    assert_eq!(a.len(), b.len());
+
+    let (a_extra, a_chunks) = a.as_rchunks();
+    let (b_extra, b_chunks) = b.as_rchunks();
+
+    // These are always true, but for emphasis:
+    assert_eq!(a_chunks.len(), b_chunks.len());
+    assert_eq!(a_extra.len(), b_extra.len());
+
+    let mut sums = [0.0; LANES];
+    for ((x, y), d) in std::iter::zip(a_extra, b_extra).zip(&mut sums) {
+        *d = x * y;
+    }
+
+    let mut sums = f32x4::from_array(sums);
+    std::iter::zip(a_chunks, b_chunks).for_each(|(x, y)| {
+        sums += f32x4::from_array(*x) * f32x4::from_array(*y);
+    });
+
+    sums.reduce_sum()
+}
+
+// Finally, we present an iterator version for handling remainders in a scalar fashion at the end of the loop.
+// Unfortunately, this is allocating 1 `XMM` register on the order of `~len(a)` - we'll see how we can get around it in the
+// next example.
+pub fn dot_prod_simd_4(a: &[f32], b: &[f32]) -> f32 {
+    let mut sum = a
+        .array_chunks::<4>()
+        .map(|&a| f32x4::from_array(a))
+        .zip(b.array_chunks::<4>().map(|&b| f32x4::from_array(b)))
+        .map(|(a, b)| a * b)
+        .fold(f32x4::splat(0.0), std::ops::Add::add)
+        .reduce_sum();
+    let remain = a.len() - (a.len() % 4);
+    sum += a[remain..]
+        .iter()
+        .zip(&b[remain..])
+        .map(|(a, b)| a * b)
+        .sum::<f32>();
+    sum
+}
+
+// This version allocates a single `XMM` register for accumulation, and the folds don't allocate on top of that.
+// Notice the the use of `mul_add`, which can do a multiply and an add operation ber iteration.
+pub fn dot_prod_simd_5(a: &[f32], b: &[f32]) -> f32 {
+    a.array_chunks::<4>()
+        .map(|&a| f32x4::from_array(a))
+        .zip(b.array_chunks::<4>().map(|&b| f32x4::from_array(b)))
+        .fold(f32x4::splat(0.), |acc, (a, b)| a.mul_add(b, acc))
+        .reduce_sum()
+}
+
+fn main() {
+    // Empty main to make cargo happy
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn smoke_test() {
+        use super::*;
+        let a: Vec<f32> = vec![1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0];
+        let b: Vec<f32> = vec![-8.0, -7.0, -6.0, -5.0, 4.0, 3.0, 2.0, 1.0];
+        let x: Vec<f32> = [0.5; 1003].to_vec();
+        let y: Vec<f32> = [2.0; 1003].to_vec();
+
+        // Basic check
+        assert_eq!(0.0, dot_prod_scalar_0(&a, &b));
+        assert_eq!(0.0, dot_prod_scalar_1(&a, &b));
+        assert_eq!(0.0, dot_prod_simd_0(&a, &b));
+        assert_eq!(0.0, dot_prod_simd_1(&a, &b));
+        assert_eq!(0.0, dot_prod_simd_2(&a, &b));
+        assert_eq!(0.0, dot_prod_simd_3(&a, &b));
+        assert_eq!(0.0, dot_prod_simd_4(&a, &b));
+        assert_eq!(0.0, dot_prod_simd_5(&a, &b));
+
+        // We can handle vectors that are non-multiples of 4
+        assert_eq!(1003.0, dot_prod_simd_3(&x, &y));
+    }
+}