chore: cascade simd usage, bench multiples of 8

FuelLabs · Dec 29, 2024 · 30248be · 30248be
1 parent 6960c51
commit 30248be
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Showing 2 changed files with 36 additions and 61 deletions.
diff --git a/fuel-vm/benches/meq_performance.rs b/fuel-vm/benches/meq_performance.rs
@@ -47,6 +47,9 @@ fn meq_performance(c: &mut Criterion) {
     let benchmark_matrix = [
         1, 10, 100, 1000, 10_000, 50_000, 100_000, 500_000, 1_000_000, 2_000_000,
         2_500_000, 5_000_000, 10_000_000, 15_000_000, 20_000_000,
+        // some exact multiples of 8 to verify alignment perf
+        8, 16, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536, 131072,
+        262144, 524288, 1048576, 2097152, 4194304, 8388608,
     ];
 
     for size in benchmark_matrix.iter() {

diff --git a/fuel-vm/src/interpreter/memory.rs b/fuel-vm/src/interpreter/memory.rs
@@ -1,7 +1,11 @@
 #![cfg(feature = "alloc")]
 
 #[cfg(feature = "experimental")]
-use core::simd::{u8x16, u8x32, u8x64};
+use core::simd::{
+    u8x16,
+    u8x32,
+    u8x64,
+};
 
 use super::{
     internal::inc_pc,
@@ -1040,76 +1044,44 @@ fn slice_eq(a: &[u8], b: &[u8]) -> bool {
             return false;
         }
 
-        enum SimdVariant {
-            U8x16,
-            U8x32,
-            U8x64,
-        }
+        // cascade of SIMD comparisons
+        let len = a.len();
+        let mut i = 0;
 
-        impl SimdVariant {
-            fn chunk_size(&self) -> usize{
-                match &self {
-                    SimdVariant::U8x16 => 16,
-                    SimdVariant::U8x32 => 32,
-                    SimdVariant::U8x64 => 64,
-                }
+        while i + 64 <= len {
+            let simd_a = u8x64::from_slice(&a[i..]);
+            let simd_b = u8x64::from_slice(&b[i..]);
+            if simd_a != simd_b {
+                return false;
             }
         }
 
-        // we check if the number of bytes is divisible by 16, 32, 64.
-        // we choose the largest number that has the smallest remainder
-
-        let remainder_16 = a.len() % 16;
-        let remainder_32 = a.len() % 32;
-        let remainder_64 = a.len() % 64;
-
-        // based on the smallest remainder, we then use the appropriate simd instruction
-        // to compare the slices
-        let variant = if remainder_16 < remainder_32 {
-            if remainder_16 < remainder_64 {
-                SimdVariant::U8x16
-            } else {
-                SimdVariant::U8x64
+        while i + 32 <= len {
+            let simd_a = u8x32::from_slice(&a[i..]);
+            let simd_b = u8x32::from_slice(&b[i..]);
+            if simd_a != simd_b {
+                return false;
             }
-        } else {
-            if remainder_32 < remainder_64 {
-                SimdVariant::U8x32
-            } else {
-                SimdVariant::U8x64
+        }
+
+        while i + 16 <= len {
+            let simd_a = u8x16::from_slice(&a[i..]);
+            let simd_b = u8x16::from_slice(&b[i..]);
+            if simd_a != simd_b {
+                return false;
             }
-        };
-
-        let chunks = a.chunks_exact(variant.chunk_size());
-        let remainder = chunks.remainder();
-
-        for (chunk_a, chunk_b) in chunks.zip(b.chunks_exact(variant.chunk_size())) {
-            match variant {
-                SimdVariant::U8x16 => {
-                    let simd_a = u8x16::from_slice(chunk_a);
-                    let simd_b = u8x16::from_slice(chunk_b);
-                    if simd_a != simd_b {
-                        return false;
-                    }
-                }
-                SimdVariant::U8x32 => {
-                    let simd_a = u8x32::from_slice(chunk_a);
-                    let simd_b = u8x32::from_slice(chunk_b);
-                    if simd_a != simd_b {
-                        return false;
-                    }
-                }
-                SimdVariant::U8x64 => {
-                    let simd_a = u8x64::from_slice(chunk_a);
-                    let simd_b = u8x64::from_slice(chunk_b);
-                    if simd_a != simd_b {
-                        return false;
-                    }
-                }
+        }
+
+        while i < len {
+            if a[i] != b[i] {
+                return false;
             }
+            i += 1;
         }
 
-        remainder == &b[a.len() - remainder.len()..]
+        true
     }
+
     #[cfg(not(feature = "experimental"))]
     {
         a == b