Add codegen test for SLP vectorization

tests/codegen-llvm/slp-vectorization-mul3.rs

@@ -0,0 +1,23 @@
+// compile-flags: -O
+#![crate_type = "lib"]
+
+// CHECK-LABEL: mul3
+// CHECK: %[[C_BPP:.*]] = phi <4 x i8>
+// CHECK: %[[V:.*]] = load <4 x i8>, ptr
+// CHECK: %[[ADD:.*]] = add <4 x i8> %[[V]], %[[C_BPP]]
+// CHECK: store {{<4 x i8>|i32}} {{.*}}, ptr
+
+pub fn mul3(previous: &[u8], current: &mut [u8]) {
+    let mut c_bpp = [0u8; 4];
+
+    for (chunk, b_bpp) in current.chunks_exact_mut(4).zip(previous.chunks_exact(4)) {
+        let new_chunk = [
+            chunk[0].wrapping_add(c_bpp[0]),
+            chunk[1].wrapping_add(c_bpp[1]),
+            chunk[2].wrapping_add(c_bpp[2]),
+            chunk[3].wrapping_add(c_bpp[3]),
+        ];
+        chunk.copy_from_slice(&new_chunk);
+        c_bpp.copy_from_slice(b_bpp);
+    }
+}