correct vpdpbusd asserts in miri

in a24022a we changed the argument types to be more accurate, and now the miri asserts on the simd type/size need to reflect that

Author: folkertdev

src/tools/miri/src/shims/x86/avx512.rs

@@ -188,23 +188,25 @@ fn vpdpbusd<'tcx>(
     let (b, b_len) = ecx.project_to_simd(b)?;
     let (dest, dest_len) = ecx.project_to_simd(dest)?;
 
-    // fn vpdpbusd(src: i32x16, a: i32x16, b: i32x16) -> i32x16;
-    // fn vpdpbusd256(src: i32x8, a: i32x8, b: i32x8) -> i32x8;
-    // fn vpdpbusd128(src: i32x4, a: i32x4, b: i32x4) -> i32x4;
+    // fn vpdpbusd(src: i32x16, a: u8x64, b: i8x64) -> i32x16;
+    // fn vpdpbusd256(src: i32x8, a: u8x32, b: i8x32) -> i32x8;
+    // fn vpdpbusd128(src: i32x4, a: u8x16, b: i8x16) -> i32x4;
     assert_eq!(dest_len, src_len);
-    assert_eq!(dest_len, a_len);
-    assert_eq!(dest_len, b_len);
+    assert_eq!(a_len, dest_len * 4);
+    assert_eq!(a_len, b_len);
 
     for i in 0..dest_len {
         let src = ecx.read_scalar(&ecx.project_index(&src, i)?)?.to_i32()?;
-        let a = ecx.read_scalar(&ecx.project_index(&a, i)?)?.to_u32()?;
-        let b = ecx.read_scalar(&ecx.project_index(&b, i)?)?.to_u32()?;
         let dest = ecx.project_index(&dest, i)?;
 
-        let zipped = a.to_le_bytes().into_iter().zip(b.to_le_bytes());
-        let intermediate_sum: i32 = zipped
-            .map(|(a, b)| i32::from(a).strict_mul(i32::from(b.cast_signed())))
-            .fold(0, |x, y| x.strict_add(y));
+        let mut intermediate_sum: i32 = 0;
+        for j in 0..4 {
+            let a = ecx.read_scalar(&ecx.project_index(&a, i * 4 + j)?)?.to_u8()?;
+            let b = ecx.read_scalar(&ecx.project_index(&b, i * 4 + j)?)?.to_i8()?;
+
+            let product = i32::from(a).strict_mul(i32::from(b));
+            intermediate_sum = intermediate_sum.strict_add(product);
+        }
 
         // Use `wrapping_add` because `src` is an arbitrary i32 and the addition can overflow.
         let res = Scalar::from_i32(intermediate_sum.wrapping_add(src));