Merge pull request #488 from Demindiro/remove-x86_64-memcmp-c32

Author: Amanieu

src/mem/x86_64.rs

@@ -170,19 +170,7 @@ pub unsafe fn compare_bytes(a: *const u8, b: *const u8, n: usize) -> i32 {
     let c4 = |a: *const u32, b, n| cmp(a, b, n, c2);
     let c8 = |a: *const u64, b, n| cmp(a, b, n, c4);
     let c16 = |a: *const u128, b, n| cmp(a, b, n, c8);
-    let c32 = |a: *const [u128; 2], b, n| cmp(a, b, n, c16);
-    // [u128; 2] internally uses raw_eq for comparisons, which may emit a call to memcmp
-    // above a certain size threshold. When SSE2 is enabled this threshold does not seem
-    // to be reached but without SSE2 a call is emitted, leading to infinite recursion.
-    //
-    // While replacing [u128; 2] with (u128, u128) fixes the issues it degrades performance
-    // severely. Likewise, removing c32() has a lesser but still significant impact. Instead the
-    // [u128; 2] case is only enabled when SSE2 is present.
-    if cfg!(target_feature = "sse2") {
-        c32(a.cast(), b.cast(), n)
-    } else {
-        c16(a.cast(), b.cast(), n)
-    }
+    c16(a.cast(), b.cast(), n)
 }
 
 /// Determine optimal parameters for a `rep` instruction.