[clang] [llvm] Clang: convert `__m64` intrinsics to unconditionally use SSE2 instead of MMX. (PR #96540)

[Phoebe Wang via llvm-commits]

================
@@ -494,10 +520,10 @@ _mm_adds_pu16(__m64 __m1, __m64 __m2)
 ///    A 64-bit integer vector of [8 x i8] containing the subtrahends.
 /// \returns A 64-bit integer vector of [8 x i8] containing the differences of
 ///    both parameters.
-static __inline__ __m64 __DEFAULT_FN_ATTRS
+static __inline__ __m64 __DEFAULT_FN_ATTRS_SSE2
 _mm_sub_pi8(__m64 __m1, __m64 __m2)
 {
-    return (__m64)__builtin_ia32_psubb((__v8qi)__m1, (__v8qi)__m2);
+    return (__m64)(((__v8qu)__m1) - ((__v8qu)__m2));
----------------
phoebewang wrote:

Seems you intended to use unsigned version. What's the reason to do so?

https://github.com/llvm/llvm-project/pull/96540