Like noticed for gas as well (binutils-gdb commit c8cad9d389b7), the
"absolute difference" aspect of the insns makes their source operands
commutative.
gcc/
2022-05-XX Jan Beulich <jbeul...@suse.com>
* config/i386/mmx.md (mmx_psadbw): Mark as commutative.
* config/i386/sse.md (<sse2_avx2>_psadbw): Likewise.
--- a/gcc/config/i386/mmx.md
+++ b/gcc/config/i386/mmx.md
@@ -4407,7 +4407,7 @@
(define_insn "mmx_psadbw"
[(set (match_operand:V1DI 0 "register_operand" "=y,x,Yw")
- (unspec:V1DI [(match_operand:V8QI 1 "register_operand" "0,0,Yw")
+ (unspec:V1DI [(match_operand:V8QI 1 "register_operand" "%0,0,Yw")
(match_operand:V8QI 2 "register_mmxmem_operand"
"ym,x,Yw")]
UNSPEC_PSADBW))]
"(TARGET_MMX || TARGET_MMX_WITH_SSE)
--- a/gcc/config/i386/sse.md
+++ b/gcc/config/i386/sse.md
@@ -19983,7 +19983,7 @@
(define_insn "<sse2_avx2>_psadbw"
[(set (match_operand:VI8_AVX2_AVX512BW 0 "register_operand" "=x,YW")
(unspec:VI8_AVX2_AVX512BW
- [(match_operand:<ssebytemode> 1 "register_operand" "0,YW")
+ [(match_operand:<ssebytemode> 1 "register_operand" "%0,YW")
(match_operand:<ssebytemode> 2 "vector_operand" "xBm,YWm")]
UNSPEC_PSADBW))]
"TARGET_SSE2"
