https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105429
--- Comment #2 from Palaiologos <kspalaiologos at gmail dot com> --- I have observed the same behaviour with and without `mov eax, eax`. CRC32 is a 32-bit checksum, so I'd presume that the high bits aren't considered by the instruction. To support my claim, Vol. 2A 3-257 of Intel Software Development Manual gives the following operation for 2 REX.W 0F 38 F1 /r: >>> TEMP1[63-0] := BIT_REFLECT64 (SRC[63-0]) TEMP2[31-0] := BIT_REFLECT32 (DEST[31-0]) TEMP3[95-0] := TEMP1[63-0] « 32 TEMP4[95-0] := TEMP2[31-0] « 64 TEMP5[95-0] := TEMP3[95-0] XOR TEMP4[95-0] TEMP6[31-0] := TEMP5[95-0] MOD2 11EDC6F41H DEST[31-0] := BIT_REFLECT (TEMP6[31-0]) DEST[63-32] := 00000000H <<<
