In Pattern, for the following example, must sub_32 correspond to the actual physical register in the architecture?

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def : MipsPat<(i64 (sext (i32 (mul GPR32:$src, GPR32:$src2)))),
(INSERT_SUBREG (i64 (IMPLICIT_DEF)),
(MUL_R6 GPR32:$src, GPR32:$src2), sub_32)>, ISA_MIPS64R6;