> In the PR we have insns: > > Trying 23 -> 24: > 23: r123:SI=zero_extend(r122:HI) > REG_DEAD r122:HI > 24: [r115:SI]=r123:SI > REG_DEAD r123:SI > > which should be combined to > > (set (mem:SI (reg/f:SI 115 [ pretmp_19 ]) [1 *pretmp_19+0 S4 A32]) > (and:SI (subreg:SI (reg:HI 122) 0) > (const_int 32767 [0x7fff]))) > > But nonzero_bits of reg:HI 122 is 0x7fff, and nonzero_bits1 thinks it > then also has that same nonzero_bits for the subreg. This is not > correct: the bit outside of HImode are undefined. load_extend_op > applies to loads from memory only, not anything else. Which means the > whole AND is optimised away.
No, this is done on purpose for WORD_REGISTER_OPERATIONS targets and your patch will pessimize them. I'm going to have a look at the PR then. -- Eric Botcazou
