> I have another issue in DCE pass after changing word_mode from SImode to > HImode. > Indeed, in subreg1 pass, SI moves such as > ... > (insn 42 41 43 (set (reg:SI 85) (reg/f:SI 83)) > (insn 46 45 47 (set (reg:SI 8 a1) (reg:SI 85)) > > are split into HImode word moves: > ... > (insn 98 97 99 2 (set (subreg:HI (reg:SI 106) 0) (reg:HI 104)) > (insn 99 98 100 2 (set (subreg:HI (reg:SI 106) 2) (reg:HI 105 [+2 ])) > (insn 100 99 47 2 (set (reg:SI 8 a1) (reg:SI 106)) > > Looking at DCE pass in (dce_process_block), it seems that when reverse > parsing the block insns for dead set eliminations, the liveness of reg > 106 which is set when parsing insn 100, is removed when parsing insn 99. > So the insn 98 is deleted because the reg 106 is not seen live anymore... > > Is it a bug, or is it because it is not possible to have hardware > registers which are not splittable in word_mode? Any thoughts?
Yes, this looks like a bug, since the SET in insn 99 doesn't modify the high part of the multi-word (reg:SI 106), as per the documented rules for SUBREG. -- Eric Botcazou
