https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105753
Georg-Johann Lay <gjl at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|target |rtl-optimization
--- Comment #15 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
The error is in the combine pass.
Prior to combine, we have the followng insn for divmod (from -da init-regs
dump):
(insn 9 7 11 3 (parallel [
(set (reg:SI 50)
(udiv:SI (reg/v:SI 47 [ n ])
(reg:SI 51)))
(set (reg:SI 49)
(umod:SI (reg/v:SI 47 [ n ])
(reg:SI 51)))
(clobber (reg:SI 18 r18))
(clobber (reg:SI 22 r22))
(clobber (reg:HI 26 r26))
(clobber (reg:HI 30 r30))
]) "bug.c":6:15 403 {udivmodsi4}
(expr_list:REG_UNUSED (reg:HI 30 r30)
(expr_list:REG_UNUSED (reg:HI 26 r26)
(expr_list:REG_UNUSED (reg:SI 22 r22)
(expr_list:REG_UNUSED (reg:SI 18 r18)
(nil))))))
This basically encodes a transparent libgcc call to __udivmodsi4 (insn
"*udivmodsi4_call").
The combine dump however reads:
(insn 9 7 11 3 (set (reg:SI 49)
(umod:SI (reg/v:SI 47 [ n ])
(reg:SI 51))) "bug.c":6:15 403 {udivmodsi4}
(expr_list:REG_UNUSED (reg:HI 30 r30)
(expr_list:REG_UNUSED (reg:HI 26 r26)
(expr_list:REG_UNUSED (reg:SI 22 r22)
(expr_list:REG_UNUSED (reg:SI 18 r18)
(nil))))))
(insn 11 9 14 3 (set (reg/v:SI 45 [ n ])
(reg/v:SI 47 [ n ])) 119 {*movsi_split}
(expr_list:REG_DEAD (reg/v:SI 47 [ n ])
(nil)))
(insn 14 11 15 3 (set (reg/v:SI 47 [ n ])
(udiv:SI (reg/v:SI 47 [ n ])
(reg:SI 51))) "bug.c":7:7 119 {*movsi_split}
(expr_list:REG_DEAD (reg:SI 50)
(nil)))
These udiv and umod insn do not exist and are unrecognizable. Combine should
never have split the original udivmodsi4.
I used the original test case from comment #0 with
$ avr-gcc bug.c -S -O1 -mmcu=atmega8 -da
where avr-gcc is from 2023-03-03 master (future v13).
With -fdisable-rtl-combine no ICE occurs.
