Erwin Unruh wrote: > I have a problem with delete_output_reload. It sometimes deletes > instructions > which are needed. Here an analysis of a recent case (In a private > version of > the S390 port). The original S390 shows almost the same reloads, but > chooses > different registers.
What GCC version your compiler based on? > Reloads for insn # 1598 > Reload 0: reload_in (SI) =3D (const_int 4080 [0xff0]) > ADDR_REGS, RELOAD_FOR_OUTPUT_ADDRESS (opnum =3D 0) > reload_in_reg: (const_int 4080 [0xff0]) > reload_reg_rtx: (reg:SI 2 2) > Reload 1: reload_in (SI) =3D (const_int 4080 [0xff0]) > ADDR_REGS, RELOAD_FOR_OTHER_ADDRESS (opnum =3D 0) > reload_in_reg: (const_int 4080 [0xff0]) > reload_reg_rtx: (reg:SI 2 2) > Reload 2: reload_in (SI) =3D (const_int 4080 [0xff0]) > ADDR_REGS, RELOAD_FOR_INPUT_ADDRESS (opnum =3D 2) > reload_in_reg: (const_int 4080 [0xff0]) > reload_reg_rtx: (reg:SI 2 2) > Reload 3: reload_in (DI) =3D (mem/c:DI (plus:SI (plus:SI (reg/f:SI 15 15) > (const_int > 4080 [0xff0])) > (const_int 3144 > [0xc48])) [0 S8 A8]) > reload_out (DI) =3D (mem/c:DI (plus:SI (plus:SI (reg/f:SI 15 15) > (const_int > 4080 [0xff0])) > (const_int 3136 > [0xc40])) [0 S8 A8]) > GENERAL_REGS, RELOAD_OTHER (opnum =3D 0), can't combine > reload_in_reg: (reg:DI 1391) > reload_out_reg: (reg:DI 1393) > reload_reg_rtx: (reg:DI 0 0) > Reload 4: ADDR_REGS, RELOAD_FOR_INPUT_ADDRESS (opnum =3D 2), can't > combine, secondary_reload_p > reload_reg_rtx: (reg:SI 3 3) > Reload 5: reload_in (SI) =3D (plus:SI (plus:SI (reg/f:SI 15 15) > (const_int 4080 > [0xff0])) > (const_int 3136 > [0xc40])) > ADDR_REGS, RELOAD_FOR_INPUT (opnum =3D 2), inc by 8 > reload_in_reg: (plus:SI (plus:SI (reg/f:SI 15 15) > (const_int 4080 > [0xff0])) > (const_int 3136 > [0xc40])) > reload_reg_rtx: (reg:SI 2 2) > secondary_in_reload =3D 4 > secondary_in_icode =3D reload_insi > > These reloads are ok. In do_output_reload it is noted that both > insn_1597.Reload_2 and insn_1598.Reload_3 write to the same stack slot. > So the compiler decides to remove the first reload and use register > (reg:DI 2) > directly. In this analysis it misses the fact that (reg:SI 2) > is used for input reloads of insn 1598. This should actually be caught by the free_for_value_p check in choose_reload_regs. You cannot inherit a value for a RELOAD_OTHER reload (3) in a register that is already in use for a RELOAD_FOR_INPUT_ ADDRESS reload (2). Could you try to find out why this doesn't work correctly? > One critical point is the timing on the variables reg_reloaded_valid and > spill_reg_store. > Within the function emit_reload_insns they are first checked (within > do_output_reload) and later updated (after the reload instructions are > written). > So they reflect the state before the "reload sequence". Not all usages > reflect > this semantics. Especially the check within delete_output_reload is not > correct. I'm not sure how delete_output_reload comes into play here. The decision to inherit was already made long ago, in choose_reload_regs, and that is already incorrect. Even if the output reload for insn 1597 were not deleted at this point, the code would still be incorrect. Bye, Ulrich -- Dr. Ulrich Weigand GNU Toolchain for Linux on System z and Cell BE [EMAIL PROTECTED]
