Re: PATCH [10/n]: Prepare x32: PR rtl-optimization/49114: Reload failed to handle (set reg:X (plus:X (subreg:X (reg:Y) 0) (const

["Ulrich Weigand" <uweigand@de.ibm.com>]

H.J. Lu wrote:

> Reloads for insn # 588
> Reload 0: reload_in (DI) =3D (reg/v/f:DI 182 [ b ])
>         GENERAL_REGS, RELOAD_FOR_OPERAND_ADDRESS (opnum =3D 0)
>         reload_in_reg: (reg/v/f:DI 182 [ b ])
>         reload_reg_rtx: (reg:DI 1 dx)
> Reload 1: reload_in (DI) =3D (zero_extend:DI (plus:SI (subreg:SI (reg/v/f:D=
> I 182
> [ b ]) 0)
>                                                         (const_int 8 [0x8])=
> ))
>         GENERAL_REGS, RELOAD_FOR_OPERAND_ADDRESS (opnum =3D 0)
>         reload_in_reg: (zero_extend:DI (plus:SI (subreg:SI (reg/v/f:DI 182 =
> [ b
> ]) 0)
>                                                         (const_int 8 [0x8])=
> ))
>         reload_reg_rtx: (reg:DI 1 dx)
> Reload 2: reload_out (DF) =3D (mem:DF (zero_extend:DI (plus:SI (subreg:SI
> (reg/v/f:DI 182 [ b ]) 0)
>                                                             (const_int 8
> [0x8]))) [4 MEM[base: b_96(D), index: D.15020_278, step: 8, offset: 0B]+0 S8
> A64])
>         NO_REGS, RELOAD_FOR_OUTPUT (opnum =3D 0), optional
>         reload_out_reg: (mem:DF (zero_extend:DI (plus:SI (subreg:SI (reg/v/=
> f:DI
> 182 [ b ]) 0)
>                                                             (const_int 8
> [0x8]))) [4 MEM[base: b_96(D), index: D.15020_278, step: 8, offset: 0B]+0 S8
> A64])
> 
> leads to
> 

> (insn 1017 587 1020 34 (set (reg:DI 1 dx)
>         (mem/c:DI (plus:DI (reg/f:DI 7 sp)
>                 (const_int 112 [0x70])) [5 %sfp+-208 S8 A64])) spooles.c:29=
> 1 62
> {*movdi_internal_rex64}
>      (nil))

So this is the reload insn generated from reload 0.  So far so good.

> (insn 1020 1017 1022 34 (set (reg:SI 1 dx)
>         (const_int 8 [0x8])) spooles.c:291 64 {*movsi_internal}
>      (nil))
> 
> (insn 1022 1020 1023 34 (set (reg:SI 1 dx)
>         (reg:SI 1 dx)) spooles.c:291 64 {*movsi_internal}
>      (nil))
> 
> (insn 1023 1022 1024 34 (set (reg:SI 1 dx)
>         (plus:SI (reg:SI 1 dx)
>             (const_int 8 [0x8]))) spooles.c:291 248 {*lea_1_x32}
>      (expr_list:REG_EQUIV (plus:SI (subreg:SI (reg:DI 1 dx) 0)
>             (const_int 8 [0x8]))
>         (nil)))
> 
> (insn 1024 1023 588 34 (set (reg:DI 1 dx)
>         (zero_extend:DI (reg:SI 1 dx))) spooles.c:291 112
> {*zero_extendsidi2_rex64}
>      (expr_list:REG_EQUIV (zero_extend:DI (plus:SI (subreg:SI (reg:DI 1 dx)=
>  0)
>                 (const_int 8 [0x8])))
>         (nil)))

All these reload insns are generated from reload 1.

> (insn 588 1024 589 34 (set (mem:DF (reg:DI 1 dx) [4 MEM[base: b_96(D), inde=
> x:
> D.15020_278, step: 8, offset: 0B]+0 S8 A64])
>         (reg:DF 0 ax [orig:340 D.14980 ] [340])) spooles.c:291 106
> {*movdf_internal_rex64}
>      (nil))

This is the original reloaded insn.

> Reload 0 puts (reg/v/f:DI 182 [ b ]) in  (reg:DI 1 dx) for input.
> However, reload 2
> puts (reg/v/f:DI 182 [ b ]) in  (reg:DI 1 dx) for output.without checking w=
> hat
> reload 0 did.

Reload 2 is an optional reload which reload chose not to utilize, so this
is not really relevant here in any case.  There is no output reload.

The wrong code above originates from how reload 1 is handled:

gen_reload is called to load the ZERO_EXTEND into (reg:DI 1).  This triggers
the "unary predicate" path, which recurses into gen_reload to load the operand
of the ZERO_EXTEND (reg:SI 1), and subsequently generates insn 1024.

The recursive call loads (plus:SI (subreg:SI (reg:DI 1)) (const_int 8)) into
(reg:SI 1).  It attempts to do that in a single SET and fails (for some
reason).  It then attempts to load the constant (const_int 8) into the
destination register (insn 1020) [** which is broken **], and re-tries.
This still fails, so it falls through to the last attempt, which is to
instead copy the subreg to the destination (which results in insn 1022
as the subreg is optimized away at this point), followed by adding the
constant.

Note that the point marked with "[** which is broken **]" is the place
I pointed out in the previous mail.

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com