Re: Issue during combine.

[Henri Cloetens <henri.cloetens@blueice.be>]

Hello all,

This seems to be a bug in the non-port code of the compiler.
It crashes in
/rtx simplify_subreg(machine_mode outer_mode, rtx op, machine_mode 
inner_mode, poly_uint64 byte)/

The crash is, because this function is called with inner_mode = 
Voidmode. (And seems illegal.)

It seems to me this "illegal" mode is the result of the /combine/ step, 
trying to "improve" by doing combinations of
instructions "at random". Here, it tries a "combination" that does not 
make sense, but it causes a crash in
the abovementioned routine. When I change the code, so that this routine 
returns 0 (=fail the operation), it passes
the '263 step without errors. The meaningless combination is refused 
elsewhere. It is not done.

Best Regards,

Henri.


On 10/19/2020 02:53 PM, Henri Cloetens wrote:
> Hello all,
>
> I am building a gcc 9.2.0 custom compiler, and I am running in an 
> issue during step 263, combine.
>
> Before combine:
>
> /(insn 2354 2352 1743 175 (set (reg/v:SI 197 [ dig ])//
> //        (if_then_else (eq (subreg:QI (reg:SI 632) 1)//
> //                (const_int 1 [0x1]))//
> //            (reg:SI 708)//
> //            (reg/v:SI 197 [ dig ]))) 
> "/home/henri/blueICe/gcc/newlib/newlib/libc/stdlib/dtoa.c":771:6 35 
> {select_internal3}//
> //     (expr_list:REG_DEAD (reg:SI 708)//
> //        (expr_list:REG_DEAD (reg:SI 632)//
> //            (nil))))//
> //(insn 1743 2354 124 175 (set (mem:QI (reg:SI 316 [ ivtmp.118 ]) [0 
> *s_304+0 S1 A8])//
> //        (subreg:QI (reg/v:SI 197 [ dig ]) 0)) 
> "/home/henri/blueICe/gcc/newlib/newlib/libc/stdlib/dtoa.c":772:13 6 
> {movqi_internal}//
> //     (expr_list:REG_DEAD (reg:SI 316 [ ivtmp.118 ])//
> //        (expr_list:REG_DEAD (reg/v:SI 197 [ dig ])//
> //            (nil))))/
>
> This is during the combine-step transformed into:
>
> /(insn 1743 2354 124 175 (set (mem:QI (reg:SI 316 [ ivtmp.118 ]) [0 
> *s_304+0 S1 A8])//
> //        (subreg:QI (if_then_else (eq (subreg:QI (reg:SI 632) 1)//
> //                    (const_int 1 [0x1]))//
> //                (reg:SI 708)//
> //                (reg/v:SI 197 [ dig ])) 0)) 
> "/home/henri/blueICe/gcc/newlib/newlib/libc/stdlib/dtoa.c":772:13 6 
> {movqi_internal}//
> //     (expr_list:REG_DEAD (reg:SI 316 [ ivtmp.118 ])//
> //        (expr_list:REG_DEAD (reg/v:SI 197 [ dig ])//
> //            (nil))))/
>
> This, of course, is not correct any more. Now, how should I prevent 
> this ?, the pattern is defined in the .md-file as:
>
> /(define_insn "movqi_internal" //
> //[(set (match_operand:QI 0 "movqi_operand_0" 
> "=r,r,r,r,r,r,u,u,W,t,r,c,*c*l,*h,*h,y")//
> //(match_operand:QI 1 "movqi_operand_1" "O,k,i,r,W,t,W,t,r,r,*h,u, 
> r,   r, 0,y"))]/
>
> /.../
> and /movqi_operand_1/ is defined as:
>
> /(define_predicate "movqi_operand_1"//
> //  (ior (match_operand 0 "gpc_reg_operand")//
> //       (ior (match_operand 0 
> "quarterword_offset21_memref_operand_or_indirect")//
> //            (match_operand 0 "immediate_operand"))))/
>
>
> and /gpc_reg_operand/ as:
>
> /(define_predicate "gpc_reg_operand"//
> //   (and (match_operand 0 "register_operand")//
> //        (match_test "(GET_CODE (op) != REG && GET_CODE(op) != SUBREG//
> //                      || (REGNO (op) >= ARG_POINTER_REGNUM//
> //                          && !CA_REGNO_P (REGNO (op)))//
> //                      || REGNO (op) == SFP_REGNO//
> //                      || REGNO (op) == ARG_POINTER_REGNUM//
> //                      || REGNO (op) <= MAX_REGFILE_REGNO)")))/
>
> Any of you any idea why the combine succeeds ?. I mean, it should fail 
> !. After combine, it does not match /movqi_internal/ pattern
> any more, but the compiler seems to think otherwise !.
>
> Best Regards,
>
> Henri.
>
>
>