Re: Issue with reload

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

Hello Segher, all,

I have the impression there is a small bug in the front-end.

//#define LOAD_EXTEND_OP(MODE) ZERO_EXTEND
#define LOAD_EXTEND_OP(MODE) UNKNOWN      // HACK HENRI !!.
(this is in my back-end)

I have to turn the LOAD_EXTEND_OP(MODE) to UNKNOWN.

The issue seems to be following:
- There are operations in the code of the type
R100:SI = zero_extend(R101:HI)
- Now, during reload, R101:HI is moved on the stack.
- Then, internally in the compiler, there is confusion on the 
zero_extend operator.
   a. If the load-extend-mode is ZERO_EXTEND:
       there is confusion as to use the MOVHI instruction or the 
ZERO_EXTEND instruction.
       (they both do the same.) This seems to lead to the strange bugs.
       (It seems to me there are optimizers that recognize the 
ZERO_EXTEND as MOVHI, and others
        that dont, leading to the crashes.)
   b. If I turn it off, all seems to go OK.
- So, I turned it off ... Hope this does not lead to problems.

Best Regards,

Henri.


On 11/3/20 6:23 PM, Segher Boessenkool wrote:
> Hi Henri,
>
> On Tue, Nov 03, 2020 at 04:25:32PM +0100, Henri Cloetens wrote:
>>> 583: r990:SI=zero_extend(r378:SI#0)
>> - The statement (r378:SI#0) takes the '0' subreg form reg r378:SI.
>> (shorthand in the reload dump.)
> And it doesn't say what mode subreg it is (QImore or HImode here).
> There are multiple cases like this, where the abbreviated RTL is not
> conclusive (so cannot be parsed back).
>
>>> (define_insn "zero_extendhisi2_internal"
>>>    [(set (match_operand:SI 0 "gpc_reg_operand" "=r,r,r")
>>>          (zero_extend:SI (match_operand:HI 1 "movhi_operand_0"
>> "Z,C,r")))]
>>
>> - However, the predicate "r" in the statement above, does not allow a
>> subreg.
> Yes it does.  See register_operand in recog.c for example.  It is of
> course possible your gpc_reg_operand doesn't allow it (bad idea, but I
> don't know your code).
>
> You would normally start the gpc_reg_operand code with something like
>
>    if (SUBREG_P (op))
>      op = SUBREG_REG (op);
>
> (as well as pretty much all other register operand predicates).
>
>
> Segher