Compiling external programs for SPIM Target results in an infinite loop afer executing cc1.

[Aniket Deole]

I did debug cc1, but was not able to figure out the exact issue.

Thanks for the explanation.
---------------------------------
Aniket Deole
9604503495
aniket.deole@gmail.com


On Tue, Jun 4, 2013 at 9:22 PM, Chung-Ju Wu <jasonwucj@gmail.com> wrote:
> 2013/6/4 Aniket Deole <aniket.deole@gmail.com>:
>> Hello,
>>
>> We are building GCC for the Mips Simulator "SPIM".
>> We have previously built the same for GCC 4.6.2, and are now trying to
>> build it for 4.7.2.
>>
>> We are experiencing an issue related to the cbranchsi4 in GCC 4.7.2,
>> machine description wherein, GCC is compiled correctly and cc1 is
>> generated. But while compiling an external C program having
>> conditional statements using cc1, the compilation goes in an infinite
>> loop.
>>
>> We were able to rectify this infinite loop by removing an SI from the
>> instruction for the first match operator clause.
>>
>> But we are not sure as to why this fix is required with respect to the
>> different GCC versions 4.6.2 and 4.7.2.
>>
>> ---------------------------------------------------------------
>> GCC 4.6.2 MD:
>> --------------------------
>> (define_insn "cbranchsi4"
>>        [(set (pc)
>>              (if_then_else
>>
>>              (match_operator:SI 0 "comparison_operator"
>>
>>              [(match_operand:SI 1 "register_operand" "")
>>              (match_operand:SI 2 "register_operand" "")])
>>              (label_ref (match_operand 3 "" ""))
>>                           (pc)))]
>>              ""
>>              "* return conditional_insn(GET_CODE(operands[0]),operands,0); "
>> )
>> --------------------------------------------------------------
>> GCC 4.7.2 MD:
>> ---------------------------
>> (define_insn "cbranchsi4"
>>      [(set (pc)
>>              (if_then_else
>>
>>              (match_operator 0 "comparison_operator"
>>
>>              [(match_operand:SI 1 "register_operand" "")
>>              (match_operand:SI 2 "register_operand" "")])
>>              (label_ref (match_operand 3 "" ""))
>>                           (pc)))]
>>               ""
>>              "* return conditional_insn(GET_CODE(operands[0]),operands,0); "
>> )
>>
>> Thank You,
>> ---------------------------------
>> Aniket Deole
>> aniket.deole@gmail.com
>
> Hi, Aniket,
>
> It's hard tell why your cc1 went into infinite loop.
> It requires tracing gcc code by yourself.
>
> However, refer to to GCC Internal, 10.10 Comparison Operations:
> "If the comparison operation is being tested
>  (e.g., the first operand of an if_then_else),
>  the mode must be VOIDmode."
>
> IIUC, the mode of cbranch pattern is determined by
> the compared operands, not comparison operator.
> The comparison operator is supposed to be VOIDmode and many
> optimization/simplification phases are based on such principle.
>
> So I would guess it was just lucky that you did not suffer
> any compilation problems with your 4.6.2 MD design.
>
>
> Best regards,
> jasonwucj