[llvm-dev] [A bug?] Failed to use BuildMI to add R7 - R12 registers for tADDi8 and tPUSH of ARM

[Craig Topper via llvm-dev]

It's in ARMRegisterInfo.td

// Thumb registers are R0-R7 normally. Some instructions can still use
// the general GPR register class above (MOV, e.g.)
def tGPR : RegisterClass<"ARM", [i32], 32, (trunc GPR, 8)> {
  let DiagnosticString = "operand must be a register in range [r0, r7]";
}

~Craig


On Sun, Apr 14, 2019 at 12:38 PM Jie Zhou <jzhou41 at cs.rochester.edu> wrote:

> Hi Craig,
>
> Thanks for the information. Can you point to the source that specifies
> tGPR to be R0 - R7?
> I tried to search in ARMInstrThumb.td but couldn’t find it.
>
> Thanks,
> - Jie
>
> On Apr 14, 2019, at 15:28, Craig Topper <craig.topper at gmail.com> wrote:
>
> I believe there is probably a separate instruction in LLVM for thumb2 add.
> Probably starting with t2 instead of t.
>
> The definition of tADDi8 looks like this. Where tGPR specifically means
> R0-R7.
>
>   def tADDi8 :                    // A8.6.4 T2
>     T1sItGenEncodeImm<{1,1,0,?,?}, (outs tGPR:$Rdn),
>                       (ins tGPR:$Rn, imm0_255:$imm8), IIC_iALUi,
>                       "add", "\t$Rdn, $imm8",
>                       [(set tGPR:$Rdn, (add tGPR:$Rn, imm8_255:$imm8))]>,
>                       Sched<[WriteALU]>;
>
> ~Craig
>
>
> On Sun, Apr 14, 2019 at 12:21 PM Jie Zhou <jzhou41 at cs.rochester.edu>
> wrote:
>
>> Sorry for not being specific enough. ARMv7-M includes Thumb and Thumb2.
>> It has 12 regular registers (R0 - R12), and R8 - R12 are used.
>> I can generate mov instruction that from/ R8-R12 to/from R0-R6.
>> From this ARM page
>> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0068b/ch03s03s01.html
>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__infocenter.arm.com_help_index.jsp-3Ftopic-3D_com.arm.doc.dui0068b_ch03s03s01.html&d=DwMFaQ&c=kbmfwr1Yojg42sGEpaQh5ofMHBeTl9EI2eaqQZhHbOU&r=KAtyTEI8n3FritxDpKpR7rv3VjdmUs0luiVKZLb_bNI&m=_fpYL_7E5zOQ4DZeiPmiSOgKp7KxZ5mAZVh9wB6CxUY&s=1r2JmIRDr3fxySkwnQU16zv8ySZfoc3nUtLdCcwb4gw&e=>
>> R9 - R12 have their conventional usage, but I don’t if this is the reason
>> we cannot
>> use them arbitrarily. The fact that we can use it to generate mov
>> instructions but
>> not add/sub and push/pop confuses me.
>>
>> - Jie
>>
>> On Apr 14, 2019, at 14:55, Craig Topper <craig.topper at gmail.com> wrote:
>>
>> I don't know much about ARM. But it looks like tADDi8 is a Thumb
>> instruction and it can only use R0-R7.
>>
>> tPUSH probably as a similar issue. But it's also a store instruction and
>> doesn't produce a register output. So you should use the form of BuildMI
>> that doesn't take a register as its last argument.
>>
>> ~Craig
>>
>>
>> On Sun, Apr 14, 2019 at 11:17 AM Jie Zhou via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> Hi all,
>>>
>>> I’m trying to insert some add/sub and push/pop instructions in a
>>> MachineFunction pass for ARMv7-M. However, I encountered something weird.
>>> For an add, when I use
>>>
>>>         BuildMI(….., TII->get(ARM::tADDi8),
>>> reg).addReg(reg).addReg(reg).addImm(imm).
>>>
>>> if reg is R0 - R7, everything is fine: I would get something like
>>>
>>>         adds r1, 4
>>>
>>> But if I use R8 - R12 as the reg in the BuildMI, I wouldn’t get the
>>> correct register in the assembly code. For example, when I pass R8 to it, I
>>> would get
>>>
>>>         adds r0, 4
>>>
>>> rather than
>>>
>>>         adds r8, 4.
>>>
>>> Similar problems happen to push and pop instructions. I can create a
>>> push/pop if the register list only contains registers R0 - R7, but
>>> for registers whose number are greater than R7, the generated asm code
>>> doesn’t have it. For example,
>>>
>>>         BuildMI(……, TII->get(ARM::tPUSH), R8)…..
>>>
>>> would give me
>>>
>>>         push {}
>>>
>>> Is this a bug in the LLVM ARM code generator? Or is there a reason why
>>> we cannot use big-number registers for add/sub and push/pop?
>>>
>>> Thanks,
>>> - Jie
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>> <https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.llvm.org_cgi-2Dbin_mailman_listinfo_llvm-2Ddev&d=DwMFaQ&c=kbmfwr1Yojg42sGEpaQh5ofMHBeTl9EI2eaqQZhHbOU&r=KAtyTEI8n3FritxDpKpR7rv3VjdmUs0luiVKZLb_bNI&m=U3D9KaSPCCtUPKPRKsCQl1uo2Kf6PSTT60lRuM6LGO8&s=VbLOmjk6zGsqyFH-PkHGWi4G9iNb4k60I8byBoTgJN4&e=>
>>>
>>
>>
>
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