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

Craig Topper via llvm-dev llvm-dev at lists.llvm.org
Sun Apr 14 11:55:03 PDT 2019

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.


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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20190414/a770fe8e/attachment.html>

More information about the llvm-dev mailing list