[LLVMdev] Replacing a Reg MachineOperand with a non-Reg MachineOperand?

[Ryan Taylor]

So I have this for ChangeToGlobalAddress(const GlobalValue *GV):

...
OpKind = MO_GlobalAddress;
Contents.OffsetedInfo.Val.GV = GV;

and then I use the function like this:

MI->getOperand(1).ChangeToGlobalAddress(MII->getOperand(1).getOperand.getGlobal());

The operand ends up being replaced with the global; however, it's also
adding a large constant immediate value with it.

For example, instead of <ga:@a> I end up with <ga:@a+2147483653> and
instead of <ga:@a+100> I end up with <ga:@a+214748564>

What might I be doing wrong?

Thanks.

On Tue, Jun 16, 2015 at 10:12 AM, Ryan Taylor <ryta1203 at gmail.com> wrote:

> Tom,
>
>   My current example is a global address; however, it could be any operand
> in theory. The arch allows for direct mem op support for ex instructions,
> so it could be any type of address or any type of imm or any type of
> register.
>
>   For example, we are using intrinsics for some instructions since LLVM
> does not support them. Table gen does not allow for matching to direct mem
> op because the intrinsics are calls, so registers are setup for the call
> parameters. So we end up with something like:
>
>   mov @a, r0
>   abs r0, r1
>
> In our arch, we should be able to do 'abs @a, r1'. So since the intrinsics
> won't match properly in the tblgen we're looking at doing a peephole where
> we want to replace the operand 'r0' with @a and remove the 'mov @a, r0'
> instruction, so it would look like:
>
>   abs @a, r1
>
> Thanks.
>
> ps. We could add these operators to LLVM instead of using intrinsics but
> that also introduces a lot of dev cost and maintenance cost and some other
> technical issues, but then we could have the operators match in the tblgen.
> We are looking to avoid this, we thought a simple peephole would do the
> trick instead.
>
> On Tue, Jun 16, 2015 at 9:57 AM, Tom Stellard <tom at stellard.net> wrote:
>
>> On Mon, Jun 15, 2015 at 10:16:47PM -0400, Ryan Taylor wrote:
>> > I have a MachineOperand that could be something other than a Reg: mem,
>> > global address, imm, etc...
>> >
>> > I want to replace a reg MachineOperand with this non-reg MachineOperand.
>> >
>> > I've tried a few different things, but it doesn't seem like there is
>> some
>> > simple functionality to do this?
>> >
>> > "RemoveOperand" and "addOperand" does not work.
>> > There doesn't seem to be a valid "ChangeTo..." function for this.
>> >
>> >
>>
>> What type of operand do you want to change it to?  If there is no
>> "ChangeTo..." function for the new type, I think the best thing to do
>> would be to add a new "ChangeTo..." function to handle the new type.
>>
>> -Tom
>>
>> > What's the best way to do this without tearing down the instructions and
>> > using BuildMI?
>> >
>> > Thanks.
>>
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
>
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