[LLVMdev] 64-bit add using 2 32-bit operations, guarantee of stuck together?

[Quentin Colombet]

Using bundles here looks like a fragile way to handle that, IMHO.
Really, using a pseudo instruction seems the best approach for you.

For instance, you can match your add64 during isel with your pseudo instruction and expand it just before emitting the assembly file (add a pass using the hook: addPreEmitPass on your target).

-Quentin

On Apr 15, 2013, at 2:37 PM, Francois Pichet <pichet2000 at gmail.com> wrote:

> 
> I really have to force them to stuck together otherwise the carry will just not work.
> 
> How about wrapping the 2 instructions in a bundle?
> Would that be a way?
> http://llvm.org/docs/CodeGenerator.html#machineinstr-bundles
> 
> 
> On Mon, Apr 15, 2013 at 5:24 PM, Quentin Colombet <qcolombet at apple.com> wrote:
> Hi Francois,
> 
> If you model the effect of your carry on the instructions, the scheduler (and the other backend passes) should ensure that nothing that affects the carry will be inserted between your two instructions (assuming they are issued with nothing affecting the carry in between in the first place).
> Therefore, you shouldn’t have to force them to be stuck together.
> 
> If you still do, what Jakob proposed is what you are looking for.
> 
> -Quentin
> 
> On Apr 15, 2013, at 2:02 PM, Francois Pichet <pichet2000 at gmail.com> wrote:
> 
>> Hi,
>> 
>> Let's say we have a 32-bit architecture where 64-bit additions are done using 2 operations.
>> 
>> Instructions are defined as follow in TableGen:
>>    defm ADD64  : ALU32<"add", 1, 1, addc>;
>>    defm ADD64C : ALU32<"addrc", 1, 2, adde>;
>> 
>> 
>> Let's assume that the carry bit is implicit and that the 2 operations must *always* be stuck together for the 64-bit add to work properly.
>> Is there a default guarantee that nothing will ever be inserted between "add" and "addrc" or is there a flag/condition to set somewhere to have that guarantee?
>> 
>> Thanks
>> 
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