[LLVMdev] All backends now use the MC asm printer

[Venkatraman Govindaraju]

On Sat, Jan 11, 2014 at 11:20 PM, Sean Silva <chisophugis at gmail.com> wrote:
>
>
> On Sat, Jan 11, 2014 at 5:26 PM, Richard Pennington <rich at pennware.com>
> wrote:
>>
>> On 01/10/2014 04:06 PM, Rafael Espíndola wrote:
>>>
>>> In r198030 the last in tree backend was converted to use MCInst for
>>> printing assembly. I removed support for the old printer in r198959.
>>>
>>> Out of tree targets have to lower MachineInstr to MCInst to use the new
>>> printer.
>>>
>>> Cheers,
>>> Rafael
>>>
>> Are there any guidelines as to how the lowering should be done? I'd like
>> to update the (defunct) Microblaze back end before I pull the latest TOT
>> this week.
>
>
> Venkatraman, I'm guessing you still have this fresh in your memory. Would
> you mind giving a hand? (bonus points for writing some documentation
> <http://llvm.org/docs/SphinxQuickstartTemplate.html> ;)
>

Here are the steps that I followed to implement the MCLowering in
SPARC backend.

1. Implement <Target>MCExpr.cpp
    Create a derived class of TargetMCExpr  to handle target specific
expressions such as %hi, %lo etc.  See examples in AArch64MCExpr.cpp,
SparcMCExpr.cpp etc.,

2. Implement <Target>MCStreamer.cpp if the target needs any special directives.
    See http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-October/066248.html
for further info.

3. Implement InstPrinter using TableGen-ed AsmWriter. (See examples in
lib/Target/<Target>/InstPrinter/)

4. Implement <Target>MCInstLower.cpp to lower MachineInstrs to MCInst.
   This is implemented by lowering MachineInstr operands to either
MCInst operands or MCExpr. Target specific expressions are lowered to
<Target>MCExpr objects.

5. Modify <Target>AsmPrinter to lower MachineInstrs to MCInst and emit
them using the MCStreamer.

6. Finally, register the InstPrinter and the MCStreamers in
<Target>MCTargetDesc.cpp

 Hope that this helps.

  For MicroBlaze target, when it removed from the trunk, it is already
using the new MCInstPrinter. So, it may easier to update it.

Thanks,
Venkatraman

> -- Sean Silva
>
>
>>
>>
>> -Rich
>>
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