[LLVMdev] New to LLVM, Help needed

[Chris Lattner]

On Wed, 12 Sep 2007 Alireza.Moshtaghi at microchip.com wrote:
> Thank you Chris,
> I had the pointer size wrong. I fixed it and now it passes that point as
> expected :) which takes me to a second question:

cool

> The processor that I am working on is 8-bit and has Harvard
> architecture; this implies different pointer types (sizes) to objects in
> data memory or program memory (functions or data in program memory)
> At this moment, I am just using only one pointer size (16-bit) just to
> get things going; however, eventually I need to model the two pointer
> types.
> I was wondering if you have any suggestion as to how best I can model
> this in LLVM.

I don't think the code generator will need significant extension to 
support this: SDISel would just lower each to a different integer size.

The place that will need extension is the LLVM IR itself.  Here I think 
that we should expand PointerType to take some sort of address space 
identifier.  This will allow the front-end to produce pointers of the 
right type and the codegen will be able to lower them to the right sized 
integer.  This is a fairly invasive change, but should be relatively 
straight-forward to do.

-Chris

> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu]
> On Behalf Of Chris Lattner
> Sent: Wednesday, September 12, 2007 1:08 PM
> To: LLVM Developers Mailing List
> Subject: Re: [LLVMdev] New to LLVM, Help needed
>
> On Tue, 11 Sep 2007 Alireza.Moshtaghi at microchip.com wrote:
>> More information on this... still not working
>> When I build the project for Debug and run the program, the following
>> message is printed before assert.
>>
>> NODE: 0x937bac8:  i64 = GlobalAddress <i32* @var> 0
>
> This implies that your target uses 64-bit pointers, but that it doesn't
> have a 64-bit register file, is this right?
>
> If you aren't using 64-bit pointers, you should investigate where this
> node came from.
>
>> I guess it is expecting that GlobalAddress be legalized before
> reaching
>> ExpandOp(). I haven't implemented anything for ISD::GlobalAddress, and
>> that may explain it, however, I couldn't find much about it in the
>> PowerPC implementation either. The only thing is in the ctor of
>> PPCTargetLowering there is setOperationAction(ISD::GlobalAddress,
>> MVT::i32, Custom);  and
>>
>> setOperationAction(ISD::GlobalAddress, MVT::i64, Custom);
>> so I also added these two function calls to my ctor of
>> PICxxTargetLowering. Nothing changed. I also tried "Expand" and
> "Legal"
>> instead of "Custom", still no progress. I'm sure I am missing some
> thing
>> here.
>
> You may be running into problems if the pointer type in the code
> generator
> isn't natively supported by your register file.  We haven't hit a target
>
> like this yet, so you will likely have to expand LegalizeDAG to handle
> these cases.
>
> -Chris
>
>>
>> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu]
>> On Behalf Of Evan Cheng
>> Sent: Monday, September 10, 2007 10:29 AM
>> To: LLVM Developers Mailing List
>> Subject: Re: [LLVMdev] New to LLVM, Help needed
>>
>>
>>
>> Please do a debug build and run it under gdb. Let us know where it is
>> asserting and what it is asserting on so we can help you.
>>
>>
>>
>> Evan
>>
>>
>>
>> On Sep 7, 2007, at 4:50 PM, Alireza.Moshtaghi at microchip.com wrote:
>>
>>
>>
>>
>>
>> Hi,
>>
>> I have started to write an llvm backend for one of our
> microcontrollers
>> (PICxx). I started studying the framework of PowerPc backend of llvm
> and
>> decided to start by following that framework. Now I have most of the
>> classes and Tblgen files written for a very basic hypothetical
>> microcontroller with very few instructions.
>>
>> The project builds and the llc recognizes the new processor, however,
>> when it reaches the point where it wants to lower llvm IR to PICxx
> DAG,
>> it asserts in LegalizeDAG.cpp in ExpandOp() function after it hits the
>> default case of switch(Node->getOpcode())
>>
>> Can someone please help me understand how am I ending up in the
> default
>> case?
>>
>>
>>
>> Thanks,
>>
>> A.
>>
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>>
>>
>>
>>
>
> -Chris
>
>

-Chris

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