[llvm-commits] [llvm] r91944 - in /llvm/trunk/lib/Target/ARM: ARMInstrThumb.td ARMRegisterInfo.td

[Chris Lattner]

On Dec 22, 2009, at 4:17 PM, Jakob Stoklund Olesen wrote:

>
> On Dec 22, 2009, at 4:01 PM, Chris Lattner wrote:
>
>>
>> On Dec 22, 2009, at 3:54 PM, Jakob Stoklund Olesen wrote:
>>
>>> Author: stoklund
>>> Date: Tue Dec 22 17:54:44 2009
>>> New Revision: 91944
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=91944&view=rev
>>> Log:
>>> Add a SPR register class to the ARM target.
>>>
>>> Certain Thumb instructions require only SP (e.g. tSTRspi).
>>
>> Hi Jakob,
>>
>> If it only allows one register, doesn't it make more sense to make  
>> it an implicit reg operand instead of a regclass operand?
>
> Maybe. How would it look in this pattern?
>
> def t_addrmode_sp : Operand<i32>,
>                    ComplexPattern<i32, 2, "SelectThumbAddrModeSP",  
> []> {
>  let PrintMethod = "printThumbAddrModeSPOperand";
>  let MIOperandInfo = (ops JustSP:$base, i32imm:$offsimm);
> }

Eww, gross.  :)  Two separate issues:

1. How to model this:  This instruction should be modeled as taking SP  
as an implicit input, and take an i32imm operand.  I think this should  
be pretty simple and any non-isel code that generates this can easily  
adjust to not passing in SP.

2. How to match this: If you really want dag isel to match these as  
loads, you'd need to write a pat pattern (or manual matching) that  
matches load(addr) and uses an SDNodeTransform to extract the  
immediate, maybe something like this:

Pat<(load (t_addrmode_sp:$addr)),
     (tLDRspi (EXTRACT_IMM_FROM_ADDRMODE_SP t_addrmode_sp:$addr))>;

Some simple examples of sdnode transforms are things like this from PPC:

def : Pat<(i32 imm:$imm),
           (ORI (LIS (HI16 imm:$imm)), (LO16 imm:$imm))>;

Which matches an arbitrary 32-bit immediate with a "ori" and "lis"  
instruction to get the two 16-bit halves.

> I was trying to break as little as possible.

I appreciate that, but single-register register classes aren't really  
register classes :). Thanks for working on this!

-Chris