[LLVMdev] Using frameindex in a pattern

[Evan Cheng]

On Dec 3, 2007, at 11:07 PM, Vladimir Prus wrote:

> Evan Cheng wrote:
>
>>
>> On Dec 3, 2007, at 12:53 PM, Vladimir Prus wrote:
>>
>>>
>>> Suppose I have a target that does not have register+constant
>>> addressing mode. Then, I have DAG like:
>>>
>>> (store ..., (frameindex))
>>>
>>> Targets like SPARC have the following patterns to catch this:
>>>
>>> def ADDRri : ComplexPattern<i32, 2,
>>> "SelectADDRri", [frameindex], []>;
>>> def STri  : F3_2<3, 0b000100,
>>>                 (outs), (ins MEMri:$addr, IntRegs:$src),
>>>                 "st $src, [$addr]",
>>>                 [(store IntRegs:$src, ADDRri:$addr)]>;
>>>
>>> Where ADDRri will eventually turn into register+constant
>>> addressing in assembler.
>>>
>>> The IA64 target has explicit case in it's Select method
>>> to handle frameindex -- which is fine, but I though I'd
>>> try a fully declarative method, so I've added to sparc
>>> the following:
>>>
>>>   def : Pat<(frameindex simm13:$val), (add G0, simm13:$val)>;
>>>
>>> (Ignore bogus G0, and '13' -- just for testing). The error
>>> I get this:
>>>
>>>   /home/ghost/Build/llvm/Release/bin/tblgen:
>>>   In anonymous.24: frameindex node requires exactly 0 operands!
>>>
>>>
>>> Is this really as designed, or nobody got around to making  
>>> frameindex
>>> have an true operand? Any way to achive frameindex->add translation
>>> using a pattern and not C++ code at all?
>>
>> This is as designed. frameindex node is considered a leaf node. The
>> lowering of frameindex into machine instructions is handled late
>
> In other words, frameindex is supposed to be carried over to  
> MachineInstruction
> level, and finally removed by eliminateFrameIndex, right? How does  
> this agrees
> with the fact that Sparc specially handles frameindex using its  
> ADDRri pattern
> (using it in patterns for most load/store instructions). Is this  
> for historic
> reasons?

ADDRri is a ComplexPattern, used to handle selection of multiple  
nodes that are too complex for tblgen to handle. It's handled by  
SelectADDRri(). The function is keeping merely translating it to  
targetframeindex with an offset 0.

>
>> for
>> many (good) reasons, e.g. allowing coloring of frame slots.
>
> What's that -- google is not helpful. Is this rearrangement of
> frame slots of minimize access overhead, or pulling data from frame
> slots to registers, or what?

Re-arrangement of frame slots to share physical memory locations to  
reduces stack size.

Evan

>
> - Volodya
>
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