[LLVMdev] Using frameindex in a pattern

[Vladimir Prus]

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?

> 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?

- Volodya