[LLVMdev] Pattern matching questions

[Evan Cheng]

On Jan 9, 2007, at 10:01 AM, Scott Michel wrote:

> I was able to resolve my previous question about dealing with custom
> loads/stores, and following Chris' suggestion, the IBM Cell SPU  
> backend
> can generate code for "int main(void) { return 0; }" without crashing
> llc. There's a lot of work still to be done... like getting frame
> offsets correctly computed and hauling in the raft of intrinsics that
> the Cell SDK defines.
>
> Three quick questions:
>
> - How does one deal with multiple instruction sequences in a pattern?
>   To load a constant is a two instruction sequence, but both
>   instructions only take two operands (assume that r3 is a 32-bit
>   register):
>
>   ilhu $3, 45             # r3 = (45 << 16)
>   iohl $3, 5              # r3 |= 5
>
>   I tried:
>
>   def : Pat<(i32 imm:$imm),
>             (IOHL (ILHU (HI16 imm:$imm)), (LO16 imm:$imm))>;

It is possible to write multi-instruction pattern, e.g.  
X86InstrSSE.td line 1911. But how are you defining HI16 and LO16?  
Sounds like you want to define them as SDNodeXform that returns upper  
and lower 16 bits respectively. Take a look at PSxLDQ_imm in  
X86InstrSSE.td as an example.

>
> - The return instruction for Cell SPU is "bi $lr". How do I jam that
>   into the instruction info w/o tblgen bitching up a storm about the
>   "$" or the extra "bi" operands?

I am not sure. Does "bi \$lr" works? Or "bi $$lr"? Or even something  
like
!strconcat("bi ", !strconcat("$", "lr")).

>
> - Immediates in a pattern: To move one register to another involves
>   using the 3-operand OR instruction, but how do I encode an immediate
>   w/o a type inference contradiction?
>
>   def : Pat<(set R32C:$rDest, R32C:$rSrc),
>             (ORIr32 R32C:$rSrc, 0)>;

I am not sure what you mean. By 3-operand, you mean 2 source operand  
and 1 destination. I don't think the error you are seeing have  
anything to do with the immediate. For a def : Pat pattern, you don't  
need to specify the "set R32C:$rDest" portion.

Evan

>
> Thanks for the clue!
>
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