[LLVMdev] HELP - tblgen -gen-asm-matcher restrictions on .td content

[Jim Grosbach]

Hi Jack,
On Jan 25, 2012, at 6:45 PM, "Carter, Jack" <jcarter at mips.com> wrote:

> I'm trying to generate MipsGenAsmMatcher.inc for MipsAsmParser.cpp. 
> 
> What added restrictions for the .td file contents are there for tblgen -gen-asm-matcher?
> 

Lots, as you're finding, almost all of them completely undocumented. :(

> For the Mips platform we create the following .inc files through tblgen.
> 
> tablegen(LLVM MipsGenRegisterInfo.inc -gen-register-info)
> tablegen(LLVM MipsGenInstrInfo.inc -gen-instr-info)
> tablegen(LLVM MipsGenCodeEmitter.inc -gen-emitter)
> tablegen(LLVM MipsGenMCCodeEmitter.inc -gen-emitter -mc-emitter)
> tablegen(LLVM MipsGenAsmWriter.inc -gen-asm-writer)
> tablegen(LLVM MipsGenDAGISel.inc -gen-dag-isel)
> tablegen(LLVM MipsGenCallingConv.inc -gen-callingconv)
> tablegen(LLVM MipsGenSubtargetInfo.inc -gen-subtarget)
> add_public_tablegen_target(MipsCommonTableGen)
> 
> When I started trying to generate MipsGenAsmMatcher.inc for the assembler I started getting errors.
> 
> tblgen -gen-asm-matcher -I ~/workarea/asm/llvm/include/  Mips.tdIncluded from Mips.td:24:
> MipsInstrInfo.td:833:14: error: Instruction 'LWL' has no tokens
> defm LWL     : LoadUnAlign32<0x22>;
> 
> How does it get a token?
> 

>From the assembly string used by the instruction printer. That's saying there's a variant in the multi class expansion that doesn't have a string associated with it that can be used to derive the syntax.

> Commenting out this code I got farther and found that a register that didn't have a formal def in MipsRegisterInfo.td would get flagged.
> 
>      !strconcat(instr_asm, "\t$$zero, $rs, $rt"),
> 
> % tblgen -gen-asm-matcher -I ~/workarea/asm/llvm/include/  Mips.td
> Included from Mips.td:24:
> Included from MipsInstrInfo.td:1120:
> Mips64InstrInfo.td:173:1: error: error: unable to find operand: 'zero'
> def DSDIV    : Div64<MipsDivRem, 0x1e, "ddiv", IIIdiv>;
> ^
> 

That's a bug/limitation of the asm matcher. For something similar, see X86InstrInfo.td's commented out definition of ShiftRotateByOneAlias.

-Jim

> Any information on this would be great.
> 
> Cheers,
> 
> Jack

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