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

Carter, Jack jcarter at mips.com
Thu Feb 2 17:34:24 PST 2012

Once again, thank you.

I will add these explanations to my assembler journal and we may end up with some documentation by the time I am done.


From: Jim Grosbach [grosbach at apple.com]
Sent: Thursday, February 02, 2012 4:50 PM
To: Carter, Jack
Cc: List
Subject: Re: HELP - tblgen -gen-asm-matcher restrictions on .td content

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

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.


Any information on this would be great.



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