[LLVMdev] Hexagon Assembly parser question

[David Young]

Hi,

I'm trying to enable the hexagon LLVM  assembly parser.   It seem like there
is a lot of work that has been done to make this parsing straightforward.  

 

But..

Hexagon assembly does not follow the "Mnemonic Rx Rx ." format that is
expected by the assembly parsing infrastructure, represented by:

StringRef Mnemonic = ((ARMOperand*)Operands[0])->getToken();

 

This Mnemonic location  assumption applies to both the Tablegen Backend
AsmMatcherEmitter processing, and the .inc file it produces where
MatchInstructionImpl is the entry point by which the assembly input is
parsed. 

 

However Hexagon assembly has some features that make it more readable, such
as r1 = r2, or if(r1) r2 = mem(#immediate).  This makes taking advantage of
the existing LLVM code difficult.

 

 

Currently, I see two options.  

 

One is to preformat the assembly string(s) obtained from the td files so
that it is matches the format that the tablegen backend expects, and also
preformat the assembly input so that it can be matched against the
preformatted assembly strings.

 

The other is to write a whole new TD backend that doesn't rely on the
Mnemonic location assumption.  And hope someday to merge this backend with
the current AsmMatcherEmitter. 

 

I am leaning toward the latter.  The other seems like it will create many
more problems in the long run.   Any thoughts, comments, or recommended
directions are appreciated.

 

Regards,

David

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