[LLVMdev] Adding Intrinsics for custom processor (frotend problem)

[Luke Dalessandro]

Richard Osborne wrote:
> Personally I would just modify the frontend - it's not that hard once 
> you know where to look . In this case all you need to do is add the 
> declaration of your builtin to the TARGET_INIT_BUILTINS target hook (see 
> the gcc internals manual) defined in the gcc/config directory 
> corresponding to your target. If the name the the declaration matches 
> the name used with GCCBuiltin in the intrinsics td file then any calls 
> to the gcc builtin in the source should get automatically translated to 
> the calls to the LLVM intrinsic.

Gil, this sounds like a much easier strategy than mine for your 
target-specific approach. The builtins that I added for my own purpose 
aren't target specific, they're more along the lines of the OpenMP stuff 
so I was looking for a general place to put them.

Luke

> 
> Gil Dogon wrote:
>> As mentioned in an earlier mail, I am working on an LLVM backend for a 
>> custom processor based on MIPS.
>> My problem is how to extend LLVM to support some esoteric/non-standard 
>> feature of the underlying hardware.
>> I saw in the "Extending LLVM" document, that the easiest / most common 
>> way to do this was using an intrinsic function,
>> and examples of the technique abound (all SSE for example).
>> My problem though as mentioned before is that  the frontend support for 
>> intrinsics, is undocumented, and implemented
>> in  llvm-gcc which I prefer not to hack with (I  use a binary 
>> precompiled one).  As far as I could see it supports the
>> intrinsics using gcc style __builtin_ function names.
>>
>> Currently what I think to do , is the following :
>>
>> 1. Define my intrinsics in a special (which would be preincluded in our 
>> build system) .h file (using whatever name convention I want)
>> 2. Then I need to add a pass to llvm which will translate the names of 
>> those intrinsics to llvm style names , since
>>    LLVM intrinsics start with "llvm." which makes them non legal as "C" 
>> identifiers.
>>
>> I have two questions :
>>
>> 1. Is that the right way to go, or is there a simpler/more standard way 
>> to have frontend support for new architecture intrinsics ?
>>
>> 2. If thats the simplest way , I would like to have a quick advice on 
>> how to write the rather trivial pass described in '2'.
>>    I guess that I need to replace a given Function object with an 
>> allmost identical one, but with a different name (the "llvm.something' name
>>   of the intrisic)   What is the correct code to do this ?
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