[LLVMdev] Tblgen and computed expressions

Tue Oct 1 05:08:26 PDT 2013

Feel free to send whatever code you can, I'll be glad to have a look.

-----Original Message-----
From: Martin O'Riordan [mailto:Martin.ORiordan at movidius.com] 
Sent: Tuesday, October 01, 2013 15:03
To: Malul, Elior; llvmdev at cs.uiuc.edu
Subject: RE: [LLVMdev] Tblgen and computed expressions

Thanks again Elior,

Yes, I tried using '!if', etc. but I just get type mismatches for the initializer (int) - probably something daft I'm doing :-(

	MartinO	

-----Original Message-----
From: Malul, Elior [mailto:elior.malul at intel.com]
Sent: 29 September 2013 09:19
To: Martin.ORiordan at movidius.com; llvmdev at cs.uiuc.edu
Subject: RE: [LLVMdev] Tblgen and computed expressions

Martin hi.

It seems like you have in fact understood the offered solution, and its disadvantages.
The thing is, that as far as I understand Tblgen (and I think I do :-) ), The idea behind it is that records only have state (i.e., fields), and not a behavior (i.e., methods) - so dynamic evaluation can only be achieved by built-in functions.
(e.g., !if(), !foreach() etc...).

Maybe you can try using one for the solution. If you can't find that fits you, please let me know - maybe we can define a new function that will meet your needs, And maybe also those of the silent crowed.

Thx, Elior

-----Original Message-----
From: Martin O'Riordan [mailto:Martin.ORiordan at movidius.com]
Sent: Friday, September 27, 2013 15:50
To: Malul, Elior; llvmdev at cs.uiuc.edu
Subject: RE: [LLVMdev] TableGen and computed expressions

Thanks Elior,

Sorry for the delay - emergencies never seem to go away in compiler development ;-)

That sounds like an interesting approach, a kind-of pre-processor for TD files.  But will this still not result in a constant, although externally provided, or have I misunderstood?

What I would like to do is compute a different value depending on which '-target-cpu <cpu>' option was selected for 'clang'.  The "[{...}]" syntax should work for this, but I haven't been able to convince TableGen to do what I want - it maybe a problem with the context I have:

	let attrList = [Attr<2, id1>, Attr<2, id2>] in { ... }

I want to be able to replace the value '2' with the value returned from a function-call.

I managed to get the opcode name issue resolved in a neat way using 'multiclass' and 'defm' controlled by a predicate, and this worked pretty well requiring a minimum amount of re-writing and giving me a good opportunity to cleanup the code, but the list construction outlined above doesn't seem to be as straight-forward. 

All the best,

	MartinO

PS:	My next bit of fun will be moving to v3.3 before v3.4 is shipped :-)

-----Original Message-----
From: Malul, Elior [mailto:elior.malul at intel.com]
Sent: 22 September 2013 08:06
To: Martin.ORiordan at movidius.com; llvmdev at cs.uiuc.edu
Subject: RE: [LLVMdev] TableGen and computed expressions

Martin hi.
I encountered a similar problem, and made a solution for it.
The solution is a tblgen enhancement, and enables tblgen code expressions to be dynamically evaluated.
It works as follows:
1. Code expressions have 'special runtime evaluation' expression (very similar to strings in ruby), e.g.:
 code c =   {[ My name is #{injected}. }.

2. I have added another command line switch for tablegen, named '--inject-value', that assigns values to records upon activation, so you could use it like so:
tblgen --inject-value=injected->Spartacus <other switches and input files>.
As a consequence, the record 'c' of 1. Will have the value:
'My name is Spartacus'.

If you find this feature helpful, I am willing to send you a patch and a small 'how to' over.
Yours, Elior.

-----Original Message-----
From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Martin O'Riordan
Sent: Monday, September 09, 2013 17:21
To: llvmdev at cs.uiuc.edu
Subject: [LLVMdev] TableGen and computed expressions

Hi LLVMDev,

I am revising an existing LLVM backend for a new variant of our CPU architecture.  I have looked at other targets, and the approach used by Hexagon seems to suit most of my needs quite well, so I am using Predicates to enable/disable instructions for the architectures.  This works very well for disabling old instructions, and enabling new instructions.

For the remaining instructions there are many which have to be revised, and these fall into three principal groups:

1.  Those that are very different
    I treat these as if they were an old instruction to be retired
    and a new instruction to be introduced.

2.  Those whose latencies have changed

3.  Those whose mnemonics have changed

For the latter two, I was wondering if there is some way of providing a computed value instead of a constant?

For example, with the latency issues, the old instruction might have a latency of 2 - expressed as the constant '2' - while the value for the revised instruction is '3'.  I would like to be able to provide this value using a function call ( e.g. 'getLatency()'), or some other externally computed value.

For the mnemonics I was wondering if it is possible to provide a fragment to 'strconcat' from a function call, or perhaps from an array with an index (e.g. 'AsmFrag[VALUE]')?

I have tried variants of '[{ code }]' but this does not seem to work for me.

I would like to avoid a wholesale replication of 100s of instruction patterns that really only differ in minute ways; are there any recommended ways of doing this type of thing with TableGen?

Thanks,

    Martin O'Riordan - Movidius Ltd.

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