[LLVMdev] [PATCH][RFC] Add llvm.codegen Intrinsic To Support Embedded LLVM IR Code Generation

[Tobias Grosser]

On 04/28/2012 01:17 PM, Yabin Hu wrote:
> Hi Tobi,
>
> 2012/4/28 Tobias Grosser <tobias at grosser.es <mailto:tobias at grosser.es>>
>
>                 Each call to the intrinsic has two arguments. One is the
>         LLVM IR
>                 string. The other is the name of the target
>         architecture. When
>                 running with tools like llc, lli, etc, this intrinsic
>         transforms
>                 the input LLVM IR string  to a new string of assembly
>         code for
>                 the target architecture firstly. Then the call to the
>         intrinsic
>                 is replaced by a pointer to the newly generated string.
>         After
>                 this, we have in our module
>
>
>             Is the Arch parameter to llvm.codegen really needed?  Since
>         codegen
>             happens when lowering the intrinsic, the target architecture
>         must be
>             known.  But if the target architecture is known, then it
>         should be
>             available in the triple for the embedded module.
>
>         Yes. It is better that the target data is set correctly in the
>         embedded
>         module. It is the user's responsibility to do this.
>
>
>     OK. Why don't we require the triple to be set and remove the arch
>     parameter again?
>
>
> I am afraid I didn't make it clear in the previous email.  And I am
> sorry that I didn't get it when you pointed out this before.

;-) I did not point it out like this. But Justin's argument seems 
correct. Requiring a triple removes the need for the 'arch' flag. And,
as requiring a triple makes sense, can and should probably take the 
chance to simplify the interface.

> There are two approaches we deal with the triple of the embedded module.
> 1. The embedded LLVM IR string contains a relatively *complete* module,
> in which the target triple is properly set. It means when a user of the
> intrinsic generates the embedded LLVM IR string, he need add not only
> the function definitions but also the target triple information. When
> the intrinsic extract the string into a module, we check whether the
> triple is empty. If it is, we return immediately or report errors. In
> this case, we needn't the arch parameter.
>
> 2. There is no triple information in the embedded LLVM IR string. We get
> it from the arch parameter.
>
> With the 1st approach, we avoid some codes about getting the arch string
> from arch llvm::Value and generate the triple from the arch string. It
> leads less changes to llvm than the 2nd approach. So maybe it is better.
> We should add some words to the document that tell the user to set the
> target triple info properly in the embedded LLVM IR string.

Yes. I think the 1st approach is a good one.

Tobi