[LLVMdev] [llvm-commits] [PATCH][RFC] Add extra arguments to TargetLowering::LowerCall() so targets have more context in which to construct call chains

[Evan Cheng]

On Apr 19, 2012, at 11:15 AM, Justin Holewinski wrote:

>  
> From: Evan Cheng [mailto:evan.cheng at apple.com] 
> Sent: Thursday, April 19, 2012 10:47 AM
> To: Justin Holewinski
> Cc: llvmdev at cs.uiuc.edu; llvm-commits at cs.uiuc.edu; Vinod Grover
> Subject: Re: [llvm-commits] [PATCH][RFC] Add extra arguments to TargetLowering::LowerCall() so targets have more context in which to construct call chains
>  
> TargetLowering::LowerCall is already a mess, I would really prefer not to extend it any further. It's especially difficult to justify extending it without a use in the open source tree.
>  
> We really should think hard about how to improve the API in two ways. Perhaps we should wrap the arguments in some struct rather than as individual ones. We should also make it easier to extend it in the future without requiring an across the change for all in-tree and out-of-tree targets. Anyone wants to take the lead on this?
>  
> The second may be solved by the first.  If the LowerCall() arguments are encapsulated within some descriptor object, then extensions to this descriptor class would be transparent to existing targets, both in-tree and out-of-tree (assuming the API is consistent).  What is the overall plan for LowerCall() and LowerCallTo()?  I noticed the comment on LowerCallTo() that implies it should be merged into SelectionDAGISel when all targets are using LowerCall (which I believe they are)?

I believe Dan has some thoughts in this topic.

Evan

>  
> Evan
>  
> On Apr 19, 2012, at 8:07 AM, Justin Holewinski <jholewinski at nvidia.com> wrote:
> 
> 
> All,
>  
> The attached patch adds two extra arguments to TargetLowering::LowerCall: RetTy and Args.  These arguments are used in TargetLowering::LowerCallTo() to construct the Ins and OutVals parameters, but are not available to the target via LowerCall().  Some targets require this additional information, and the LowerCallTo() method is not virtual in TargetLowering.   Instead of making that method virtual, this patch adds the extra arguments so targets needing this information do not need to replace LowerCallTo() which would lead to a lot of code duplication.  While this does change the API for targets, existing targets can just safely ignore these parameters.  This patch updates the LowerCall() prototypes for all in-tree targets.
>  
> We would like to get the community’s feedback on this so as to make sure this patch is as universally applicable as possible.  While not currently used in the open-source tree, this patch lays some groundwork for submission of the NVIDIA NVPTX back-end into the open-source tree.
>  
>  
> Thanks,
>  
> Justin Holewinski
>  
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