[PATCH] Generic support for sub/super registers in AsmPrinter::EmitDwarfRegOp()

[Adrian Prantl]

Hi Eric,

Here is some additional context to help with the review. I posted three patches in the last 2 weeks that all use some form of DW_OP_piece to deal with partial variables and/or subregisters:

1) A small variable is in a subregister (e.g.: eax on x86_64) that is not representable in DWARF.
   Can represent this using a DW_OP_piece of a representable superregister (e.g.: rax) in DWARF.
   Committed in r201190 ( http://llvm.org/viewvc/llvm-project?rev=201190&view=rev )

2) A larger variable is in a superregister (e.g.: Q0 on ARM) that is not representable in DWARF.
   Can represent this using multiple DW_OP_pieces stored in representable subregisters (e.g.: D0+D1) in DWARF.
   This is the patch attached to this thread.

3) A large (aggregate) variable is split up across multiple unrelated registers, e.g, during SROA.
   Can represent this using multiple DW_OP_pieces in DWARF.
   Ready for review over here: http://llvm-reviews.chandlerc.com/D2680.

The confusing part IMO is that the same operation DW_OP_piece is used to mean both a piece of a large variable in a small register _and_ a small variable occupying part of a large register. (Side-note: yes, these situations can happen simultaneously, this is where DW_OP_shr comes in).

-- adrian

On Feb 14, 2014, at 19:54, Adrian Prantl <aprantl at apple.com> wrote:

> Earlier this week (r201190) I added generic support for super-registers in AsmPrinter::EmitDwarfRegOp(). This patch does the opposite, by substituting multiple sub-registers for super-registers without valid DWARF numbers. The result is general enough that we can get rid of ARMAsmPrinter::EmitDwarfRegOp().
> 
> While I think this patch is rather uncontroversial; it is removing code, so I’m posting this for review first.
> 
> thanks,
> adrian
> 
> PS: these two patches also from the basis for the updated revision of http://llvm-reviews.chandlerc.com/D2680 I just uploaded.
> <0001-Debug-info-Refactor-AsmPrinter-EmitDwarfRegOp-to-mak.patch><0002-Debug-info-Remove-ARMAsmPrinter-EmitDwarfRegOp-.-Asm.patch>_______________________________________________
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