llvm dev - Nov 2014 - [LLVMdev] LLVM IR to ISA

Hello,

After instruction selection I would like to print out the selected 
instructions with the corresponding LLVM instructions. Something like this:

LLVM Instruction -> { MCInst,
                                    MCInst,
                                    MCInst,
                                    MCInst
                                 }

Is there a build-in way to do it?

Thank you

On 3 Nov 2014, at 08:54, Konstantinos Parasyris <koparasy at gmail.com>
wrote:
> Hello,
> 
> After instruction selection I would like to print out the selected
instructions with the corresponding LLVM instructions. Something like this:
> 
> LLVM Instruction -> { MCInst,
>                                   MCInst,
>                                   MCInst,
>                                   MCInst
>                                }
> 
> Is there a build-in way to do it?
Instruction selection happens on a basic block basis.  You can dump the IR basic
block and the machine basic block relatively easily, but N IR instructions may
correspond to M machine instructions.  There's no simple mapping from one IR
instruction to multiple native instructions.  For example, consider a GEP
followed by a load.  On x86 or ARM, this will typically be folded into a single
instruction.  Similarly, a ptrtoint, followed by a sequence of arithmetic,
followed by an inttoptr, followed by a load or store may become a single
instruction.  The various SelectionDAG phases will split and combine
instructions in various ways.

David