[llvm-dev] Computing unique ID of IR instructions that can be mapped back

[Daniel Berlin via llvm-dev]

When you say the ID must survive across runs, you mean that instructions
that look the same must have the same ID?
Or that the instructions from the first run must have the same ID?

Because doing a unique positive ID is easy.
Things are always constructed in the order they appear in the file.
So using a single counter, walking every function in the module, and then
every instruction in the function, and giving each an ID, should be unique,
positive, and consistent across runs for the same file.


On Thu, May 4, 2017 at 4:47 PM, Dipanjan Das via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>
> I am writing an analysis pass on LLVM which requires to:
>
>    [1] generate unique, positive ID corresponding to each instruction
>    [2] the ID must survive across runs
>    [3] given the ID, corresponding instruction has to be mapped back
>
> For [1], the general suggestion is to use the Value* instr_ptr associated
> to each instruction. The instr_ptr points to specific instruction in
> memory, hence unique. However, it does change at every run, thus violating
> [2]. I have a hacking workaround of getting the first instruction of 'main'
> method and computing the offset. The problem is, this gives me negative
> offset for instructions lying in lower memory region than 'main'. Even if I
> circumvent the problem by adding a positive bias high enough, I have no
> clue how can I map the instr_ptr back to corresponding IR instruction. Can
> anyone suggest any elegant workaround?
>
> --
>
> Thanks & Regards,
> Dipanjan
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20170505/8c3df1eb/attachment.html>