assembly data flow graph

[Trass3r]

I just discovered the llvm-mca integration, that's awesome!
With the -timeline option you do get an idea of the instruction dependency chains:
https://godbolt.org/z/-cMrJI

But it would be nicer if there was a graph like the following, just on an MCInst level:
https://github.com/k3ut0i/llvm-dataflow-graphs

[mattgodbolt]

Agreed: I'd ideally love to parse llvm-mca output, or better still have it output parseable JSON of what happened. Then I can use any number of graph library layouts to try and show the information.

We already have CFG: https://godbolt.org/z/dFqf4H

[Trass3r]

Yeah though the current CFG code is quite ad-hoc, parsing the assembly manually.
It should ideally be implemented inside of llvm along the lines of opt -dot-cfg or in a tool based on the llvm API like https://github.com/pfalcon/graph-llvm-ir or the one mentioned above. There is also a node-llvm binding.

Edit: I quickly hacked dot file emission into mca for a simple execution order visualization:

L1:
    movapd xmm1, [esi+eax]
    mulpd  xmm1, xmm2     
    movapd xmm0, [edi+eax]
    subpd  xmm0, xmm1     
    movapd [edi+eax], xmm0
    add eax, 16           
    cmp eax, ecx
    jz L1

[OfekShilon]

Please note that

opt -passes="view-cfg" -cfg-func-name=<func> <ll filename> -disable-output

produces better graphs - colors encoding regions. Maybe useful.

[jeremy-rifkin]

@OfekShilon Is there an equivalent of this for data flow? It looks like opt is generating a control flow graph here

[OfekShilon]

@OfekShilon Is there an equivalent of this for data flow? It looks like opt is generating a control flow graph here

No ,sorry. I was lead hear by a link from the suggestion regarding cfg + data-dep, and saw that the start of the discussion touched on cfg so thought I'd comment here.

Please note that IR cfg (as the opt passes dot-cfg or view-cfg emit) is not strictly equivalent to assembly cfg (which is already available). Personally I think both are useful.