[llvm-dev] Inner Loop extraction in LLVM (original) (raw)

iulian brumar via llvm-dev llvm-dev at lists.llvm.org
Wed Jul 1 15:36:27 PDT 2020

Hi Johannes,

This is very helpful and thank you for the quick response.

I imagine that the usual nested loop structure is something like:

loop1_header_bb bbs_between_loop1_header_and_loop2_header loop2_header_bb loop_body_bbs br loop2_header_bb instructions_before_loop1_end_and_after_loop2_end br loop1_header_bb

In this case you mean that loop2_header_bb might need to be split before extracting loop 2 into its own function? I'm not sure yet about how to use bb splitting to enable inner-loop extraction and what splitting edges means.

Sincerely, Iulian On Wednesday, July 1, 2020, 06:06:01 PM EDT, Johannes Doerfert <johannesdoerfert at gmail.com> wrote:

Hi Iulian,

On first thought I would think that extracting top-level loops is only minimally easier than extracting any other loop level,

if you consider arbitrary input, e.g,. potential irreducible "outer-outer-most" loops. For inner ones you might want to split

some blocks and edges to make sure they are not shared with the outer loop but other than that, I imagine it to be pretty similar.

(This assumes you do not want to preserve things like LoopInfo, ScalarEvolution, ...).

Extracting a single basic block is probably easier still. Again, assuming you do not want to update analyses.

If you want more details or think I haven't grasped the essence of your questions, feel free to say so :)

~ Johannes

On 7/1/20 4:23 PM, iulian brumar via llvm-dev wrote:

Hello everyone,Quick question about loop extraction in llvm. I've been using the LoopExtractor pass in llvm/lib/Transforms/IPO/LoopExtractor.cpp to extract top level loops from programs.I'm wondering if extracting inner-most loops is any more complex than using the BlockExtractor pass in llvm/lib/Transforms/IPO/BlockExtractor.cpp and making sure that the basic blocks in the extracted region are single entry-single exit. Would there be any fundamental differences wrt what LoopExtractor is doing for top-level loops?Thanks,Iulian_______________________________________________LLVM Developers mailing listllvm-dev at lists.llvm.orghttps://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

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