[llvm-dev] Inner Loop extraction in LLVM

[iulian brumar via llvm-dev]

 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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