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<p><font face="Hack Nerd Font Mono">In the case below you probably
don't need to split much.</font></p>
<p><font face="Hack Nerd Font Mono">It might be more complicated if
the two loops share edges, i.a.,</font></p>
<p><font face="Hack Nerd Font Mono"><br>
</font></p>
<p><font face="Hack Nerd Font Mono">```<br>
</font></p>
<p><font face="Hack Nerd Font Mono">for (...) {<br>
</font></p>
<p><font face="Hack Nerd Font Mono"> for (...) {<br>
</font></p>
<p><font face="Hack Nerd Font Mono"> if (...)</font></p>
<p><font face="Hack Nerd Font Mono"> return;</font></p>
<p><font face="Hack Nerd Font Mono"> }</font></p>
<p><font face="Hack Nerd Font Mono">}</font></p>
<p><font face="Hack Nerd Font Mono">```</font></p>
<p><font face="Hack Nerd Font Mono"><br>
</font></p>
<p><font face="Hack Nerd Font Mono">I guess the trick is to isolate
the inner loop properly so that extraction becomes trivial.</font></p>
<p><font face="Hack Nerd Font Mono">If you for example make sure
there is a single "entering" edge (from outside the loop to the
header),</font></p>
<p><font face="Hack Nerd Font Mono"> and a single "exiting" edge
(from the loop to a block not in the loop), outlining can be
done with</font></p>
<p><font face="Hack Nerd Font Mono">the code extractor for blocks we
already have. (Unclear about updating analyses though).</font></p>
<p><font face="Hack Nerd Font Mono"><br>
</font></p>
<p><font face="Hack Nerd Font Mono"><br>
</font></p>
<p><font face="Hack Nerd Font Mono"><br>
</font></p>
<p><font face="Hack Nerd Font Mono"></font><br>
</p>
<div class="moz-cite-prefix">On 7/1/20 5:36 PM, iulian brumar wrote:<br>
</div>
<blockquote type="cite"
cite="mid:119797216.22416.1593642987216@mail.yahoo.com">
<pre class="moz-quote-pre" wrap=""> 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 <a class="moz-txt-link-rfc2396E" href="mailto:johannesdoerfert@gmail.com"><johannesdoerfert@gmail.com></a> 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 <a class="moz-txt-link-abbreviated" href="mailto:listllvm-dev@lists.llvm.orghttps://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev">listllvm-dev@lists.llvm.orghttps://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a>
</pre>
</blockquote>
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