<html><body><p><font size="2">---------------------------</font><br><font size="2">Wed, July 3rd, 2019:</font><br><font size="2">---------------------------</font><br><font size="2">- Status Updates</font><br><br><font size="2"> - Directed Graph (</font><a href="https://reviews.llvm.org/D64088"><font size="2">https://reviews.llvm.org/D64088</font></a><font size="2">) (Bardia)</font><br><font size="2"> - Patch posted for review on Tuesday July 2nd. Awaiting comments.</font><br><br><font size="2"> - Loop Cache Cost Analysis (</font><a href="https://reviews.llvm.org/D63459"><font size="2">https://reviews.llvm.org/D63459</font></a><font size="2">) (Ettore)</font><br><font size="2"> - Addressed all review comments, awaiting further comments or approval.</font><br><br><font size="2"> - Survey of Loop Canonical Form expected by various passes (Min-Yih Hsu)</font><br><font size="2"> - Detailed information can be found here: </font><a href="https://tinyurl.com/y3s7trrx"><font size="2">https://tinyurl.com/y3s7trrx</font></a><br><br><font size="2"> - Survey of Loop related bugs in Bugzilla (Vivek)</font><br><font size="2"> - About 180 bugs were found many of which are quite old (open since 2015).</font><br><font size="2"> - A few were already fixed so they were closed by Vivek.</font><br><font size="2"> - Some bugs are reproducible many of which are compiler crashes. The tracebacks for these </font><br><font size="2"> crashes seem to be all unique.</font><br><br><font size="2">------------------------------</font><br><font size="2">Decisions and To Do's:</font><br><font size="2">------------------------------</font><br><br><font size="2">1. LCSSA form is fairly easy to maintain and is required to be preserved by loop passes in the </font><br><font size="2"> New Pass Manager, so it could be considered as part of loop canonical form.</font><br><br><font size="2">2. Look further into the possibility of having Loop Rotate as part of canonical form.</font><br><font size="2"> 2a. Look into whether existing passes are able to perform their transformations if loops are in </font><br><font size="2"> rotated form (Min-Yih)</font><br><font size="2"> 2b. There are concerns over code size increase if loop rotation becomes part of the canonical </font><br><font size="2"> form. One way to address this concern is to have a pass that reverses the effect of loop </font><br><font size="2"> rotation (ie "unrotate" loops). "Unrotating" loops require us to be able to identify loop guards</font><br><font size="2"> and match them with the loop latch branch condition. Look into enhancing loop guard </font><br><font size="2"> detection. (Whitney)</font><br><font size="2"> 2c. Come up with a test case that shows the code size increase as a result of loop rotation. </font><br><font size="2"> The test case can help evaluate the impact of loop "unrotation" pass. (Volunteer needed!)</font><br><br><font size="2">3. Look for patterns in the loop-related bugs in bugzilla, so we can identify weak areas and see </font><br><font size="2"> what can be done about them. (Vivek)</font><br><br><font size="2">4. Postpone discussion on DDG and delinearization to the next meeting. Share a link to the DDG </font><br><font size="2"> presentation. (Bardia)</font><br><br><br><font size="2">--------------------------------------</font><br><font size="2">Tentative Agenda (July 17th):</font><br><font size="2">--------------------------------------</font><br><br><font size="2"> - Data Dependence Graph Presentation (Bardia)</font><br><font size="2"> - Delinearization (Gary Elsesser)</font><br><font size="2"> - Loop vs Function pass (Jamie Schmeiser)</font><br><font size="2"> - Status Updates</font><br><font size="2"> - Directed Graph (</font><a href="https://reviews.llvm.org/D64088"><font size="2">https://reviews.llvm.org/D64088</font></a><font size="2">) (Bardia)</font><br><font size="2"> - Loop Cache Cost Analysis (</font><a href="https://reviews.llvm.org/D63459"><font size="2">https://reviews.llvm.org/D63459</font></a><font size="2">) (Ettore)</font><br><font size="2"> - Impact of Loop Rotation on existing passes (Min-Yih)</font><br><font size="2"> - Bugzilla bugs update (Vivek)</font><br><br><br><font size="2">Bardia Mahjour<br>Compiler Optimizations<br>IBM Toronto Software Lab<br>bmahjour@ca.ibm.com (905) 413-2336</font><BR>
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