<html><body><div style="color:#000; background-color:#fff; font-family:arial, helvetica, sans-serif;font-size:10pt"><div>Hello,</div><div><br></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;">I am trying to simplify the CFG of a given code and eliminate the conditionals, even though I will obtain codes that are not semantically equivalent. <br></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;">For example, given a simple loop:</div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;"><br></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;">for(i=0; i<N;
i++){</div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;"> a[i] = i;</div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;"><span class="tab"> if (i%2==0)</span></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;"><span class="tab"> a[i] += 12;<br></span></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;">}</div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;"><br></div><div style="color: rgb(0, 0, 0);
font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;">I would keep only the loop, without the if statement:</div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;"><br></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;">for(i=0; i<N; i++){</div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;"> a[i] = i;</div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;">}</div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent;
font-style: normal;"><br></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;">I can eliminate such conditionals on simple codes, however, the problem arises when optimization passes such as loop-rotate embed the original loop in a conditional. In this case, I want to keep the loop, but distinguish it from other loops that were embedded in conditionals in the original source code (the latter should still be eliminated).</div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;"><br></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;">Since I found no clues on how distinguish such loops, I tried to disable loop-rotate. For this purpose, I got the list of passes
executed by O3, I eliminate loop-rotate and I call the reduced list of passes from opt: <br></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;"><br></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;">opt -targetdata -no-aa -tbaa -targetlibinfo -basicaa -preverify -domtree -verify -simplifycfg -domtree -scalarrepl -early-cse -lower-expect -targetlibinfo -targetdata -no-aa -tbaa -basicaa -globalopt -ipsccp -deadargelim -instcombine -simplifycfg -basiccg -prune-eh -inline -functionattrs -argpromotion -scalarrepl-ssa -domtree -early-cse -simplify-libcalls -lazy-value-info -jump-threading -correlated-propagation -simplifycfg -instcombine -tailcallelim -simplifycfg -reassociate -domtree -loops -loop-simplify -lcssa -loop-rotate -licm -lcssa -loop-unswitch
-instcombine -scalar-evolution -loop-simplify -lcssa -indvars -loop-idiom -loop-deletion -loop-unroll -memdep -gvn -memdep -memcpyopt -sccp -instcombine -lazy-value-info -jump-threading -correlated-propagation -domtree -memdep -dse -adce -simplifycfg -instcombine -strip-dead-prototypes -globaldce -constmerge -preverify -domtree -verify file.ll</div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color: transparent; font-style: normal;"><br></div>However, I am not successful in calling the passes in this form, as I already get an error on the first pass: <br>LLVM ERROR: Bad TargetData ctor used. Tool did not specify a TargetData to use?<br><br>Any advice on how can I either:<br>(i) disable loop rotation<br>(ii) inhibit embedding the loop in a conditional<br>(iii) distinguish rotated loops from other loops originally embedded in conditionals in the source code<br>(iv) run the list of
optimization passes by hand (specify the TargetData) ?<br><br>Any help is appreciated.<br><br>Thank you,<br>Alexandra<br><br></div></body></html>