llvm dev - Aug 2013 - [LLVMdev] How to disbale loop-rotate in opt -O3 ?

Hello,

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.

For example, given a simple loop:

for(i=0; i<N; i++){
   a[i] = i;
    if (i%2==0)
      a[i] += 12;

}

I would keep only the loop, without the if statement:

for(i=0; i<N; i++){
   a[i] = i;
}

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).

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:


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
However, I am not successful in calling the passes in this form, as I already
get an error on the first pass:
LLVM ERROR: Bad TargetData ctor used.  Tool did not specify a TargetData to use?

Any advice on how can I either:
(i) disable loop rotation
(ii) inhibit embedding the loop in a conditional
(iii) distinguish rotated loops from other loops originally embedded in
conditionals in the source code
(iv) run the list of optimization passes by hand (specify the TargetData)   ?

Any help is appreciated.

Thank you,
Alexandra
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> However, I am not successful in calling the passes in this form, as I
already get an error on the first pass:
Just remove -targetdata from the list of options, and it should work:

$ opt -no-aa -tbaa -targetlibinfo -basicaa -preverify -domtree -verify
-simplifycfg -domtree -scalarrepl -early-cse -lower-expect
-targetlibinfo -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 -S -o -