llvm dev - Nov 2011 - [LLVMdev] opt -O2 optimization passes

Hi all,

I would like to know which optimization passes are performed at -O2 by opt.
So I used following command:

llvm-as < /dev/null | opt -O2 -std-compile-opts -disable-output
-debug-pass=Arguments

I've got following output for LLVM opt 2.9:

Pass Arguments:  -no-aa -tbaa -basicaa -simplifycfg -domtree -scalarrepl
-early-cse
Pass Arguments:  -targetlibinfo -no-aa -tbaa -basicaa -preverify -domtree
-verify -lowersetjmp -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 -iv-users -indvars -loop-idiom
-loop-deletion -loop-unroll -instcombine -memdep -gvn -memdep -memcpyopt
-sccp -instcombine -lazy-value-info -jump-threading -correlated-propagation
-domtree -memdep -dse -adce -simplifycfg -strip-dead-prototypes
-print-used-types -deadtypeelim -globaldce -constmerge -globalopt -ipsccp
-deadargelim -instcombine -simplifycfg -basiccg -prune-eh -inline
-functionattrs -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 -iv-users -indvars -loop-idiom
-loop-deletion -loop-unroll -instcombine -memdep -gvn -memdep -memcpyopt
-sccp -instcombine -lazy-value-info -jump-threading -correlated-propagation
-domtree -memdep -dse -adce -simplifycfg -strip-dead-prototypes
-print-used-types -deadtypeelim -constmerge -preverify -domtree -verify

Why is there two lines stating with 'Pass Argument:' ?

To reproduce opt-O2 behavior should I copy options from the two lines or
only second one ?
Thanks for your answers
Best Regards
Seb
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Hi Seb,
> I would like to know which optimization passes are performed at -O2 by opt.
So I
> used following command:
>
> llvm-as < /dev/null | opt -O2 -std-compile-opts -disable-output
> -debug-pass=Arguments
first off, if you pass -O2 there is no need for -std-compile-opts and vice
versa.
>
> I've got following output for LLVM opt 2.9:
>
> Pass Arguments:  -no-aa -tbaa -basicaa -simplifycfg -domtree -scalarrepl
-early-cse
> Pass Arguments:  -targetlibinfo -no-aa -tbaa -basicaa -preverify -domtree
...
>
> Why is there two lines stating with 'Pass Argument:' ?
This is coming from -O2.  When a front-end outputs a function, it immediately
runs the per-function passes in the first line on it.  This tends to shrink
functions a lot, reducing memory usage.  When all of the functions have been
output all of the other passes are run.
>
> To reproduce opt-O2 behavior should I copy options from the two lines or
only
> second one ?
Both of them.  To be most accurate, you can do the following:

   opt bitcode.bc pass-list-from-first-line | opt pass-list-from-second line

Ciao, Duncan.
> Thanks for your answers
> Best Regards
> Seb
>
>
>
>
>
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