[LLVMbugs] Reassociation Transform

Casey Carter ccarter at cs.uiuc.edu
Thu Oct 31 10:21:57 PST 2002

Chris Lattner wrote:

>>For each of these bytecodes, I collected stats for -reassociate, -licm,
>>and -reassociate -licm (attached). Reassociation was always followed by
>>-constprop -instcombine (this reduces the inflation of LICM statistics
>>due to the negation instructions from reassociation). There were no
>>fatalaties in either the original bytecodes or any of the transformed
>Sounds great!  I'll go ahead and install the patch.  Note that gcse is
>also helped by reassociation: -reassociate -instcombine -licm -gcse is a
>good combination (not that I expect you to regen the results!  :)
Its only a one-line change in the Makefile that generates the results, 
so I will redo them. (attached)

>>The results read like an advertisement for reassociation.  For
>>example, 254.gap.bc has no LICM without reassociation, and 486 hoisted
>>instructions with reassociation.
>Sounds great!  You should forward your results to the llvmbugs list so
>they can be archived.  They are really good, especially considering these
>bytecode files are already optimized.  I'll go ahead and reenable
>reassociation in gccas also.
254.gap.bc looks good for gcse as well: reassociation exposes 163 gcs's 
to e.

Casey Carter
Casey at Carter.net
ccarter at uiuc.edu
AIM: cartec69

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