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RE: branch probabilities on multiway branches
The other case I'm working on is to selectively apply tailcall
optimization when optimizing for size. Clearly tail call optimiztion
is desirable along frequently executed edges. Otherwise we found
tailcall optimization generates a sicall_epilogue for each tailcall
which has a significant impact on size. This is true if the generated
epilogue is large. I have a patch which prunes tail calls along edges
which are determined to be infrequently executed from profile
information. When no profile information is available we are reduced
to using a heuristic whether the optimization will increase code size.
However it would be useful to also use estimated branch probabilities
The cases I'm looking at use switch cases heavily where branch
probability information is reduced to even probabilities across all
cases.
We're keen on improving the estimated branch probabilities in switch
cases because we cannot always gather profile information on all code
paths through a program.
Cheers,
Rahul