Hi,
say I've a LLVM module with a call instruction. The called function is
"pure", that is it has no side-effects at all. How can I communicate this
to LLVM, so that the function call can be removed if the return value is
never used?
Thanks,
Volodya
There isn't a way to do this from the source code yet. However, if this is a standard library function, you can add it to the end of lib/Analysis/BasicAliasAnalysis.cpp. Search of "isspace".
-Chris
That's a bit of a hack. Can we not deduce "pure" functions
conservatively? Basically, anything that doesn't do any load or store
outside of its parameters and no malloc or free? Maybe a few other
constraints. Sounds fairly easy to deduce and might be useful for
optimization.
Reid.
That's a bit of a hack. Can we not deduce "pure" functions
conservatively?
Yes, and we do.
Basically, anything that doesn't do any load or store
outside of its parameters and no malloc or free? Maybe a few other
constraints. Sounds fairly easy to deduce and might be useful for
optimization.
We already do that, but it doesn't help for external functions (e.g. strlen).
-Chris
I see. Just another reason why *everything* should be compiled with
LLVM 
Reid.
Chris Lattner wrote:
Reid Spencer wrote: