[llvm-commits] [llvm] r122399 - in /llvm/trunk: lib/Transforms/InstCombine/InstCombine.h lib/Transforms/InstCombine/InstCombineAddSub.cpp lib/Transforms/InstCombine/InstCombineAndOrXor.cpp lib/Transforms/InstCombine/InstCombineMulDivRem.cpp lib/Transforms/InstCombine/InstructionCombining.cpp test/Transforms/InstCombine/2010-11-23-Distributed.ll

[Duncan Sands]

Hi Chris,

>> Add a generic expansion transform: A op (B op' C) ->  (A op B) op' (A op C)
>> if both A op B and A op C simplify.  This fires fairly often but doesn't
>> make that much difference.  On gcc-as-one-file it removes two "and"s and
>> turns one branch into a select.
>
> Hi Duncan,
>
> I'm a bit concerned about the compile time cost of this.  If this isn't kicking in much, is it really worth it?  Have you looked to see if this causes a compile time hit?

I checked compilation time on gcc-as-one-big-file and I didn't see any
significant difference in compile time.  If anything instcombine is faster
with this change!  That's actually possible: the new logic fires quite often
but doesn't make much difference because the existing logic caught most of the
cases already some other way.  If the new logic gets them faster/cheaper than
the old logic, for example in one step rather than after several, then that
would result in a speedup.  But as I said, the difference isn't statistically
significant.

Ciao, Duncan.