[llvm-commits] [llvm] r85346 - in /llvm/trunk: include/llvm/CodeGen/Passes.h lib/CodeGen/BranchFolding.cpp lib/CodeGen/BranchFolding.h lib/CodeGen/IfConversion.cpp lib/CodeGen/LLVMTargetMachine.cpp lib/Target/ARM/ARMTargetMachine.cpp

[Chris Lattner]

On Oct 28, 2009, at 11:18 AM, Evan Cheng wrote:
>
> This is tricky. I don't think there is a *right* answer. On x86, I  
> don't believe the extra branch matters. To me, tail merge for 1  
> instruction tails is not saving much code size and it's potentially  
> bad for performance. We should disable it except for -Os.
>
> I don't know if we want to differentiate between -O2 and -O3 here.  
> We either do tail merging or we disable tail merging. Unless we can  
> show it does hurt performance I'd prefer to leave it along.

I agree with Evan: the only case that should change is tail merge of 1  
instruction, which should be enabled at -Os only, and only when it  
actually reduces # instructions.  O2 and O3 should have the same  
policy IMO.

-Chris