[llvm-commits] [llvm] r108109 - /llvm/trunk/lib/CodeGen/MachineLICM.cpp

[Chris Lattner]

On Jul 12, 2010, at 12:57 AM, Evan Cheng wrote:

>> change machinelicm to use MachineInstr::isSafeToMove.  No
>> intended functionality change.
>> 
>> The avoidance of hoistiing implicitdef seems wrong though.
> 
> It's not. We want to avoid creating implicitdef with no trivial live intervals. The trivial ones will be converted to undef machine operands which do not take up registers. 

Why?  The register allocator treats them specially just so they don't use a register (according to Jakob).

-Chris