[llvm-commits] [llvm] r44874 - /llvm/trunk/lib/CodeGen/MachineLICM.cpp

[Evan Cheng]

On Dec 12, 2007, at 2:02 PM, Bill Wendling wrote:

> On Dec 12, 2007 11:32 AM, Evan Cheng <evan.cheng at apple.com> wrote:
>> On Dec 12, 2007, at 11:12 AM, Bill Wendling wrote:
>>> I'm sure I could move it, but as Chris asked, isn't it trivial to  
>>> get
>>> this information anyway? Also, I'm kind of hesitant to put so much
>>> effort into compile-time performance issues when it doesn't even  
>>> have
>>> partial (let alone full) functionality right now. We don't know what
>>> impact any of those optimizations have or if they are necessary yet.
>>> :-)
>>
>> It's something to keep in mind. Not critical right now if we are not
>> hoisting anything with implicit defs / uses.
>>
> Sounds good. :-)
>
>> If we are keeping LICM before livevariables, we will have to compute
>> liveness in the BB's where the invariants are hoisted to. Now that I
>> think about it, we *cannot* use the register scavenger to do this
>> because it also depends on kill / dead markers on the operands. The
>> scavenger's job is not to add the kill / dead markers, it is to track
>> what registers are live at any point of the BB. This means you'll
>> have to walk the BB and track all physical register defs and uses in
>> the BB.
>>
> I see. Okay, so by the time I get to the point where I'm moving
> instructions that access physical registers, I should have the pass
> after LiveVariables...

Yeah, maybe. :-) We'll discuss some more.

Evan

>
> -bw
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