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

[Bill Wendling]

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...

-bw