[LLVMdev] Question About Target Dependent Optimization

[Isaac Asay]

Thanks for your response. I'm just now realizing that keeping track of
<kill> flags is harder than I thought it would be.

Regards,

Isaac


On Mon, Nov 29, 2010 at 10:47 AM, Jakob Stoklund Olesen <stoklund at 2pi.dk>wrote:

>
> On Nov 28, 2010, at 8:29 PM, Isaac Asay wrote:
> >
> > I am continuing to look over the code in the ARMLoadStoreOptimizer.cpp
> file, but I was wondering if you had a specific suggestion or a
> documentation resource that I could use to perform this instruction
> rearrangement in an LLVM idiomatic way. Using my algorithm, I already know
> where I can move MachineInstrs without effecting program correctness, but I
> don't know how I can reorder the MachineInstrs while maintaining all the
> associated live-range information.
>
> After register allocation is complete, liveness information is kept in the
> live-in lists on basic blocks, and kill flags on register operands.
>
> Simply put, a register is live from a <def> operand to a <use,kill>
> operand. It must not be used when it isn't live.
>
> The rules get tricky when sub-registers are involved.
>
> Your best bet for documentation is to read MachineVerifier.cpp and perhaps
> RegisterScavenging.cpp.
>
> If you are rearranging instructions, you must make sure that any kill flags
> are moved to the last instruction using a register.
>
> /jakob
>
>
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