llvm dev - May 2016 - Missing kill flag on Machine Instruction operands

Hi all,

I'm writing a MachineFunction pass that relies on the kill flag to be
appropriately set on operands of Machine Instructions, but it isn't. My
pass runs before register allocation. What I'm seeing when I print an
instruction is something like:

%vreg218<def> = FOO %vreg217, %vreg369

but what I need is:

%vreg218<def> = FOO %vreg217<kill>, %vreg369<kill>

On this same instruction, the kill flag is being set on vreg217 and vreg369
in preceding and succeeding passes, but not in my pass. Is there some
analysis pass that I need to add as required in my pass's
"getAnalysisUsage" to get this flag to be set?

Thanks,
Stephen
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Hi Stephen,

The kill flags are conservatively correct and not mandatory; if they are set,
they are correct, if they are not, you cannot say anything.
> On May 9, 2016, at 8:37 AM, Stephen Rogers via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hi all,
> 
> I'm writing a MachineFunction pass that relies on the kill flag to be
appropriately set on operands of Machine Instructions, but it isn't. My pass
runs before register allocation. What I'm seeing when I print an instruction
is something like:
> 
> %vreg218<def> = FOO %vreg217, %vreg369
> 
> but what I need is:
> 
> %vreg218<def> = FOO %vreg217<kill>, %vreg369<kill>
> 
> On this same instruction, the kill flag is being set on vreg217 and vreg369
in preceding and succeeding passes, but not in my pass. Is there some analysis
pass that I need to add as required in my pass's
"getAnalysisUsage" to get this flag to be set?
I would recommend to rely on the LiveInterval analysis.

Cheers,
-Quentin
> 
> Thanks,
> Stephen
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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Hi Quentin,

That's unfortunate to hear. I'll take a look into using the LiveInterval
analysis for this.

Thanks for the advice,
Stephen

On 9 May 2016 at 17:05, Quentin Colombet <qcolombet at apple.com> wrote:
> Hi Stephen,
>
> The kill flags are conservatively correct and not mandatory; if they are
> set, they are correct, if they are not, you cannot say anything.
>
> On May 9, 2016, at 8:37 AM, Stephen Rogers via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> Hi all,
>
> I'm writing a MachineFunction pass that relies on the kill flag to be
> appropriately set on operands of Machine Instructions, but it isn't. My
> pass runs before register allocation. What I'm seeing when I print an
> instruction is something like:
>
> %vreg218<def> = FOO %vreg217, %vreg369
>
> but what I need is:
>
> %vreg218<def> = FOO %vreg217<kill>, %vreg369<kill>
>
> On this same instruction, the kill flag is being set on vreg217 and
> vreg369 in preceding and succeeding passes, but not in my pass. Is there
> some analysis pass that I need to add as required in my pass's
> "getAnalysisUsage" to get this flag to be set?
>
>
> I would recommend to rely on the LiveInterval analysis.
>
> Cheers,
> -Quentin
>
>
> Thanks,
> Stephen
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
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