[LLVMdev] Question about simple constant propagation pass

[Duncan Sands]

Hi Yunming,

On 28/03/13 03:15, yunming zhang wrote:
> Hi,
>
> I just started working with llvm, I am trying to test and improve the constant
> propagation pass (-constprop),
>
> I have two main questions,
>
> 1. I wrote my own test file, which has something like
>     int a = 1
>     int b = a + 2;
>     int c = b + 3;
>     print c
>
>      However, non of the instruction was killed according to -stat. I think it
> might due to the fact the llvm instructions generated was a bit convoluted, but
> overall, I am not sure why this simple test case has no instruction killed?
> Shouldn't c be just 6 and show at least two instructions killed?

optimization passes usually assume you have run at least -mem2reg (or -sroa)
first and won't do much if you haven't.

Ciao, Duncan.

>
> 2. The description states that this pass is very simple. Can anyone point me to
> a few directions that might be interesting to improve it? I am not sure about
> why is it labeled "simple" ?
>
> Thanks
>
> Yunming
>
>
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