[LLVMdev] Question about simple constant propagation pass

[yunming zhang]

Thanks a lot Duncan!!

It worked like magic,

Yunming


On Thu, Mar 28, 2013 at 7:11 AM, Duncan Sands <baldrick at free.fr> wrote:

> 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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>>
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