[LLVMdev] Possible LiveInterval Bug

[Evan Cheng]

On Jan 30, 2008, at 1:21 PM, David Greene wrote:

> On Wednesday 30 January 2008 15:06, Evan Cheng wrote:
>> Hrm, I see a bug here. Let's say the liverange in question is [13,20)
>> and the interval it's being merged to is something like this: [1, 4),
>> [10, 15)
>>
>>     IP = std::upper_bound(IP, end(), Start);
>>     if (IP != begin() && IP[-1].end > Start) {
>>        if (IP->valno != LHSValNo) {
>>          ReplacedValNos.push_back(IP->valno);
>>          IP->valno = LHSValNo; // Update val#.
>>        }
>>
>> IP is end() and we would be pushing junk into ReplacedValNos. Is this
>> what you saw?
>
> Yep, exactly.
>
>> I wonder if the fix should be changing the inner if to:
>> if (IP[-1].valno != LHSValNo) {
>>   ReplacedValNos.push_back(IP[-1].valno);
>>   IP[-1].valno = LHSValNo;
>> }
>
> I was thinking along the same lines.  But does this work for the  
> cases where
> IP is _not_ end()?  Is it true that we always want to look one back  
> from IP?

I think so. That's the intention and it's safe because IP != begin().

Evan

>
>
>                                             -Dave
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev