[LLVMdev] Possible LiveInterval Bug

[Evan Cheng]

AFAIK std::upper_bound() would not return end(), right?

Evan

On Jan 29, 2008, at 3:08 PM, David Greene wrote:

> I just ran into a problem here.  I'm in SimpleRegisterCoalescing at  
> the point
> where EXTRACT_SUBREG coalescing updates live ranges of aliased
> registers (around line 473 of SimpleRegisterCoalescing.cpp).
>
> There's a call to MergeValueInAsValue at line 50.   
> MergeValueInAsValue has
> this code:
>
> void LiveInterval::MergeValueInAsValue(const LiveInterval &RHS,
>                                     const VNInfo *RHSValNo, VNInfo  
> *LHSValNo)
> {
>  SmallVector<VNInfo*, 4> ReplacedValNos;
>  iterator IP = begin();
>  for (const_iterator I = RHS.begin(), E = RHS.end(); I != E; ++I) {
>    if (I->valno != RHSValNo)
>      continue;
>    unsigned Start = I->start, End = I->end;
>    IP = std::upper_bound(IP, end(), Start);
>    // If the start of this range overlaps with an existing  
> liverange, trim
> it.
>    if (IP != begin() && IP[-1].end > Start) {
>      if (IP->valno != LHSValNo) {
>        ReplacedValNos.push_back(IP->valno);
>
> What happens if IP == end()?  We're pushing bogus information onto
> ReplacedvalNos (IP->valno is not valid).
>
> Is this a bug or should IP never be end() at this point?  If the  
> latter is
> true then I've got a bug somewhere else I need to hunt down.
>
>                                                   -Dave
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