[BPI] Push exit block rather than exiting ones in getSccExitBlocks

[bin.cheng]

Summary

Hi,
See comment before BranchProbabilityInfo::SccInfo::getSccExitBlocks:
" /// Fills in \p Exits vector with all such blocks that don't belong to

/// SCC with \p SccNum ID but there is an edge from a block belonging to the
/// SCC."

Also see the comment/implementation of related function BranchProbabilityInfo::getLoopExitBlocks,
I believe the current implement has typo pushing copies of exiting block into result vector. This simple
patch fixes the typo by pushing exit blocks.

I spot this when going through the code, unfortunately I didn't come up with any test for this.
I tried to instrument the function if it's triggered, though the function is only called in one
function from spec2k17int, it's not really triggered because push_back operation is never executed.

Any comments?

Thanks,
bin

[ebrevnov]

LGTM.
PS: I think it should be possible to create targeted test case by hands though.

llvm/lib/Analysis/BranchProbabilityInfo.cpp

 
 void BranchProbabilityInfo::SccInfo::getSccExitBlocks(
     int SccNum, SmallVectorImpl<BasicBlock *> &Exits) const {
   for (auto MapIt : SccBlocks[SccNum]) {
     const auto *BB = MapIt.first;
     if (isSCCExitingBlock(BB, SccNum))
       for (const auto *Succ : successors(BB))
         if (getSCCNum(Succ) != SccNum)
-          Exits.push_back(const_cast<BasicBlock *>(BB));
+          Exits.push_back(const_cast<BasicBlock *>(Succ));
   }
 }
 
 uint32_t BranchProbabilityInfo::SccInfo::getSccBlockType(const BasicBlock *BB,
                                                          int SccNum) const {
   assert(getSCCNum(BB) == SccNum);
 
   assert(SccBlocks.size() > static_cast<unsigned>(SccNum) && "Unknown SCC");