Add maybe-unused attribute to a variable.

[nickdesaulniers]

Summary

Mark a variable as maybe-unused to prevent a -Wunused-but-set-variable
warning in optimized builds where asserts are removed.Test/first commit
to check setup and understand patch submission process.

[nickdesaulniers]

oops, meant to update: https://reviews.llvm.org/D49751

[nickdesaulniers]

Alternatively, we can surround the definition and use of Listed with #ifndef NDEBUG blocks, but it would be ugly to have two of those IMO.

[nickdesaulniers]

• Prefer cast to void than variable attribute.

[dblaikie]

Looks good - thanks! (do you need me to commit this change for you?)

[nickdesaulniers]

Thanks for the review. Should be all set.

lib/IR/SafepointIRVerifier.cpp

static const Use& getEdge(const_pred_iterator &PredIt) {
     return PU.getUser()->getOperandUse(PU.getOperandNo());
   }
 
   /// Return true if there is at least one live edge that corresponds to the
   /// basic block InBB listed in the phi node.
   bool hasLiveIncomingEdge(const PHINode *PN, const BasicBlock *InBB) const {
     assert(!isDeadBlock(InBB) && "block must be live");
     const BasicBlock* BB = PN->getParent();
-    bool Listed = false;
+    [[maybe_unused]] bool Listed = false;
     for (const_pred_iterator PredIt(BB), End(BB, true); PredIt != End; ++PredIt) {
       if (InBB == *PredIt) {
         if (!isDeadEdge(&getEdge(PredIt)))
           return true;
         Listed = true;
       }
     }
     assert(Listed && "basic block is not found among incoming blocks");