[JumpThreading] Use emplace_back instead of push_back (NFC)

[kazu]

Summary

This patch replaces push_back with emplace_back where appropriate.

llvm/lib/Transforms/Scalar/JumpThreading.cpp

bool JumpThreadingPass::ComputeValueKnownInPredecessorsImpl(
   // prevent this, keep track of what (value, block) pairs we've already visited
   // and terminate the search if we loop back to them
   if (!RecursionSet.insert(V).second)
     return false;
 
   // If V is a constant, then it is known in all predecessors.
   if (Constant *KC = getKnownConstant(V, Preference)) {
     for (BasicBlock *Pred : predecessors(BB))
-      Result.push_back(std::make_pair(KC, Pred));
+      Result.emplace_back(KC, Pred);
 
     return !Result.empty();
   }
 
   // If V is a non-instruction value, or an instruction in a different block,
   // then it can't be derived from a PHI.
   Instruction *I = dyn_cast<Instruction>(V);
   if (!I || I->getParent() != BB) {
if (!I || I->getParent() != BB) {
     // able to handle value inequalities better, for example if the compare is
     // "X < 4" and "X < 3" is known true but "X < 4" itself is not available.
     // Perhaps getConstantOnEdge should be smart enough to do this?
     for (BasicBlock *P : predecessors(BB)) {
       // If the value is known by LazyValueInfo to be a constant in a
       // predecessor, use that information to try to thread this block.
       Constant *PredCst = LVI->getConstantOnEdge(V, P, BB, CxtI);
       if (Constant *KC = getKnownConstant(PredCst, Preference))
-        Result.push_back(std::make_pair(KC, P));
+        Result.emplace_back(KC, P);
     }
 
     return !Result.empty();
   }
 
   /// If I is a PHI node, then we know the incoming values for any constants.
   if (PHINode *PN = dyn_cast<PHINode>(I)) {
     for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
       Value *InVal = PN->getIncomingValue(i);
       if (Constant *KC = getKnownConstant(InVal, Preference)) {
-        Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i)));
+        Result.emplace_back(KC, PN->getIncomingBlock(i));
       } else {
         Constant *CI = LVI->getConstantOnEdge(InVal,
                                               PN->getIncomingBlock(i),
                                               BB, CxtI);
         if (Constant *KC = getKnownConstant(CI, Preference))
-          Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i)));
+          Result.emplace_back(KC, PN->getIncomingBlock(i));
       }
     }
 
     return !Result.empty();
   }
 
   // Handle Cast instructions.  Only see through Cast when the source operand is
   // PHI or Cmp to save the compilation time.
if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1))) {
                                           WantInteger, RecursionSet, CxtI);
 
       // Try to use constant folding to simplify the binary operator.
       for (const auto &LHSVal : LHSVals) {
         Constant *V = LHSVal.first;
         Constant *Folded = ConstantExpr::get(BO->getOpcode(), V, CI);
 
         if (Constant *KC = getKnownConstant(Folded, WantInteger))
-          Result.push_back(std::make_pair(KC, LHSVal.second));
+          Result.emplace_back(KC, LHSVal.second);
       }
     }
 
     return !Result.empty();
   }
 
   // Handle compare with phi operand, where the PHI is defined in this block.
   if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
if (PN && PN->getParent() == BB) {
                                            cast<Constant>(RHS), PredBB, BB,
                                            CxtI ? CxtI : Cmp);
           if (ResT == LazyValueInfo::Unknown)
             continue;
           Res = ConstantInt::get(Type::getInt1Ty(LHS->getContext()), ResT);
         }
 
         if (Constant *KC = getKnownConstant(Res, WantInteger))
-          Result.push_back(std::make_pair(KC, PredBB));
+          Result.emplace_back(KC, PredBB);
       }
 
       return !Result.empty();
     }
 
     // If comparing a live-in value against a constant, see if we know the
     // live-in value on any predecessors.
     if (isa<Constant>(CmpRHS) && !CmpType->isVectorTy()) {
       Constant *CmpConst = cast<Constant>(CmpRHS);
 
       if (!isa<Instruction>(CmpLHS) ||
           cast<Instruction>(CmpLHS)->getParent() != BB) {
         for (BasicBlock *P : predecessors(BB)) {
           // If the value is known by LazyValueInfo to be a constant in a
           // predecessor, use that information to try to thread this block.
           LazyValueInfo::Tristate Res =
             LVI->getPredicateOnEdge(Pred, CmpLHS,
                                     CmpConst, P, BB, CxtI ? CxtI : Cmp);
           if (Res == LazyValueInfo::Unknown)
             continue;
 
           Constant *ResC = ConstantInt::get(CmpType, Res);
-          Result.push_back(std::make_pair(ResC, P));
+          Result.emplace_back(ResC, P);
         }
 
         return !Result.empty();
       }
 
       // InstCombine can fold some forms of constant range checks into
       // (icmp (add (x, C1)), C2). See if we have we have such a thing with
       // x as a live-in.
if (isa<Constant>(CmpRHS) && !CmpType->isVectorTy()) {
               Constant *ResC;
               if (CmpRange.contains(CR))
                 ResC = ConstantInt::getTrue(CmpType);
               else if (CmpRange.inverse().contains(CR))
                 ResC = ConstantInt::getFalse(CmpType);
               else
                 continue;
 
-              Result.push_back(std::make_pair(ResC, P));
+              Result.emplace_back(ResC, P);
             }
 
             return !Result.empty();
           }
         }
       }
 
       // Try to find a constant value for the LHS of a comparison,
       // and evaluate it statically if we can.
       PredValueInfoTy LHSVals;
       ComputeValueKnownInPredecessorsImpl(I->getOperand(0), BB, LHSVals,
                                           WantInteger, RecursionSet, CxtI);
 
       for (const auto &LHSVal : LHSVals) {
         Constant *V = LHSVal.first;
         Constant *Folded = ConstantExpr::getCompare(Pred, V, CmpConst);
         if (Constant *KC = getKnownConstant(Folded, WantInteger))
-          Result.push_back(std::make_pair(KC, LHSVal.second));
+          Result.emplace_back(KC, LHSVal.second);
       }
 
       return !Result.empty();
     }
   }
 
   if (SelectInst *SI = dyn_cast<SelectInst>(I)) {
     // Handle select instructions where at least one operand is a known constant
if ((TrueVal || FalseVal) &&
           // Either operand will do, so be sure to pick the one that's a known
           // constant.
           // FIXME: Do this more cleverly if both values are known constants?
           KnownCond = (TrueVal != nullptr);
         }
 
         // See if the select has a known constant value for this predecessor.
         if (Constant *Val = KnownCond ? TrueVal : FalseVal)
-          Result.push_back(std::make_pair(Val, C.second));
+          Result.emplace_back(Val, C.second);
       }
 
       return !Result.empty();
     }
   }
 
   // If all else fails, see if LVI can figure out a constant value for us.
   Constant *CI = LVI->getConstant(V, BB, CxtI);
   if (Constant *KC = getKnownConstant(CI, Preference)) {
     for (BasicBlock *Pred : predecessors(BB))
-      Result.push_back(std::make_pair(KC, Pred));
+      Result.emplace_back(KC, Pred);
   }
 
   return !Result.empty();
 }
 
 /// GetBestDestForBranchOnUndef - If we determine that the specified block ends
 /// in an undefined jump, decide which block is best to revector to.
 ///
if (!PredAvailable) {
       continue;
     }
 
     if (IsLoadCSE)
       CSELoads.push_back(cast<LoadInst>(PredAvailable));
 
     // If so, this load is partially redundant.  Remember this info so that we
     // can create a PHI node.
-    AvailablePreds.push_back(std::make_pair(PredBB, PredAvailable));
+    AvailablePreds.emplace_back(PredBB, PredAvailable);
   }
 
   // If the loaded value isn't available in any predecessor, it isn't partially
   // redundant.
   if (AvailablePreds.empty()) return false;
 
   // Okay, the loaded value is available in at least one (and maybe all!)
   // predecessors.  If the value is unavailable in more than one unique
LoadInst *NewVal = new LoadInst(
         LoadI->getType(), LoadedPtr->DoPHITranslation(LoadBB, UnavailablePred),
         LoadI->getName() + ".pr", false, LoadI->getAlign(),
         LoadI->getOrdering(), LoadI->getSyncScopeID(),
         UnavailablePred->getTerminator());
     NewVal->setDebugLoc(LoadI->getDebugLoc());
     if (AATags)
       NewVal->setAAMetadata(AATags);
 
-    AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal));
+    AvailablePreds.emplace_back(UnavailablePred, NewVal);
   }
 
   // Now we know that each predecessor of this block has a value in
   // AvailablePreds, sort them for efficient access as we're walking the preds.
   array_pod_sort(AvailablePreds.begin(), AvailablePreds.end());
 
   // Create a PHI node at the start of the block for the PRE'd load value.
   pred_iterator PB = pred_begin(LoadBB), PE = pred_end(LoadBB);
for (const auto &PredValue : PredValues) {
     }
 
     // If the predecessor ends with an indirect goto, we can't change its
     // destination. Same for CallBr.
     if (isa<IndirectBrInst>(Pred->getTerminator()) ||
         isa<CallBrInst>(Pred->getTerminator()))
       continue;
 
-    PredToDestList.push_back(std::make_pair(Pred, DestBB));
+    PredToDestList.emplace_back(Pred, DestBB);
   }
 
   // If all edges were unthreadable, we fail.
   if (PredToDestList.empty())
     return false;
 
   // If all the predecessors go to a single known successor, we want to fold,
   // not thread. By doing so, we do not need to duplicate the current block and