[Instruction] add moveAfter() convenience function; NFCI

[spatel]

Summary

As suggested in D37121, here's a wrapper for removeFromParent() + insertAfter().

[• dberlin]

lib/IR/Instruction.cpp

101

I believe you can just use moveBefore(*MovePos->getParent(), ++MovePos->getIterator());

(Which should be a bit more efficient, and also will match the moveBefore code)

[spatel]

Patch updated:
Implement moveAfter with moveBefore for symmetry and efficiency.

[fhahn]

LGTM, I haven't done much work in this area but @dberlin's comment has been addressed and it looks like a straight forward NFC.

include/llvm/IR/Instruction.h

public:
   /// the basic block that MovePos lives in, right before MovePos.
   void moveBefore(Instruction *MovePos);
 
   /// Unlink this instruction and insert into BB before I.
   ///
   /// \pre I is a valid iterator into BB.
   void moveBefore(BasicBlock &BB, SymbolTableList<Instruction>::iterator I);
 
+  /// Unlink this instruction from its current basic block and insert it into
+  /// the basic block that MovePos lives in, right after MovePos.
+  void moveAfter(Instruction *MovePos);
+
   //===--------------------------------------------------------------------===//
   // Subclass classification.
   //===--------------------------------------------------------------------===//
 
   /// Returns a member of one of the enums like Instruction::Add.
   unsigned getOpcode() const { return getValueID() - InstructionVal; }
 
   const char *getOpcodeName() const { return getOpcodeName(getOpcode()); }

lib/CodeGen/AtomicExpandPass.cpp

 }
 
 bool AtomicExpand::bracketInstWithFences(Instruction *I, AtomicOrdering Order) {
   IRBuilder<> Builder(I);
 
   auto LeadingFence = TLI->emitLeadingFence(Builder, I, Order);
 
   auto TrailingFence = TLI->emitTrailingFence(Builder, I, Order);
-  // The trailing fence is emitted before the instruction instead of after
-  // because there is no easy way of setting Builder insertion point after
-  // an instruction. So we must erase it from the BB, and insert it back
-  // in the right place.
   // We have a guard here because not every atomic operation generates a
   // trailing fence.
-  if (TrailingFence) {
-    TrailingFence->removeFromParent();
-    TrailingFence->insertAfter(I);
-  }
+  if (TrailingFence)
+    TrailingFence->moveAfter(I);
 
   return (LeadingFence || TrailingFence);
 }
 
 /// Get the iX type with the same bitwidth as T.
 IntegerType *AtomicExpand::getCorrespondingIntegerType(Type *T,
                                                        const DataLayout &DL) {
   EVT VT = TLI->getValueType(DL, T);

lib/CodeGen/CodeGenPrepare.cpp

Value *TypePromotionHelper::promoteOperandForOther(
   CreatedInstsCost = 0;
   if (!ExtOpnd->hasOneUse()) {
     // ExtOpnd will be promoted.
     // All its uses, but Ext, will need to use a truncated value of the
     // promoted version.
     // Create the truncate now.
     Value *Trunc = TPT.createTrunc(Ext, ExtOpnd->getType());
     if (Instruction *ITrunc = dyn_cast<Instruction>(Trunc)) {
-      ITrunc->removeFromParent();
       // Insert it just after the definition.
-      ITrunc->insertAfter(ExtOpnd);
+      ITrunc->moveAfter(ExtOpnd);
       if (Truncs)
         Truncs->push_back(ITrunc);
     }
 
     TPT.replaceAllUsesWith(ExtOpnd, Trunc);
     // Restore the operand of Ext (which has been replaced by the previous call
     // to replaceAllUsesWith) to avoid creating a cycle trunc <-> sext.
     TPT.setOperand(Ext, 0, ExtOpnd);
bool CodeGenPrepare::optimizeExt(Instruction *&Inst) {
   Instruction *ExtFedByLoad;
 
   // Try to promote a chain of computation if it allows to form an extended
   // load.
   if (canFormExtLd(SpeculativelyMovedExts, LI, ExtFedByLoad, HasPromoted)) {
     assert(LI && ExtFedByLoad && "Expect a valid load and extension");
     TPT.commit();
     // Move the extend into the same block as the load
-    ExtFedByLoad->removeFromParent();
-    ExtFedByLoad->insertAfter(LI);
+    ExtFedByLoad->moveAfter(LI);
     // CGP does not check if the zext would be speculatively executed when moved
     // to the same basic block as the load. Preserving its original location
     // would pessimize the debugging experience, as well as negatively impact
     // the quality of sample pgo. We don't want to use "line 0" as that has a
     // size cost in the line-table section and logically the zext can be seen as
     // part of the load. Therefore we conservatively reuse the same debug
     // location for the load and the zext.
     ExtFedByLoad->setDebugLoc(LI->getDebugLoc());
else if (isa<UndefValue>(Val) || isa<ConstantInt>(Val) ||
           cast<Constant>(Val),
           isa<UndefValue>(Val) ||
               canCauseUndefinedBehavior(ToBePromoted, U.getOperandNo()));
     } else
       llvm_unreachable("Did you modified shouldPromote and forgot to update "
                        "this?");
     ToBePromoted->setOperand(U.getOperandNo(), NewVal);
   }
-  Transition->removeFromParent();
-  Transition->insertAfter(ToBePromoted);
+  Transition->moveAfter(ToBePromoted);
   Transition->setOperand(getTransitionOriginalValueIdx(), ToBePromoted);
 }
 
 /// Some targets can do store(extractelement) with one instruction.
 /// Try to push the extractelement towards the stores when the target
 /// has this feature and this is profitable.
 bool CodeGenPrepare::optimizeExtractElementInst(Instruction *Inst) {
   unsigned CombineCost = UINT_MAX;

lib/IR/Instruction.cpp

 }
 
 void Instruction::moveBefore(BasicBlock &BB,
                              SymbolTableList<Instruction>::iterator I) {
   assert(I == BB.end() || I->getParent() == &BB);
   BB.getInstList().splice(I, getParent()->getInstList(), getIterator());
 }
 
+void Instruction::moveAfter(Instruction *MovePos) {
+  removeFromParent();
+  insertAfter(MovePos);
+}
+
 void Instruction::setHasNoUnsignedWrap(bool b) {
   cast<OverflowingBinaryOperator>(this)->setHasNoUnsignedWrap(b);
 }
 
 void Instruction::setHasNoSignedWrap(bool b) {
   cast<OverflowingBinaryOperator>(this)->setHasNoSignedWrap(b);
 }
 

lib/Transforms/Vectorize/SLPVectorizer.cpp

for (unsigned I = NextInst; I < MaxInst; ++I) {
             IRBuilder<NoFolder> Builder(InsertAfter->getParent(),
                                         ++BasicBlock::iterator(InsertAfter));
             Instruction *I = cast<Instruction>(V);
             assert(isa<InsertElementInst>(I) || isa<InsertValueInst>(I));
             Instruction *Extract =
                 cast<Instruction>(Builder.CreateExtractElement(
                     VectorizedRoot, Builder.getInt32(VecIdx++)));
             I->setOperand(1, Extract);
-            I->removeFromParent();
-            I->insertAfter(Extract);
+            I->moveAfter(Extract);
             InsertAfter = I;
           }
         }
         // Move to the next bundle.
         I += VF - 1;
         NextInst = I + 1;
         Changed = true;
       }