[InstCombine][NFC] refactor roundtripcast

[Krishnakariya]

Summary

Split from D107822.
Refactoring "simplifyIntToPtrRoundTripCast" and "isIntToPtrRoundTripCast".

[aqjune]

In terms of correctness, I think the patch looks okay.

[lebedev.ri]

This review seems to be stuck/dead, consider abandoning if no longer relevant.

llvm/lib/Transforms/InstCombine/InstCombineInternal.h

private:
   /// \return 0 if the cast pair cannot be eliminated, otherwise returns an
   /// Instruction::CastOps value for a cast that can replace the pair, casting
   /// CI1->getSrcTy() to CI2->getDstTy().
   ///
   /// \see CastInst::isEliminableCastPair
   Instruction::CastOps isEliminableCastPair(const CastInst *CI1,
                                             const CastInst *CI2);
   Value *simplifyIntToPtrRoundTripCast(Value *Val);
+  Value *isIntToPtrRoundTripCast(Value *Val);
 
   Value *foldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS, BinaryOperator &And);
   Value *foldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS, BinaryOperator &Or);
   Value *foldXorOfICmps(ICmpInst *LHS, ICmpInst *RHS, BinaryOperator &Xor);
 
   /// Optimize (fcmp)&(fcmp) or (fcmp)|(fcmp).
   /// NOTE: Unlike most of instcombine, this returns a Value which should
   /// already be inserted into the function.

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

static bool simplifyAssocCastAssoc(BinaryOperator *BinOp1,
   IC.replaceOperand(*Cast, 0, BinOp2->getOperand(0));
   IC.replaceOperand(*BinOp1, 1, FoldedC);
   return true;
 }
 
 // Simplifies IntToPtr/PtrToInt RoundTrip Cast To BitCast.
 // inttoptr ( ptrtoint (x) ) --> x
 Value *InstCombinerImpl::simplifyIntToPtrRoundTripCast(Value *Val) {
+  if (Value *Ptr = isIntToPtrRoundTripCast(Val)) {
+    return CastInst::CreateBitOrPointerCast(Ptr, Val->getType(), "",
+                                            cast<Instruction>(Val));
+  }
+  return nullptr;
+}
+
+Value *InstCombinerImpl::isIntToPtrRoundTripCast(Value *Val) {
   auto *IntToPtr = dyn_cast<IntToPtrInst>(Val);
   if (IntToPtr && DL.getPointerTypeSizeInBits(IntToPtr->getDestTy()) ==
                       DL.getTypeSizeInBits(IntToPtr->getSrcTy())) {
     auto *PtrToInt = dyn_cast<PtrToIntInst>(IntToPtr->getOperand(0));
     Type *CastTy = IntToPtr->getDestTy();
     if (PtrToInt &&
         CastTy->getPointerAddressSpace() ==
             PtrToInt->getSrcTy()->getPointerAddressSpace() &&
         DL.getPointerTypeSizeInBits(PtrToInt->getSrcTy()) ==
             DL.getTypeSizeInBits(PtrToInt->getDestTy())) {
-      return CastInst::CreateBitOrPointerCast(PtrToInt->getOperand(0), CastTy,
-                                              "", PtrToInt);
+      return PtrToInt->getOperand(0);
     }
   }
   return nullptr;
 }
 
 /// This performs a few simplifications for operators that are associative or
 /// commutative:
 ///