[NFC] Refactor SimplifyCFG to make propagating information easier.

[jdoerfert]

LGTM.

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

class SimplifyCFGOpt {
   bool simplifyCommonResume(ResumeInst *RI);
   bool simplifyCleanupReturn(CleanupReturnInst *RI);
   bool simplifyUnreachable(UnreachableInst *UI);
   bool simplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
   bool simplifyIndirectBr(IndirectBrInst *IBI);
   bool simplifyBranch(BranchInst *Branch, IRBuilder<> &Builder);
   bool simplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder);
   bool simplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder);
+  bool SimplifyCondBranchToTwoReturns(BranchInst *BI, IRBuilder<> &Builder);
 
   bool tryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
                                              IRBuilder<> &Builder);
 
+  bool HoistThenElseCodeToIf(BranchInst *BI, const TargetTransformInfo &TTI);
+  bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
+                              const TargetTransformInfo &TTI);
+  bool SimplifyTerminatorOnSelect(Instruction *OldTerm, Value *Cond,
+                                  BasicBlock *TrueBB, BasicBlock *FalseBB,
+                                  uint32_t TrueWeight, uint32_t FalseWeight);
+  bool SimplifyBranchOnICmpChain(BranchInst *BI, IRBuilder<> &Builder,
+                                 const DataLayout &DL);
+  bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select);
+  bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI);
+  bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder);
+
 public:
   SimplifyCFGOpt(const TargetTransformInfo &TTI, const DataLayout &DL,
                  SmallPtrSetImpl<BasicBlock *> *LoopHeaders,
                  const SimplifyCFGOptions &Opts)
       : TTI(TTI), DL(DL), LoopHeaders(LoopHeaders), Options(Opts) {}
 
   bool run(BasicBlock *BB);
   bool simplifyOnce(BasicBlock *BB);
static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
   return true;
 }
 
 static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I);
 
 /// Given a conditional branch that goes to BB1 and BB2, hoist any common code
 /// in the two blocks up into the branch block. The caller of this function
 /// guarantees that BI's block dominates BB1 and BB2.
-static bool HoistThenElseCodeToIf(BranchInst *BI,
+bool SimplifyCFGOpt::HoistThenElseCodeToIf(BranchInst *BI,
                                            const TargetTransformInfo &TTI) {
   // This does very trivial matching, with limited scanning, to find identical
   // instructions in the two blocks.  In particular, we don't want to get into
   // O(M*N) situations here where M and N are the sizes of BB1 and BB2.  As
   // such, we currently just scan for obviously identical instructions in an
   // identical order.
   BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
   BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
 

 ///   BB:
 ///     %cmp = icmp ult %x, %y
 ///     %sub = sub %x, %y
 ///     %cond = select i1 %cmp, 0, %sub
 ///     ...
 /// \endcode
 ///
 /// \returns true if the conditional block is removed.
-static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
+bool SimplifyCFGOpt::SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
                                             const TargetTransformInfo &TTI) {
   // Be conservative for now. FP select instruction can often be expensive.
   Value *BrCond = BI->getCondition();
   if (isa<FCmpInst>(BrCond))
     return false;
 
   BasicBlock *BB = BI->getParent();
   BasicBlock *EndBB = ThenBB->getTerminator()->getSuccessor(0);
 
static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
   Builder.CreateBr(BB);
   OldTI->eraseFromParent();
   return true;
 }
 
 /// If we found a conditional branch that goes to two returning blocks,
 /// try to merge them together into one return,
 /// introducing a select if the return values disagree.
-static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
+bool SimplifyCFGOpt::SimplifyCondBranchToTwoReturns(BranchInst *BI,
                                                     IRBuilder<> &Builder) {
   assert(BI->isConditional() && "Must be a conditional branch");
   BasicBlock *TrueSucc = BI->getSuccessor(0);
   BasicBlock *FalseSucc = BI->getSuccessor(1);
   ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
   ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
 
   // Check to ensure both blocks are empty (just a return) or optionally empty
   // with PHI nodes.  If there are other instructions, merging would cause extra
static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
   return true;
 }
 
 // Simplifies a terminator by replacing it with a branch to TrueBB if Cond is
 // true or to FalseBB if Cond is false.
 // Takes care of updating the successors and removing the old terminator.
 // Also makes sure not to introduce new successors by assuming that edges to
 // non-successor TrueBBs and FalseBBs aren't reachable.
-static bool SimplifyTerminatorOnSelect(Instruction *OldTerm, Value *Cond,
-                                       BasicBlock *TrueBB, BasicBlock *FalseBB,
+bool SimplifyCFGOpt::SimplifyTerminatorOnSelect(Instruction *OldTerm,
+                                                Value *Cond, BasicBlock *TrueBB,
+                                                BasicBlock *FalseBB,
                                                 uint32_t TrueWeight,
                                                 uint32_t FalseWeight) {
   // Remove any superfluous successor edges from the CFG.
   // First, figure out which successors to preserve.
   // If TrueBB and FalseBB are equal, only try to preserve one copy of that
   // successor.
   BasicBlock *KeepEdge1 = TrueBB;
   BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : nullptr;
 
   // Then remove the rest.
bool SimplifyCFGOpt::SimplifyTerminatorOnSelect(Instruction *OldTerm,
   EraseTerminatorAndDCECond(OldTerm);
   return true;
 }
 
 // Replaces
 //   (switch (select cond, X, Y)) on constant X, Y
 // with a branch - conditional if X and Y lead to distinct BBs,
 // unconditional otherwise.
-static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
+bool SimplifyCFGOpt::SimplifySwitchOnSelect(SwitchInst *SI,
+                                            SelectInst *Select) {
   // Check for constant integer values in the select.
   ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
   ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
   if (!TrueVal || !FalseVal)
     return false;
 
   // Find the relevant condition and destinations.
   Value *Condition = Select->getCondition();
return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB, TrueWeight,
                                     FalseWeight);
 }
 
 // Replaces
 //   (indirectbr (select cond, blockaddress(@fn, BlockA),
 //                             blockaddress(@fn, BlockB)))
 // with
 //   (br cond, BlockA, BlockB).
-static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
+bool SimplifyCFGOpt::SimplifyIndirectBrOnSelect(IndirectBrInst *IBI,
+                                                SelectInst *SI) {
   // Check that both operands of the select are block addresses.
   BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
   BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
   if (!TBA || !FBA)
     return false;
 
   // Extract the actual blocks.
   BasicBlock *TrueBB = TBA->getBasicBlock();
bool SimplifyCFGOpt::tryToSimplifyUncondBranchWithICmpInIt(
   Builder.CreateBr(SuccBlock);
   PHIUse->addIncoming(NewCst, NewBB);
   return true;
 }
 
 /// The specified branch is a conditional branch.
 /// Check to see if it is branching on an or/and chain of icmp instructions, and
 /// fold it into a switch instruction if so.
-static bool SimplifyBranchOnICmpChain(BranchInst *BI, IRBuilder<> &Builder,
+bool SimplifyCFGOpt::SimplifyBranchOnICmpChain(BranchInst *BI,
+                                               IRBuilder<> &Builder,
                                                const DataLayout &DL) {
   Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
   if (!Cond)
     return false;
 
   // Change br (X == 0 | X == 1), T, F into a switch instruction.
   // If this is a bunch of seteq's or'd together, or if it's a bunch of
   // 'setne's and'ed together, collect them.
 
static void createUnreachableSwitchDefault(SwitchInst *Switch) {
   SplitBlock(&*NewDefaultBlock, &NewDefaultBlock->front());
   auto *NewTerminator = NewDefaultBlock->getTerminator();
   new UnreachableInst(Switch->getContext(), NewTerminator);
   EraseTerminatorAndDCECond(NewTerminator);
 }
 
 /// Turn a switch with two reachable destinations into an integer range
 /// comparison and branch.
-static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
+bool SimplifyCFGOpt::TurnSwitchRangeIntoICmp(SwitchInst *SI,
+                                             IRBuilder<> &Builder) {
   assert(SI->getNumCases() > 1 && "Degenerate switch?");
 
   bool HasDefault =
       !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
 
   // Partition the cases into two sets with different destinations.
   BasicBlock *DestA = HasDefault ? SI->getDefaultDest() : nullptr;
   BasicBlock *DestB = nullptr;