[InstCombine] matchBSwapOrBitReverse - remove pattern matching early-out. NFCI.

[RKSimon]

Summary

recognizeBSwapOrBitReverseIdiom + collectBitParts have pattern matching to bail if a bswap/bitreverse pattern isn't possible - we should be able to rely on this instead.

This is part of a cleanup towards letting matchBSwapOrBitReverse /recognizeBSwapOrBitReverseIdiom use 'root' instructions that aren't ORs (FSHL/FSHRs in particular which can be prematurely created).

[nikic]

LGTM. Don't see any compile-time impact from removing the early exit.

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

Instruction *InstCombinerImpl::visitAnd(BinaryOperator &I) {
 
   // (~x) & y  -->  ~(x | (~y))  iff that gets rid of inversions
   if (sinkNotIntoOtherHandOfAndOrOr(I))
     return &I;
 
   return nullptr;
 }
 
-Instruction *InstCombinerImpl::matchBSwapOrBitReverse(BinaryOperator &Or,
+Instruction *InstCombinerImpl::matchBSwapOrBitReverse(Instruction &I,
                                                       bool MatchBSwaps,
                                                       bool MatchBitReversals) {
-  assert(Or.getOpcode() == Instruction::Or && "bswap requires an 'or'");
-  Value *Op0 = Or.getOperand(0), *Op1 = Or.getOperand(1);
-
-  // Look through zero extends.
-  if (Instruction *Ext = dyn_cast<ZExtInst>(Op0))
-    Op0 = Ext->getOperand(0);
-
-  if (Instruction *Ext = dyn_cast<ZExtInst>(Op1))
-    Op1 = Ext->getOperand(0);
-
-  // (A | B) | C  and  A | (B | C)                  -> bswap if possible.
-  bool OrWithOrs = match(Op0, m_Or(m_Value(), m_Value())) ||
-                   match(Op1, m_Or(m_Value(), m_Value()));
-
-  // (A >> B) | C  and  (A << B) | C                -> bswap if possible.
-  bool OrWithShifts = match(Op0, m_LogicalShift(m_Value(), m_Value())) ||
-                      match(Op1, m_LogicalShift(m_Value(), m_Value()));
-
-  // (A & B) | C  and  A | (B & C)                  -> bswap if possible.
-  bool OrWithAnds = match(Op0, m_And(m_Value(), m_Value())) ||
-                    match(Op1, m_And(m_Value(), m_Value()));
-
-  // fshl(A,B,C) | D  and  A | fshl(B,C,D)          -> bswap if possible.
-  // fshr(A,B,C) | D  and  A | fshr(B,C,D)          -> bswap if possible.
-  bool OrWithFunnels = match(Op0, m_FShl(m_Value(), m_Value(), m_Value())) ||
-                       match(Op0, m_FShr(m_Value(), m_Value(), m_Value())) ||
-                       match(Op0, m_FShl(m_Value(), m_Value(), m_Value())) ||
-                       match(Op0, m_FShr(m_Value(), m_Value(), m_Value()));
-
-  // TODO: Do we need all these filtering checks or should we just rely on
-  // recognizeBSwapOrBitReverseIdiom + collectBitParts to reject them quickly?
-  if (!OrWithOrs && !OrWithShifts && !OrWithAnds && !OrWithFunnels)
-    return nullptr;
-
   SmallVector<Instruction *, 4> Insts;
-  if (!recognizeBSwapOrBitReverseIdiom(&Or, MatchBSwaps, MatchBitReversals,
+  if (!recognizeBSwapOrBitReverseIdiom(&I, MatchBSwaps, MatchBitReversals,
                                        Insts))
     return nullptr;
   Instruction *LastInst = Insts.pop_back_val();
   LastInst->removeFromParent();
 
   for (auto *Inst : Insts)
     Worklist.push(Inst);
   return LastInst;

llvm/lib/Transforms/InstCombine/InstCombineInternal.h

public:
   Instruction *foldSelectInstWithICmp(SelectInst &SI, ICmpInst *ICI);
   Instruction *foldSelectValueEquivalence(SelectInst &SI, ICmpInst &ICI);
 
   Value *insertRangeTest(Value *V, const APInt &Lo, const APInt &Hi,
                          bool isSigned, bool Inside);
   Instruction *PromoteCastOfAllocation(BitCastInst &CI, AllocaInst &AI);
   bool mergeStoreIntoSuccessor(StoreInst &SI);
 
-  /// Given an 'or' instruction, check to see if it is part of a
+  /// Given an initial instruction, check to see if it is the root of a
   /// bswap/bitreverse idiom. If so, return the equivalent bswap/bitreverse
   /// intrinsic.
-  Instruction *matchBSwapOrBitReverse(BinaryOperator &Or, bool MatchBSwaps,
+  Instruction *matchBSwapOrBitReverse(Instruction &I, bool MatchBSwaps,
                                       bool MatchBitReversals);
 
   Instruction *SimplifyAnyMemTransfer(AnyMemTransferInst *MI);
   Instruction *SimplifyAnyMemSet(AnyMemSetInst *MI);
 
   Value *EvaluateInDifferentType(Value *V, Type *Ty, bool isSigned);
 
   /// Returns a value X such that Val = X * Scale, or null if none.