[CodeGenPrepare] Sink and duplicate more 'and' instructions.

Summary:
Rework the code that was sinking/duplicating (icmp and, 0) sequences
into blocks where they were being used by conditional branches to form
more tbz instructions on AArch64.  The new code is more general in that
it just looks for 'and's that have all icmp 0's as users, with a target
hook used to select which subset of 'and' instructions to consider.
This change also enables 'and' sinking for X86, where it is more widely
beneficial than on AArch64.

The 'and' sinking/duplicating code is moved into the optimizeInst phase
of CodeGenPrepare, where it can take advantage of the fact the
OptimizeCmpExpression has already sunk/duplicated any icmps into the
blocks where they are used.  One minor complication from this change is
that optimizeLoadExt needed to be updated to always mark 'and's it has
determined should be in the same block as their feeding load in the
InsertedInsts set to avoid an infinite loop of hoisting and sinking the
same 'and'.

This change fixes a regression on X86 in the tsan runtime caused by
moving GVNHoist to a later place in the optimization pipeline (see
PR31382).

Reviewers: t.p.northover, qcolombet, MatzeB

Subscribers: aemerson, mcrosier, sebpop, llvm-commits

Differential Revision: https://reviews.llvm.org/D28813

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@295746 91177308-0d34-0410-b5e6-96231b3b80d8

Author: geoffberry

include/llvm/Target/TargetLowering.h

@@ -395,16 +395,15 @@ class TargetLoweringBase {
   /// \brief Return if the target supports combining a
   /// chain like:
   /// \code
-  ///   %andResult = and %val1, #imm-with-one-bit-set;
+  ///   %andResult = and %val1, #mask
   ///   %icmpResult = icmp %andResult, 0
-  ///   br i1 %icmpResult, label %dest1, label %dest2
   /// \endcode
   /// into a single machine instruction of a form like:
   /// \code
-  ///   brOnBitSet %register, #bitNumber, dest
+  ///   cc = test %register, #mask
   /// \endcode
-  bool isMaskAndBranchFoldingLegal() const {
-    return MaskAndBranchFoldingIsLegal;
+  virtual bool isMaskAndCmp0FoldingBeneficial(const Instruction &AndI) const {
+    return false;
   }
 
   /// Return true if the target should transform:
@@ -2202,10 +2201,6 @@ class TargetLoweringBase {
   /// the branch is usually predicted right.
   bool PredictableSelectIsExpensive;
 
-  /// MaskAndBranchFoldingIsLegal - Indicates if the target supports folding
-  /// a mask of a single bit, a compare, and a branch into a single instruction.
-  bool MaskAndBranchFoldingIsLegal;
-
   /// \see enableExtLdPromotion.
   bool EnableExtLdPromotion;
 

lib/CodeGen/CodeGenPrepare.cpp

@@ -77,7 +77,6 @@ STATISTIC(NumAndUses, "Number of uses of and mask instructions optimized");
 STATISTIC(NumRetsDup,    "Number of return instructions duplicated");
 STATISTIC(NumDbgValueMoved, "Number of debug value instructions moved");
 STATISTIC(NumSelectsExpanded, "Number of selects turned into branches");
-STATISTIC(NumAndCmpsMoved, "Number of and/cmp's pushed into branches");
 STATISTIC(NumStoreExtractExposed, "Number of store(extractelement) exposed");
 
 static cl::opt<bool> DisableBranchOpts(
@@ -217,7 +216,6 @@ class TypePromotionTransaction;
     bool optimizeExtractElementInst(Instruction *Inst);
     bool dupRetToEnableTailCallOpts(BasicBlock *BB);
     bool placeDbgValues(Function &F);
-    bool sinkAndCmp(Function &F);
     bool extLdPromotion(TypePromotionTransaction &TPT, LoadInst *&LI,
                         Instruction *&Inst,
                         const SmallVectorImpl<Instruction *> &Exts,
@@ -295,14 +293,8 @@ bool CodeGenPrepare::runOnFunction(Function &F) {
   // find a node corresponding to the value.
   EverMadeChange |= placeDbgValues(F);
 
-  // If there is a mask, compare against zero, and branch that can be combined
-  // into a single target instruction, push the mask and compare into branch
-  // users. Do this before OptimizeBlock -> OptimizeInst ->
-  // OptimizeCmpExpression, which perturbs the pattern being searched for.
-  if (!DisableBranchOpts) {
-    EverMadeChange |= sinkAndCmp(F);
+  if (!DisableBranchOpts)
     EverMadeChange |= splitBranchCondition(F);
-  }
 
   bool MadeChange = true;
   while (MadeChange) {
@@ -1095,6 +1087,83 @@ static bool OptimizeCmpExpression(CmpInst *CI, const TargetLowering *TLI) {
   return false;
 }
 
+/// Duplicate and sink the given 'and' instruction into user blocks where it is
+/// used in a compare to allow isel to generate better code for targets where
+/// this operation can be combined.
+///
+/// Return true if any changes are made.
+static bool sinkAndCmp0Expression(Instruction *AndI,
+                                  const TargetLowering &TLI,
+                                  SetOfInstrs &InsertedInsts) {
+  // Double-check that we're not trying to optimize an instruction that was
+  // already optimized by some other part of this pass.
+  assert(!InsertedInsts.count(AndI) &&
+         "Attempting to optimize already optimized and instruction");
+  (void) InsertedInsts;
+
+  // Nothing to do for single use in same basic block.
+  if (AndI->hasOneUse() &&
+      AndI->getParent() == cast<Instruction>(*AndI->user_begin())->getParent())
+    return false;
+
+  // Try to avoid cases where sinking/duplicating is likely to increase register
+  // pressure.
+  if (!isa<ConstantInt>(AndI->getOperand(0)) &&
+      !isa<ConstantInt>(AndI->getOperand(1)) &&
+      AndI->getOperand(0)->hasOneUse() && AndI->getOperand(1)->hasOneUse())
+    return false;
+
+  for (auto *U : AndI->users()) {
+    Instruction *User = cast<Instruction>(U);
+
+    // Only sink for and mask feeding icmp with 0.
+    if (!isa<ICmpInst>(User))
+      return false;
+
+    auto *CmpC = dyn_cast<ConstantInt>(User->getOperand(1));
+    if (!CmpC || !CmpC->isZero())
+      return false;
+  }
+
+  if (!TLI.isMaskAndCmp0FoldingBeneficial(*AndI))
+    return false;
+
+  DEBUG(dbgs() << "found 'and' feeding only icmp 0;\n");
+  DEBUG(AndI->getParent()->dump());
+
+  // Push the 'and' into the same block as the icmp 0.  There should only be
+  // one (icmp (and, 0)) in each block, since CSE/GVN should have removed any
+  // others, so we don't need to keep track of which BBs we insert into.
+  for (Value::user_iterator UI = AndI->user_begin(), E = AndI->user_end();
+       UI != E; ) {
+    Use &TheUse = UI.getUse();
+    Instruction *User = cast<Instruction>(*UI);
+
+    // Preincrement use iterator so we don't invalidate it.
+    ++UI;
+
+    DEBUG(dbgs() << "sinking 'and' use: " << *User << "\n");
+
+    // Keep the 'and' in the same place if the use is already in the same block.
+    Instruction *InsertPt =
+        User->getParent() == AndI->getParent() ? AndI : User;
+    Instruction *InsertedAnd =
+        BinaryOperator::Create(Instruction::And, AndI->getOperand(0),
+                               AndI->getOperand(1), "", InsertPt);
+    // Propagate the debug info.
+    InsertedAnd->setDebugLoc(AndI->getDebugLoc());
+
+    // Replace a use of the 'and' with a use of the new 'and'.
+    TheUse = InsertedAnd;
+    ++NumAndUses;
+    DEBUG(User->getParent()->dump());
+  }
+
+  // We removed all uses, nuke the and.
+  AndI->eraseFromParent();
+  return true;
+}
+
 /// Check if the candidates could be combined with a shift instruction, which
 /// includes:
 /// 1. Truncate instruction
@@ -4544,13 +4613,10 @@ bool CodeGenPrepare::optimizeLoadExt(LoadInst *Load) {
       !(Load->getType()->isIntegerTy() || Load->getType()->isPointerTy()))
     return false;
 
-  // Skip loads we've already transformed or have no reason to transform.
-  if (Load->hasOneUse()) {
-    User *LoadUser = *Load->user_begin();
-    if (cast<Instruction>(LoadUser)->getParent() == Load->getParent() &&
-        !dyn_cast<PHINode>(LoadUser))
-      return false;
-  }
+  // Skip loads we've already transformed.
+  if (Load->hasOneUse() &&
+      InsertedInsts.count(cast<Instruction>(*Load->user_begin())))
+    return false;
 
   // Look at all uses of Load, looking through phis, to determine how many bits
   // of the loaded value are needed.
@@ -4646,6 +4712,9 @@ bool CodeGenPrepare::optimizeLoadExt(LoadInst *Load) {
   IRBuilder<> Builder(Load->getNextNode());
   auto *NewAnd = dyn_cast<Instruction>(
       Builder.CreateAnd(Load, ConstantInt::get(Ctx, DemandBits)));
+  // Mark this instruction as "inserted by CGP", so that other
+  // optimizations don't touch it.
+  InsertedInsts.insert(NewAnd);
 
   // Replace all uses of load with new and (except for the use of load in the
   // new and itself).
@@ -5560,6 +5629,10 @@ bool CodeGenPrepare::optimizeInst(Instruction *I, bool& ModifiedDT) {
 
   BinaryOperator *BinOp = dyn_cast<BinaryOperator>(I);
 
+  if (BinOp && (BinOp->getOpcode() == Instruction::And) &&
+      EnableAndCmpSinking && TLI)
+    return sinkAndCmp0Expression(BinOp, *TLI, InsertedInsts);
+
   if (BinOp && (BinOp->getOpcode() == Instruction::AShr ||
                 BinOp->getOpcode() == Instruction::LShr)) {
     ConstantInt *CI = dyn_cast<ConstantInt>(BinOp->getOperand(1));
@@ -5689,68 +5762,6 @@ bool CodeGenPrepare::placeDbgValues(Function &F) {
   return MadeChange;
 }
 
-// If there is a sequence that branches based on comparing a single bit
-// against zero that can be combined into a single instruction, and the
-// target supports folding these into a single instruction, sink the
-// mask and compare into the branch uses. Do this before OptimizeBlock ->
-// OptimizeInst -> OptimizeCmpExpression, which perturbs the pattern being
-// searched for.
-bool CodeGenPrepare::sinkAndCmp(Function &F) {
-  if (!EnableAndCmpSinking)
-    return false;
-  if (!TLI || !TLI->isMaskAndBranchFoldingLegal())
-    return false;
-  bool MadeChange = false;
-  for (BasicBlock &BB : F) {
-    // Does this BB end with the following?
-    //   %andVal = and %val, #single-bit-set
-    //   %icmpVal = icmp %andResult, 0
-    //   br i1 %cmpVal label %dest1, label %dest2"
-    BranchInst *Brcc = dyn_cast<BranchInst>(BB.getTerminator());
-    if (!Brcc || !Brcc->isConditional())
-      continue;
-    ICmpInst *Cmp = dyn_cast<ICmpInst>(Brcc->getOperand(0));
-    if (!Cmp || Cmp->getParent() != &BB)
-      continue;
-    ConstantInt *Zero = dyn_cast<ConstantInt>(Cmp->getOperand(1));
-    if (!Zero || !Zero->isZero())
-      continue;
-    Instruction *And = dyn_cast<Instruction>(Cmp->getOperand(0));
-    if (!And || And->getOpcode() != Instruction::And || And->getParent() != &BB)
-      continue;
-    ConstantInt* Mask = dyn_cast<ConstantInt>(And->getOperand(1));
-    if (!Mask || !Mask->getUniqueInteger().isPowerOf2())
-      continue;
-    DEBUG(dbgs() << "found and; icmp ?,0; brcc\n"); DEBUG(BB.dump());
-
-    // Push the "and; icmp" for any users that are conditional branches.
-    // Since there can only be one branch use per BB, we don't need to keep
-    // track of which BBs we insert into.
-    for (Use &TheUse : Cmp->uses()) {
-      // Find brcc use.
-      BranchInst *BrccUser = dyn_cast<BranchInst>(TheUse);
-      if (!BrccUser || !BrccUser->isConditional())
-        continue;
-      BasicBlock *UserBB = BrccUser->getParent();
-      if (UserBB == &BB) continue;
-      DEBUG(dbgs() << "found Brcc use\n");
-
-      // Sink the "and; icmp" to use.
-      MadeChange = true;
-      BinaryOperator *NewAnd =
-        BinaryOperator::CreateAnd(And->getOperand(0), And->getOperand(1), "",
-                                  BrccUser);
-      CmpInst *NewCmp =
-        CmpInst::Create(Cmp->getOpcode(), Cmp->getPredicate(), NewAnd, Zero,
-                        "", BrccUser);
-      TheUse = NewCmp;
-      ++NumAndCmpsMoved;
-      DEBUG(BrccUser->getParent()->dump());
-    }
-  }
-  return MadeChange;
-}
-
 /// \brief Scale down both weights to fit into uint32_t.
 static void scaleWeights(uint64_t &NewTrue, uint64_t &NewFalse) {
   uint64_t NewMax = (NewTrue > NewFalse) ? NewTrue : NewFalse;

lib/CodeGen/TargetLoweringBase.cpp

@@ -838,7 +838,6 @@ TargetLoweringBase::TargetLoweringBase(const TargetMachine &tm) : TM(tm) {
   HasExtractBitsInsn = false;
   JumpIsExpensive = JumpIsExpensiveOverride;
   PredictableSelectIsExpensive = false;
-  MaskAndBranchFoldingIsLegal = false;
   EnableExtLdPromotion = false;
   HasFloatingPointExceptions = true;
   StackPointerRegisterToSaveRestore = 0;

lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -555,8 +555,6 @@ AArch64TargetLowering::AArch64TargetLowering(const TargetMachine &TM,
 
   setSchedulingPreference(Sched::Hybrid);
 
-  // Enable TBZ/TBNZ
-  MaskAndBranchFoldingIsLegal = true;
   EnableExtLdPromotion = true;
 
   // Set required alignment.
@@ -10644,6 +10642,19 @@ Value *AArch64TargetLowering::getSafeStackPointerLocation(IRBuilder<> &IRB) cons
       Type::getInt8PtrTy(IRB.getContext())->getPointerTo(0));
 }
 
+bool AArch64TargetLowering::isMaskAndCmp0FoldingBeneficial(
+    const Instruction &AndI) const {
+  // Only sink 'and' mask to cmp use block if it is masking a single bit, since
+  // this is likely to be fold the and/cmp/br into a single tbz instruction.  It
+  // may be beneficial to sink in other cases, but we would have to check that
+  // the cmp would not get folded into the br to form a cbz for these to be
+  // beneficial.
+  ConstantInt* Mask = dyn_cast<ConstantInt>(AndI.getOperand(1));
+  if (!Mask)
+    return false;
+  return Mask->getUniqueInteger().isPowerOf2();
+}
+
 void AArch64TargetLowering::initializeSplitCSR(MachineBasicBlock *Entry) const {
   // Update IsSplitCSR in AArch64unctionInfo.
   AArch64FunctionInfo *AFI = Entry->getParent()->getInfo<AArch64FunctionInfo>();

lib/Target/AArch64/AArch64ISelLowering.h

@@ -412,6 +412,8 @@ class AArch64TargetLowering : public TargetLowering {
     return true;
   }
 
+  bool isMaskAndCmp0FoldingBeneficial(const Instruction &AndI) const override;
+
   bool hasAndNotCompare(SDValue) const override {
     // 'bics'
     return true;

lib/Target/X86/X86ISelLowering.cpp

@@ -4455,6 +4455,11 @@ bool X86TargetLowering::isCtlzFast() const {
   return Subtarget.hasFastLZCNT();
 }
 
+bool X86TargetLowering::isMaskAndCmp0FoldingBeneficial(
+    const Instruction &AndI) const {
+  return true;
+}
+
 bool X86TargetLowering::hasAndNotCompare(SDValue Y) const {
   if (!Subtarget.hasBMI())
     return false;

lib/Target/X86/X86ISelLowering.h

@@ -808,6 +808,8 @@ namespace llvm {
       return false;
     }
 
+    bool isMaskAndCmp0FoldingBeneficial(const Instruction &AndI) const override;
+
     bool hasAndNotCompare(SDValue Y) const override;
 
     /// Return the value type to use for ISD::SETCC.