Generalize lsr code that optimize loop to count down towards zero.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86715 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/LoopStrengthReduce.cpp

@@ -51,6 +51,7 @@ STATISTIC(NumEliminated,  "Number of strides eliminated");
 STATISTIC(NumShadow,      "Number of Shadow IVs optimized");
 STATISTIC(NumImmSunk,     "Number of common expr immediates sunk into uses");
 STATISTIC(NumLoopCond,    "Number of loop terminating conds optimized");
+STATISTIC(NumCountZero,   "Number of count iv optimized to count toward zero");
 
 static cl::opt<bool> EnableFullLSRMode("enable-full-lsr",
                                        cl::init(false),
@@ -136,7 +137,8 @@ namespace {
                                   const SCEV *const *  &CondStride);
 
     void OptimizeIndvars(Loop *L);
-    void OptimizeLoopCountIV(Loop *L);
+    void OptimizeLoopCountIV(const SCEV *Stride,
+                             IVUsersOfOneStride &Uses, Loop *L);
     void OptimizeLoopTermCond(Loop *L);
 
     /// OptimizeShadowIV - If IV is used in a int-to-float cast
@@ -1519,8 +1521,8 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEV *const &Stride,
   // have the full access expression to rewrite the use.
   std::vector<BasedUser> UsersToProcess;
   const SCEV *CommonExprs = CollectIVUsers(Stride, Uses, L, AllUsesAreAddresses,
-                                          AllUsesAreOutsideLoop,
+                                           AllUsesAreOutsideLoop,
-                                          UsersToProcess);
+                                           UsersToProcess);
 
   // Sort the UsersToProcess array so that users with common bases are
   // next to each other.
@@ -1593,8 +1595,8 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEV *const &Stride,
                                     Type::getInt32Ty(Preheader->getContext())),
                    0);
 
-  /// Choose a strength-reduction strategy and prepare for it by creating
+  // Choose a strength-reduction strategy and prepare for it by creating
-  /// the necessary PHIs and adjusting the bookkeeping.
+  // the necessary PHIs and adjusting the bookkeeping.
   if (ShouldUseFullStrengthReductionMode(UsersToProcess, L,
                                          AllUsesAreAddresses, Stride)) {
     PrepareToStrengthReduceFully(UsersToProcess, Stride, CommonExprs, L,
@@ -2418,107 +2420,142 @@ void LoopStrengthReduce::OptimizeLoopTermCond(Loop *L) {
   ++NumLoopCond;
 }
 
+/// isUsedByExitBranch - Return true if icmp is used by a loop terminating
+/// conditional branch or it's and / or with other conditions before being used
+/// as the condition.
+static bool isUsedByExitBranch(ICmpInst *Cond, Loop *L) {
+ BasicBlock *CondBB = Cond->getParent();
+  if (!L->isLoopExiting(CondBB))
+    return false;
+  BranchInst *TermBr = dyn_cast<BranchInst>(CondBB->getTerminator());
+  if (!TermBr->isConditional())
+    return false;
+
+  Value *User = *Cond->use_begin();
+  Instruction *UserInst = dyn_cast<Instruction>(User);
+  while (UserInst &&
+         (UserInst->getOpcode() == Instruction::And ||
+          UserInst->getOpcode() == Instruction::Or)) {
+    if (!UserInst->hasOneUse() || UserInst->getParent() != CondBB)
+      return false;
+    User = *User->use_begin();
+    UserInst = dyn_cast<Instruction>(User);
+  }
+  return User == TermBr;
+}
+
 /// OptimizeLoopCountIV - If, after all sharing of IVs, the IV used for deciding
 /// when to exit the loop is used only for that purpose, try to rearrange things
-/// so it counts down to a test against zero.
+/// so it counts down to a test against zero which tends to be cheaper.
-void LoopStrengthReduce::OptimizeLoopCountIV(Loop *L) {
+void LoopStrengthReduce::OptimizeLoopCountIV(const SCEV *Stride,
-
+                                             IVUsersOfOneStride &Uses,
-  // If the number of times the loop is executed isn't computable, give up.
+                                             Loop *L) {
-  const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
+  if (Uses.Users.size() != 1)
-  if (isa<SCEVCouldNotCompute>(BackedgeTakenCount))
     return;
 
-  // Get the terminating condition for the loop if possible (this isn't
+  // If the only use is an icmp of an loop exiting conditional branch, then
-  // necessarily in the latch, or a block that's a predecessor of the header).
+  // attempts the optimization.
-  if (!L->getExitBlock())
+  BasedUser User = BasedUser(*Uses.Users.begin(), SE);
-    return; // More than one loop exit blocks.
+  Instruction *Inst = User.Inst;
-
+  if (!L->contains(Inst->getParent()))
-  // Okay, there is one exit block.  Try to find the condition that causes the
-  // loop to be exited.
-  BasicBlock *ExitingBlock = L->getExitingBlock();
-  if (!ExitingBlock)
-    return; // More than one block exiting!
-
-  // Okay, we've computed the exiting block.  See what condition causes us to
-  // exit.
-  //
-  // FIXME: we should be able to handle switch instructions (with a single exit)
-  BranchInst *TermBr = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
-  if (TermBr == 0) return;
-  assert(TermBr->isConditional() && "If unconditional, it can't be in loop!");
-  if (!isa<ICmpInst>(TermBr->getCondition()))
     return;
-  ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition());
 
-  // Handle only tests for equality for the moment, and only stride 1.
+  ICmpInst *Cond = dyn_cast<ICmpInst>(Inst);
-  if (Cond->getPredicate() != CmpInst::ICMP_EQ)
+  if (!Cond)
     return;
-  const SCEV *IV = SE->getSCEV(Cond->getOperand(0));
+  // Handle only tests for equality for the moment.
+  if (Cond->getPredicate() != CmpInst::ICMP_EQ || !Cond->hasOneUse())
+    return;
+  if (!isUsedByExitBranch(Cond, L))
+    return;
+ 
+  Value *CondOp0 = Cond->getOperand(0);
+  const SCEV *IV = SE->getSCEV(CondOp0);
   const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV);
-  const SCEV *One = SE->getIntegerSCEV(1, BackedgeTakenCount->getType());
+  if (!AR || !AR->isAffine())
-  if (!AR || !AR->isAffine() || AR->getStepRecurrence(*SE) != One)
+    return;
+
+  const SCEVConstant *SC = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*SE));
+  if (!SC || SC->getValue()->getSExtValue() < 0)
+    // If it's already counting down, don't do anything.
+    return;
+
+  // If the RHS of the comparison is not an loop invariant, the rewrite
+  // cannot be done. Also bail out if it's already comparing against a zero.
+  Value *RHS = Cond->getOperand(1);
+  if (!L->isLoopInvariant(RHS) ||
+      (isa<ConstantInt>(RHS) && cast<ConstantInt>(RHS)->isZero()))
     return;
-  // If the RHS of the comparison is defined inside the loop, the rewrite
-  // cannot be done.
-  if (Instruction *CR = dyn_cast<Instruction>(Cond->getOperand(1)))
-    if (L->contains(CR->getParent()))
-      return;
 
   // Make sure the IV is only used for counting.  Value may be preinc or
   // postinc; 2 uses in either case.
-  if (!Cond->getOperand(0)->hasNUses(2))
+  if (!CondOp0->hasNUses(2))
     return;
-  PHINode *phi = dyn_cast<PHINode>(Cond->getOperand(0));
+  PHINode *PHIExpr;
-  Instruction *incr;
+  Instruction *Incr;
-  if (phi && phi->getParent()==L->getHeader()) {
+  if (User.isUseOfPostIncrementedValue) {
-    // value tested is preinc.  Find the increment.
+    // Value tested is postinc. Find the phi node.
-    // A CmpInst is not a BinaryOperator; we depend on this.
+    Incr = dyn_cast<BinaryOperator>(CondOp0);
-    Instruction::use_iterator UI = phi->use_begin();
+    if (!Incr || Incr->getOpcode() != Instruction::Add)
-    incr = dyn_cast<BinaryOperator>(UI);
-    if (!incr)
-      incr = dyn_cast<BinaryOperator>(++UI);
-    // 1 use for postinc value, the phi.  Unnecessarily conservative?
-    if (!incr || !incr->hasOneUse() || incr->getOpcode()!=Instruction::Add)
-      return;
-  } else {
-    // Value tested is postinc.  Find the phi node.
-    incr = dyn_cast<BinaryOperator>(Cond->getOperand(0));
-    if (!incr || incr->getOpcode()!=Instruction::Add)
       return;
 
-    Instruction::use_iterator UI = Cond->getOperand(0)->use_begin();
+    Instruction::use_iterator UI = CondOp0->use_begin();
-    phi = dyn_cast<PHINode>(UI);
+    PHIExpr = dyn_cast<PHINode>(UI);
-    if (!phi)
+    if (!PHIExpr)
-      phi = dyn_cast<PHINode>(++UI);
+      PHIExpr = dyn_cast<PHINode>(++UI);
     // 1 use for preinc value, the increment.
-    if (!phi || phi->getParent()!=L->getHeader() || !phi->hasOneUse())
+    if (!PHIExpr || !PHIExpr->hasOneUse())
+      return;
+  } else {
+    assert(isa<PHINode>(CondOp0) &&
+           "Unexpected loop exiting counting instruction sequence!");
+    PHIExpr = cast<PHINode>(CondOp0);
+    // Value tested is preinc.  Find the increment.
+    // A CmpInst is not a BinaryOperator; we depend on this.
+    Instruction::use_iterator UI = PHIExpr->use_begin();
+    Incr = dyn_cast<BinaryOperator>(UI);
+    if (!Incr)
+      Incr = dyn_cast<BinaryOperator>(++UI);
+    // One use for postinc value, the phi.  Unnecessarily conservative?
+    if (!Incr || !Incr->hasOneUse() || Incr->getOpcode() != Instruction::Add)
       return;
   }
 
   // Replace the increment with a decrement.
-  BinaryOperator *decr = 
+  DEBUG(errs() << "    Examining ");
-    BinaryOperator::Create(Instruction::Sub, incr->getOperand(0),
+  if (User.isUseOfPostIncrementedValue)
-                           incr->getOperand(1), "tmp", incr);
+    DEBUG(errs() << "postinc");
-  incr->replaceAllUsesWith(decr);
+  else
-  incr->eraseFromParent();
+    DEBUG(errs() << "preinc");
+  DEBUG(errs() << " use ");
+  DEBUG(WriteAsOperand(errs(), CondOp0, /*PrintType=*/false));
+  DEBUG(errs() << " in Inst: " << *Inst << '\n');
+  BinaryOperator *Decr =  BinaryOperator::Create(Instruction::Sub,
+                         Incr->getOperand(0), Incr->getOperand(1), "tmp", Incr);
+  Incr->replaceAllUsesWith(Decr);
+  Incr->eraseFromParent();
 
   // Substitute endval-startval for the original startval, and 0 for the
   // original endval.  Since we're only testing for equality this is OK even 
   // if the computation wraps around.
   BasicBlock  *Preheader = L->getLoopPreheader();
   Instruction *PreInsertPt = Preheader->getTerminator();
-  int inBlock = L->contains(phi->getIncomingBlock(0)) ? 1 : 0;
+  unsigned InBlock = L->contains(PHIExpr->getIncomingBlock(0)) ? 1 : 0;
-  Value *startVal = phi->getIncomingValue(inBlock);
+  Value *StartVal = PHIExpr->getIncomingValue(InBlock);
-  Value *endVal = Cond->getOperand(1);
+  Value *EndVal = Cond->getOperand(1);
-  // FIXME check for case where both are constant
+  DEBUG(errs() << "    Optimize loop counting iv to count down ["
+        << *EndVal << " .. " << *StartVal << "]\n");
+
+  // FIXME: check for case where both are constant.
   Constant* Zero = ConstantInt::get(Cond->getOperand(1)->getType(), 0);
-  BinaryOperator *NewStartVal = 
+  BinaryOperator *NewStartVal = BinaryOperator::Create(Instruction::Sub,
-    BinaryOperator::Create(Instruction::Sub, endVal, startVal,
+                                          EndVal, StartVal, "tmp", PreInsertPt);
-                           "tmp", PreInsertPt);
+  PHIExpr->setIncomingValue(InBlock, NewStartVal);
-  phi->setIncomingValue(inBlock, NewStartVal);
   Cond->setOperand(1, Zero);
+  DEBUG(errs() << "    New icmp: " << *Cond << "\n");
 
   Changed = true;
+  ++NumCountZero;
 }
 
 bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager &LPM) {
@@ -2581,11 +2618,20 @@ bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager &LPM) {
         continue;
       StrengthReduceStridedIVUsers(SI->first, *SI->second, L);
     }
-  }
 
-  // After all sharing is done, see if we can adjust the loop to test against
+    // After all sharing is done, see if we can adjust the loop to test against
-  // zero instead of counting up to a maximum.  This is usually faster.
+    // zero instead of counting up to a maximum.  This is usually faster.
-  OptimizeLoopCountIV(L);
+    for (unsigned Stride = 0, e = IU->StrideOrder.size();
+         Stride != e; ++Stride) {
+      std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI =
+        IU->IVUsesByStride.find(IU->StrideOrder[Stride]);
+      assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
+      // FIXME: Generalize to non-affine IV's.
+      if (!SI->first->isLoopInvariant(L))
+        continue;
+      OptimizeLoopCountIV(SI->first, *SI->second, L);
+    }
+  }
 
   // We're done analyzing this loop; release all the state we built up for it.
   IVsByStride.clear();

test/Transforms/LoopStrengthReduce/count-to-zero.ll

@@ -0,0 +1,42 @@
+; RUN: opt < %s -loop-reduce -S | FileCheck %s
+; rdar://7382068
+
+define void @t(i32 %c) nounwind optsize {
+entry:
+  br label %bb6
+
+bb1:                                              ; preds = %bb6
+  %tmp = icmp eq i32 %c_addr.1, 20                ; <i1> [#uses=1]
+  br i1 %tmp, label %bb2, label %bb3
+
+bb2:                                              ; preds = %bb1
+  %tmp1 = tail call i32 @f20(i32 %c_addr.1) nounwind ; <i32> [#uses=1]
+  br label %bb7
+
+bb3:                                              ; preds = %bb1
+  %tmp2 = icmp slt i32 %c_addr.1, 10              ; <i1> [#uses=1]
+  %tmp3 = add nsw i32 %c_addr.1, 1                ; <i32> [#uses=1]
+  %tmp4 = add i32 %c_addr.1, -1                   ; <i32> [#uses=1]
+  %c_addr.1.be = select i1 %tmp2, i32 %tmp3, i32 %tmp4 ; <i32> [#uses=1]
+  %indvar.next = add i32 %indvar, 1               ; <i32> [#uses=1]
+; CHECK: sub i32 %lsr.iv, 1
+  br label %bb6
+
+bb6:                                              ; preds = %bb3, %entry
+  %indvar = phi i32 [ %indvar.next, %bb3 ], [ 0, %entry ] ; <i32> [#uses=2]
+  %c_addr.1 = phi i32 [ %c_addr.1.be, %bb3 ], [ %c, %entry ] ; <i32> [#uses=7]
+  %tmp5 = icmp eq i32 %indvar, 9999               ; <i1> [#uses=1]
+; CHECK: icmp eq i32 %lsr.iv, 0
+  %tmp6 = icmp eq i32 %c_addr.1, 100              ; <i1> [#uses=1]
+  %or.cond = or i1 %tmp5, %tmp6                   ; <i1> [#uses=1]
+  br i1 %or.cond, label %bb7, label %bb1
+
+bb7:                                              ; preds = %bb6, %bb2
+  %c_addr.0 = phi i32 [ %tmp1, %bb2 ], [ %c_addr.1, %bb6 ] ; <i32> [#uses=1]
+  tail call void @bar(i32 %c_addr.0) nounwind
+  ret void
+}
+
+declare i32 @f20(i32)
+
+declare void @bar(i32)