Move PHIElimination's SplitCriticalEdge for MachineBasicBlocks out

into a utility routine, teach it how to update MachineLoopInfo, and
make use of it in MachineLICM to split critical edges on demand.

llvm-svn: 106555

llvm/include/llvm/CodeGen/MachineBasicBlock.h

@@ -19,6 +19,7 @@
 
 namespace llvm {
 
+class Pass;
 class BasicBlock;
 class MachineFunction;
 class MCSymbol;
@@ -281,6 +282,14 @@ public:
   /// it returns end()
   iterator getFirstTerminator();
 
+  /// SplitCriticalEdge - Split the critical edge from this block to the
+  /// given successor block, and return the newly created block, or null
+  /// if splitting is not possible.
+  ///
+  /// This function updates LiveVariables, MachineDominatorTree, and
+  /// MachineLoopInfo, as applicable.
+  MachineBasicBlock *SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P);
+
   void pop_front() { Insts.pop_front(); }
   void pop_back() { Insts.pop_back(); }
   void push_back(MachineInstr *MI) { Insts.push_back(MI); }

llvm/include/llvm/CodeGen/MachineLoopInfo.h

@@ -64,13 +64,13 @@ class MachineLoopInfo : public MachineFunctionPass {
   void operator=(const MachineLoopInfo &);  // do not implement
   MachineLoopInfo(const MachineLoopInfo &); // do not implement
 
-  LoopInfoBase<MachineBasicBlock, MachineLoop>& getBase() { return LI; }
-
 public:
   static char ID; // Pass identification, replacement for typeid
 
   MachineLoopInfo() : MachineFunctionPass(&ID) {}
 
+  LoopInfoBase<MachineBasicBlock, MachineLoop>& getBase() { return LI; }
+
   /// iterator/begin/end - The interface to the top-level loops in the current
   /// function.
   ///

llvm/lib/CodeGen/MachineBasicBlock.cpp

@@ -13,7 +13,10 @@
 
 #include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/BasicBlock.h"
+#include "llvm/CodeGen/LiveVariables.h"
+#include "llvm/CodeGen/MachineDominators.h"
 #include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/Target/TargetRegisterInfo.h"
@@ -396,6 +399,82 @@ bool MachineBasicBlock::canFallThrough() {
   return FBB == 0;
 }
 
+MachineBasicBlock *
+MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
+  MachineFunction *MF = getParent();
+  DebugLoc dl;  // FIXME: this is nowhere
+
+  // We may need to update this's terminator, but we can't do that if AnalyzeBranch
+  // fails. If this uses a jump table, we won't touch it.
+  const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
+  MachineBasicBlock *TBB = 0, *FBB = 0;
+  SmallVector<MachineOperand, 4> Cond;
+  if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
+    return NULL;
+
+  MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
+  MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
+  DEBUG(dbgs() << "PHIElimination splitting critical edge:"
+        " BB#" << getNumber()
+        << " -- BB#" << NMBB->getNumber()
+        << " -- BB#" << Succ->getNumber() << '\n');
+
+  ReplaceUsesOfBlockWith(Succ, NMBB);
+  updateTerminator();
+
+  // Insert unconditional "jump Succ" instruction in NMBB if necessary.
+  NMBB->addSuccessor(Succ);
+  if (!NMBB->isLayoutSuccessor(Succ)) {
+    Cond.clear();
+    MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl);
+  }
+
+  // Fix PHI nodes in Succ so they refer to NMBB instead of this
+  for (MachineBasicBlock::iterator i = Succ->begin(), e = Succ->end();
+       i != e && i->isPHI(); ++i)
+    for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
+      if (i->getOperand(ni+1).getMBB() == this)
+        i->getOperand(ni+1).setMBB(NMBB);
+
+  if (LiveVariables *LV =
+        P->getAnalysisIfAvailable<LiveVariables>())
+    LV->addNewBlock(NMBB, this, Succ);
+
+  if (MachineDominatorTree *MDT =
+        P->getAnalysisIfAvailable<MachineDominatorTree>())
+    MDT->addNewBlock(NMBB, this);
+
+  if (MachineLoopInfo *MLI =
+        P->getAnalysisIfAvailable<MachineLoopInfo>())
+    if (MachineLoop *TIL = MLI->getLoopFor(this)) {
+      // If one or the other blocks were not in a loop, the new block is not
+      // either, and thus LI doesn't need to be updated.
+      if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) {
+        if (TIL == DestLoop) {
+          // Both in the same loop, the NMBB joins loop.
+          DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
+        } else if (TIL->contains(DestLoop)) {
+          // Edge from an outer loop to an inner loop.  Add to the outer loop.
+          TIL->addBasicBlockToLoop(NMBB, MLI->getBase());
+        } else if (DestLoop->contains(TIL)) {
+          // Edge from an inner loop to an outer loop.  Add to the outer loop.
+          DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
+        } else {
+          // Edge from two loops with no containment relation.  Because these
+          // are natural loops, we know that the destination block must be the
+          // header of its loop (adding a branch into a loop elsewhere would
+          // create an irreducible loop).
+          assert(DestLoop->getHeader() == Succ &&
+                 "Should not create irreducible loops!");
+          if (MachineLoop *P = DestLoop->getParentLoop())
+            P->addBasicBlockToLoop(NMBB, MLI->getBase());
+        }
+      }
+    }
+
+  return NMBB;
+}
+
 /// removeFromParent - This method unlinks 'this' from the containing function,
 /// and returns it, but does not delete it.
 MachineBasicBlock *MachineBasicBlock::removeFromParent() {

llvm/lib/CodeGen/MachineLICM.cpp

@@ -83,7 +83,6 @@ namespace {
 
     const char *getPassName() const { return "Machine Instruction LICM"; }
 
-    // FIXME: Loop preheaders?
     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
       AU.setPreservesCFG();
       AU.addRequired<MachineLoopInfo>();
@@ -182,6 +181,10 @@ namespace {
     /// current loop preheader that may become duplicates of instructions that
     /// are hoisted out of the loop.
     void InitCSEMap(MachineBasicBlock *BB);
+
+    /// getCurPreheader - Get the preheader for the current loop, splitting
+    /// a critical edge if needed.
+    MachineBasicBlock *getCurPreheader();
   };
 } // end anonymous namespace
 
@@ -193,11 +196,11 @@ FunctionPass *llvm::createMachineLICMPass(bool PreRegAlloc) {
   return new MachineLICM(PreRegAlloc);
 }
 
-/// LoopIsOuterMostWithPreheader - Test if the given loop is the outer-most
+/// LoopIsOuterMostWithPredecessor - Test if the given loop is the outer-most
-/// loop that has a preheader.
+/// loop that has a unique predecessor.
-static bool LoopIsOuterMostWithPreheader(MachineLoop *CurLoop) {
+static bool LoopIsOuterMostWithPredecessor(MachineLoop *CurLoop) {
   for (MachineLoop *L = CurLoop->getParentLoop(); L; L = L->getParentLoop())
-    if (L->getLoopPreheader())
+    if (L->getLoopPredecessor())
       return false;
   return true;
 }
@@ -223,20 +226,11 @@ bool MachineLICM::runOnMachineFunction(MachineFunction &MF) {
 
   for (MachineLoopInfo::iterator I = MLI->begin(), E = MLI->end(); I != E; ++I){
     CurLoop = *I;
+    CurPreheader = 0;
 
     // If this is done before regalloc, only visit outer-most preheader-sporting
     // loops.
-    if (PreRegAlloc && !LoopIsOuterMostWithPreheader(CurLoop))
+    if (PreRegAlloc && !LoopIsOuterMostWithPredecessor(CurLoop))
-      continue;
-
-    // Determine the block to which to hoist instructions. If we can't find a
-    // suitable loop preheader, we can't do any hoisting.
-    //
-    // FIXME: We are only hoisting if the basic block coming into this loop
-    // has only one successor. This isn't the case in general because we haven't
-    // broken critical edges or added preheaders.
-    CurPreheader = CurLoop->getLoopPreheader();
-    if (!CurPreheader)
       continue;
 
     if (!PreRegAlloc)
@@ -438,13 +432,16 @@ void MachineLICM::AddToLiveIns(unsigned Reg) {
 /// operands that is safe to hoist, this instruction is called to do the
 /// dirty work.
 void MachineLICM::HoistPostRA(MachineInstr *MI, unsigned Def) {
+  MachineBasicBlock *Preheader = getCurPreheader();
+  if (!Preheader) return;
+
   // Now move the instructions to the predecessor, inserting it before any
   // terminator instructions.
   DEBUG({
       dbgs() << "Hoisting " << *MI;
-      if (CurPreheader->getBasicBlock())
+      if (Preheader->getBasicBlock())
         dbgs() << " to MachineBasicBlock "
-               << CurPreheader->getName();
+               << Preheader->getName();
       if (MI->getParent()->getBasicBlock())
         dbgs() << " from MachineBasicBlock "
                << MI->getParent()->getName();
@@ -453,7 +450,7 @@ void MachineLICM::HoistPostRA(MachineInstr *MI, unsigned Def) {
 
   // Splice the instruction to the preheader.
   MachineBasicBlock *MBB = MI->getParent();
-  CurPreheader->splice(CurPreheader->getFirstTerminator(), MBB, MI);
+  Preheader->splice(Preheader->getFirstTerminator(), MBB, MI);
 
   // Add register to livein list to all the BBs in the current loop since a 
   // loop invariant must be kept live throughout the whole loop. This is
@@ -756,6 +753,9 @@ bool MachineLICM::EliminateCSE(MachineInstr *MI,
 /// that are safe to hoist, this instruction is called to do the dirty work.
 ///
 void MachineLICM::Hoist(MachineInstr *MI) {
+  MachineBasicBlock *Preheader = getCurPreheader();
+  if (!Preheader) return;
+
   // First check whether we should hoist this instruction.
   if (!IsLoopInvariantInst(*MI) || !IsProfitableToHoist(*MI)) {
     // If not, try unfolding a hoistable load.
@@ -767,9 +767,9 @@ void MachineLICM::Hoist(MachineInstr *MI) {
   // terminator instructions.
   DEBUG({
       dbgs() << "Hoisting " << *MI;
-      if (CurPreheader->getBasicBlock())
+      if (Preheader->getBasicBlock())
         dbgs() << " to MachineBasicBlock "
-               << CurPreheader->getName();
+               << Preheader->getName();
       if (MI->getParent()->getBasicBlock())
         dbgs() << " from MachineBasicBlock "
                << MI->getParent()->getName();
@@ -779,7 +779,7 @@ void MachineLICM::Hoist(MachineInstr *MI) {
   // If this is the first instruction being hoisted to the preheader,
   // initialize the CSE map with potential common expressions.
   if (FirstInLoop) {
-    InitCSEMap(CurPreheader);
+    InitCSEMap(Preheader);
     FirstInLoop = false;
   }
 
@@ -789,7 +789,7 @@ void MachineLICM::Hoist(MachineInstr *MI) {
     CI = CSEMap.find(Opcode);
   if (!EliminateCSE(MI, CI)) {
     // Otherwise, splice the instruction to the preheader.
-    CurPreheader->splice(CurPreheader->getFirstTerminator(),MI->getParent(),MI);
+    Preheader->splice(Preheader->getFirstTerminator(),MI->getParent(),MI);
 
     // Clear the kill flags of any register this instruction defines,
     // since they may need to be live throughout the entire loop
@@ -813,3 +813,30 @@ void MachineLICM::Hoist(MachineInstr *MI) {
   ++NumHoisted;
   Changed = true;
 }
+
+MachineBasicBlock *MachineLICM::getCurPreheader() {
+  // Determine the block to which to hoist instructions. If we can't find a
+  // suitable loop predecessor, we can't do any hoisting.
+
+  // If we've tried to get a preheader and failed, don't try again.
+  if (CurPreheader == reinterpret_cast<MachineBasicBlock *>(-1))
+    return 0;
+
+  if (!CurPreheader) {
+    CurPreheader = CurLoop->getLoopPreheader();
+    if (!CurPreheader) {
+      MachineBasicBlock *Pred = CurLoop->getLoopPredecessor();
+      if (!Pred) {
+        CurPreheader = reinterpret_cast<MachineBasicBlock *>(-1);
+        return 0;
+      }
+
+      CurPreheader = Pred->SplitCriticalEdge(CurLoop->getHeader(), this);
+      if (!CurPreheader) {
+        CurPreheader = reinterpret_cast<MachineBasicBlock *>(-1);
+        return 0;
+      }
+    }
+  }
+  return CurPreheader;
+}

llvm/lib/CodeGen/PHIElimination.cpp

@@ -34,7 +34,6 @@
 using namespace llvm;
 
 STATISTIC(NumAtomic, "Number of atomic phis lowered");
-STATISTIC(NumSplits, "Number of critical edges split on demand");
 STATISTIC(NumReused, "Number of reused lowered phis");
 
 char PHIElimination::ID = 0;
@@ -391,58 +390,8 @@ bool llvm::PHIElimination::SplitPHIEdges(MachineFunction &MF,
       // (not considering PHI nodes). If the register is live in to this block
       // anyway, we would gain nothing from splitting.
       if (!LV.isLiveIn(Reg, MBB) && LV.isLiveOut(Reg, *PreMBB))
-        SplitCriticalEdge(PreMBB, &MBB);
+        PreMBB->SplitCriticalEdge(&MBB, this);
     }
   }
   return true;
 }
-
-MachineBasicBlock *PHIElimination::SplitCriticalEdge(MachineBasicBlock *A,
-                                                     MachineBasicBlock *B) {
-  assert(A && B && "Missing MBB end point");
-
-  MachineFunction *MF = A->getParent();
-  DebugLoc dl;  // FIXME: this is nowhere
-
-  // We may need to update A's terminator, but we can't do that if AnalyzeBranch
-  // fails. If A uses a jump table, we won't touch it.
-  const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
-  MachineBasicBlock *TBB = 0, *FBB = 0;
-  SmallVector<MachineOperand, 4> Cond;
-  if (TII->AnalyzeBranch(*A, TBB, FBB, Cond))
-    return NULL;
-
-  ++NumSplits;
-
-  MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
-  MF->insert(llvm::next(MachineFunction::iterator(A)), NMBB);
-  DEBUG(dbgs() << "PHIElimination splitting critical edge:"
-        " BB#" << A->getNumber()
-        << " -- BB#" << NMBB->getNumber()
-        << " -- BB#" << B->getNumber() << '\n');
-
-  A->ReplaceUsesOfBlockWith(B, NMBB);
-  A->updateTerminator();
-
-  // Insert unconditional "jump B" instruction in NMBB if necessary.
-  NMBB->addSuccessor(B);
-  if (!NMBB->isLayoutSuccessor(B)) {
-    Cond.clear();
-    MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, B, NULL, Cond, dl);
-  }
-
-  // Fix PHI nodes in B so they refer to NMBB instead of A
-  for (MachineBasicBlock::iterator i = B->begin(), e = B->end();
-       i != e && i->isPHI(); ++i)
-    for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
-      if (i->getOperand(ni+1).getMBB() == A)
-        i->getOperand(ni+1).setMBB(NMBB);
-
-  if (LiveVariables *LV=getAnalysisIfAvailable<LiveVariables>())
-    LV->addNewBlock(NMBB, A, B);
-
-  if (MachineDominatorTree *MDT=getAnalysisIfAvailable<MachineDominatorTree>())
-    MDT->addNewBlock(NMBB, A);
-
-  return NMBB;
-}