Initial commit of the machine code LICM pass. It successfully hoists this:

_foo:
        li r2, 0
LBB1_1: ; bb
        li r5, 0
        stw r5, 0(r3)
        addi r2, r2, 1
        addi r3, r3, 4
        cmplw cr0, r2, r4
        bne cr0, LBB1_1 ; bb
LBB1_2: ; return
        blr 

to:

_foo:
        li r2, 0
        li r5, 0
LBB1_1: ; bb
        stw r5, 0(r3)
        addi r2, r2, 1
        addi r3, r3, 4
        cmplw cr0, r2, r4
        bne cr0, LBB1_1 ; bb
LBB1_2: ; return
        blr

ZOMG!! :-)

Moar to come...

llvm-svn: 44687

include/llvm/CodeGen/Passes.h

@@ -135,6 +135,10 @@ namespace llvm {
   /// for the Sparc.
   FunctionPass *getRegisterAllocator(TargetMachine &T);
 
+  /// createMachineLICMPass - This pass performs LICM on machine instructions.
+  /// 
+  FunctionPass *createMachineLICMPass();
+
 } // End llvm namespace
 
 #endif

lib/CodeGen/LLVMTargetMachine.cpp

@@ -66,7 +66,9 @@ LLVMTargetMachine::addPassesToEmitFile(FunctionPassManager &PM,
   // Print the instruction selected machine code...
   if (PrintMachineCode)
     PM.add(createMachineFunctionPrinterPass(cerr));
-  
+
+  PM.add(createMachineLICMPass());
+
   // Perform register allocation to convert to a concrete x86 representation
   PM.add(createRegisterAllocator());
   
@@ -92,7 +94,7 @@ LLVMTargetMachine::addPassesToEmitFile(FunctionPassManager &PM,
   // Branch folding must be run after regalloc and prolog/epilog insertion.
   if (!Fast)
     PM.add(createBranchFoldingPass(getEnableTailMergeDefault()));
-    
+
   // Fold redundant debug labels.
   PM.add(createDebugLabelFoldingPass());
   
@@ -175,7 +177,9 @@ bool LLVMTargetMachine::addPassesToEmitMachineCode(FunctionPassManager &PM,
   // Print the instruction selected machine code...
   if (PrintMachineCode)
     PM.add(createMachineFunctionPrinterPass(cerr));
-  
+
+  PM.add(createMachineLICMPass());
+
   // Perform register allocation to convert to a concrete x86 representation
   PM.add(createRegisterAllocator());
   
@@ -204,7 +208,7 @@ bool LLVMTargetMachine::addPassesToEmitMachineCode(FunctionPassManager &PM,
   // Branch folding must be run after regalloc and prolog/epilog insertion.
   if (!Fast)
     PM.add(createBranchFoldingPass(getEnableTailMergeDefault()));
-  
+
   if (addPreEmitPass(PM, Fast) && PrintMachineCode)
     PM.add(createMachineFunctionPrinterPass(cerr));
 

lib/CodeGen/MachineLICM.cpp

@@ -0,0 +1,336 @@
+//===-- MachineLICM.cpp - Machine Loop Invariant Code Motion Pass ---------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by Bill Wendling and is distributed under the
+// University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass performs loop invariant code motion on machine instructions. We
+// attempt to remove as much code from the body of a loop as possible.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "machine-licm"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineDominators.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Target/MRegisterInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include <map>
+
+using namespace llvm;
+
+namespace {
+  // Hidden options to help debugging
+  cl::opt<bool>
+  PerformLICM("machine-licm",
+              cl::init(false), cl::Hidden);
+}
+
+namespace {
+  class VISIBILITY_HIDDEN MachineLICM : public MachineFunctionPass {
+    // Various analyses that we use...
+    MachineLoopInfo      *LI;   // Current MachineLoopInfo
+    MachineDominatorTree *DT;   // Machine dominator tree for the current Loop
+
+    const TargetInstrInfo *TII;
+
+    // State that is updated as we process loops
+    bool         Changed;       // True if a loop is changed.
+    MachineLoop *CurLoop;       // The current loop we are working on.
+
+    // Map the def of a virtual register to the machine instruction.
+    std::map<unsigned, const MachineInstr*> VRegDefs;
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    MachineLICM() : MachineFunctionPass((intptr_t)&ID) {}
+
+    virtual bool runOnMachineFunction(MachineFunction &MF);
+
+    /// FIXME: Loop preheaders?
+    ///
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.setPreservesCFG();
+      AU.addRequired<MachineLoopInfo>();
+      AU.addRequired<MachineDominatorTree>();
+    }
+  private:
+    /// GatherAllLoops - Get all loops in depth first order.
+    /// 
+    void GatherAllLoops(MachineLoop *L, SmallVectorImpl<MachineLoop*> &Loops) {
+      const std::vector<MachineLoop*> &SubLoops = L->getSubLoops();
+
+      for (MachineLoop::iterator
+             I = SubLoops.begin(), E = SubLoops.end(); I != E; ++I)
+        GatherAllLoops(*I, Loops);
+
+      Loops.push_back(L);
+    }
+
+    /// MapVirtualRegisterDefs - Create a map of which machine instruction
+    /// defines a virtual register.
+    /// 
+    void MapVirtualRegisterDefs(const MachineFunction &MF);
+
+    /// isInSubLoop - A little predicate that returns true if the specified
+    /// basic block is in a subloop of the current one, not the current one
+    /// itself.
+    ///
+    bool isInSubLoop(MachineBasicBlock *BB) {
+      assert(CurLoop->contains(BB) && "Only valid if BB is IN the loop");
+
+      for (MachineLoop::iterator
+             I = CurLoop->begin(), E = CurLoop->end(); I != E; ++I)
+        if ((*I)->contains(BB))
+          return true;  // A subloop actually contains this block!
+
+      return false;
+    }
+
+    /// CanHoistInst - Checks that this instructions is one that can be hoisted
+    /// out of the loop. I.e., it has no side effects, isn't a control flow
+    /// instr, etc.
+    ///
+    bool CanHoistInst(MachineInstr &I) const {
+      const TargetInstrDescriptor *TID = I.getInstrDescriptor();
+      MachineOpCode Opcode = TID->Opcode;
+
+      return TII->isTriviallyReMaterializable(&I) &&
+        // FIXME: Below necessary?
+        !(TII->isReturn(Opcode) ||
+          TII->isTerminatorInstr(Opcode) ||
+          TII->isBranch(Opcode) ||
+          TII->isIndirectBranch(Opcode) ||
+          TII->isBarrier(Opcode) ||
+          TII->isCall(Opcode) ||
+          TII->isLoad(Opcode) || // TODO: Do loads and stores.
+          TII->isStore(Opcode));
+    }
+
+    /// isLoopInvariantInst - Returns true if the instruction is loop
+    /// invariant. I.e., all virtual register operands are defined outside of
+    /// the loop, physical registers aren't accessed (explicitly or implicitly),
+    /// and the instruction is hoistable.
+    /// 
+    bool isLoopInvariantInst(MachineInstr &I);
+
+    /// FindPredecessors - Get all of the predecessors of the loop that are not
+    /// back-edges.
+    /// 
+    void FindPredecessors(std::vector<MachineBasicBlock*> &Preds){
+      const MachineBasicBlock *Header = CurLoop->getHeader();
+
+      for (MachineBasicBlock::const_pred_iterator
+             I = Header->pred_begin(), E = Header->pred_end(); I != E; ++I)
+        if (!CurLoop->contains(*I))
+          Preds.push_back(*I);
+    }
+
+    /// MoveInstToBlock - Moves the machine instruction to the bottom of the
+    /// predecessor basic block (but before the terminator instructions).
+    /// 
+    void MoveInstToBlock(MachineBasicBlock *MBB, MachineInstr *MI) {
+      MachineBasicBlock::iterator Iter = MBB->getFirstTerminator();
+      MBB->insert(Iter, MI);
+    }
+
+    /// HoistRegion - Walk the specified region of the CFG (defined by all
+    /// blocks dominated by the specified block, and that are in the current
+    /// loop) in depth first order w.r.t the DominatorTree. This allows us to
+    /// visit definitions before uses, allowing us to hoist a loop body in one
+    /// pass without iteration.
+    ///
+    void HoistRegion(MachineDomTreeNode *N);
+
+    /// Hoist - When an instruction is found to only use loop invariant operands
+    /// that is safe to hoist, this instruction is called to do the dirty work.
+    ///
+    bool Hoist(MachineInstr &MI);
+  };
+
+  char MachineLICM::ID = 0;
+  RegisterPass<MachineLICM> X("machine-licm",
+                              "Machine Loop Invariant Code Motion");
+} // end anonymous namespace
+
+FunctionPass *llvm::createMachineLICMPass() { return new MachineLICM(); }
+
+/// Hoist expressions out of the specified loop. Note, alias info for inner loop
+/// is not preserved so it is not a good idea to run LICM multiple times on one
+/// loop.
+///
+bool MachineLICM::runOnMachineFunction(MachineFunction &MF) {
+  if (!PerformLICM) return false; // For debugging.
+
+  Changed = false;
+  TII = MF.getTarget().getInstrInfo();
+
+  // Get our Loop information...
+  LI = &getAnalysis<MachineLoopInfo>();
+  DT = &getAnalysis<MachineDominatorTree>();
+
+  for (MachineLoopInfo::iterator
+         I = LI->begin(), E = LI->end(); I != E; ++I) {
+    MachineLoop *L = *I;
+    CurLoop = L;
+
+    // Visit all of the instructions of the loop. We want to visit the subloops
+    // first, though, so that we can hoist their invariants first into their
+    // containing loop before we process that loop.
+    SmallVector<MachineLoop*, 16> Loops;
+    GatherAllLoops(L, Loops);
+
+    for (SmallVector<MachineLoop*, 8>::iterator
+           II = Loops.begin(), IE = Loops.end(); II != IE; ++II) {
+      L = *II;
+
+      // Traverse the body of the loop in depth first order on the dominator
+      // tree so that we are guaranteed to see definitions before we see uses.
+      HoistRegion(DT->getNode(L->getHeader()));
+    }
+  }
+
+  return Changed;
+}
+
+/// MapVirtualRegisterDefs - Create a map of which machine instruction defines a
+/// virtual register.
+/// 
+void MachineLICM::MapVirtualRegisterDefs(const MachineFunction &MF) {
+  for (MachineFunction::const_iterator
+         I = MF.begin(), E = MF.end(); I != E; ++I) {
+    const MachineBasicBlock &MBB = *I;
+
+    for (MachineBasicBlock::const_iterator
+           II = MBB.begin(), IE = MBB.end(); II != IE; ++II) {
+      const MachineInstr &MI = *II;
+
+      if (MI.getNumOperands() > 0) {
+        const MachineOperand &MO = MI.getOperand(0);
+
+        if (MO.isRegister() && MO.isDef() &&
+            MRegisterInfo::isVirtualRegister(MO.getReg()))
+          VRegDefs[MO.getReg()] = &MI;
+      }
+    }
+  }
+}
+
+/// HoistRegion - Walk the specified region of the CFG (defined by all blocks
+/// dominated by the specified block, and that are in the current loop) in depth
+/// first order w.r.t the DominatorTree. This allows us to visit definitions
+/// before uses, allowing us to hoist a loop body in one pass without iteration.
+///
+void MachineLICM::HoistRegion(MachineDomTreeNode *N) {
+  assert(N != 0 && "Null dominator tree node?");
+  MachineBasicBlock *BB = N->getBlock();
+
+  // If this subregion is not in the top level loop at all, exit.
+  if (!CurLoop->contains(BB)) return;
+
+  // Only need to process the contents of this block if it is not part of a
+  // subloop (which would already have been processed).
+  if (!isInSubLoop(BB))
+    for (MachineBasicBlock::iterator
+           I = BB->begin(), E = BB->end(); I != E; ) {
+      MachineInstr &MI = *I++;
+
+      // Try hoisting the instruction out of the loop. We can only do this if
+      // all of the operands of the instruction are loop invariant and if it is
+      // safe to hoist the instruction.
+      if (Hoist(MI))
+        // Hoisting was successful! Remove bothersome instruction now.
+        MI.getParent()->remove(&MI);
+    }
+
+  const std::vector<MachineDomTreeNode*> &Children = N->getChildren();
+
+  for (unsigned I = 0, E = Children.size(); I != E; ++I)
+    HoistRegion(Children[I]);
+}
+
+/// isLoopInvariantInst - Returns true if the instruction is loop
+/// invariant. I.e., all virtual register operands are defined outside of the
+/// loop, physical registers aren't accessed (explicitly or implicitly), and the
+/// instruction is hoistable.
+/// 
+bool MachineLICM::isLoopInvariantInst(MachineInstr &I) {
+  const TargetInstrDescriptor *TID = I.getInstrDescriptor();
+
+  // Don't hoist if this instruction implicitly reads physical registers or
+  // doesn't take any operands.
+  if (TID->ImplicitUses || !I.getNumOperands()) return false;
+
+  if (!CanHoistInst(I)) return false;
+
+  // The instruction is loop invariant if all of its operands are loop-invariant
+  for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
+    const MachineOperand &MO = I.getOperand(i);
+
+    if (!MO.isRegister() || !MO.isUse())
+      continue;
+
+    unsigned Reg = MO.getReg();
+
+    // Don't hoist instructions that access physical registers.
+    if (!MRegisterInfo::isVirtualRegister(Reg))
+      return false;
+
+    assert(VRegDefs[Reg] && "Machine instr not mapped for this vreg?!");
+
+    // If the loop contains the definition of an operand, then the instruction
+    // isn't loop invariant.
+    if (CurLoop->contains(VRegDefs[Reg]->getParent()))
+      return false;
+  }
+
+  // If we got this far, the instruction is loop invariant!
+  return true;
+}
+
+/// Hoist - When an instruction is found to only use loop invariant operands
+/// that is safe to hoist, this instruction is called to do the dirty work.
+///
+bool MachineLICM::Hoist(MachineInstr &MI) {
+  if (!isLoopInvariantInst(MI)) return false;
+
+  std::vector<MachineBasicBlock*> Preds;
+
+  // Non-back-edge predecessors.
+  FindPredecessors(Preds);
+  if (Preds.empty()) return false;
+
+  // Check that the predecessors are qualified to take the hoisted
+  // instruction. I.e., there is only one edge from each predecessor, and it's
+  // to the loop header.
+  for (std::vector<MachineBasicBlock*>::iterator
+         I = Preds.begin(), E = Preds.end(); I != E; ++I) {
+    MachineBasicBlock *MBB = *I;
+
+    // FIXME: We are assuming at first that the basic blocks coming into this
+    // loop have only one successor each. This isn't the case in general because
+    // we haven't broken critical edges or added preheaders.
+    if (MBB->succ_size() != 1) return false;
+    assert(*MBB->succ_begin() == CurLoop->getHeader() &&
+           "The predecessor doesn't feed directly into the loop header!");
+  }
+
+  // Now move the instructions to the predecessors.
+  for (std::vector<MachineBasicBlock*>::iterator
+         I = Preds.begin(), E = Preds.end(); I != E; ++I)
+    MoveInstToBlock(*I, MI.clone());
+
+  Changed = true;
+  return true;
+}

lib/Target/PowerPC/PPCInstrInfo.td

@@ -684,12 +684,15 @@ def MULLI  : DForm_2< 7, (outs GPRC:$rD), (ins GPRC:$rA, s16imm:$imm),
 def SUBFIC : DForm_2< 8, (outs GPRC:$rD), (ins GPRC:$rA, s16imm:$imm),
                      "subfic $rD, $rA, $imm", IntGeneral,
                      [(set GPRC:$rD, (subc immSExt16:$imm, GPRC:$rA))]>;
-def LI  : DForm_2_r0<14, (outs GPRC:$rD), (ins symbolLo:$imm),
-                     "li $rD, $imm", IntGeneral,
-                     [(set GPRC:$rD, immSExt16:$imm)]>;
-def LIS : DForm_2_r0<15, (outs GPRC:$rD), (ins symbolHi:$imm),
-                     "lis $rD, $imm", IntGeneral,
-                     [(set GPRC:$rD, imm16ShiftedSExt:$imm)]>;
+
+let isReMaterializable = 1 in {
+  def LI  : DForm_2_r0<14, (outs GPRC:$rD), (ins symbolLo:$imm),
+                       "li $rD, $imm", IntGeneral,
+                       [(set GPRC:$rD, immSExt16:$imm)]>;
+  def LIS : DForm_2_r0<15, (outs GPRC:$rD), (ins symbolHi:$imm),
+                       "lis $rD, $imm", IntGeneral,
+                       [(set GPRC:$rD, imm16ShiftedSExt:$imm)]>;
+}
 }
 
 let PPC970_Unit = 1 in {  // FXU Operations.