--- /dev/null
+//===-- MachineSink.cpp - Sinking for machine instructions ----------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "machine-sink"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/MachineDominators.h"
+#include "llvm/Target/MRegisterInfo.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
+using namespace llvm;
+
+STATISTIC(NumSunk, "Number of machine instructions sunk");
+
+namespace {
+ class VISIBILITY_HIDDEN MachineSinking : public MachineFunctionPass {
+ const TargetMachine *TM;
+ const TargetInstrInfo *TII;
+ MachineFunction *CurMF; // Current MachineFunction
+ MachineRegisterInfo *RegInfo; // Machine register information
+ MachineDominatorTree *DT; // Machine dominator tree for the current Loop
+
+ public:
+ static char ID; // Pass identification
+ MachineSinking() : MachineFunctionPass((intptr_t)&ID) {}
+
+ virtual bool runOnMachineFunction(MachineFunction &MF);
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ MachineFunctionPass::getAnalysisUsage(AU);
+ AU.addRequired<MachineDominatorTree>();
+ AU.addPreserved<MachineDominatorTree>();
+ }
+ private:
+ bool ProcessBlock(MachineBasicBlock &MBB);
+ bool SinkInstruction(MachineInstr *MI);
+ bool AllUsesDominatedByBlock(unsigned Reg, MachineBasicBlock *MBB) const;
+ };
+
+ char MachineSinking::ID = 0;
+ RegisterPass<MachineSinking> X("machine-sink", "Machine code sinking");
+} // end anonymous namespace
+
+FunctionPass *llvm::createMachineSinkingPass() { return new MachineSinking(); }
+
+/// AllUsesDominatedByBlock - Return true if all uses of the specified register
+/// occur in blocks dominated by the specified block.
+bool MachineSinking::AllUsesDominatedByBlock(unsigned Reg,
+ MachineBasicBlock *MBB) const {
+ assert(MRegisterInfo::isVirtualRegister(Reg) && "Only makes sense for vregs");
+ for (MachineRegisterInfo::reg_iterator I = RegInfo->reg_begin(Reg),
+ E = RegInfo->reg_end(); I != E; ++I) {
+ if (I.getOperand().isDef()) continue; // ignore def.
+
+ // Determine the block of the use.
+ MachineInstr *UseInst = &*I;
+ MachineBasicBlock *UseBlock = UseInst->getParent();
+ if (UseInst->getOpcode() == TargetInstrInfo::PHI) {
+ // PHI nodes use the operand in the predecessor block, not the block with
+ // the PHI.
+ UseBlock = UseInst->getOperand(I.getOperandNo()+1).getMBB();
+ }
+ // Check that it dominates.
+ if (!DT->dominates(MBB, UseBlock))
+ return false;
+ }
+ return true;
+}
+
+
+
+bool MachineSinking::runOnMachineFunction(MachineFunction &MF) {
+ DOUT << "******** Machine Sinking ********\n";
+
+ CurMF = &MF;
+ TM = &CurMF->getTarget();
+ TII = TM->getInstrInfo();
+ RegInfo = &CurMF->getRegInfo();
+ DT = &getAnalysis<MachineDominatorTree>();
+
+ bool EverMadeChange = false;
+
+ while (1) {
+ bool MadeChange = false;
+
+ // Process all basic blocks.
+ for (MachineFunction::iterator I = CurMF->begin(), E = CurMF->end();
+ I != E; ++I)
+ MadeChange |= ProcessBlock(*I);
+
+ // If this iteration over the code changed anything, keep iterating.
+ if (!MadeChange) break;
+ EverMadeChange = true;
+ }
+ return EverMadeChange;
+}
+
+bool MachineSinking::ProcessBlock(MachineBasicBlock &MBB) {
+ bool MadeChange = false;
+
+ // Can't sink anything out of a block that has less than two successors.
+ if (MBB.succ_size() <= 1) return false;
+
+ // Walk the basic block bottom-up
+ for (MachineBasicBlock::iterator I = MBB.end(); I != MBB.begin(); ){
+ MachineBasicBlock::iterator LastIt = I;
+ if (SinkInstruction(--I)) {
+ I = LastIt;
+ ++NumSunk;
+ }
+ }
+
+ return MadeChange;
+}
+
+/// SinkInstruction - Determine whether it is safe to sink the specified machine
+/// instruction out of its current block into a successor.
+bool MachineSinking::SinkInstruction(MachineInstr *MI) {
+ // Loop over all the operands of the specified instruction. If there is
+ // anything we can't handle, bail out.
+ MachineBasicBlock *ParentBlock = MI->getParent();
+
+ // SuccToSinkTo - This is the successor to sink this instruction to, once we
+ // decide.
+ MachineBasicBlock *SuccToSinkTo = 0;
+
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ const MachineOperand &MO = MI->getOperand(i);
+ if (!MO.isReg()) continue; // Ignore non-register operands.
+
+ unsigned Reg = MO.getReg();
+ if (Reg == 0) continue;
+
+ if (MRegisterInfo::isPhysicalRegister(Reg)) {
+ // If this is a physical register use, we can't move it. If it is a def,
+ // we can move it, but only if the def is dead.
+ if (MO.isUse() || !MO.isDead())
+ return false;
+ } else {
+ // Virtual register uses are always safe to sink.
+ if (MO.isUse()) continue;
+
+ // Virtual register defs can only be sunk if all their uses are in blocks
+ // dominated by one of the successors.
+ if (SuccToSinkTo) {
+ // If a previous operand picked a block to sink to, then this operand
+ // must be sinkable to the same block.
+ if (!AllUsesDominatedByBlock(Reg, SuccToSinkTo))
+ return false;
+ continue;
+ }
+
+ // Otherwise, we should look at all the successors and decide which one
+ // we should sink to.
+ for (MachineBasicBlock::succ_iterator SI = ParentBlock->succ_begin(),
+ E = ParentBlock->succ_end(); SI != E; ++SI) {
+ if (AllUsesDominatedByBlock(Reg, *SI)) {
+ SuccToSinkTo = *SI;
+ break;
+ }
+ }
+
+ // If we couldn't find a block to sink to, ignore this instruction.
+ if (SuccToSinkTo == 0)
+ return false;
+ }
+ }
+
+ // FIXME: Check that the instr doesn't have side effects etc.
+
+ DEBUG(cerr << "Sink instr " << *MI);
+ DEBUG(cerr << "to block " << *SuccToSinkTo);
+
+ // If the block has multiple predecessors, this would introduce computation on
+ // a path that it doesn't already exist. We could split the critical edge,
+ // but for now we just punt.
+ if (SuccToSinkTo->pred_size() > 1) {
+ DEBUG(cerr << " *** PUNTING: Critical edge found\n");
+ return false;
+ }
+
+ // Determine where to insert into. Skip phi nodes.
+ MachineBasicBlock::iterator InsertPos = SuccToSinkTo->begin();
+ while (InsertPos != SuccToSinkTo->end() &&
+ InsertPos->getOpcode() == TargetInstrInfo::PHI)
+ ++InsertPos;
+
+ // Move the instruction.
+ SuccToSinkTo->splice(InsertPos, ParentBlock, MI,
+ ++MachineBasicBlock::iterator(MI));
+ return true;
+}
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