1 //===-- MachineSink.cpp - Sinking for machine instructions ----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "machine-sink"
15 #include "llvm/CodeGen/Passes.h"
16 #include "llvm/CodeGen/MachineRegisterInfo.h"
17 #include "llvm/CodeGen/MachineDominators.h"
18 #include "llvm/Target/MRegisterInfo.h"
19 #include "llvm/Target/TargetInstrInfo.h"
20 #include "llvm/Target/TargetMachine.h"
21 #include "llvm/ADT/SmallVector.h"
22 #include "llvm/ADT/Statistic.h"
23 #include "llvm/Support/Compiler.h"
24 #include "llvm/Support/Debug.h"
27 STATISTIC(NumSunk, "Number of machine instructions sunk");
30 class VISIBILITY_HIDDEN MachineSinking : public MachineFunctionPass {
31 const TargetMachine *TM;
32 const TargetInstrInfo *TII;
33 MachineFunction *CurMF; // Current MachineFunction
34 MachineRegisterInfo *RegInfo; // Machine register information
35 MachineDominatorTree *DT; // Machine dominator tree for the current Loop
38 static char ID; // Pass identification
39 MachineSinking() : MachineFunctionPass((intptr_t)&ID) {}
41 virtual bool runOnMachineFunction(MachineFunction &MF);
43 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
44 MachineFunctionPass::getAnalysisUsage(AU);
45 AU.addRequired<MachineDominatorTree>();
46 AU.addPreserved<MachineDominatorTree>();
49 bool ProcessBlock(MachineBasicBlock &MBB);
50 bool SinkInstruction(MachineInstr *MI);
51 bool AllUsesDominatedByBlock(unsigned Reg, MachineBasicBlock *MBB) const;
54 char MachineSinking::ID = 0;
55 RegisterPass<MachineSinking> X("machine-sink", "Machine code sinking");
56 } // end anonymous namespace
58 FunctionPass *llvm::createMachineSinkingPass() { return new MachineSinking(); }
60 /// AllUsesDominatedByBlock - Return true if all uses of the specified register
61 /// occur in blocks dominated by the specified block.
62 bool MachineSinking::AllUsesDominatedByBlock(unsigned Reg,
63 MachineBasicBlock *MBB) const {
64 assert(MRegisterInfo::isVirtualRegister(Reg) && "Only makes sense for vregs");
65 for (MachineRegisterInfo::reg_iterator I = RegInfo->reg_begin(Reg),
66 E = RegInfo->reg_end(); I != E; ++I) {
67 if (I.getOperand().isDef()) continue; // ignore def.
69 // Determine the block of the use.
70 MachineInstr *UseInst = &*I;
71 MachineBasicBlock *UseBlock = UseInst->getParent();
72 if (UseInst->getOpcode() == TargetInstrInfo::PHI) {
73 // PHI nodes use the operand in the predecessor block, not the block with
75 UseBlock = UseInst->getOperand(I.getOperandNo()+1).getMBB();
77 // Check that it dominates.
78 if (!DT->dominates(MBB, UseBlock))
86 bool MachineSinking::runOnMachineFunction(MachineFunction &MF) {
87 DOUT << "******** Machine Sinking ********\n";
90 TM = &CurMF->getTarget();
91 TII = TM->getInstrInfo();
92 RegInfo = &CurMF->getRegInfo();
93 DT = &getAnalysis<MachineDominatorTree>();
95 bool EverMadeChange = false;
98 bool MadeChange = false;
100 // Process all basic blocks.
101 for (MachineFunction::iterator I = CurMF->begin(), E = CurMF->end();
103 MadeChange |= ProcessBlock(*I);
105 // If this iteration over the code changed anything, keep iterating.
106 if (!MadeChange) break;
107 EverMadeChange = true;
109 return EverMadeChange;
112 bool MachineSinking::ProcessBlock(MachineBasicBlock &MBB) {
113 bool MadeChange = false;
115 // Can't sink anything out of a block that has less than two successors.
116 if (MBB.succ_size() <= 1) return false;
118 // Walk the basic block bottom-up
119 for (MachineBasicBlock::iterator I = MBB.end(); I != MBB.begin(); ){
120 MachineBasicBlock::iterator LastIt = I;
121 if (SinkInstruction(--I)) {
130 /// SinkInstruction - Determine whether it is safe to sink the specified machine
131 /// instruction out of its current block into a successor.
132 bool MachineSinking::SinkInstruction(MachineInstr *MI) {
133 // Don't sink things with side-effects we don't understand.
134 if (TII->hasUnmodelledSideEffects(MI))
137 // Loop over all the operands of the specified instruction. If there is
138 // anything we can't handle, bail out.
139 MachineBasicBlock *ParentBlock = MI->getParent();
141 // SuccToSinkTo - This is the successor to sink this instruction to, once we
143 MachineBasicBlock *SuccToSinkTo = 0;
145 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
146 const MachineOperand &MO = MI->getOperand(i);
147 if (!MO.isReg()) continue; // Ignore non-register operands.
149 unsigned Reg = MO.getReg();
150 if (Reg == 0) continue;
152 if (MRegisterInfo::isPhysicalRegister(Reg)) {
153 // If this is a physical register use, we can't move it. If it is a def,
154 // we can move it, but only if the def is dead.
155 if (MO.isUse() || !MO.isDead())
158 // Virtual register uses are always safe to sink.
159 if (MO.isUse()) continue;
161 // Virtual register defs can only be sunk if all their uses are in blocks
162 // dominated by one of the successors.
164 // If a previous operand picked a block to sink to, then this operand
165 // must be sinkable to the same block.
166 if (!AllUsesDominatedByBlock(Reg, SuccToSinkTo))
171 // Otherwise, we should look at all the successors and decide which one
172 // we should sink to.
173 for (MachineBasicBlock::succ_iterator SI = ParentBlock->succ_begin(),
174 E = ParentBlock->succ_end(); SI != E; ++SI) {
175 if (AllUsesDominatedByBlock(Reg, *SI)) {
181 // If we couldn't find a block to sink to, ignore this instruction.
182 if (SuccToSinkTo == 0)
187 // If there are no outputs, it must have side-effects.
188 if (SuccToSinkTo == 0)
191 // FIXME: Check that the instr doesn't have side effects etc.
193 DEBUG(cerr << "Sink instr " << *MI);
194 DEBUG(cerr << "to block " << *SuccToSinkTo);
196 // If the block has multiple predecessors, this would introduce computation on
197 // a path that it doesn't already exist. We could split the critical edge,
198 // but for now we just punt.
199 if (SuccToSinkTo->pred_size() > 1) {
200 DEBUG(cerr << " *** PUNTING: Critical edge found\n");
204 // Determine where to insert into. Skip phi nodes.
205 MachineBasicBlock::iterator InsertPos = SuccToSinkTo->begin();
206 while (InsertPos != SuccToSinkTo->end() &&
207 InsertPos->getOpcode() == TargetInstrInfo::PHI)
210 // Move the instruction.
211 SuccToSinkTo->splice(InsertPos, ParentBlock, MI,
212 ++MachineBasicBlock::iterator(MI));