diff options
Diffstat (limited to 'lib/CodeGen/MachineSink.cpp')
-rw-r--r-- | lib/CodeGen/MachineSink.cpp | 60 |
1 files changed, 56 insertions, 4 deletions
diff --git a/lib/CodeGen/MachineSink.cpp b/lib/CodeGen/MachineSink.cpp index 72676fa..7b4bc15 100644 --- a/lib/CodeGen/MachineSink.cpp +++ b/lib/CodeGen/MachineSink.cpp @@ -25,6 +25,7 @@ #include "llvm/Target/TargetRegisterInfo.h" #include "llvm/Target/TargetInstrInfo.h" #include "llvm/Target/TargetMachine.h" +#include "llvm/ADT/SmallSet.h" #include "llvm/ADT/Statistic.h" #include "llvm/Support/Debug.h" #include "llvm/Support/raw_ostream.h" @@ -61,6 +62,7 @@ namespace { bool ProcessBlock(MachineBasicBlock &MBB); bool SinkInstruction(MachineInstr *MI, bool &SawStore); bool AllUsesDominatedByBlock(unsigned Reg, MachineBasicBlock *MBB) const; + bool LiveOutOfBasicBlock(const MachineInstr *MI, unsigned Reg) const; }; } // end anonymous namespace @@ -166,6 +168,44 @@ bool MachineSinking::ProcessBlock(MachineBasicBlock &MBB) { return MadeChange; } +/// LiveOutOfBasicBlock - Determine if the physical register, defined and dead +/// in MI, is live on exit from the basic block. +bool MachineSinking::LiveOutOfBasicBlock(const MachineInstr *MI, + unsigned Reg) const { + assert(TargetRegisterInfo::isPhysicalRegister(Reg) && + "Only want to determine if a physical register is live out of a BB!"); + + const MachineBasicBlock *MBB = MI->getParent(); + SmallSet<unsigned, 8> KilledRegs; + MachineBasicBlock::const_iterator I = MBB->end(); + MachineBasicBlock::const_iterator E = MBB->begin(); + assert(I != E && "How can there be an empty block at this point?!"); + + // Loop through the instructions bottom-up. If we see a kill of the preg + // first, then it's not live out of the BB. If we see a use or def first, then + // we assume that it is live out of the BB. + do { + const MachineInstr &CurMI = *--I; + + for (unsigned i = 0, e = CurMI.getNumOperands(); i != e; ++i) { + const MachineOperand &MO = CurMI.getOperand(i); + if (!MO.isReg()) continue; // Ignore non-register operands. + + unsigned MOReg = MO.getReg(); + if (MOReg == 0) continue; + + if (MOReg == Reg) { + if (MO.isKill()) + return false; + if (MO.isUse() || MO.isDef()) + return true; + } + } + } while (I != E); + + return false; +} + /// 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, bool &SawStore) { @@ -188,6 +228,7 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) { // SuccToSinkTo - This is the successor to sink this instruction to, once we // decide. MachineBasicBlock *SuccToSinkTo = 0; + SmallVector<unsigned, 4> PhysRegs; for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { const MachineOperand &MO = MI->getOperand(i); @@ -216,9 +257,12 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) { if (AllocatableSet.test(AliasReg)) return false; } - } else if (!MO.isDead()) { - // A def that isn't dead. We can't move it. - return false; + } else { + if (!MO.isDead()) + // A def that isn't dead. We can't move it. + return false; + else + PhysRegs.push_back(Reg); } } else { // Virtual register uses are always safe to sink. @@ -281,7 +325,15 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) { // happen with loops. if (MI->getParent() == SuccToSinkTo) return false; - + + // If the instruction to move defines a dead physical register which is live + // when leaving the basic block, don't move it because it could turn into a + // "zombie" define of that preg. E.g., EFLAGS. (<rdar://problem/8030636>) + for (SmallVectorImpl<unsigned>::const_iterator + I = PhysRegs.begin(), E = PhysRegs.end(); I != E; ++I) + if (LiveOutOfBasicBlock(MI, *I)) + return false; + DEBUG(dbgs() << "Sink instr " << *MI << "\tinto block " << *SuccToSinkTo); // If the block has multiple predecessors, this would introduce computation on |