From f14a648d80bcb45fa07db35f8f1f58e47111dc9e Mon Sep 17 00:00:00 2001 From: Jakob Stoklund Olesen Date: Tue, 31 Aug 2010 21:51:05 +0000 Subject: Track liveness of unallocatable, unreserved registers in machine DCE. Reserved registers are unpredictable, and are treated as always live by machine DCE. Allocatable registers are never reserved, and can be used for virtual registers. Unreserved, unallocatable registers can not be used for virtual registers, but otherwise behave like a normal allocatable register. Most targets only have the flag register in this set. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112649 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/CodeGen/DeadMachineInstructionElim.cpp | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/lib/CodeGen/DeadMachineInstructionElim.cpp b/lib/CodeGen/DeadMachineInstructionElim.cpp index 138b83d4b6..318d922ade 100644 --- a/lib/CodeGen/DeadMachineInstructionElim.cpp +++ b/lib/CodeGen/DeadMachineInstructionElim.cpp @@ -80,9 +80,8 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) { TRI = MF.getTarget().getRegisterInfo(); TII = MF.getTarget().getInstrInfo(); - // Compute a bitvector to represent all non-allocatable physregs. - BitVector NonAllocatableRegs = TRI->getAllocatableSet(MF); - NonAllocatableRegs.flip(); + // Treat reserved registers as always live. + BitVector ReservedRegs = TRI->getReservedRegs(MF); // Loop over all instructions in all blocks, from bottom to top, so that it's // more likely that chains of dependent but ultimately dead instructions will @@ -91,9 +90,8 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) { I != E; ++I) { MachineBasicBlock *MBB = &*I; - // Start out assuming that all non-allocatable registers are live - // out of this block. - LivePhysRegs = NonAllocatableRegs; + // Start out assuming that reserved registers are live out of this block. + LivePhysRegs = ReservedRegs; // Also add any explicit live-out physregs for this block. if (!MBB->empty() && MBB->back().getDesc().isReturn()) @@ -104,6 +102,10 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) { LivePhysRegs.set(Reg); } + // FIXME: Add live-ins from sucessors to LivePhysRegs. Normally, physregs + // are not live across blocks, but some targets (x86) can have flags live + // out of a block. + // Now scan the instructions and delete dead ones, tracking physreg // liveness as we go. for (MachineBasicBlock::reverse_iterator MII = MBB->rbegin(), -- cgit v1.2.3