diff --git a/lib/CodeGen/RegAllocLocal.cpp b/lib/CodeGen/RegAllocLocal.cpp index 04303cff5bf..d61c3ff2cb5 100644 --- a/lib/CodeGen/RegAllocLocal.cpp +++ b/lib/CodeGen/RegAllocLocal.cpp @@ -671,7 +671,8 @@ void RALocal::ComputeLocalLiveness(MachineBasicBlock& MBB) { // Live-out (of the function) registers contain return values of the function, // so we need to make sure they are alive at return time. - if (!MBB.empty() && MBB.back().getDesc().isReturn()) { + bool BBEndsInReturn = !MBB.empty() && MBB.back().getDesc().isReturn(); + if (BBEndsInReturn) { MachineInstr* Ret = &MBB.back(); for (MachineRegisterInfo::liveout_iterator I = MF->getRegInfo().liveout_begin(), @@ -696,7 +697,10 @@ void RALocal::ComputeLocalLiveness(MachineBasicBlock& MBB) { bool usedOutsideBlock = isPhysReg ? false : UsedInMultipleBlocks.test(MO.getReg() - TargetRegisterInfo::FirstVirtualRegister); - if (!isPhysReg && !usedOutsideBlock) { + + // If the machine BB ends in a return instruction, then the value isn't used + // outside of the BB. + if (!isPhysReg && (!usedOutsideBlock || BBEndsInReturn)) { // DBG_VALUE complicates this: if the only refs of a register outside // this block are DBG_VALUE, we can't keep the reg live just for that, // as it will cause the reg to be spilled at the end of this block when @@ -704,7 +708,7 @@ void RALocal::ComputeLocalLiveness(MachineBasicBlock& MBB) { // happens. bool UsedByDebugValueOnly = false; for (MachineRegisterInfo::reg_iterator UI = MRI.reg_begin(MO.getReg()), - UE = MRI.reg_end(); UI != UE; ++UI) + UE = MRI.reg_end(); UI != UE; ++UI) { // Two cases: // - used in another block // - used in the same block before it is defined (loop) @@ -714,6 +718,7 @@ void RALocal::ComputeLocalLiveness(MachineBasicBlock& MBB) { UsedByDebugValueOnly = true; continue; } + // A non-DBG_VALUE use means we can leave DBG_VALUE uses alone. UsedInMultipleBlocks.set(MO.getReg() - TargetRegisterInfo::FirstVirtualRegister); @@ -721,6 +726,8 @@ void RALocal::ComputeLocalLiveness(MachineBasicBlock& MBB) { UsedByDebugValueOnly = false; break; } + } + if (UsedByDebugValueOnly) for (MachineRegisterInfo::reg_iterator UI = MRI.reg_begin(MO.getReg()), UE = MRI.reg_end(); UI != UE; ++UI) @@ -730,16 +737,16 @@ void RALocal::ComputeLocalLiveness(MachineBasicBlock& MBB) { UI.getOperand().setReg(0U); } - // Physical registers and those that are not live-out of the block - // are killed/dead at their last use/def within this block. - if (isPhysReg || !usedOutsideBlock) { + // Physical registers and those that are not live-out of the block are + // killed/dead at their last use/def within this block. + if (isPhysReg || !usedOutsideBlock || BBEndsInReturn) if (MO.isUse()) { // Don't mark uses that are tied to defs as kills. if (!MI->isRegTiedToDefOperand(idx)) MO.setIsKill(true); - } else + } else { MO.setIsDead(true); - } + } } }