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Summary: The RegisterScavenger explicitly ignores <kill> flags on operands of predicated instructions and therefore assumes that such registers remain live. When it then scavenges such a register, it inserts a spill of this (killed) register. This is invalid code and gets flagged up by the verifier. Nowadays kill flags are set correctly on predicated instructions. This patch makes the Scavenger respect them. The bug has so far only been triggered by an internal pass, so I don't have a test case unfortunately. Fixes PR23119. Reviewers: hfinkel, tobiasvk_caf Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D9039 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239439 91177308-0d34-0410-b5e6-96231b3b80d8
443 lines
14 KiB
C++
443 lines
14 KiB
C++
//===-- RegisterScavenging.cpp - Machine register scavenging --------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the machine register scavenger. It can provide
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// information, such as unused registers, at any point in a machine basic block.
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// It also provides a mechanism to make registers available by evicting them to
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// spill slots.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/RegisterScavenging.h"
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#include "llvm/CodeGen/MachineBasicBlock.h"
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#include "llvm/CodeGen/MachineFrameInfo.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineInstr.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetRegisterInfo.h"
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#include "llvm/Target/TargetSubtargetInfo.h"
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using namespace llvm;
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#define DEBUG_TYPE "reg-scavenging"
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/// setUsed - Set the register units of this register as used.
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void RegScavenger::setRegUsed(unsigned Reg) {
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for (MCRegUnitIterator RUI(Reg, TRI); RUI.isValid(); ++RUI)
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RegUnitsAvailable.reset(*RUI);
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}
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void RegScavenger::initRegState() {
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for (SmallVectorImpl<ScavengedInfo>::iterator I = Scavenged.begin(),
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IE = Scavenged.end(); I != IE; ++I) {
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I->Reg = 0;
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I->Restore = nullptr;
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}
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// All register units start out unused.
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RegUnitsAvailable.set();
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if (!MBB)
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return;
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// Live-in registers are in use.
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for (MachineBasicBlock::livein_iterator I = MBB->livein_begin(),
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E = MBB->livein_end(); I != E; ++I)
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setRegUsed(*I);
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// Pristine CSRs are also unavailable.
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const MachineFunction &MF = *MBB->getParent();
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BitVector PR = MF.getFrameInfo()->getPristineRegs(MF);
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for (int I = PR.find_first(); I>0; I = PR.find_next(I))
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setRegUsed(I);
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}
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void RegScavenger::enterBasicBlock(MachineBasicBlock *mbb) {
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MachineFunction &MF = *mbb->getParent();
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TII = MF.getSubtarget().getInstrInfo();
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TRI = MF.getSubtarget().getRegisterInfo();
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MRI = &MF.getRegInfo();
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assert((NumRegUnits == 0 || NumRegUnits == TRI->getNumRegUnits()) &&
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"Target changed?");
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// It is not possible to use the register scavenger after late optimization
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// passes that don't preserve accurate liveness information.
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assert(MRI->tracksLiveness() &&
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"Cannot use register scavenger with inaccurate liveness");
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// Self-initialize.
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if (!MBB) {
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NumRegUnits = TRI->getNumRegUnits();
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RegUnitsAvailable.resize(NumRegUnits);
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KillRegUnits.resize(NumRegUnits);
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DefRegUnits.resize(NumRegUnits);
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TmpRegUnits.resize(NumRegUnits);
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}
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MBB = mbb;
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initRegState();
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Tracking = false;
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}
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void RegScavenger::addRegUnits(BitVector &BV, unsigned Reg) {
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for (MCRegUnitIterator RUI(Reg, TRI); RUI.isValid(); ++RUI)
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BV.set(*RUI);
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}
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void RegScavenger::determineKillsAndDefs() {
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assert(Tracking && "Must be tracking to determine kills and defs");
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MachineInstr *MI = MBBI;
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assert(!MI->isDebugValue() && "Debug values have no kills or defs");
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// Find out which registers are early clobbered, killed, defined, and marked
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// def-dead in this instruction.
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KillRegUnits.reset();
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DefRegUnits.reset();
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for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
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const MachineOperand &MO = MI->getOperand(i);
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if (MO.isRegMask()) {
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TmpRegUnits.clear();
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for (unsigned RU = 0, RUEnd = TRI->getNumRegUnits(); RU != RUEnd; ++RU) {
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for (MCRegUnitRootIterator RURI(RU, TRI); RURI.isValid(); ++RURI) {
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if (MO.clobbersPhysReg(*RURI)) {
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TmpRegUnits.set(RU);
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break;
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}
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}
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}
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// Apply the mask.
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KillRegUnits |= TmpRegUnits;
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}
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if (!MO.isReg())
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continue;
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unsigned Reg = MO.getReg();
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if (!Reg || TargetRegisterInfo::isVirtualRegister(Reg) || isReserved(Reg))
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continue;
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if (MO.isUse()) {
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// Ignore undef uses.
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if (MO.isUndef())
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continue;
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if (MO.isKill())
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addRegUnits(KillRegUnits, Reg);
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} else {
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assert(MO.isDef());
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if (MO.isDead())
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addRegUnits(KillRegUnits, Reg);
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else
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addRegUnits(DefRegUnits, Reg);
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}
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}
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}
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void RegScavenger::unprocess() {
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assert(Tracking && "Cannot unprocess because we're not tracking");
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MachineInstr *MI = MBBI;
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if (!MI->isDebugValue()) {
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determineKillsAndDefs();
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// Commit the changes.
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setUsed(KillRegUnits);
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setUnused(DefRegUnits);
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}
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if (MBBI == MBB->begin()) {
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MBBI = MachineBasicBlock::iterator(nullptr);
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Tracking = false;
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} else
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--MBBI;
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}
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void RegScavenger::forward() {
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// Move ptr forward.
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if (!Tracking) {
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MBBI = MBB->begin();
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Tracking = true;
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} else {
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assert(MBBI != MBB->end() && "Already past the end of the basic block!");
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MBBI = std::next(MBBI);
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}
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assert(MBBI != MBB->end() && "Already at the end of the basic block!");
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MachineInstr *MI = MBBI;
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for (SmallVectorImpl<ScavengedInfo>::iterator I = Scavenged.begin(),
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IE = Scavenged.end(); I != IE; ++I) {
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if (I->Restore != MI)
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continue;
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I->Reg = 0;
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I->Restore = nullptr;
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}
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if (MI->isDebugValue())
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return;
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determineKillsAndDefs();
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// Verify uses and defs.
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#ifndef NDEBUG
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for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
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const MachineOperand &MO = MI->getOperand(i);
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if (!MO.isReg())
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continue;
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unsigned Reg = MO.getReg();
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if (!Reg || TargetRegisterInfo::isVirtualRegister(Reg) || isReserved(Reg))
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continue;
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if (MO.isUse()) {
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if (MO.isUndef())
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continue;
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if (!isRegUsed(Reg)) {
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// Check if it's partial live: e.g.
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// D0 = insert_subreg D0<undef>, S0
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// ... D0
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// The problem is the insert_subreg could be eliminated. The use of
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// D0 is using a partially undef value. This is not *incorrect* since
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// S1 is can be freely clobbered.
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// Ideally we would like a way to model this, but leaving the
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// insert_subreg around causes both correctness and performance issues.
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bool SubUsed = false;
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for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs)
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if (isRegUsed(*SubRegs)) {
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SubUsed = true;
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break;
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}
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bool SuperUsed = false;
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for (MCSuperRegIterator SR(Reg, TRI); SR.isValid(); ++SR) {
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if (isRegUsed(*SR)) {
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SuperUsed = true;
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break;
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}
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}
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if (!SubUsed && !SuperUsed) {
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MBB->getParent()->verify(nullptr, "In Register Scavenger");
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llvm_unreachable("Using an undefined register!");
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}
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(void)SubUsed;
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(void)SuperUsed;
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}
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} else {
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assert(MO.isDef());
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#if 0
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// FIXME: Enable this once we've figured out how to correctly transfer
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// implicit kills during codegen passes like the coalescer.
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assert((KillRegs.test(Reg) || isUnused(Reg) ||
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isLiveInButUnusedBefore(Reg, MI, MBB, TRI, MRI)) &&
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"Re-defining a live register!");
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#endif
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}
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}
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#endif // NDEBUG
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// Commit the changes.
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setUnused(KillRegUnits);
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setUsed(DefRegUnits);
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}
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bool RegScavenger::isRegUsed(unsigned Reg, bool includeReserved) const {
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if (includeReserved && isReserved(Reg))
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return true;
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for (MCRegUnitIterator RUI(Reg, TRI); RUI.isValid(); ++RUI)
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if (!RegUnitsAvailable.test(*RUI))
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return true;
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return false;
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}
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unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RC) const {
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for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end();
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I != E; ++I)
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if (!isRegUsed(*I)) {
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DEBUG(dbgs() << "Scavenger found unused reg: " << TRI->getName(*I) <<
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"\n");
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return *I;
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}
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return 0;
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}
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/// getRegsAvailable - Return all available registers in the register class
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/// in Mask.
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BitVector RegScavenger::getRegsAvailable(const TargetRegisterClass *RC) {
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BitVector Mask(TRI->getNumRegs());
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for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end();
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I != E; ++I)
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if (!isRegUsed(*I))
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Mask.set(*I);
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return Mask;
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}
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/// findSurvivorReg - Return the candidate register that is unused for the
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/// longest after StartMII. UseMI is set to the instruction where the search
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/// stopped.
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///
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/// No more than InstrLimit instructions are inspected.
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///
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unsigned RegScavenger::findSurvivorReg(MachineBasicBlock::iterator StartMI,
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BitVector &Candidates,
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unsigned InstrLimit,
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MachineBasicBlock::iterator &UseMI) {
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int Survivor = Candidates.find_first();
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assert(Survivor > 0 && "No candidates for scavenging");
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MachineBasicBlock::iterator ME = MBB->getFirstTerminator();
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assert(StartMI != ME && "MI already at terminator");
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MachineBasicBlock::iterator RestorePointMI = StartMI;
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MachineBasicBlock::iterator MI = StartMI;
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bool inVirtLiveRange = false;
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for (++MI; InstrLimit > 0 && MI != ME; ++MI, --InstrLimit) {
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if (MI->isDebugValue()) {
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++InstrLimit; // Don't count debug instructions
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continue;
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}
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bool isVirtKillInsn = false;
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bool isVirtDefInsn = false;
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// Remove any candidates touched by instruction.
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for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
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const MachineOperand &MO = MI->getOperand(i);
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if (MO.isRegMask())
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Candidates.clearBitsNotInMask(MO.getRegMask());
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if (!MO.isReg() || MO.isUndef() || !MO.getReg())
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continue;
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if (TargetRegisterInfo::isVirtualRegister(MO.getReg())) {
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if (MO.isDef())
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isVirtDefInsn = true;
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else if (MO.isKill())
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isVirtKillInsn = true;
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continue;
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}
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for (MCRegAliasIterator AI(MO.getReg(), TRI, true); AI.isValid(); ++AI)
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Candidates.reset(*AI);
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}
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// If we're not in a virtual reg's live range, this is a valid
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// restore point.
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if (!inVirtLiveRange) RestorePointMI = MI;
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// Update whether we're in the live range of a virtual register
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if (isVirtKillInsn) inVirtLiveRange = false;
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if (isVirtDefInsn) inVirtLiveRange = true;
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// Was our survivor untouched by this instruction?
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if (Candidates.test(Survivor))
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continue;
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// All candidates gone?
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if (Candidates.none())
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break;
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Survivor = Candidates.find_first();
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}
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// If we ran off the end, that's where we want to restore.
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if (MI == ME) RestorePointMI = ME;
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assert (RestorePointMI != StartMI &&
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"No available scavenger restore location!");
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// We ran out of candidates, so stop the search.
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UseMI = RestorePointMI;
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return Survivor;
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}
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static unsigned getFrameIndexOperandNum(MachineInstr *MI) {
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unsigned i = 0;
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while (!MI->getOperand(i).isFI()) {
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++i;
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assert(i < MI->getNumOperands() &&
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"Instr doesn't have FrameIndex operand!");
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}
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return i;
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}
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unsigned RegScavenger::scavengeRegister(const TargetRegisterClass *RC,
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MachineBasicBlock::iterator I,
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int SPAdj) {
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// Consider all allocatable registers in the register class initially
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BitVector Candidates =
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TRI->getAllocatableSet(*I->getParent()->getParent(), RC);
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// Exclude all the registers being used by the instruction.
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for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
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MachineOperand &MO = I->getOperand(i);
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if (MO.isReg() && MO.getReg() != 0 && !(MO.isUse() && MO.isUndef()) &&
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!TargetRegisterInfo::isVirtualRegister(MO.getReg()))
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Candidates.reset(MO.getReg());
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}
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// Try to find a register that's unused if there is one, as then we won't
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// have to spill.
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BitVector Available = getRegsAvailable(RC);
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Available &= Candidates;
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if (Available.any())
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Candidates = Available;
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// Find the register whose use is furthest away.
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MachineBasicBlock::iterator UseMI;
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unsigned SReg = findSurvivorReg(I, Candidates, 25, UseMI);
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// If we found an unused register there is no reason to spill it.
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if (!isRegUsed(SReg)) {
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DEBUG(dbgs() << "Scavenged register: " << TRI->getName(SReg) << "\n");
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return SReg;
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}
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// Find an available scavenging slot.
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unsigned SI;
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for (SI = 0; SI < Scavenged.size(); ++SI)
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if (Scavenged[SI].Reg == 0)
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break;
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if (SI == Scavenged.size()) {
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// We need to scavenge a register but have no spill slot, the target
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// must know how to do it (if not, we'll assert below).
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Scavenged.push_back(ScavengedInfo());
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}
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// Avoid infinite regress
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Scavenged[SI].Reg = SReg;
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// If the target knows how to save/restore the register, let it do so;
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// otherwise, use the emergency stack spill slot.
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if (!TRI->saveScavengerRegister(*MBB, I, UseMI, RC, SReg)) {
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// Spill the scavenged register before I.
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assert(Scavenged[SI].FrameIndex >= 0 &&
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"Cannot scavenge register without an emergency spill slot!");
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TII->storeRegToStackSlot(*MBB, I, SReg, true, Scavenged[SI].FrameIndex,
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RC, TRI);
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MachineBasicBlock::iterator II = std::prev(I);
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unsigned FIOperandNum = getFrameIndexOperandNum(II);
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TRI->eliminateFrameIndex(II, SPAdj, FIOperandNum, this);
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// Restore the scavenged register before its use (or first terminator).
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TII->loadRegFromStackSlot(*MBB, UseMI, SReg, Scavenged[SI].FrameIndex,
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RC, TRI);
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II = std::prev(UseMI);
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FIOperandNum = getFrameIndexOperandNum(II);
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TRI->eliminateFrameIndex(II, SPAdj, FIOperandNum, this);
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}
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Scavenged[SI].Restore = std::prev(UseMI);
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// Doing this here leads to infinite regress.
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// Scavenged[SI].Reg = SReg;
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DEBUG(dbgs() << "Scavenged register (with spill): " << TRI->getName(SReg) <<
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"\n");
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return SReg;
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}
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