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The greedy register allocator tries to split a live-range around each instruction where it is used or defined to relax the constraints on the entire live-range (this is a last chance split before falling back to spill). The goal is to have a big live-range that is unconstrained (i.e., that can use the largest legal register class) and several small local live-range that carry the constraints implied by each instruction. E.g., Let csti be the constraints on operation i. V1= op1 V1(cst1) op2 V1(cst2) V1 live-range is constrained on the intersection of cst1 and cst2. tryInstructionSplit relaxes those constraints by aggressively splitting each def/use point: V1= V2 = V1 V3 = V2 op1 V3(cst1) V4 = V2 op2 V4(cst2) Because of how the coalescer infrastructure works, each new variable (V3, V4) that is alive at the same time as V1 (or its copy, here V2) interfere with V1. Thus, we end up with an uncoalescable copy for each split point. To make tryInstructionSplit less aggressive, we check if the split point actually relaxes the constraints on the whole live-range. If it does not, we do not insert it. Indeed, it will not help the global allocation problem: - V1 will have the same constraints. - V1 will have the same interference + possibly the newly added split variable VS. - VS will produce an uncoalesceable copy if alive at the same time as V1. <rdar://problem/15570057> git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198369 91177308-0d34-0410-b5e6-96231b3b80d8
417 lines
14 KiB
C++
417 lines
14 KiB
C++
//===-- lib/Codegen/MachineRegisterInfo.cpp -------------------------------===//
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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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// Implementation of the MachineRegisterInfo class.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Support/raw_os_ostream.h"
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using namespace llvm;
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// Pin the vtable to this file.
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void MachineRegisterInfo::Delegate::anchor() {}
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MachineRegisterInfo::MachineRegisterInfo(const TargetMachine &TM)
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: TM(TM), TheDelegate(0), IsSSA(true), TracksLiveness(true) {
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VRegInfo.reserve(256);
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RegAllocHints.reserve(256);
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UsedRegUnits.resize(getTargetRegisterInfo()->getNumRegUnits());
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UsedPhysRegMask.resize(getTargetRegisterInfo()->getNumRegs());
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// Create the physreg use/def lists.
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PhysRegUseDefLists =
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new MachineOperand*[getTargetRegisterInfo()->getNumRegs()];
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memset(PhysRegUseDefLists, 0,
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sizeof(MachineOperand*)*getTargetRegisterInfo()->getNumRegs());
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}
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MachineRegisterInfo::~MachineRegisterInfo() {
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delete [] PhysRegUseDefLists;
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}
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/// setRegClass - Set the register class of the specified virtual register.
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///
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void
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MachineRegisterInfo::setRegClass(unsigned Reg, const TargetRegisterClass *RC) {
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assert(RC && RC->isAllocatable() && "Invalid RC for virtual register");
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VRegInfo[Reg].first = RC;
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}
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const TargetRegisterClass *
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MachineRegisterInfo::constrainRegClass(unsigned Reg,
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const TargetRegisterClass *RC,
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unsigned MinNumRegs) {
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const TargetRegisterClass *OldRC = getRegClass(Reg);
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if (OldRC == RC)
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return RC;
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const TargetRegisterClass *NewRC =
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getTargetRegisterInfo()->getCommonSubClass(OldRC, RC);
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if (!NewRC || NewRC == OldRC)
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return NewRC;
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if (NewRC->getNumRegs() < MinNumRegs)
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return 0;
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setRegClass(Reg, NewRC);
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return NewRC;
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}
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bool
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MachineRegisterInfo::recomputeRegClass(unsigned Reg, const TargetMachine &TM) {
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const TargetInstrInfo *TII = TM.getInstrInfo();
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const TargetRegisterClass *OldRC = getRegClass(Reg);
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const TargetRegisterClass *NewRC =
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getTargetRegisterInfo()->getLargestLegalSuperClass(OldRC);
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// Stop early if there is no room to grow.
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if (NewRC == OldRC)
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return false;
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// Accumulate constraints from all uses.
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for (reg_nodbg_iterator I = reg_nodbg_begin(Reg), E = reg_nodbg_end(); I != E;
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++I) {
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// Apply the effect of the given operand to NewRC.
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NewRC = I->getRegClassConstraintEffect(I.getOperandNo(), NewRC, TII,
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getTargetRegisterInfo());
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if (!NewRC || NewRC == OldRC)
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return false;
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}
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setRegClass(Reg, NewRC);
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return true;
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}
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/// createVirtualRegister - Create and return a new virtual register in the
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/// function with the specified register class.
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///
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unsigned
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MachineRegisterInfo::createVirtualRegister(const TargetRegisterClass *RegClass){
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assert(RegClass && "Cannot create register without RegClass!");
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assert(RegClass->isAllocatable() &&
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"Virtual register RegClass must be allocatable.");
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// New virtual register number.
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unsigned Reg = TargetRegisterInfo::index2VirtReg(getNumVirtRegs());
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VRegInfo.grow(Reg);
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VRegInfo[Reg].first = RegClass;
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RegAllocHints.grow(Reg);
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if (TheDelegate)
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TheDelegate->MRI_NoteNewVirtualRegister(Reg);
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return Reg;
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}
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/// clearVirtRegs - Remove all virtual registers (after physreg assignment).
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void MachineRegisterInfo::clearVirtRegs() {
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#ifndef NDEBUG
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for (unsigned i = 0, e = getNumVirtRegs(); i != e; ++i) {
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unsigned Reg = TargetRegisterInfo::index2VirtReg(i);
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if (!VRegInfo[Reg].second)
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continue;
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verifyUseList(Reg);
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llvm_unreachable("Remaining virtual register operands");
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}
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#endif
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VRegInfo.clear();
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}
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void MachineRegisterInfo::verifyUseList(unsigned Reg) const {
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#ifndef NDEBUG
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bool Valid = true;
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for (reg_iterator I = reg_begin(Reg), E = reg_end(); I != E; ++I) {
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MachineOperand *MO = &I.getOperand();
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MachineInstr *MI = MO->getParent();
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if (!MI) {
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errs() << PrintReg(Reg, getTargetRegisterInfo())
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<< " use list MachineOperand " << MO
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<< " has no parent instruction.\n";
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Valid = false;
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}
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MachineOperand *MO0 = &MI->getOperand(0);
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unsigned NumOps = MI->getNumOperands();
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if (!(MO >= MO0 && MO < MO0+NumOps)) {
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errs() << PrintReg(Reg, getTargetRegisterInfo())
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<< " use list MachineOperand " << MO
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<< " doesn't belong to parent MI: " << *MI;
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Valid = false;
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}
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if (!MO->isReg()) {
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errs() << PrintReg(Reg, getTargetRegisterInfo())
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<< " MachineOperand " << MO << ": " << *MO
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<< " is not a register\n";
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Valid = false;
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}
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if (MO->getReg() != Reg) {
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errs() << PrintReg(Reg, getTargetRegisterInfo())
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<< " use-list MachineOperand " << MO << ": "
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<< *MO << " is the wrong register\n";
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Valid = false;
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}
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}
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assert(Valid && "Invalid use list");
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#endif
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}
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void MachineRegisterInfo::verifyUseLists() const {
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#ifndef NDEBUG
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for (unsigned i = 0, e = getNumVirtRegs(); i != e; ++i)
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verifyUseList(TargetRegisterInfo::index2VirtReg(i));
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for (unsigned i = 1, e = getTargetRegisterInfo()->getNumRegs(); i != e; ++i)
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verifyUseList(i);
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#endif
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}
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/// Add MO to the linked list of operands for its register.
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void MachineRegisterInfo::addRegOperandToUseList(MachineOperand *MO) {
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assert(!MO->isOnRegUseList() && "Already on list");
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MachineOperand *&HeadRef = getRegUseDefListHead(MO->getReg());
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MachineOperand *const Head = HeadRef;
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// Head points to the first list element.
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// Next is NULL on the last list element.
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// Prev pointers are circular, so Head->Prev == Last.
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// Head is NULL for an empty list.
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if (!Head) {
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MO->Contents.Reg.Prev = MO;
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MO->Contents.Reg.Next = 0;
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HeadRef = MO;
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return;
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}
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assert(MO->getReg() == Head->getReg() && "Different regs on the same list!");
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// Insert MO between Last and Head in the circular Prev chain.
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MachineOperand *Last = Head->Contents.Reg.Prev;
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assert(Last && "Inconsistent use list");
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assert(MO->getReg() == Last->getReg() && "Different regs on the same list!");
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Head->Contents.Reg.Prev = MO;
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MO->Contents.Reg.Prev = Last;
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// Def operands always precede uses. This allows def_iterator to stop early.
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// Insert def operands at the front, and use operands at the back.
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if (MO->isDef()) {
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// Insert def at the front.
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MO->Contents.Reg.Next = Head;
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HeadRef = MO;
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} else {
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// Insert use at the end.
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MO->Contents.Reg.Next = 0;
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Last->Contents.Reg.Next = MO;
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}
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}
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/// Remove MO from its use-def list.
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void MachineRegisterInfo::removeRegOperandFromUseList(MachineOperand *MO) {
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assert(MO->isOnRegUseList() && "Operand not on use list");
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MachineOperand *&HeadRef = getRegUseDefListHead(MO->getReg());
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MachineOperand *const Head = HeadRef;
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assert(Head && "List already empty");
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// Unlink this from the doubly linked list of operands.
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MachineOperand *Next = MO->Contents.Reg.Next;
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MachineOperand *Prev = MO->Contents.Reg.Prev;
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// Prev links are circular, next link is NULL instead of looping back to Head.
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if (MO == Head)
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HeadRef = Next;
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else
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Prev->Contents.Reg.Next = Next;
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(Next ? Next : Head)->Contents.Reg.Prev = Prev;
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MO->Contents.Reg.Prev = 0;
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MO->Contents.Reg.Next = 0;
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}
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/// Move NumOps operands from Src to Dst, updating use-def lists as needed.
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///
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/// The Dst range is assumed to be uninitialized memory. (Or it may contain
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/// operands that won't be destroyed, which is OK because the MO destructor is
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/// trivial anyway).
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///
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/// The Src and Dst ranges may overlap.
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void MachineRegisterInfo::moveOperands(MachineOperand *Dst,
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MachineOperand *Src,
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unsigned NumOps) {
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assert(Src != Dst && NumOps && "Noop moveOperands");
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// Copy backwards if Dst is within the Src range.
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int Stride = 1;
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if (Dst >= Src && Dst < Src + NumOps) {
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Stride = -1;
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Dst += NumOps - 1;
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Src += NumOps - 1;
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}
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// Copy one operand at a time.
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do {
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new (Dst) MachineOperand(*Src);
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// Dst takes Src's place in the use-def chain.
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if (Src->isReg()) {
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MachineOperand *&Head = getRegUseDefListHead(Src->getReg());
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MachineOperand *Prev = Src->Contents.Reg.Prev;
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MachineOperand *Next = Src->Contents.Reg.Next;
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assert(Head && "List empty, but operand is chained");
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assert(Prev && "Operand was not on use-def list");
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// Prev links are circular, next link is NULL instead of looping back to
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// Head.
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if (Src == Head)
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Head = Dst;
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else
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Prev->Contents.Reg.Next = Dst;
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// Update Prev pointer. This also works when Src was pointing to itself
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// in a 1-element list. In that case Head == Dst.
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(Next ? Next : Head)->Contents.Reg.Prev = Dst;
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}
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Dst += Stride;
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Src += Stride;
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} while (--NumOps);
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}
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/// replaceRegWith - Replace all instances of FromReg with ToReg in the
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/// machine function. This is like llvm-level X->replaceAllUsesWith(Y),
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/// except that it also changes any definitions of the register as well.
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void MachineRegisterInfo::replaceRegWith(unsigned FromReg, unsigned ToReg) {
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assert(FromReg != ToReg && "Cannot replace a reg with itself");
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// TODO: This could be more efficient by bulk changing the operands.
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for (reg_iterator I = reg_begin(FromReg), E = reg_end(); I != E; ) {
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MachineOperand &O = I.getOperand();
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++I;
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O.setReg(ToReg);
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}
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}
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/// getVRegDef - Return the machine instr that defines the specified virtual
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/// register or null if none is found. This assumes that the code is in SSA
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/// form, so there should only be one definition.
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MachineInstr *MachineRegisterInfo::getVRegDef(unsigned Reg) const {
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// Since we are in SSA form, we can use the first definition.
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def_iterator I = def_begin(Reg);
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assert((I.atEnd() || llvm::next(I) == def_end()) &&
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"getVRegDef assumes a single definition or no definition");
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return !I.atEnd() ? &*I : 0;
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}
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/// getUniqueVRegDef - Return the unique machine instr that defines the
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/// specified virtual register or null if none is found. If there are
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/// multiple definitions or no definition, return null.
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MachineInstr *MachineRegisterInfo::getUniqueVRegDef(unsigned Reg) const {
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if (def_empty(Reg)) return 0;
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def_iterator I = def_begin(Reg);
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if (llvm::next(I) != def_end())
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return 0;
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return &*I;
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}
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bool MachineRegisterInfo::hasOneNonDBGUse(unsigned RegNo) const {
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use_nodbg_iterator UI = use_nodbg_begin(RegNo);
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if (UI == use_nodbg_end())
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return false;
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return ++UI == use_nodbg_end();
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}
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/// clearKillFlags - Iterate over all the uses of the given register and
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/// clear the kill flag from the MachineOperand. This function is used by
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/// optimization passes which extend register lifetimes and need only
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/// preserve conservative kill flag information.
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void MachineRegisterInfo::clearKillFlags(unsigned Reg) const {
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for (use_iterator UI = use_begin(Reg), UE = use_end(); UI != UE; ++UI)
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UI.getOperand().setIsKill(false);
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}
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bool MachineRegisterInfo::isLiveIn(unsigned Reg) const {
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for (livein_iterator I = livein_begin(), E = livein_end(); I != E; ++I)
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if (I->first == Reg || I->second == Reg)
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return true;
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return false;
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}
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/// getLiveInPhysReg - If VReg is a live-in virtual register, return the
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/// corresponding live-in physical register.
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unsigned MachineRegisterInfo::getLiveInPhysReg(unsigned VReg) const {
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for (livein_iterator I = livein_begin(), E = livein_end(); I != E; ++I)
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if (I->second == VReg)
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return I->first;
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return 0;
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}
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/// getLiveInVirtReg - If PReg is a live-in physical register, return the
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/// corresponding live-in physical register.
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unsigned MachineRegisterInfo::getLiveInVirtReg(unsigned PReg) const {
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for (livein_iterator I = livein_begin(), E = livein_end(); I != E; ++I)
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if (I->first == PReg)
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return I->second;
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return 0;
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}
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/// EmitLiveInCopies - Emit copies to initialize livein virtual registers
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/// into the given entry block.
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void
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MachineRegisterInfo::EmitLiveInCopies(MachineBasicBlock *EntryMBB,
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const TargetRegisterInfo &TRI,
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const TargetInstrInfo &TII) {
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// Emit the copies into the top of the block.
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for (unsigned i = 0, e = LiveIns.size(); i != e; ++i)
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if (LiveIns[i].second) {
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if (use_empty(LiveIns[i].second)) {
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// The livein has no uses. Drop it.
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//
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// It would be preferable to have isel avoid creating live-in
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// records for unused arguments in the first place, but it's
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// complicated by the debug info code for arguments.
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LiveIns.erase(LiveIns.begin() + i);
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--i; --e;
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} else {
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// Emit a copy.
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BuildMI(*EntryMBB, EntryMBB->begin(), DebugLoc(),
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TII.get(TargetOpcode::COPY), LiveIns[i].second)
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.addReg(LiveIns[i].first);
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// Add the register to the entry block live-in set.
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EntryMBB->addLiveIn(LiveIns[i].first);
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}
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} else {
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// Add the register to the entry block live-in set.
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EntryMBB->addLiveIn(LiveIns[i].first);
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}
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}
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#ifndef NDEBUG
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void MachineRegisterInfo::dumpUses(unsigned Reg) const {
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for (use_iterator I = use_begin(Reg), E = use_end(); I != E; ++I)
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I.getOperand().getParent()->dump();
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}
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#endif
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void MachineRegisterInfo::freezeReservedRegs(const MachineFunction &MF) {
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ReservedRegs = getTargetRegisterInfo()->getReservedRegs(MF);
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assert(ReservedRegs.size() == getTargetRegisterInfo()->getNumRegs() &&
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"Invalid ReservedRegs vector from target");
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}
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bool MachineRegisterInfo::isConstantPhysReg(unsigned PhysReg,
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const MachineFunction &MF) const {
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assert(TargetRegisterInfo::isPhysicalRegister(PhysReg));
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// Check if any overlapping register is modified, or allocatable so it may be
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// used later.
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for (MCRegAliasIterator AI(PhysReg, getTargetRegisterInfo(), true);
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AI.isValid(); ++AI)
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if (!def_empty(*AI) || isAllocatable(*AI))
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return false;
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return true;
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}
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