forked from OSchip/llvm-project
906 lines
32 KiB
C++
906 lines
32 KiB
C++
//===-- LiveVariables.cpp - Live Variable Analysis for Machine Code -------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the LiveVariable analysis pass. For each machine
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// instruction in the function, this pass calculates the set of registers that
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// are immediately dead after the instruction (i.e., the instruction calculates
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// the value, but it is never used) and the set of registers that are used by
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// the instruction, but are never used after the instruction (i.e., they are
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// killed).
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//
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// This class computes live variables using a sparse implementation based on
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// the machine code SSA form. This class computes live variable information for
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// each virtual and _register allocatable_ physical register in a function. It
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// uses the dominance properties of SSA form to efficiently compute live
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// variables for virtual registers, and assumes that physical registers are only
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// live within a single basic block (allowing it to do a single local analysis
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// to resolve physical register lifetimes in each basic block). If a physical
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// register is not register allocatable, it is not tracked. This is useful for
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// things like the stack pointer and condition codes.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/LiveVariables.h"
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#include "llvm/ADT/DenseSet.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallSet.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/CodeGen/Passes.h"
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#include "llvm/Config/llvm-config.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 <algorithm>
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using namespace llvm;
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char LiveVariables::ID = 0;
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char &llvm::LiveVariablesID = LiveVariables::ID;
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INITIALIZE_PASS_BEGIN(LiveVariables, "livevars",
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"Live Variable Analysis", false, false)
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INITIALIZE_PASS_DEPENDENCY(UnreachableMachineBlockElim)
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INITIALIZE_PASS_END(LiveVariables, "livevars",
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"Live Variable Analysis", false, false)
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void LiveVariables::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequiredID(UnreachableMachineBlockElimID);
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AU.setPreservesAll();
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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MachineInstr *
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LiveVariables::VarInfo::findKill(const MachineBasicBlock *MBB) const {
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for (MachineInstr *MI : Kills)
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if (MI->getParent() == MBB)
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return MI;
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return nullptr;
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}
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#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
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LLVM_DUMP_METHOD void LiveVariables::VarInfo::dump() const {
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dbgs() << " Alive in blocks: ";
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for (unsigned AB : AliveBlocks)
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dbgs() << AB << ", ";
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dbgs() << "\n Killed by:";
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if (Kills.empty())
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dbgs() << " No instructions.\n";
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else {
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for (unsigned i = 0, e = Kills.size(); i != e; ++i)
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dbgs() << "\n #" << i << ": " << *Kills[i];
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dbgs() << "\n";
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}
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}
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#endif
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/// getVarInfo - Get (possibly creating) a VarInfo object for the given vreg.
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LiveVariables::VarInfo &LiveVariables::getVarInfo(Register Reg) {
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assert(Reg.isVirtual() && "getVarInfo: not a virtual register!");
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VirtRegInfo.grow(Reg);
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return VirtRegInfo[Reg];
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}
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void LiveVariables::MarkVirtRegAliveInBlock(
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VarInfo &VRInfo, MachineBasicBlock *DefBlock, MachineBasicBlock *MBB,
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SmallVectorImpl<MachineBasicBlock *> &WorkList) {
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unsigned BBNum = MBB->getNumber();
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// Check to see if this basic block is one of the killing blocks. If so,
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// remove it.
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for (unsigned i = 0, e = VRInfo.Kills.size(); i != e; ++i)
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if (VRInfo.Kills[i]->getParent() == MBB) {
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VRInfo.Kills.erase(VRInfo.Kills.begin()+i); // Erase entry
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break;
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}
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if (MBB == DefBlock) return; // Terminate recursion
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if (VRInfo.AliveBlocks.test(BBNum))
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return; // We already know the block is live
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// Mark the variable known alive in this bb
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VRInfo.AliveBlocks.set(BBNum);
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assert(MBB != &MF->front() && "Can't find reaching def for virtreg");
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WorkList.insert(WorkList.end(), MBB->pred_rbegin(), MBB->pred_rend());
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}
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void LiveVariables::MarkVirtRegAliveInBlock(VarInfo &VRInfo,
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MachineBasicBlock *DefBlock,
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MachineBasicBlock *MBB) {
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SmallVector<MachineBasicBlock *, 16> WorkList;
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MarkVirtRegAliveInBlock(VRInfo, DefBlock, MBB, WorkList);
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while (!WorkList.empty()) {
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MachineBasicBlock *Pred = WorkList.pop_back_val();
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MarkVirtRegAliveInBlock(VRInfo, DefBlock, Pred, WorkList);
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}
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}
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void LiveVariables::HandleVirtRegUse(Register Reg, MachineBasicBlock *MBB,
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MachineInstr &MI) {
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assert(MRI->getVRegDef(Reg) && "Register use before def!");
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unsigned BBNum = MBB->getNumber();
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VarInfo &VRInfo = getVarInfo(Reg);
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// Check to see if this basic block is already a kill block.
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if (!VRInfo.Kills.empty() && VRInfo.Kills.back()->getParent() == MBB) {
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// Yes, this register is killed in this basic block already. Increase the
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// live range by updating the kill instruction.
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VRInfo.Kills.back() = &MI;
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return;
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}
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#ifndef NDEBUG
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for (MachineInstr *Kill : VRInfo.Kills)
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assert(Kill->getParent() != MBB && "entry should be at end!");
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#endif
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// This situation can occur:
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//
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// ,------.
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// | |
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// | v
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// | t2 = phi ... t1 ...
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// | |
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// | v
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// | t1 = ...
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// | ... = ... t1 ...
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// | |
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// `------'
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//
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// where there is a use in a PHI node that's a predecessor to the defining
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// block. We don't want to mark all predecessors as having the value "alive"
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// in this case.
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if (MBB == MRI->getVRegDef(Reg)->getParent())
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return;
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// Add a new kill entry for this basic block. If this virtual register is
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// already marked as alive in this basic block, that means it is alive in at
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// least one of the successor blocks, it's not a kill.
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if (!VRInfo.AliveBlocks.test(BBNum))
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VRInfo.Kills.push_back(&MI);
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// Update all dominating blocks to mark them as "known live".
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for (MachineBasicBlock *Pred : MBB->predecessors())
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MarkVirtRegAliveInBlock(VRInfo, MRI->getVRegDef(Reg)->getParent(), Pred);
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}
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void LiveVariables::HandleVirtRegDef(Register Reg, MachineInstr &MI) {
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VarInfo &VRInfo = getVarInfo(Reg);
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if (VRInfo.AliveBlocks.empty())
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// If vr is not alive in any block, then defaults to dead.
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VRInfo.Kills.push_back(&MI);
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}
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/// FindLastPartialDef - Return the last partial def of the specified register.
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/// Also returns the sub-registers that're defined by the instruction.
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MachineInstr *
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LiveVariables::FindLastPartialDef(Register Reg,
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SmallSet<unsigned, 4> &PartDefRegs) {
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unsigned LastDefReg = 0;
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unsigned LastDefDist = 0;
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MachineInstr *LastDef = nullptr;
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for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
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unsigned SubReg = *SubRegs;
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MachineInstr *Def = PhysRegDef[SubReg];
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if (!Def)
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continue;
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unsigned Dist = DistanceMap[Def];
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if (Dist > LastDefDist) {
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LastDefReg = SubReg;
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LastDef = Def;
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LastDefDist = Dist;
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}
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}
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if (!LastDef)
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return nullptr;
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PartDefRegs.insert(LastDefReg);
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for (unsigned i = 0, e = LastDef->getNumOperands(); i != e; ++i) {
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MachineOperand &MO = LastDef->getOperand(i);
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if (!MO.isReg() || !MO.isDef() || MO.getReg() == 0)
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continue;
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Register DefReg = MO.getReg();
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if (TRI->isSubRegister(Reg, DefReg)) {
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for (MCSubRegIterator SubRegs(DefReg, TRI, /*IncludeSelf=*/true);
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SubRegs.isValid(); ++SubRegs)
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PartDefRegs.insert(*SubRegs);
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}
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}
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return LastDef;
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}
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/// HandlePhysRegUse - Turn previous partial def's into read/mod/writes. Add
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/// implicit defs to a machine instruction if there was an earlier def of its
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/// super-register.
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void LiveVariables::HandlePhysRegUse(Register Reg, MachineInstr &MI) {
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MachineInstr *LastDef = PhysRegDef[Reg];
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// If there was a previous use or a "full" def all is well.
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if (!LastDef && !PhysRegUse[Reg]) {
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// Otherwise, the last sub-register def implicitly defines this register.
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// e.g.
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// AH =
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// AL = ... implicit-def EAX, implicit killed AH
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// = AH
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// ...
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// = EAX
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// All of the sub-registers must have been defined before the use of Reg!
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SmallSet<unsigned, 4> PartDefRegs;
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MachineInstr *LastPartialDef = FindLastPartialDef(Reg, PartDefRegs);
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// If LastPartialDef is NULL, it must be using a livein register.
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if (LastPartialDef) {
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LastPartialDef->addOperand(MachineOperand::CreateReg(Reg, true/*IsDef*/,
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true/*IsImp*/));
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PhysRegDef[Reg] = LastPartialDef;
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SmallSet<unsigned, 8> Processed;
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for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
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unsigned SubReg = *SubRegs;
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if (Processed.count(SubReg))
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continue;
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if (PartDefRegs.count(SubReg))
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continue;
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// This part of Reg was defined before the last partial def. It's killed
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// here.
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LastPartialDef->addOperand(MachineOperand::CreateReg(SubReg,
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false/*IsDef*/,
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true/*IsImp*/));
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PhysRegDef[SubReg] = LastPartialDef;
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for (MCSubRegIterator SS(SubReg, TRI); SS.isValid(); ++SS)
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Processed.insert(*SS);
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}
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}
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} else if (LastDef && !PhysRegUse[Reg] &&
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!LastDef->findRegisterDefOperand(Reg))
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// Last def defines the super register, add an implicit def of reg.
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LastDef->addOperand(MachineOperand::CreateReg(Reg, true/*IsDef*/,
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true/*IsImp*/));
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// Remember this use.
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for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
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SubRegs.isValid(); ++SubRegs)
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PhysRegUse[*SubRegs] = &MI;
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}
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/// FindLastRefOrPartRef - Return the last reference or partial reference of
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/// the specified register.
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MachineInstr *LiveVariables::FindLastRefOrPartRef(Register Reg) {
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MachineInstr *LastDef = PhysRegDef[Reg];
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MachineInstr *LastUse = PhysRegUse[Reg];
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if (!LastDef && !LastUse)
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return nullptr;
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MachineInstr *LastRefOrPartRef = LastUse ? LastUse : LastDef;
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unsigned LastRefOrPartRefDist = DistanceMap[LastRefOrPartRef];
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unsigned LastPartDefDist = 0;
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for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
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unsigned SubReg = *SubRegs;
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MachineInstr *Def = PhysRegDef[SubReg];
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if (Def && Def != LastDef) {
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// There was a def of this sub-register in between. This is a partial
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// def, keep track of the last one.
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unsigned Dist = DistanceMap[Def];
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if (Dist > LastPartDefDist)
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LastPartDefDist = Dist;
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} else if (MachineInstr *Use = PhysRegUse[SubReg]) {
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unsigned Dist = DistanceMap[Use];
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if (Dist > LastRefOrPartRefDist) {
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LastRefOrPartRefDist = Dist;
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LastRefOrPartRef = Use;
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}
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}
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}
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return LastRefOrPartRef;
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}
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bool LiveVariables::HandlePhysRegKill(Register Reg, MachineInstr *MI) {
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MachineInstr *LastDef = PhysRegDef[Reg];
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MachineInstr *LastUse = PhysRegUse[Reg];
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if (!LastDef && !LastUse)
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return false;
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MachineInstr *LastRefOrPartRef = LastUse ? LastUse : LastDef;
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unsigned LastRefOrPartRefDist = DistanceMap[LastRefOrPartRef];
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// The whole register is used.
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// AL =
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// AH =
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//
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// = AX
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// = AL, implicit killed AX
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// AX =
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//
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// Or whole register is defined, but not used at all.
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// dead AX =
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// ...
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// AX =
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//
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// Or whole register is defined, but only partly used.
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// dead AX = implicit-def AL
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// = killed AL
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// AX =
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MachineInstr *LastPartDef = nullptr;
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unsigned LastPartDefDist = 0;
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SmallSet<unsigned, 8> PartUses;
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for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
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unsigned SubReg = *SubRegs;
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MachineInstr *Def = PhysRegDef[SubReg];
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if (Def && Def != LastDef) {
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// There was a def of this sub-register in between. This is a partial
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// def, keep track of the last one.
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unsigned Dist = DistanceMap[Def];
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if (Dist > LastPartDefDist) {
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LastPartDefDist = Dist;
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LastPartDef = Def;
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}
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continue;
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}
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if (MachineInstr *Use = PhysRegUse[SubReg]) {
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for (MCSubRegIterator SS(SubReg, TRI, /*IncludeSelf=*/true); SS.isValid();
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++SS)
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PartUses.insert(*SS);
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unsigned Dist = DistanceMap[Use];
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if (Dist > LastRefOrPartRefDist) {
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LastRefOrPartRefDist = Dist;
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LastRefOrPartRef = Use;
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}
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}
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}
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if (!PhysRegUse[Reg]) {
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// Partial uses. Mark register def dead and add implicit def of
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// sub-registers which are used.
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// dead EAX = op implicit-def AL
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// That is, EAX def is dead but AL def extends pass it.
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PhysRegDef[Reg]->addRegisterDead(Reg, TRI, true);
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for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
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unsigned SubReg = *SubRegs;
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if (!PartUses.count(SubReg))
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continue;
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bool NeedDef = true;
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if (PhysRegDef[Reg] == PhysRegDef[SubReg]) {
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MachineOperand *MO = PhysRegDef[Reg]->findRegisterDefOperand(SubReg);
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if (MO) {
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NeedDef = false;
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assert(!MO->isDead());
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}
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}
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if (NeedDef)
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PhysRegDef[Reg]->addOperand(MachineOperand::CreateReg(SubReg,
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true/*IsDef*/, true/*IsImp*/));
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MachineInstr *LastSubRef = FindLastRefOrPartRef(SubReg);
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if (LastSubRef)
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LastSubRef->addRegisterKilled(SubReg, TRI, true);
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else {
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LastRefOrPartRef->addRegisterKilled(SubReg, TRI, true);
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for (MCSubRegIterator SS(SubReg, TRI, /*IncludeSelf=*/true);
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SS.isValid(); ++SS)
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PhysRegUse[*SS] = LastRefOrPartRef;
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}
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for (MCSubRegIterator SS(SubReg, TRI); SS.isValid(); ++SS)
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PartUses.erase(*SS);
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}
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} else if (LastRefOrPartRef == PhysRegDef[Reg] && LastRefOrPartRef != MI) {
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if (LastPartDef)
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// The last partial def kills the register.
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LastPartDef->addOperand(MachineOperand::CreateReg(Reg, false/*IsDef*/,
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true/*IsImp*/, true/*IsKill*/));
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else {
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MachineOperand *MO =
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LastRefOrPartRef->findRegisterDefOperand(Reg, false, false, TRI);
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bool NeedEC = MO->isEarlyClobber() && MO->getReg() != Reg;
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// If the last reference is the last def, then it's not used at all.
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// That is, unless we are currently processing the last reference itself.
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LastRefOrPartRef->addRegisterDead(Reg, TRI, true);
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if (NeedEC) {
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// If we are adding a subreg def and the superreg def is marked early
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// clobber, add an early clobber marker to the subreg def.
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MO = LastRefOrPartRef->findRegisterDefOperand(Reg);
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if (MO)
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MO->setIsEarlyClobber();
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}
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}
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} else
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LastRefOrPartRef->addRegisterKilled(Reg, TRI, true);
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return true;
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}
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void LiveVariables::HandleRegMask(const MachineOperand &MO) {
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// Call HandlePhysRegKill() for all live registers clobbered by Mask.
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// Clobbered registers are always dead, sp there is no need to use
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// HandlePhysRegDef().
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for (unsigned Reg = 1, NumRegs = TRI->getNumRegs(); Reg != NumRegs; ++Reg) {
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// Skip dead regs.
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if (!PhysRegDef[Reg] && !PhysRegUse[Reg])
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continue;
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// Skip mask-preserved regs.
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if (!MO.clobbersPhysReg(Reg))
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continue;
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// Kill the largest clobbered super-register.
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// This avoids needless implicit operands.
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unsigned Super = Reg;
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for (MCSuperRegIterator SR(Reg, TRI); SR.isValid(); ++SR)
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if ((PhysRegDef[*SR] || PhysRegUse[*SR]) && MO.clobbersPhysReg(*SR))
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Super = *SR;
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HandlePhysRegKill(Super, nullptr);
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}
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}
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void LiveVariables::HandlePhysRegDef(Register Reg, MachineInstr *MI,
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SmallVectorImpl<unsigned> &Defs) {
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// What parts of the register are previously defined?
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SmallSet<unsigned, 32> Live;
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if (PhysRegDef[Reg] || PhysRegUse[Reg]) {
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for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
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SubRegs.isValid(); ++SubRegs)
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Live.insert(*SubRegs);
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} else {
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for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
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unsigned SubReg = *SubRegs;
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// If a register isn't itself defined, but all parts that make up of it
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// are defined, then consider it also defined.
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// e.g.
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// AL =
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// AH =
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// = AX
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if (Live.count(SubReg))
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continue;
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if (PhysRegDef[SubReg] || PhysRegUse[SubReg]) {
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for (MCSubRegIterator SS(SubReg, TRI, /*IncludeSelf=*/true);
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SS.isValid(); ++SS)
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Live.insert(*SS);
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}
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}
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}
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// Start from the largest piece, find the last time any part of the register
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// is referenced.
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HandlePhysRegKill(Reg, MI);
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// Only some of the sub-registers are used.
|
|
for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
|
|
unsigned SubReg = *SubRegs;
|
|
if (!Live.count(SubReg))
|
|
// Skip if this sub-register isn't defined.
|
|
continue;
|
|
HandlePhysRegKill(SubReg, MI);
|
|
}
|
|
|
|
if (MI)
|
|
Defs.push_back(Reg); // Remember this def.
|
|
}
|
|
|
|
void LiveVariables::UpdatePhysRegDefs(MachineInstr &MI,
|
|
SmallVectorImpl<unsigned> &Defs) {
|
|
while (!Defs.empty()) {
|
|
Register Reg = Defs.pop_back_val();
|
|
for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
|
|
SubRegs.isValid(); ++SubRegs) {
|
|
unsigned SubReg = *SubRegs;
|
|
PhysRegDef[SubReg] = &MI;
|
|
PhysRegUse[SubReg] = nullptr;
|
|
}
|
|
}
|
|
}
|
|
|
|
void LiveVariables::runOnInstr(MachineInstr &MI,
|
|
SmallVectorImpl<unsigned> &Defs) {
|
|
assert(!MI.isDebugOrPseudoInstr());
|
|
// Process all of the operands of the instruction...
|
|
unsigned NumOperandsToProcess = MI.getNumOperands();
|
|
|
|
// Unless it is a PHI node. In this case, ONLY process the DEF, not any
|
|
// of the uses. They will be handled in other basic blocks.
|
|
if (MI.isPHI())
|
|
NumOperandsToProcess = 1;
|
|
|
|
// Clear kill and dead markers. LV will recompute them.
|
|
SmallVector<unsigned, 4> UseRegs;
|
|
SmallVector<unsigned, 4> DefRegs;
|
|
SmallVector<unsigned, 1> RegMasks;
|
|
for (unsigned i = 0; i != NumOperandsToProcess; ++i) {
|
|
MachineOperand &MO = MI.getOperand(i);
|
|
if (MO.isRegMask()) {
|
|
RegMasks.push_back(i);
|
|
continue;
|
|
}
|
|
if (!MO.isReg() || MO.getReg() == 0)
|
|
continue;
|
|
Register MOReg = MO.getReg();
|
|
if (MO.isUse()) {
|
|
if (!(Register::isPhysicalRegister(MOReg) && MRI->isReserved(MOReg)))
|
|
MO.setIsKill(false);
|
|
if (MO.readsReg())
|
|
UseRegs.push_back(MOReg);
|
|
} else {
|
|
assert(MO.isDef());
|
|
// FIXME: We should not remove any dead flags. However the MIPS RDDSP
|
|
// instruction needs it at the moment: http://llvm.org/PR27116.
|
|
if (Register::isPhysicalRegister(MOReg) && !MRI->isReserved(MOReg))
|
|
MO.setIsDead(false);
|
|
DefRegs.push_back(MOReg);
|
|
}
|
|
}
|
|
|
|
MachineBasicBlock *MBB = MI.getParent();
|
|
// Process all uses.
|
|
for (unsigned MOReg : UseRegs) {
|
|
if (Register::isVirtualRegister(MOReg))
|
|
HandleVirtRegUse(MOReg, MBB, MI);
|
|
else if (!MRI->isReserved(MOReg))
|
|
HandlePhysRegUse(MOReg, MI);
|
|
}
|
|
|
|
// Process all masked registers. (Call clobbers).
|
|
for (unsigned Mask : RegMasks)
|
|
HandleRegMask(MI.getOperand(Mask));
|
|
|
|
// Process all defs.
|
|
for (unsigned MOReg : DefRegs) {
|
|
if (Register::isVirtualRegister(MOReg))
|
|
HandleVirtRegDef(MOReg, MI);
|
|
else if (!MRI->isReserved(MOReg))
|
|
HandlePhysRegDef(MOReg, &MI, Defs);
|
|
}
|
|
UpdatePhysRegDefs(MI, Defs);
|
|
}
|
|
|
|
void LiveVariables::runOnBlock(MachineBasicBlock *MBB, const unsigned NumRegs) {
|
|
// Mark live-in registers as live-in.
|
|
SmallVector<unsigned, 4> Defs;
|
|
for (const auto &LI : MBB->liveins()) {
|
|
assert(Register::isPhysicalRegister(LI.PhysReg) &&
|
|
"Cannot have a live-in virtual register!");
|
|
HandlePhysRegDef(LI.PhysReg, nullptr, Defs);
|
|
}
|
|
|
|
// Loop over all of the instructions, processing them.
|
|
DistanceMap.clear();
|
|
unsigned Dist = 0;
|
|
for (MachineInstr &MI : *MBB) {
|
|
if (MI.isDebugOrPseudoInstr())
|
|
continue;
|
|
DistanceMap.insert(std::make_pair(&MI, Dist++));
|
|
|
|
runOnInstr(MI, Defs);
|
|
}
|
|
|
|
// Handle any virtual assignments from PHI nodes which might be at the
|
|
// bottom of this basic block. We check all of our successor blocks to see
|
|
// if they have PHI nodes, and if so, we simulate an assignment at the end
|
|
// of the current block.
|
|
if (!PHIVarInfo[MBB->getNumber()].empty()) {
|
|
SmallVectorImpl<unsigned> &VarInfoVec = PHIVarInfo[MBB->getNumber()];
|
|
|
|
for (unsigned I : VarInfoVec)
|
|
// Mark it alive only in the block we are representing.
|
|
MarkVirtRegAliveInBlock(getVarInfo(I), MRI->getVRegDef(I)->getParent(),
|
|
MBB);
|
|
}
|
|
|
|
// MachineCSE may CSE instructions which write to non-allocatable physical
|
|
// registers across MBBs. Remember if any reserved register is liveout.
|
|
SmallSet<unsigned, 4> LiveOuts;
|
|
for (const MachineBasicBlock *SuccMBB : MBB->successors()) {
|
|
if (SuccMBB->isEHPad())
|
|
continue;
|
|
for (const auto &LI : SuccMBB->liveins()) {
|
|
if (!TRI->isInAllocatableClass(LI.PhysReg))
|
|
// Ignore other live-ins, e.g. those that are live into landing pads.
|
|
LiveOuts.insert(LI.PhysReg);
|
|
}
|
|
}
|
|
|
|
// Loop over PhysRegDef / PhysRegUse, killing any registers that are
|
|
// available at the end of the basic block.
|
|
for (unsigned i = 0; i != NumRegs; ++i)
|
|
if ((PhysRegDef[i] || PhysRegUse[i]) && !LiveOuts.count(i))
|
|
HandlePhysRegDef(i, nullptr, Defs);
|
|
}
|
|
|
|
bool LiveVariables::runOnMachineFunction(MachineFunction &mf) {
|
|
MF = &mf;
|
|
MRI = &mf.getRegInfo();
|
|
TRI = MF->getSubtarget().getRegisterInfo();
|
|
|
|
const unsigned NumRegs = TRI->getNumRegs();
|
|
PhysRegDef.assign(NumRegs, nullptr);
|
|
PhysRegUse.assign(NumRegs, nullptr);
|
|
PHIVarInfo.resize(MF->getNumBlockIDs());
|
|
PHIJoins.clear();
|
|
|
|
// FIXME: LiveIntervals will be updated to remove its dependence on
|
|
// LiveVariables to improve compilation time and eliminate bizarre pass
|
|
// dependencies. Until then, we can't change much in -O0.
|
|
if (!MRI->isSSA())
|
|
report_fatal_error("regalloc=... not currently supported with -O0");
|
|
|
|
analyzePHINodes(mf);
|
|
|
|
// Calculate live variable information in depth first order on the CFG of the
|
|
// function. This guarantees that we will see the definition of a virtual
|
|
// register before its uses due to dominance properties of SSA (except for PHI
|
|
// nodes, which are treated as a special case).
|
|
MachineBasicBlock *Entry = &MF->front();
|
|
df_iterator_default_set<MachineBasicBlock*,16> Visited;
|
|
|
|
for (MachineBasicBlock *MBB : depth_first_ext(Entry, Visited)) {
|
|
runOnBlock(MBB, NumRegs);
|
|
|
|
PhysRegDef.assign(NumRegs, nullptr);
|
|
PhysRegUse.assign(NumRegs, nullptr);
|
|
}
|
|
|
|
// Convert and transfer the dead / killed information we have gathered into
|
|
// VirtRegInfo onto MI's.
|
|
for (unsigned i = 0, e1 = VirtRegInfo.size(); i != e1; ++i) {
|
|
const Register Reg = Register::index2VirtReg(i);
|
|
for (unsigned j = 0, e2 = VirtRegInfo[Reg].Kills.size(); j != e2; ++j)
|
|
if (VirtRegInfo[Reg].Kills[j] == MRI->getVRegDef(Reg))
|
|
VirtRegInfo[Reg].Kills[j]->addRegisterDead(Reg, TRI);
|
|
else
|
|
VirtRegInfo[Reg].Kills[j]->addRegisterKilled(Reg, TRI);
|
|
}
|
|
|
|
// Check to make sure there are no unreachable blocks in the MC CFG for the
|
|
// function. If so, it is due to a bug in the instruction selector or some
|
|
// other part of the code generator if this happens.
|
|
#ifndef NDEBUG
|
|
for (const MachineBasicBlock &MBB : *MF)
|
|
assert(Visited.contains(&MBB) && "unreachable basic block found");
|
|
#endif
|
|
|
|
PhysRegDef.clear();
|
|
PhysRegUse.clear();
|
|
PHIVarInfo.clear();
|
|
|
|
return false;
|
|
}
|
|
|
|
void LiveVariables::recomputeForSingleDefVirtReg(Register Reg) {
|
|
assert(Reg.isVirtual());
|
|
|
|
VarInfo &VI = getVarInfo(Reg);
|
|
VI.AliveBlocks.clear();
|
|
VI.Kills.clear();
|
|
|
|
MachineInstr &DefMI = *MRI->getUniqueVRegDef(Reg);
|
|
MachineBasicBlock &DefBB = *DefMI.getParent();
|
|
|
|
// Handle the case where all uses have been removed.
|
|
if (MRI->use_nodbg_empty(Reg)) {
|
|
VI.Kills.push_back(&DefMI);
|
|
DefMI.addRegisterDead(Reg, nullptr);
|
|
return;
|
|
}
|
|
DefMI.clearRegisterDeads(Reg);
|
|
|
|
// Initialize a worklist of BBs that Reg is live-to-end of. (Here
|
|
// "live-to-end" means Reg is live at the end of a block even if it is only
|
|
// live because of phi uses in a successor. This is different from isLiveOut()
|
|
// which does not consider phi uses.)
|
|
SmallVector<MachineBasicBlock *> LiveToEndBlocks;
|
|
SparseBitVector<> UseBlocks;
|
|
for (auto &UseMO : MRI->use_nodbg_operands(Reg)) {
|
|
UseMO.setIsKill(false);
|
|
MachineInstr &UseMI = *UseMO.getParent();
|
|
MachineBasicBlock &UseBB = *UseMI.getParent();
|
|
UseBlocks.set(UseBB.getNumber());
|
|
if (UseMI.isPHI()) {
|
|
// If Reg is used in a phi then it is live-to-end of the corresponding
|
|
// predecessor.
|
|
unsigned Idx = UseMI.getOperandNo(&UseMO);
|
|
LiveToEndBlocks.push_back(UseMI.getOperand(Idx + 1).getMBB());
|
|
} else if (&UseBB == &DefBB) {
|
|
// A non-phi use in the same BB as the single def must come after the def.
|
|
} else {
|
|
// Otherwise Reg must be live-to-end of all predecessors.
|
|
LiveToEndBlocks.append(UseBB.pred_begin(), UseBB.pred_end());
|
|
}
|
|
}
|
|
|
|
// Iterate over the worklist adding blocks to AliveBlocks.
|
|
bool LiveToEndOfDefBB = false;
|
|
while (!LiveToEndBlocks.empty()) {
|
|
MachineBasicBlock &BB = *LiveToEndBlocks.pop_back_val();
|
|
if (&BB == &DefBB) {
|
|
LiveToEndOfDefBB = true;
|
|
continue;
|
|
}
|
|
if (VI.AliveBlocks.test(BB.getNumber()))
|
|
continue;
|
|
VI.AliveBlocks.set(BB.getNumber());
|
|
LiveToEndBlocks.append(BB.pred_begin(), BB.pred_end());
|
|
}
|
|
|
|
// Recompute kill flags. For each block in which Reg is used but is not
|
|
// live-through, find the last instruction that uses Reg. Ignore phi nodes
|
|
// because they should not be included in Kills.
|
|
for (unsigned UseBBNum : UseBlocks) {
|
|
if (VI.AliveBlocks.test(UseBBNum))
|
|
continue;
|
|
MachineBasicBlock &UseBB = *MF->getBlockNumbered(UseBBNum);
|
|
if (&UseBB == &DefBB && LiveToEndOfDefBB)
|
|
continue;
|
|
for (auto &MI : reverse(UseBB)) {
|
|
if (MI.isDebugOrPseudoInstr())
|
|
continue;
|
|
if (MI.isPHI())
|
|
break;
|
|
if (MI.readsRegister(Reg)) {
|
|
assert(!MI.killsRegister(Reg));
|
|
MI.addRegisterKilled(Reg, nullptr);
|
|
VI.Kills.push_back(&MI);
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// replaceKillInstruction - Update register kill info by replacing a kill
|
|
/// instruction with a new one.
|
|
void LiveVariables::replaceKillInstruction(Register Reg, MachineInstr &OldMI,
|
|
MachineInstr &NewMI) {
|
|
VarInfo &VI = getVarInfo(Reg);
|
|
std::replace(VI.Kills.begin(), VI.Kills.end(), &OldMI, &NewMI);
|
|
}
|
|
|
|
/// removeVirtualRegistersKilled - Remove all killed info for the specified
|
|
/// instruction.
|
|
void LiveVariables::removeVirtualRegistersKilled(MachineInstr &MI) {
|
|
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
|
|
MachineOperand &MO = MI.getOperand(i);
|
|
if (MO.isReg() && MO.isKill()) {
|
|
MO.setIsKill(false);
|
|
Register Reg = MO.getReg();
|
|
if (Register::isVirtualRegister(Reg)) {
|
|
bool removed = getVarInfo(Reg).removeKill(MI);
|
|
assert(removed && "kill not in register's VarInfo?");
|
|
(void)removed;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// analyzePHINodes - Gather information about the PHI nodes in here. In
|
|
/// particular, we want to map the variable information of a virtual register
|
|
/// which is used in a PHI node. We map that to the BB the vreg is coming from.
|
|
///
|
|
void LiveVariables::analyzePHINodes(const MachineFunction& Fn) {
|
|
for (const auto &MBB : Fn)
|
|
for (const auto &BBI : MBB) {
|
|
if (!BBI.isPHI())
|
|
break;
|
|
for (unsigned i = 1, e = BBI.getNumOperands(); i != e; i += 2)
|
|
if (BBI.getOperand(i).readsReg())
|
|
PHIVarInfo[BBI.getOperand(i + 1).getMBB()->getNumber()]
|
|
.push_back(BBI.getOperand(i).getReg());
|
|
}
|
|
}
|
|
|
|
bool LiveVariables::VarInfo::isLiveIn(const MachineBasicBlock &MBB,
|
|
Register Reg, MachineRegisterInfo &MRI) {
|
|
unsigned Num = MBB.getNumber();
|
|
|
|
// Reg is live-through.
|
|
if (AliveBlocks.test(Num))
|
|
return true;
|
|
|
|
// Registers defined in MBB cannot be live in.
|
|
const MachineInstr *Def = MRI.getVRegDef(Reg);
|
|
if (Def && Def->getParent() == &MBB)
|
|
return false;
|
|
|
|
// Reg was not defined in MBB, was it killed here?
|
|
return findKill(&MBB);
|
|
}
|
|
|
|
bool LiveVariables::isLiveOut(Register Reg, const MachineBasicBlock &MBB) {
|
|
LiveVariables::VarInfo &VI = getVarInfo(Reg);
|
|
|
|
SmallPtrSet<const MachineBasicBlock *, 8> Kills;
|
|
for (MachineInstr *MI : VI.Kills)
|
|
Kills.insert(MI->getParent());
|
|
|
|
// Loop over all of the successors of the basic block, checking to see if
|
|
// the value is either live in the block, or if it is killed in the block.
|
|
for (const MachineBasicBlock *SuccMBB : MBB.successors()) {
|
|
// Is it alive in this successor?
|
|
unsigned SuccIdx = SuccMBB->getNumber();
|
|
if (VI.AliveBlocks.test(SuccIdx))
|
|
return true;
|
|
// Or is it live because there is a use in a successor that kills it?
|
|
if (Kills.count(SuccMBB))
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/// addNewBlock - Add a new basic block BB as an empty succcessor to DomBB. All
|
|
/// variables that are live out of DomBB will be marked as passing live through
|
|
/// BB.
|
|
void LiveVariables::addNewBlock(MachineBasicBlock *BB,
|
|
MachineBasicBlock *DomBB,
|
|
MachineBasicBlock *SuccBB) {
|
|
const unsigned NumNew = BB->getNumber();
|
|
|
|
DenseSet<unsigned> Defs, Kills;
|
|
|
|
MachineBasicBlock::iterator BBI = SuccBB->begin(), BBE = SuccBB->end();
|
|
for (; BBI != BBE && BBI->isPHI(); ++BBI) {
|
|
// Record the def of the PHI node.
|
|
Defs.insert(BBI->getOperand(0).getReg());
|
|
|
|
// All registers used by PHI nodes in SuccBB must be live through BB.
|
|
for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2)
|
|
if (BBI->getOperand(i+1).getMBB() == BB)
|
|
getVarInfo(BBI->getOperand(i).getReg()).AliveBlocks.set(NumNew);
|
|
}
|
|
|
|
// Record all vreg defs and kills of all instructions in SuccBB.
|
|
for (; BBI != BBE; ++BBI) {
|
|
for (const MachineOperand &Op : BBI->operands()) {
|
|
if (Op.isReg() && Register::isVirtualRegister(Op.getReg())) {
|
|
if (Op.isDef())
|
|
Defs.insert(Op.getReg());
|
|
else if (Op.isKill())
|
|
Kills.insert(Op.getReg());
|
|
}
|
|
}
|
|
}
|
|
|
|
// Update info for all live variables
|
|
for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
|
|
Register Reg = Register::index2VirtReg(i);
|
|
|
|
// If the Defs is defined in the successor it can't be live in BB.
|
|
if (Defs.count(Reg))
|
|
continue;
|
|
|
|
// If the register is either killed in or live through SuccBB it's also live
|
|
// through BB.
|
|
VarInfo &VI = getVarInfo(Reg);
|
|
if (Kills.count(Reg) || VI.AliveBlocks.test(SuccBB->getNumber()))
|
|
VI.AliveBlocks.set(NumNew);
|
|
}
|
|
}
|
|
|
|
/// addNewBlock - Add a new basic block BB as an empty succcessor to DomBB. All
|
|
/// variables that are live out of DomBB will be marked as passing live through
|
|
/// BB. LiveInSets[BB] is *not* updated (because it is not needed during
|
|
/// PHIElimination).
|
|
void LiveVariables::addNewBlock(MachineBasicBlock *BB,
|
|
MachineBasicBlock *DomBB,
|
|
MachineBasicBlock *SuccBB,
|
|
std::vector<SparseBitVector<>> &LiveInSets) {
|
|
const unsigned NumNew = BB->getNumber();
|
|
|
|
SparseBitVector<> &BV = LiveInSets[SuccBB->getNumber()];
|
|
for (unsigned R : BV) {
|
|
Register VirtReg = Register::index2VirtReg(R);
|
|
LiveVariables::VarInfo &VI = getVarInfo(VirtReg);
|
|
VI.AliveBlocks.set(NumNew);
|
|
}
|
|
// All registers used by PHI nodes in SuccBB must be live through BB.
|
|
for (MachineBasicBlock::iterator BBI = SuccBB->begin(),
|
|
BBE = SuccBB->end();
|
|
BBI != BBE && BBI->isPHI(); ++BBI) {
|
|
for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2)
|
|
if (BBI->getOperand(i + 1).getMBB() == BB &&
|
|
BBI->getOperand(i).readsReg())
|
|
getVarInfo(BBI->getOperand(i).getReg())
|
|
.AliveBlocks.set(NumNew);
|
|
}
|
|
}
|