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llvm-6502/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
Daniel Dunbar a279bc3da5 Tabs -> spaces, and remove trailing whitespace. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@82355 91177308-0d34-0410-b5e6-96231b3b80d8
2009-09-20 02:20:51 +00:00

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//===-- SelectionDAGISel.cpp - Implement the SelectionDAGISel class -------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This implements the SelectionDAGISel class.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "isel"
#include "ScheduleDAGSDNodes.h"
#include "SelectionDAGBuild.h"
#include "llvm/CodeGen/SelectionDAGISel.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/DebugInfo.h"
#include "llvm/Constants.h"
#include "llvm/CallingConv.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/GlobalVariable.h"
#include "llvm/InlineAsm.h"
#include "llvm/Instructions.h"
#include "llvm/Intrinsics.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/CodeGen/FastISel.h"
#include "llvm/CodeGen/GCStrategy.h"
#include "llvm/CodeGen/GCMetadata.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionAnalysis.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineJumpTableInfo.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/ScheduleHazardRecognizer.h"
#include "llvm/CodeGen/SchedulerRegistry.h"
#include "llvm/CodeGen/SelectionDAG.h"
#include "llvm/CodeGen/DwarfWriter.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetFrameInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/Timer.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
using namespace llvm;
static cl::opt<bool>
DisableLegalizeTypes("disable-legalize-types", cl::Hidden);
static cl::opt<bool>
EnableFastISelVerbose("fast-isel-verbose", cl::Hidden,
cl::desc("Enable verbose messages in the \"fast\" "
"instruction selector"));
static cl::opt<bool>
EnableFastISelAbort("fast-isel-abort", cl::Hidden,
cl::desc("Enable abort calls when \"fast\" instruction fails"));
static cl::opt<bool>
SchedLiveInCopies("schedule-livein-copies",
cl::desc("Schedule copies of livein registers"),
cl::init(false));
#ifndef NDEBUG
static cl::opt<bool>
ViewDAGCombine1("view-dag-combine1-dags", cl::Hidden,
cl::desc("Pop up a window to show dags before the first "
"dag combine pass"));
static cl::opt<bool>
ViewLegalizeTypesDAGs("view-legalize-types-dags", cl::Hidden,
cl::desc("Pop up a window to show dags before legalize types"));
static cl::opt<bool>
ViewLegalizeDAGs("view-legalize-dags", cl::Hidden,
cl::desc("Pop up a window to show dags before legalize"));
static cl::opt<bool>
ViewDAGCombine2("view-dag-combine2-dags", cl::Hidden,
cl::desc("Pop up a window to show dags before the second "
"dag combine pass"));
static cl::opt<bool>
ViewDAGCombineLT("view-dag-combine-lt-dags", cl::Hidden,
cl::desc("Pop up a window to show dags before the post legalize types"
" dag combine pass"));
static cl::opt<bool>
ViewISelDAGs("view-isel-dags", cl::Hidden,
cl::desc("Pop up a window to show isel dags as they are selected"));
static cl::opt<bool>
ViewSchedDAGs("view-sched-dags", cl::Hidden,
cl::desc("Pop up a window to show sched dags as they are processed"));
static cl::opt<bool>
ViewSUnitDAGs("view-sunit-dags", cl::Hidden,
cl::desc("Pop up a window to show SUnit dags after they are processed"));
#else
static const bool ViewDAGCombine1 = false,
ViewLegalizeTypesDAGs = false, ViewLegalizeDAGs = false,
ViewDAGCombine2 = false,
ViewDAGCombineLT = false,
ViewISelDAGs = false, ViewSchedDAGs = false,
ViewSUnitDAGs = false;
#endif
//===---------------------------------------------------------------------===//
///
/// RegisterScheduler class - Track the registration of instruction schedulers.
///
//===---------------------------------------------------------------------===//
MachinePassRegistry RegisterScheduler::Registry;
//===---------------------------------------------------------------------===//
///
/// ISHeuristic command line option for instruction schedulers.
///
//===---------------------------------------------------------------------===//
static cl::opt<RegisterScheduler::FunctionPassCtor, false,
RegisterPassParser<RegisterScheduler> >
ISHeuristic("pre-RA-sched",
cl::init(&createDefaultScheduler),
cl::desc("Instruction schedulers available (before register"
" allocation):"));
static RegisterScheduler
defaultListDAGScheduler("default", "Best scheduler for the target",
createDefaultScheduler);
namespace llvm {
//===--------------------------------------------------------------------===//
/// createDefaultScheduler - This creates an instruction scheduler appropriate
/// for the target.
ScheduleDAGSDNodes* createDefaultScheduler(SelectionDAGISel *IS,
CodeGenOpt::Level OptLevel) {
const TargetLowering &TLI = IS->getTargetLowering();
if (OptLevel == CodeGenOpt::None)
return createFastDAGScheduler(IS, OptLevel);
if (TLI.getSchedulingPreference() == TargetLowering::SchedulingForLatency)
return createTDListDAGScheduler(IS, OptLevel);
assert(TLI.getSchedulingPreference() ==
TargetLowering::SchedulingForRegPressure && "Unknown sched type!");
return createBURRListDAGScheduler(IS, OptLevel);
}
}
// EmitInstrWithCustomInserter - This method should be implemented by targets
// that mark instructions with the 'usesCustomDAGSchedInserter' flag. These
// instructions are special in various ways, which require special support to
// insert. The specified MachineInstr is created but not inserted into any
// basic blocks, and the scheduler passes ownership of it to this method.
MachineBasicBlock *TargetLowering::EmitInstrWithCustomInserter(MachineInstr *MI,
MachineBasicBlock *MBB,
DenseMap<MachineBasicBlock*, MachineBasicBlock*> *EM) const {
#ifndef NDEBUG
errs() << "If a target marks an instruction with "
"'usesCustomDAGSchedInserter', it must implement "
"TargetLowering::EmitInstrWithCustomInserter!";
#endif
llvm_unreachable(0);
return 0;
}
/// EmitLiveInCopy - Emit a copy for a live in physical register. If the
/// physical register has only a single copy use, then coalesced the copy
/// if possible.
static void EmitLiveInCopy(MachineBasicBlock *MBB,
MachineBasicBlock::iterator &InsertPos,
unsigned VirtReg, unsigned PhysReg,
const TargetRegisterClass *RC,
DenseMap<MachineInstr*, unsigned> &CopyRegMap,
const MachineRegisterInfo &MRI,
const TargetRegisterInfo &TRI,
const TargetInstrInfo &TII) {
unsigned NumUses = 0;
MachineInstr *UseMI = NULL;
for (MachineRegisterInfo::use_iterator UI = MRI.use_begin(VirtReg),
UE = MRI.use_end(); UI != UE; ++UI) {
UseMI = &*UI;
if (++NumUses > 1)
break;
}
// If the number of uses is not one, or the use is not a move instruction,
// don't coalesce. Also, only coalesce away a virtual register to virtual
// register copy.
bool Coalesced = false;
unsigned SrcReg, DstReg, SrcSubReg, DstSubReg;
if (NumUses == 1 &&
TII.isMoveInstr(*UseMI, SrcReg, DstReg, SrcSubReg, DstSubReg) &&
TargetRegisterInfo::isVirtualRegister(DstReg)) {
VirtReg = DstReg;
Coalesced = true;
}
// Now find an ideal location to insert the copy.
MachineBasicBlock::iterator Pos = InsertPos;
while (Pos != MBB->begin()) {
MachineInstr *PrevMI = prior(Pos);
DenseMap<MachineInstr*, unsigned>::iterator RI = CopyRegMap.find(PrevMI);
// copyRegToReg might emit multiple instructions to do a copy.
unsigned CopyDstReg = (RI == CopyRegMap.end()) ? 0 : RI->second;
if (CopyDstReg && !TRI.regsOverlap(CopyDstReg, PhysReg))
// This is what the BB looks like right now:
// r1024 = mov r0
// ...
// r1 = mov r1024
//
// We want to insert "r1025 = mov r1". Inserting this copy below the
// move to r1024 makes it impossible for that move to be coalesced.
//
// r1025 = mov r1
// r1024 = mov r0
// ...
// r1 = mov 1024
// r2 = mov 1025
break; // Woot! Found a good location.
--Pos;
}
bool Emitted = TII.copyRegToReg(*MBB, Pos, VirtReg, PhysReg, RC, RC);
assert(Emitted && "Unable to issue a live-in copy instruction!\n");
(void) Emitted;
CopyRegMap.insert(std::make_pair(prior(Pos), VirtReg));
if (Coalesced) {
if (&*InsertPos == UseMI) ++InsertPos;
MBB->erase(UseMI);
}
}
/// EmitLiveInCopies - If this is the first basic block in the function,
/// and if it has live ins that need to be copied into vregs, emit the
/// copies into the block.
static void EmitLiveInCopies(MachineBasicBlock *EntryMBB,
const MachineRegisterInfo &MRI,
const TargetRegisterInfo &TRI,
const TargetInstrInfo &TII) {
if (SchedLiveInCopies) {
// Emit the copies at a heuristically-determined location in the block.
DenseMap<MachineInstr*, unsigned> CopyRegMap;
MachineBasicBlock::iterator InsertPos = EntryMBB->begin();
for (MachineRegisterInfo::livein_iterator LI = MRI.livein_begin(),
E = MRI.livein_end(); LI != E; ++LI)
if (LI->second) {
const TargetRegisterClass *RC = MRI.getRegClass(LI->second);
EmitLiveInCopy(EntryMBB, InsertPos, LI->second, LI->first,
RC, CopyRegMap, MRI, TRI, TII);
}
} else {
// Emit the copies into the top of the block.
for (MachineRegisterInfo::livein_iterator LI = MRI.livein_begin(),
E = MRI.livein_end(); LI != E; ++LI)
if (LI->second) {
const TargetRegisterClass *RC = MRI.getRegClass(LI->second);
bool Emitted = TII.copyRegToReg(*EntryMBB, EntryMBB->begin(),
LI->second, LI->first, RC, RC);
assert(Emitted && "Unable to issue a live-in copy instruction!\n");
(void) Emitted;
}
}
}
//===----------------------------------------------------------------------===//
// SelectionDAGISel code
//===----------------------------------------------------------------------===//
SelectionDAGISel::SelectionDAGISel(TargetMachine &tm, CodeGenOpt::Level OL) :
MachineFunctionPass(&ID), TM(tm), TLI(*tm.getTargetLowering()),
FuncInfo(new FunctionLoweringInfo(TLI)),
CurDAG(new SelectionDAG(TLI, *FuncInfo)),
SDL(new SelectionDAGLowering(*CurDAG, TLI, *FuncInfo, OL)),
GFI(),
OptLevel(OL),
DAGSize(0)
{}
SelectionDAGISel::~SelectionDAGISel() {
delete SDL;
delete CurDAG;
delete FuncInfo;
}
unsigned SelectionDAGISel::MakeReg(EVT VT) {
return RegInfo->createVirtualRegister(TLI.getRegClassFor(VT));
}
void SelectionDAGISel::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<AliasAnalysis>();
AU.addPreserved<AliasAnalysis>();
AU.addRequired<GCModuleInfo>();
AU.addPreserved<GCModuleInfo>();
AU.addRequired<DwarfWriter>();
AU.addPreserved<DwarfWriter>();
MachineFunctionPass::getAnalysisUsage(AU);
}
bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
Function &Fn = *mf.getFunction();
// Do some sanity-checking on the command-line options.
assert((!EnableFastISelVerbose || EnableFastISel) &&
"-fast-isel-verbose requires -fast-isel");
assert((!EnableFastISelAbort || EnableFastISel) &&
"-fast-isel-abort requires -fast-isel");
// Get alias analysis for load/store combining.
AA = &getAnalysis<AliasAnalysis>();
MF = &mf;
const TargetInstrInfo &TII = *TM.getInstrInfo();
const TargetRegisterInfo &TRI = *TM.getRegisterInfo();
if (Fn.hasGC())
GFI = &getAnalysis<GCModuleInfo>().getFunctionInfo(Fn);
else
GFI = 0;
RegInfo = &MF->getRegInfo();
DEBUG(errs() << "\n\n\n=== " << Fn.getName() << "\n");
MachineModuleInfo *MMI = getAnalysisIfAvailable<MachineModuleInfo>();
DwarfWriter *DW = getAnalysisIfAvailable<DwarfWriter>();
CurDAG->init(*MF, MMI, DW);
FuncInfo->set(Fn, *MF, *CurDAG, EnableFastISel);
SDL->init(GFI, *AA);
for (Function::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I)
if (InvokeInst *Invoke = dyn_cast<InvokeInst>(I->getTerminator()))
// Mark landing pad.
FuncInfo->MBBMap[Invoke->getSuccessor(1)]->setIsLandingPad();
SelectAllBasicBlocks(Fn, *MF, MMI, DW, TII);
// If the first basic block in the function has live ins that need to be
// copied into vregs, emit the copies into the top of the block before
// emitting the code for the block.
EmitLiveInCopies(MF->begin(), *RegInfo, TRI, TII);
// Add function live-ins to entry block live-in set.
for (MachineRegisterInfo::livein_iterator I = RegInfo->livein_begin(),
E = RegInfo->livein_end(); I != E; ++I)
MF->begin()->addLiveIn(I->first);
#ifndef NDEBUG
assert(FuncInfo->CatchInfoFound.size() == FuncInfo->CatchInfoLost.size() &&
"Not all catch info was assigned to a landing pad!");
#endif
FuncInfo->clear();
return true;
}
static void copyCatchInfo(BasicBlock *SrcBB, BasicBlock *DestBB,
MachineModuleInfo *MMI, FunctionLoweringInfo &FLI) {
for (BasicBlock::iterator I = SrcBB->begin(), E = --SrcBB->end(); I != E; ++I)
if (EHSelectorInst *EHSel = dyn_cast<EHSelectorInst>(I)) {
// Apply the catch info to DestBB.
AddCatchInfo(*EHSel, MMI, FLI.MBBMap[DestBB]);
#ifndef NDEBUG
if (!FLI.MBBMap[SrcBB]->isLandingPad())
FLI.CatchInfoFound.insert(EHSel);
#endif
}
}
void SelectionDAGISel::SelectBasicBlock(BasicBlock *LLVMBB,
BasicBlock::iterator Begin,
BasicBlock::iterator End) {
SDL->setCurrentBasicBlock(BB);
Metadata &TheMetadata = LLVMBB->getParent()->getContext().getMetadata();
MDKindID MDDbgKind = TheMetadata.getMDKind("dbg");
// Lower all of the non-terminator instructions. If a call is emitted
// as a tail call, cease emitting nodes for this block.
for (BasicBlock::iterator I = Begin; I != End && !SDL->HasTailCall; ++I) {
if (MDDbgKind) {
// Update DebugLoc if debug information is attached with this
// instruction.
if (MDNode *Dbg =
dyn_cast_or_null<MDNode>(TheMetadata.getMD(MDDbgKind, I))) {
DILocation DILoc(Dbg);
DebugLoc Loc = ExtractDebugLocation(DILoc, MF->getDebugLocInfo());
SDL->setCurDebugLoc(Loc);
}
}
if (!isa<TerminatorInst>(I))
SDL->visit(*I);
}
if (!SDL->HasTailCall) {
// Ensure that all instructions which are used outside of their defining
// blocks are available as virtual registers. Invoke is handled elsewhere.
for (BasicBlock::iterator I = Begin; I != End; ++I)
if (!isa<PHINode>(I) && !isa<InvokeInst>(I))
SDL->CopyToExportRegsIfNeeded(I);
// Handle PHI nodes in successor blocks.
if (End == LLVMBB->end()) {
HandlePHINodesInSuccessorBlocks(LLVMBB);
// Lower the terminator after the copies are emitted.
SDL->visit(*LLVMBB->getTerminator());
}
}
// Make sure the root of the DAG is up-to-date.
CurDAG->setRoot(SDL->getControlRoot());
// Final step, emit the lowered DAG as machine code.
CodeGenAndEmitDAG();
SDL->clear();
}
void SelectionDAGISel::ComputeLiveOutVRegInfo() {
SmallPtrSet<SDNode*, 128> VisitedNodes;
SmallVector<SDNode*, 128> Worklist;
Worklist.push_back(CurDAG->getRoot().getNode());
APInt Mask;
APInt KnownZero;
APInt KnownOne;
while (!Worklist.empty()) {
SDNode *N = Worklist.back();
Worklist.pop_back();
// If we've already seen this node, ignore it.
if (!VisitedNodes.insert(N))
continue;
// Otherwise, add all chain operands to the worklist.
for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
if (N->getOperand(i).getValueType() == MVT::Other)
Worklist.push_back(N->getOperand(i).getNode());
// If this is a CopyToReg with a vreg dest, process it.
if (N->getOpcode() != ISD::CopyToReg)
continue;
unsigned DestReg = cast<RegisterSDNode>(N->getOperand(1))->getReg();
if (!TargetRegisterInfo::isVirtualRegister(DestReg))
continue;
// Ignore non-scalar or non-integer values.
SDValue Src = N->getOperand(2);
EVT SrcVT = Src.getValueType();
if (!SrcVT.isInteger() || SrcVT.isVector())
continue;
unsigned NumSignBits = CurDAG->ComputeNumSignBits(Src);
Mask = APInt::getAllOnesValue(SrcVT.getSizeInBits());
CurDAG->ComputeMaskedBits(Src, Mask, KnownZero, KnownOne);
// Only install this information if it tells us something.
if (NumSignBits != 1 || KnownZero != 0 || KnownOne != 0) {
DestReg -= TargetRegisterInfo::FirstVirtualRegister;
if (DestReg >= FuncInfo->LiveOutRegInfo.size())
FuncInfo->LiveOutRegInfo.resize(DestReg+1);
FunctionLoweringInfo::LiveOutInfo &LOI =
FuncInfo->LiveOutRegInfo[DestReg];
LOI.NumSignBits = NumSignBits;
LOI.KnownOne = KnownOne;
LOI.KnownZero = KnownZero;
}
}
}
void SelectionDAGISel::CodeGenAndEmitDAG() {
std::string GroupName;
if (TimePassesIsEnabled)
GroupName = "Instruction Selection and Scheduling";
std::string BlockName;
if (ViewDAGCombine1 || ViewLegalizeTypesDAGs || ViewLegalizeDAGs ||
ViewDAGCombine2 || ViewDAGCombineLT || ViewISelDAGs || ViewSchedDAGs ||
ViewSUnitDAGs)
BlockName = MF->getFunction()->getNameStr() + ":" +
BB->getBasicBlock()->getNameStr();
DEBUG(errs() << "Initial selection DAG:\n");
DEBUG(CurDAG->dump());
if (ViewDAGCombine1) CurDAG->viewGraph("dag-combine1 input for " + BlockName);
// Run the DAG combiner in pre-legalize mode.
if (TimePassesIsEnabled) {
NamedRegionTimer T("DAG Combining 1", GroupName);
CurDAG->Combine(Unrestricted, *AA, OptLevel);
} else {
CurDAG->Combine(Unrestricted, *AA, OptLevel);
}
DEBUG(errs() << "Optimized lowered selection DAG:\n");
DEBUG(CurDAG->dump());
// Second step, hack on the DAG until it only uses operations and types that
// the target supports.
if (!DisableLegalizeTypes) {
if (ViewLegalizeTypesDAGs) CurDAG->viewGraph("legalize-types input for " +
BlockName);
bool Changed;
if (TimePassesIsEnabled) {
NamedRegionTimer T("Type Legalization", GroupName);
Changed = CurDAG->LegalizeTypes();
} else {
Changed = CurDAG->LegalizeTypes();
}
DEBUG(errs() << "Type-legalized selection DAG:\n");
DEBUG(CurDAG->dump());
if (Changed) {
if (ViewDAGCombineLT)
CurDAG->viewGraph("dag-combine-lt input for " + BlockName);
// Run the DAG combiner in post-type-legalize mode.
if (TimePassesIsEnabled) {
NamedRegionTimer T("DAG Combining after legalize types", GroupName);
CurDAG->Combine(NoIllegalTypes, *AA, OptLevel);
} else {
CurDAG->Combine(NoIllegalTypes, *AA, OptLevel);
}
DEBUG(errs() << "Optimized type-legalized selection DAG:\n");
DEBUG(CurDAG->dump());
}
if (TimePassesIsEnabled) {
NamedRegionTimer T("Vector Legalization", GroupName);
Changed = CurDAG->LegalizeVectors();
} else {
Changed = CurDAG->LegalizeVectors();
}
if (Changed) {
if (TimePassesIsEnabled) {
NamedRegionTimer T("Type Legalization 2", GroupName);
Changed = CurDAG->LegalizeTypes();
} else {
Changed = CurDAG->LegalizeTypes();
}
if (ViewDAGCombineLT)
CurDAG->viewGraph("dag-combine-lv input for " + BlockName);
// Run the DAG combiner in post-type-legalize mode.
if (TimePassesIsEnabled) {
NamedRegionTimer T("DAG Combining after legalize vectors", GroupName);
CurDAG->Combine(NoIllegalOperations, *AA, OptLevel);
} else {
CurDAG->Combine(NoIllegalOperations, *AA, OptLevel);
}
DEBUG(errs() << "Optimized vector-legalized selection DAG:\n");
DEBUG(CurDAG->dump());
}
}
if (ViewLegalizeDAGs) CurDAG->viewGraph("legalize input for " + BlockName);
if (TimePassesIsEnabled) {
NamedRegionTimer T("DAG Legalization", GroupName);
CurDAG->Legalize(DisableLegalizeTypes, OptLevel);
} else {
CurDAG->Legalize(DisableLegalizeTypes, OptLevel);
}
DEBUG(errs() << "Legalized selection DAG:\n");
DEBUG(CurDAG->dump());
if (ViewDAGCombine2) CurDAG->viewGraph("dag-combine2 input for " + BlockName);
// Run the DAG combiner in post-legalize mode.
if (TimePassesIsEnabled) {
NamedRegionTimer T("DAG Combining 2", GroupName);
CurDAG->Combine(NoIllegalOperations, *AA, OptLevel);
} else {
CurDAG->Combine(NoIllegalOperations, *AA, OptLevel);
}
DEBUG(errs() << "Optimized legalized selection DAG:\n");
DEBUG(CurDAG->dump());
if (ViewISelDAGs) CurDAG->viewGraph("isel input for " + BlockName);
if (OptLevel != CodeGenOpt::None)
ComputeLiveOutVRegInfo();
// Third, instruction select all of the operations to machine code, adding the
// code to the MachineBasicBlock.
if (TimePassesIsEnabled) {
NamedRegionTimer T("Instruction Selection", GroupName);
InstructionSelect();
} else {
InstructionSelect();
}
DEBUG(errs() << "Selected selection DAG:\n");
DEBUG(CurDAG->dump());
if (ViewSchedDAGs) CurDAG->viewGraph("scheduler input for " + BlockName);
// Schedule machine code.
ScheduleDAGSDNodes *Scheduler = CreateScheduler();
if (TimePassesIsEnabled) {
NamedRegionTimer T("Instruction Scheduling", GroupName);
Scheduler->Run(CurDAG, BB, BB->end());
} else {
Scheduler->Run(CurDAG, BB, BB->end());
}
if (ViewSUnitDAGs) Scheduler->viewGraph();
// Emit machine code to BB. This can change 'BB' to the last block being
// inserted into.
if (TimePassesIsEnabled) {
NamedRegionTimer T("Instruction Creation", GroupName);
BB = Scheduler->EmitSchedule(&SDL->EdgeMapping);
} else {
BB = Scheduler->EmitSchedule(&SDL->EdgeMapping);
}
// Free the scheduler state.
if (TimePassesIsEnabled) {
NamedRegionTimer T("Instruction Scheduling Cleanup", GroupName);
delete Scheduler;
} else {
delete Scheduler;
}
DEBUG(errs() << "Selected machine code:\n");
DEBUG(BB->dump());
}
void SelectionDAGISel::SelectAllBasicBlocks(Function &Fn,
MachineFunction &MF,
MachineModuleInfo *MMI,
DwarfWriter *DW,
const TargetInstrInfo &TII) {
// Initialize the Fast-ISel state, if needed.
FastISel *FastIS = 0;
if (EnableFastISel)
FastIS = TLI.createFastISel(MF, MMI, DW,
FuncInfo->ValueMap,
FuncInfo->MBBMap,
FuncInfo->StaticAllocaMap
#ifndef NDEBUG
, FuncInfo->CatchInfoLost
#endif
);
Metadata &TheMetadata = Fn.getContext().getMetadata();
MDKindID MDDbgKind = TheMetadata.getMDKind("dbg");
// Iterate over all basic blocks in the function.
for (Function::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
BasicBlock *LLVMBB = &*I;
BB = FuncInfo->MBBMap[LLVMBB];
BasicBlock::iterator const Begin = LLVMBB->begin();
BasicBlock::iterator const End = LLVMBB->end();
BasicBlock::iterator BI = Begin;
// Lower any arguments needed in this block if this is the entry block.
bool SuppressFastISel = false;
if (LLVMBB == &Fn.getEntryBlock()) {
LowerArguments(LLVMBB);
// If any of the arguments has the byval attribute, forgo
// fast-isel in the entry block.
if (FastIS) {
unsigned j = 1;
for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end();
I != E; ++I, ++j)
if (Fn.paramHasAttr(j, Attribute::ByVal)) {
if (EnableFastISelVerbose || EnableFastISelAbort)
errs() << "FastISel skips entry block due to byval argument\n";
SuppressFastISel = true;
break;
}
}
}
if (MMI && BB->isLandingPad()) {
// Add a label to mark the beginning of the landing pad. Deletion of the
// landing pad can thus be detected via the MachineModuleInfo.
unsigned LabelID = MMI->addLandingPad(BB);
const TargetInstrDesc &II = TII.get(TargetInstrInfo::EH_LABEL);
BuildMI(BB, SDL->getCurDebugLoc(), II).addImm(LabelID);
// Mark exception register as live in.
unsigned Reg = TLI.getExceptionAddressRegister();
if (Reg) BB->addLiveIn(Reg);
// Mark exception selector register as live in.
Reg = TLI.getExceptionSelectorRegister();
if (Reg) BB->addLiveIn(Reg);
// FIXME: Hack around an exception handling flaw (PR1508): the personality
// function and list of typeids logically belong to the invoke (or, if you
// like, the basic block containing the invoke), and need to be associated
// with it in the dwarf exception handling tables. Currently however the
// information is provided by an intrinsic (eh.selector) that can be moved
// to unexpected places by the optimizers: if the unwind edge is critical,
// then breaking it can result in the intrinsics being in the successor of
// the landing pad, not the landing pad itself. This results in exceptions
// not being caught because no typeids are associated with the invoke.
// This may not be the only way things can go wrong, but it is the only way
// we try to work around for the moment.
BranchInst *Br = dyn_cast<BranchInst>(LLVMBB->getTerminator());
if (Br && Br->isUnconditional()) { // Critical edge?
BasicBlock::iterator I, E;
for (I = LLVMBB->begin(), E = --LLVMBB->end(); I != E; ++I)
if (isa<EHSelectorInst>(I))
break;
if (I == E)
// No catch info found - try to extract some from the successor.
copyCatchInfo(Br->getSuccessor(0), LLVMBB, MMI, *FuncInfo);
}
}
// Before doing SelectionDAG ISel, see if FastISel has been requested.
if (FastIS && !SuppressFastISel) {
// Emit code for any incoming arguments. This must happen before
// beginning FastISel on the entry block.
if (LLVMBB == &Fn.getEntryBlock()) {
CurDAG->setRoot(SDL->getControlRoot());
CodeGenAndEmitDAG();
SDL->clear();
}
FastIS->startNewBlock(BB);
// Do FastISel on as many instructions as possible.
for (; BI != End; ++BI) {
if (MDDbgKind) {
// Update DebugLoc if debug information is attached with this
// instruction.
if (MDNode *Dbg =
dyn_cast_or_null<MDNode>(TheMetadata.getMD(MDDbgKind, BI))) {
DILocation DILoc(Dbg);
DebugLoc Loc = ExtractDebugLocation(DILoc,
MF.getDebugLocInfo());
FastIS->setCurDebugLoc(Loc);
}
}
// Just before the terminator instruction, insert instructions to
// feed PHI nodes in successor blocks.
if (isa<TerminatorInst>(BI))
if (!HandlePHINodesInSuccessorBlocksFast(LLVMBB, FastIS)) {
if (EnableFastISelVerbose || EnableFastISelAbort) {
errs() << "FastISel miss: ";
BI->dump();
}
assert(!EnableFastISelAbort &&
"FastISel didn't handle a PHI in a successor");
break;
}
// First try normal tablegen-generated "fast" selection.
if (FastIS->SelectInstruction(BI))
continue;
// Next, try calling the target to attempt to handle the instruction.
if (FastIS->TargetSelectInstruction(BI))
continue;
// Then handle certain instructions as single-LLVM-Instruction blocks.
if (isa<CallInst>(BI)) {
if (EnableFastISelVerbose || EnableFastISelAbort) {
errs() << "FastISel missed call: ";
BI->dump();
}
if (BI->getType() != Type::getVoidTy(*CurDAG->getContext())) {
unsigned &R = FuncInfo->ValueMap[BI];
if (!R)
R = FuncInfo->CreateRegForValue(BI);
}
SDL->setCurDebugLoc(FastIS->getCurDebugLoc());
SelectBasicBlock(LLVMBB, BI, next(BI));
// If the instruction was codegen'd with multiple blocks,
// inform the FastISel object where to resume inserting.
FastIS->setCurrentBlock(BB);
continue;
}
// Otherwise, give up on FastISel for the rest of the block.
// For now, be a little lenient about non-branch terminators.
if (!isa<TerminatorInst>(BI) || isa<BranchInst>(BI)) {
if (EnableFastISelVerbose || EnableFastISelAbort) {
errs() << "FastISel miss: ";
BI->dump();
}
if (EnableFastISelAbort)
// The "fast" selector couldn't handle something and bailed.
// For the purpose of debugging, just abort.
llvm_unreachable("FastISel didn't select the entire block");
}
break;
}
}
// Run SelectionDAG instruction selection on the remainder of the block
// not handled by FastISel. If FastISel is not run, this is the entire
// block.
if (BI != End) {
// If FastISel is run and it has known DebugLoc then use it.
if (FastIS && !FastIS->getCurDebugLoc().isUnknown())
SDL->setCurDebugLoc(FastIS->getCurDebugLoc());
SelectBasicBlock(LLVMBB, BI, End);
}
FinishBasicBlock();
}
delete FastIS;
}
void
SelectionDAGISel::FinishBasicBlock() {
DEBUG(errs() << "Target-post-processed machine code:\n");
DEBUG(BB->dump());
DEBUG(errs() << "Total amount of phi nodes to update: "
<< SDL->PHINodesToUpdate.size() << "\n");
DEBUG(for (unsigned i = 0, e = SDL->PHINodesToUpdate.size(); i != e; ++i)
errs() << "Node " << i << " : ("
<< SDL->PHINodesToUpdate[i].first
<< ", " << SDL->PHINodesToUpdate[i].second << ")\n");
// Next, now that we know what the last MBB the LLVM BB expanded is, update
// PHI nodes in successors.
if (SDL->SwitchCases.empty() &&
SDL->JTCases.empty() &&
SDL->BitTestCases.empty()) {
for (unsigned i = 0, e = SDL->PHINodesToUpdate.size(); i != e; ++i) {
MachineInstr *PHI = SDL->PHINodesToUpdate[i].first;
assert(PHI->getOpcode() == TargetInstrInfo::PHI &&
"This is not a machine PHI node that we are updating!");
PHI->addOperand(MachineOperand::CreateReg(SDL->PHINodesToUpdate[i].second,
false));
PHI->addOperand(MachineOperand::CreateMBB(BB));
}
SDL->PHINodesToUpdate.clear();
return;
}
for (unsigned i = 0, e = SDL->BitTestCases.size(); i != e; ++i) {
// Lower header first, if it wasn't already lowered
if (!SDL->BitTestCases[i].Emitted) {
// Set the current basic block to the mbb we wish to insert the code into
BB = SDL->BitTestCases[i].Parent;
SDL->setCurrentBasicBlock(BB);
// Emit the code
SDL->visitBitTestHeader(SDL->BitTestCases[i]);
CurDAG->setRoot(SDL->getRoot());
CodeGenAndEmitDAG();
SDL->clear();
}
for (unsigned j = 0, ej = SDL->BitTestCases[i].Cases.size(); j != ej; ++j) {
// Set the current basic block to the mbb we wish to insert the code into
BB = SDL->BitTestCases[i].Cases[j].ThisBB;
SDL->setCurrentBasicBlock(BB);
// Emit the code
if (j+1 != ej)
SDL->visitBitTestCase(SDL->BitTestCases[i].Cases[j+1].ThisBB,
SDL->BitTestCases[i].Reg,
SDL->BitTestCases[i].Cases[j]);
else
SDL->visitBitTestCase(SDL->BitTestCases[i].Default,
SDL->BitTestCases[i].Reg,
SDL->BitTestCases[i].Cases[j]);
CurDAG->setRoot(SDL->getRoot());
CodeGenAndEmitDAG();
SDL->clear();
}
// Update PHI Nodes
for (unsigned pi = 0, pe = SDL->PHINodesToUpdate.size(); pi != pe; ++pi) {
MachineInstr *PHI = SDL->PHINodesToUpdate[pi].first;
MachineBasicBlock *PHIBB = PHI->getParent();
assert(PHI->getOpcode() == TargetInstrInfo::PHI &&
"This is not a machine PHI node that we are updating!");
// This is "default" BB. We have two jumps to it. From "header" BB and
// from last "case" BB.
if (PHIBB == SDL->BitTestCases[i].Default) {
PHI->addOperand(MachineOperand::CreateReg(SDL->PHINodesToUpdate[pi].second,
false));
PHI->addOperand(MachineOperand::CreateMBB(SDL->BitTestCases[i].Parent));
PHI->addOperand(MachineOperand::CreateReg(SDL->PHINodesToUpdate[pi].second,
false));
PHI->addOperand(MachineOperand::CreateMBB(SDL->BitTestCases[i].Cases.
back().ThisBB));
}
// One of "cases" BB.
for (unsigned j = 0, ej = SDL->BitTestCases[i].Cases.size();
j != ej; ++j) {
MachineBasicBlock* cBB = SDL->BitTestCases[i].Cases[j].ThisBB;
if (cBB->succ_end() !=
std::find(cBB->succ_begin(),cBB->succ_end(), PHIBB)) {
PHI->addOperand(MachineOperand::CreateReg(SDL->PHINodesToUpdate[pi].second,
false));
PHI->addOperand(MachineOperand::CreateMBB(cBB));
}
}
}
}
SDL->BitTestCases.clear();
// If the JumpTable record is filled in, then we need to emit a jump table.
// Updating the PHI nodes is tricky in this case, since we need to determine
// whether the PHI is a successor of the range check MBB or the jump table MBB
for (unsigned i = 0, e = SDL->JTCases.size(); i != e; ++i) {
// Lower header first, if it wasn't already lowered
if (!SDL->JTCases[i].first.Emitted) {
// Set the current basic block to the mbb we wish to insert the code into
BB = SDL->JTCases[i].first.HeaderBB;
SDL->setCurrentBasicBlock(BB);
// Emit the code
SDL->visitJumpTableHeader(SDL->JTCases[i].second, SDL->JTCases[i].first);
CurDAG->setRoot(SDL->getRoot());
CodeGenAndEmitDAG();
SDL->clear();
}
// Set the current basic block to the mbb we wish to insert the code into
BB = SDL->JTCases[i].second.MBB;
SDL->setCurrentBasicBlock(BB);
// Emit the code
SDL->visitJumpTable(SDL->JTCases[i].second);
CurDAG->setRoot(SDL->getRoot());
CodeGenAndEmitDAG();
SDL->clear();
// Update PHI Nodes
for (unsigned pi = 0, pe = SDL->PHINodesToUpdate.size(); pi != pe; ++pi) {
MachineInstr *PHI = SDL->PHINodesToUpdate[pi].first;
MachineBasicBlock *PHIBB = PHI->getParent();
assert(PHI->getOpcode() == TargetInstrInfo::PHI &&
"This is not a machine PHI node that we are updating!");
// "default" BB. We can go there only from header BB.
if (PHIBB == SDL->JTCases[i].second.Default) {
PHI->addOperand
(MachineOperand::CreateReg(SDL->PHINodesToUpdate[pi].second, false));
PHI->addOperand
(MachineOperand::CreateMBB(SDL->JTCases[i].first.HeaderBB));
}
// JT BB. Just iterate over successors here
if (BB->succ_end() != std::find(BB->succ_begin(),BB->succ_end(), PHIBB)) {
PHI->addOperand
(MachineOperand::CreateReg(SDL->PHINodesToUpdate[pi].second, false));
PHI->addOperand(MachineOperand::CreateMBB(BB));
}
}
}
SDL->JTCases.clear();
// If the switch block involved a branch to one of the actual successors, we
// need to update PHI nodes in that block.
for (unsigned i = 0, e = SDL->PHINodesToUpdate.size(); i != e; ++i) {
MachineInstr *PHI = SDL->PHINodesToUpdate[i].first;
assert(PHI->getOpcode() == TargetInstrInfo::PHI &&
"This is not a machine PHI node that we are updating!");
if (BB->isSuccessor(PHI->getParent())) {
PHI->addOperand(MachineOperand::CreateReg(SDL->PHINodesToUpdate[i].second,
false));
PHI->addOperand(MachineOperand::CreateMBB(BB));
}
}
// If we generated any switch lowering information, build and codegen any
// additional DAGs necessary.
for (unsigned i = 0, e = SDL->SwitchCases.size(); i != e; ++i) {
// Set the current basic block to the mbb we wish to insert the code into
MachineBasicBlock *ThisBB = BB = SDL->SwitchCases[i].ThisBB;
SDL->setCurrentBasicBlock(BB);
// Emit the code
SDL->visitSwitchCase(SDL->SwitchCases[i]);
CurDAG->setRoot(SDL->getRoot());
CodeGenAndEmitDAG();
// Handle any PHI nodes in successors of this chunk, as if we were coming
// from the original BB before switch expansion. Note that PHI nodes can
// occur multiple times in PHINodesToUpdate. We have to be very careful to
// handle them the right number of times.
while ((BB = SDL->SwitchCases[i].TrueBB)) { // Handle LHS and RHS.
// If new BB's are created during scheduling, the edges may have been
// updated. That is, the edge from ThisBB to BB may have been split and
// BB's predecessor is now another block.
DenseMap<MachineBasicBlock*, MachineBasicBlock*>::iterator EI =
SDL->EdgeMapping.find(BB);
if (EI != SDL->EdgeMapping.end())
ThisBB = EI->second;
for (MachineBasicBlock::iterator Phi = BB->begin();
Phi != BB->end() && Phi->getOpcode() == TargetInstrInfo::PHI; ++Phi){
// This value for this PHI node is recorded in PHINodesToUpdate, get it.
for (unsigned pn = 0; ; ++pn) {
assert(pn != SDL->PHINodesToUpdate.size() &&
"Didn't find PHI entry!");
if (SDL->PHINodesToUpdate[pn].first == Phi) {
Phi->addOperand(MachineOperand::CreateReg(SDL->PHINodesToUpdate[pn].
second, false));
Phi->addOperand(MachineOperand::CreateMBB(ThisBB));
break;
}
}
}
// Don't process RHS if same block as LHS.
if (BB == SDL->SwitchCases[i].FalseBB)
SDL->SwitchCases[i].FalseBB = 0;
// If we haven't handled the RHS, do so now. Otherwise, we're done.
SDL->SwitchCases[i].TrueBB = SDL->SwitchCases[i].FalseBB;
SDL->SwitchCases[i].FalseBB = 0;
}
assert(SDL->SwitchCases[i].TrueBB == 0 && SDL->SwitchCases[i].FalseBB == 0);
SDL->clear();
}
SDL->SwitchCases.clear();
SDL->PHINodesToUpdate.clear();
}
/// Create the scheduler. If a specific scheduler was specified
/// via the SchedulerRegistry, use it, otherwise select the
/// one preferred by the target.
///
ScheduleDAGSDNodes *SelectionDAGISel::CreateScheduler() {
RegisterScheduler::FunctionPassCtor Ctor = RegisterScheduler::getDefault();
if (!Ctor) {
Ctor = ISHeuristic;
RegisterScheduler::setDefault(Ctor);
}
return Ctor(this, OptLevel);
}
ScheduleHazardRecognizer *SelectionDAGISel::CreateTargetHazardRecognizer() {
return new ScheduleHazardRecognizer();
}
//===----------------------------------------------------------------------===//
// Helper functions used by the generated instruction selector.
//===----------------------------------------------------------------------===//
// Calls to these methods are generated by tblgen.
/// CheckAndMask - The isel is trying to match something like (and X, 255). If
/// the dag combiner simplified the 255, we still want to match. RHS is the
/// actual value in the DAG on the RHS of an AND, and DesiredMaskS is the value
/// specified in the .td file (e.g. 255).
bool SelectionDAGISel::CheckAndMask(SDValue LHS, ConstantSDNode *RHS,
int64_t DesiredMaskS) const {
const APInt &ActualMask = RHS->getAPIntValue();
const APInt &DesiredMask = APInt(LHS.getValueSizeInBits(), DesiredMaskS);
// If the actual mask exactly matches, success!
if (ActualMask == DesiredMask)
return true;
// If the actual AND mask is allowing unallowed bits, this doesn't match.
if (ActualMask.intersects(~DesiredMask))
return false;
// Otherwise, the DAG Combiner may have proven that the value coming in is
// either already zero or is not demanded. Check for known zero input bits.
APInt NeededMask = DesiredMask & ~ActualMask;
if (CurDAG->MaskedValueIsZero(LHS, NeededMask))
return true;
// TODO: check to see if missing bits are just not demanded.
// Otherwise, this pattern doesn't match.
return false;
}
/// CheckOrMask - The isel is trying to match something like (or X, 255). If
/// the dag combiner simplified the 255, we still want to match. RHS is the
/// actual value in the DAG on the RHS of an OR, and DesiredMaskS is the value
/// specified in the .td file (e.g. 255).
bool SelectionDAGISel::CheckOrMask(SDValue LHS, ConstantSDNode *RHS,
int64_t DesiredMaskS) const {
const APInt &ActualMask = RHS->getAPIntValue();
const APInt &DesiredMask = APInt(LHS.getValueSizeInBits(), DesiredMaskS);
// If the actual mask exactly matches, success!
if (ActualMask == DesiredMask)
return true;
// If the actual AND mask is allowing unallowed bits, this doesn't match.
if (ActualMask.intersects(~DesiredMask))
return false;
// Otherwise, the DAG Combiner may have proven that the value coming in is
// either already zero or is not demanded. Check for known zero input bits.
APInt NeededMask = DesiredMask & ~ActualMask;
APInt KnownZero, KnownOne;
CurDAG->ComputeMaskedBits(LHS, NeededMask, KnownZero, KnownOne);
// If all the missing bits in the or are already known to be set, match!
if ((NeededMask & KnownOne) == NeededMask)
return true;
// TODO: check to see if missing bits are just not demanded.
// Otherwise, this pattern doesn't match.
return false;
}
/// SelectInlineAsmMemoryOperands - Calls to this are automatically generated
/// by tblgen. Others should not call it.
void SelectionDAGISel::
SelectInlineAsmMemoryOperands(std::vector<SDValue> &Ops) {
std::vector<SDValue> InOps;
std::swap(InOps, Ops);
Ops.push_back(InOps[0]); // input chain.
Ops.push_back(InOps[1]); // input asm string.
unsigned i = 2, e = InOps.size();
if (InOps[e-1].getValueType() == MVT::Flag)
--e; // Don't process a flag operand if it is here.
while (i != e) {
unsigned Flags = cast<ConstantSDNode>(InOps[i])->getZExtValue();
if ((Flags & 7) != 4 /*MEM*/) {
// Just skip over this operand, copying the operands verbatim.
Ops.insert(Ops.end(), InOps.begin()+i,
InOps.begin()+i+InlineAsm::getNumOperandRegisters(Flags) + 1);
i += InlineAsm::getNumOperandRegisters(Flags) + 1;
} else {
assert(InlineAsm::getNumOperandRegisters(Flags) == 1 &&
"Memory operand with multiple values?");
// Otherwise, this is a memory operand. Ask the target to select it.
std::vector<SDValue> SelOps;
if (SelectInlineAsmMemoryOperand(InOps[i+1], 'm', SelOps)) {
llvm_report_error("Could not match memory address. Inline asm"
" failure!");
}
// Add this to the output node.
EVT IntPtrTy = TLI.getPointerTy();
Ops.push_back(CurDAG->getTargetConstant(4/*MEM*/ | (SelOps.size()<< 3),
IntPtrTy));
Ops.insert(Ops.end(), SelOps.begin(), SelOps.end());
i += 2;
}
}
// Add the flag input back if present.
if (e != InOps.size())
Ops.push_back(InOps.back());
}
/// findFlagUse - Return use of EVT::Flag value produced by the specified
/// SDNode.
///
static SDNode *findFlagUse(SDNode *N) {
unsigned FlagResNo = N->getNumValues()-1;
for (SDNode::use_iterator I = N->use_begin(), E = N->use_end(); I != E; ++I) {
SDUse &Use = I.getUse();
if (Use.getResNo() == FlagResNo)
return Use.getUser();
}
return NULL;
}
/// findNonImmUse - Return true if "Use" is a non-immediate use of "Def".
/// This function recursively traverses up the operand chain, ignoring
/// certain nodes.
static bool findNonImmUse(SDNode *Use, SDNode* Def, SDNode *ImmedUse,
SDNode *Root,
SmallPtrSet<SDNode*, 16> &Visited) {
if (Use->getNodeId() < Def->getNodeId() ||
!Visited.insert(Use))
return false;
for (unsigned i = 0, e = Use->getNumOperands(); i != e; ++i) {
SDNode *N = Use->getOperand(i).getNode();
if (N == Def) {
if (Use == ImmedUse || Use == Root)
continue; // We are not looking for immediate use.
assert(N != Root);
return true;
}
// Traverse up the operand chain.
if (findNonImmUse(N, Def, ImmedUse, Root, Visited))
return true;
}
return false;
}
/// isNonImmUse - Start searching from Root up the DAG to check is Def can
/// be reached. Return true if that's the case. However, ignore direct uses
/// by ImmedUse (which would be U in the example illustrated in
/// IsLegalAndProfitableToFold) and by Root (which can happen in the store
/// case).
/// FIXME: to be really generic, we should allow direct use by any node
/// that is being folded. But realisticly since we only fold loads which
/// have one non-chain use, we only need to watch out for load/op/store
/// and load/op/cmp case where the root (store / cmp) may reach the load via
/// its chain operand.
static inline bool isNonImmUse(SDNode *Root, SDNode *Def, SDNode *ImmedUse) {
SmallPtrSet<SDNode*, 16> Visited;
return findNonImmUse(Root, Def, ImmedUse, Root, Visited);
}
/// IsLegalAndProfitableToFold - Returns true if the specific operand node N of
/// U can be folded during instruction selection that starts at Root and
/// folding N is profitable.
bool SelectionDAGISel::IsLegalAndProfitableToFold(SDNode *N, SDNode *U,
SDNode *Root) const {
if (OptLevel == CodeGenOpt::None) return false;
// If Root use can somehow reach N through a path that that doesn't contain
// U then folding N would create a cycle. e.g. In the following
// diagram, Root can reach N through X. If N is folded into into Root, then
// X is both a predecessor and a successor of U.
//
// [N*] //
// ^ ^ //
// / \ //
// [U*] [X]? //
// ^ ^ //
// \ / //
// \ / //
// [Root*] //
//
// * indicates nodes to be folded together.
//
// If Root produces a flag, then it gets (even more) interesting. Since it
// will be "glued" together with its flag use in the scheduler, we need to
// check if it might reach N.
//
// [N*] //
// ^ ^ //
// / \ //
// [U*] [X]? //
// ^ ^ //
// \ \ //
// \ | //
// [Root*] | //
// ^ | //
// f | //
// | / //
// [Y] / //
// ^ / //
// f / //
// | / //
// [FU] //
//
// If FU (flag use) indirectly reaches N (the load), and Root folds N
// (call it Fold), then X is a predecessor of FU and a successor of
// Fold. But since Fold and FU are flagged together, this will create
// a cycle in the scheduling graph.
EVT VT = Root->getValueType(Root->getNumValues()-1);
while (VT == MVT::Flag) {
SDNode *FU = findFlagUse(Root);
if (FU == NULL)
break;
Root = FU;
VT = Root->getValueType(Root->getNumValues()-1);
}
return !isNonImmUse(Root, N, U);
}
char SelectionDAGISel::ID = 0;
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