llvm-6502/lib/Target/X86/X86VZeroUpper.cpp
Lang Hames 3dd951e842 [X86] New and improved VZeroUpperInserter optimization.
- Adds support for inserting vzerouppers before tail-calls.
  This is enabled implicitly by having MachineInstr::copyImplicitOps preserve
  regmask operands, which allows VZeroUpperInserter to see where tail-calls use
  vector registers.

- Fixes a bug that caused the previous version of this optimization to miss some
  vzeroupper insertion points in loops. (Loops-with-vector-code that followed
  loops-without-vector-code were mistakenly overlooked by the previous version).

- New algorithm never revisits instructions.

Fixes <rdar://problem/16228798>



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204021 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-17 01:22:54 +00:00

315 lines
11 KiB
C++

//===-- X86VZeroUpper.cpp - AVX vzeroupper instruction inserter -----------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the pass which inserts x86 AVX vzeroupper instructions
// before calls to SSE encoded functions. This avoids transition latency
// penalty when tranfering control between AVX encoded instructions and old
// SSE encoding mode.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "x86-vzeroupper"
#include "X86.h"
#include "X86InstrInfo.h"
#include "X86Subtarget.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
using namespace llvm;
STATISTIC(NumVZU, "Number of vzeroupper instructions inserted");
namespace {
class VZeroUpperInserter : public MachineFunctionPass {
public:
VZeroUpperInserter() : MachineFunctionPass(ID) {}
bool runOnMachineFunction(MachineFunction &MF) override;
const char *getPassName() const override {return "X86 vzeroupper inserter";}
private:
void processBasicBlock(MachineBasicBlock &MBB);
void insertVZeroUpper(MachineBasicBlock::iterator I,
MachineBasicBlock &MBB);
void addDirtySuccessor(MachineBasicBlock &MBB);
typedef enum { PASS_THROUGH, EXITS_CLEAN, EXITS_DIRTY } BlockExitState;
static const char* getBlockExitStateName(BlockExitState ST);
// Core algorithm state:
// BlockState - Each block is either:
// - PASS_THROUGH: There are neither YMM dirtying instructions nor
// vzeroupper instructions in this block.
// - EXITS_CLEAN: There is (or will be) a vzeroupper instruction in this
// block that will ensure that YMM is clean on exit.
// - EXITS_DIRTY: An instruction in the block dirties YMM and no
// subsequent vzeroupper in the block clears it.
//
// AddedToDirtySuccessors - This flag is raised when a block is added to the
// DirtySuccessors list to ensure that it's not
// added multiple times.
//
// FirstUnguardedCall - Records the location of the first unguarded call in
// each basic block that may need to be guarded by a
// vzeroupper. We won't know whether it actually needs
// to be guarded until we discover a predecessor that
// is DIRTY_OUT.
struct BlockState {
BlockState() : ExitState(PASS_THROUGH), AddedToDirtySuccessors(false) {}
BlockExitState ExitState;
bool AddedToDirtySuccessors;
MachineBasicBlock::iterator FirstUnguardedCall;
};
typedef SmallVector<BlockState, 8> BlockStateMap;
typedef SmallVector<MachineBasicBlock*, 8> DirtySuccessorsWorkList;
BlockStateMap BlockStates;
DirtySuccessorsWorkList DirtySuccessors;
bool EverMadeChange;
const TargetInstrInfo *TII;
static char ID;
};
char VZeroUpperInserter::ID = 0;
}
FunctionPass *llvm::createX86IssueVZeroUpperPass() {
return new VZeroUpperInserter();
}
const char* VZeroUpperInserter::getBlockExitStateName(BlockExitState ST) {
switch (ST) {
case PASS_THROUGH: return "Pass-through";
case EXITS_DIRTY: return "Exits-dirty";
case EXITS_CLEAN: return "Exits-clean";
}
llvm_unreachable("Invalid block exit state.");
}
static bool isYmmReg(unsigned Reg) {
return (Reg >= X86::YMM0 && Reg <= X86::YMM15);
}
static bool checkFnHasLiveInYmm(MachineRegisterInfo &MRI) {
for (MachineRegisterInfo::livein_iterator I = MRI.livein_begin(),
E = MRI.livein_end(); I != E; ++I)
if (isYmmReg(I->first))
return true;
return false;
}
static bool clobbersAllYmmRegs(const MachineOperand &MO) {
for (unsigned reg = X86::YMM0; reg <= X86::YMM15; ++reg) {
if (!MO.clobbersPhysReg(reg))
return false;
}
return true;
}
static bool hasYmmReg(MachineInstr *MI) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (MI->isCall() && MO.isRegMask() && !clobbersAllYmmRegs(MO))
return true;
if (!MO.isReg())
continue;
if (MO.isDebug())
continue;
if (isYmmReg(MO.getReg()))
return true;
}
return false;
}
/// clobbersAnyYmmReg() - Check if any YMM register will be clobbered by this
/// instruction.
static bool callClobbersAnyYmmReg(MachineInstr *MI) {
assert(MI->isCall() && "Can only be called on call instructions.");
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isRegMask())
continue;
for (unsigned reg = X86::YMM0; reg <= X86::YMM15; ++reg) {
if (MO.clobbersPhysReg(reg))
return true;
}
}
return false;
}
// Insert a vzeroupper instruction before I.
void VZeroUpperInserter::insertVZeroUpper(MachineBasicBlock::iterator I,
MachineBasicBlock &MBB) {
DebugLoc dl = I->getDebugLoc();
BuildMI(MBB, I, dl, TII->get(X86::VZEROUPPER));
++NumVZU;
EverMadeChange = true;
}
// Add MBB to the DirtySuccessors list if it hasn't already been added.
void VZeroUpperInserter::addDirtySuccessor(MachineBasicBlock &MBB) {
if (!BlockStates[MBB.getNumber()].AddedToDirtySuccessors) {
DirtySuccessors.push_back(&MBB);
BlockStates[MBB.getNumber()].AddedToDirtySuccessors = true;
}
}
/// processBasicBlock - Loop over all of the instructions in the basic block,
/// inserting vzero upper instructions before function calls.
void VZeroUpperInserter::processBasicBlock(MachineBasicBlock &MBB) {
// Start by assuming that the block PASS_THROUGH, which implies no unguarded
// calls.
BlockExitState CurState = PASS_THROUGH;
BlockStates[MBB.getNumber()].FirstUnguardedCall = MBB.end();
for (MachineBasicBlock::iterator I = MBB.begin(); I != MBB.end(); ++I) {
MachineInstr *MI = I;
bool isControlFlow = MI->isCall() || MI->isReturn();
// Shortcut: don't need to check regular instructions in dirty state.
if (!isControlFlow && CurState == EXITS_DIRTY)
continue;
if (hasYmmReg(MI)) {
// We found a ymm-using instruction; this could be an AVX instruction,
// or it could be control flow.
CurState = EXITS_DIRTY;
continue;
}
// Check for control-flow out of the current function (which might
// indirectly execute SSE instructions).
if (!isControlFlow)
continue;
// If the call won't clobber any YMM register, skip it as well. It usually
// happens on helper function calls (such as '_chkstk', '_ftol2') where
// standard calling convention is not used (RegMask is not used to mark
// register clobbered and register usage (def/imp-def/use) is well-dfined
// and explicitly specified.
if (MI->isCall() && !callClobbersAnyYmmReg(MI))
continue;
// The VZEROUPPER instruction resets the upper 128 bits of all Intel AVX
// registers. This instruction has zero latency. In addition, the processor
// changes back to Clean state, after which execution of Intel SSE
// instructions or Intel AVX instructions has no transition penalty. Add
// the VZEROUPPER instruction before any function call/return that might
// execute SSE code.
// FIXME: In some cases, we may want to move the VZEROUPPER into a
// predecessor block.
if (CurState == EXITS_DIRTY) {
// After the inserted VZEROUPPER the state becomes clean again, but
// other YMM may appear before other subsequent calls or even before
// the end of the BB.
insertVZeroUpper(I, MBB);
CurState = EXITS_CLEAN;
} else if (CurState == PASS_THROUGH) {
// If this block is currently in pass-through state and we encounter a
// call then whether we need a vzeroupper or not depends on whether this
// block has successors that exit dirty. Record the location of the call,
// and set the state to EXITS_CLEAN, but do not insert the vzeroupper yet.
// It will be inserted later if necessary.
BlockStates[MBB.getNumber()].FirstUnguardedCall = I;
CurState = EXITS_CLEAN;
}
}
DEBUG(dbgs() << "MBB #" << MBB.getNumber() << " exit state: "
<< getBlockExitStateName(CurState) << '\n');
if (CurState == EXITS_DIRTY)
for (MachineBasicBlock::succ_iterator SI = MBB.succ_begin(),
SE = MBB.succ_end();
SI != SE; ++SI)
addDirtySuccessor(**SI);
BlockStates[MBB.getNumber()].ExitState = CurState;
}
/// runOnMachineFunction - Loop over all of the basic blocks, inserting
/// vzero upper instructions before function calls.
bool VZeroUpperInserter::runOnMachineFunction(MachineFunction &MF) {
if (MF.getTarget().getSubtarget<X86Subtarget>().hasAVX512())
return false;
TII = MF.getTarget().getInstrInfo();
MachineRegisterInfo &MRI = MF.getRegInfo();
EverMadeChange = false;
// Fast check: if the function doesn't use any ymm registers, we don't need
// to insert any VZEROUPPER instructions. This is constant-time, so it is
// cheap in the common case of no ymm use.
bool YMMUsed = false;
const TargetRegisterClass *RC = &X86::VR256RegClass;
for (TargetRegisterClass::iterator i = RC->begin(), e = RC->end();
i != e; i++) {
if (!MRI.reg_nodbg_empty(*i)) {
YMMUsed = true;
break;
}
}
if (!YMMUsed) {
return false;
}
assert(BlockStates.empty() && DirtySuccessors.empty() &&
"X86VZeroUpper state should be clear");
BlockStates.resize(MF.getNumBlockIDs());
// Process all blocks. This will compute block exit states, record the first
// unguarded call in each block, and add successors of dirty blocks to the
// DirtySuccessors list.
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
processBasicBlock(*I);
// If any YMM regs are live in to this function, add the entry block to the
// DirtySuccessors list
if (checkFnHasLiveInYmm(MRI))
addDirtySuccessor(MF.front());
// Re-visit all blocks that are successors of EXITS_DIRTY bsocks. Add
// vzeroupper instructions to unguarded calls, and propagate EXITS_DIRTY
// through PASS_THROUGH blocks.
while (!DirtySuccessors.empty()) {
MachineBasicBlock &MBB = *DirtySuccessors.back();
DirtySuccessors.pop_back();
BlockState &BBState = BlockStates[MBB.getNumber()];
// MBB is a successor of a dirty block, so its first call needs to be
// guarded.
if (BBState.FirstUnguardedCall != MBB.end())
insertVZeroUpper(BBState.FirstUnguardedCall, MBB);
// If this successor was a pass-through block then it is now dirty, and its
// successors need to be added to the worklist (if they haven't been
// already).
if (BBState.ExitState == PASS_THROUGH) {
DEBUG(dbgs() << "MBB #" << MBB.getNumber()
<< " was Pass-through, is now Dirty-out.\n");
for (MachineBasicBlock::succ_iterator SI = MBB.succ_begin(),
SE = MBB.succ_end();
SI != SE; ++SI)
addDirtySuccessor(**SI);
}
}
BlockStates.clear();
return EverMadeChange;
}