llvm-julia-licm.cpp
// This file is a part of Julia. License is MIT: https://julialang.org/license
#include "llvm-version.h"
#include "passes.h"
#include <llvm/Analysis/LoopInfo.h>
#include <llvm/Analysis/LoopPass.h>
#include <llvm/Analysis/LoopIterator.h>
#include <llvm/Analysis/MemorySSA.h>
#include <llvm/Analysis/MemorySSAUpdater.h>
#include <llvm/Analysis/OptimizationRemarkEmitter.h>
#include <llvm/Analysis/ValueTracking.h>
#include <llvm/Analysis/ScalarEvolution.h>
#include <llvm/ADT/Statistic.h>
#include <llvm/IR/Dominators.h>
#include <llvm/IR/Verifier.h>
#include <llvm/Transforms/Utils/LoopUtils.h>
#include "llvm-pass-helpers.h"
#include "julia.h"
#include "llvm-alloc-helpers.h"
#include "llvm-codegen-shared.h"
#define DEBUG_TYPE "julia-licm"
using namespace llvm;
STATISTIC(HoistedPreserveBegin, "Number of gc_preserve_begin instructions hoisted out of a loop");
STATISTIC(SunkPreserveEnd, "Number of gc_preserve_end instructions sunk out of a loop");
STATISTIC(ErasedPreserveEnd, "Number of gc_preserve_end instructions removed from nonterminating loops");
STATISTIC(HoistedWriteBarrier, "Number of write barriers hoisted out of a loop");
STATISTIC(HoistedAllocation, "Number of allocations hoisted out of a loop");
/*
* Julia LICM pass.
* This takes care of some julia intrinsics that is safe to move around/out of loops but
* can't be handled by LLVM's LICM. These intrinsics can be moved outside of
* loop context as well but it is inside a loop where they matter the most.
*/
#ifndef __clang_gcanalyzer__
#define REMARK(remark) ORE.emit(remark)
#else
#define REMARK(remark) (void) 0;
#endif
namespace {
//Stolen and modified from LICM.cpp
static void eraseInstruction(Instruction &I,
MemorySSAUpdater &MSSAU) {
if (MSSAU.getMemorySSA())
MSSAU.removeMemoryAccess(&I);
I.eraseFromParent();
}
//Stolen and modified from LICM.cpp
static void moveInstructionBefore(Instruction &I, Instruction &Dest,
MemorySSAUpdater &MSSAU,
ScalarEvolution *SE,
MemorySSA::InsertionPlace Place = MemorySSA::BeforeTerminator) {
I.moveBefore(&Dest);
if (MSSAU.getMemorySSA())
if (MemoryUseOrDef *OldMemAcc = cast_or_null<MemoryUseOrDef>(
MSSAU.getMemorySSA()->getMemoryAccess(&I)))
MSSAU.moveToPlace(OldMemAcc, Dest.getParent(), Place);
if (SE)
SE->forgetValue(&I);
}
static void createNewInstruction(Instruction *New, Instruction *Ref, MemorySSAUpdater &MSSAU) {
if (MSSAU.getMemorySSA() && MSSAU.getMemorySSA()->getMemoryAccess(Ref)) {
// Create a new MemoryAccess and let MemorySSA set its defining access.
MemoryAccess *NewMemAcc = MSSAU.createMemoryAccessInBB(
New, nullptr, New->getParent(), MemorySSA::Beginning);
if (NewMemAcc) {
if (auto *MemDef = dyn_cast<MemoryDef>(NewMemAcc))
MSSAU.insertDef(MemDef, /*RenameUses=*/true);
else {
auto *MemUse = cast<MemoryUse>(NewMemAcc);
MSSAU.insertUse(MemUse, /*RenameUses=*/true);
}
}
}
}
//Stolen and modified to update SE from LoopInfo.cpp
static bool makeLoopInvariant(Loop *L, Value *V, bool &Changed, Instruction *InsertPt, MemorySSAUpdater &MSSAU, ScalarEvolution *SE);
static bool makeLoopInvariant(Loop *L, Instruction *I, bool &Changed, Instruction *InsertPt, MemorySSAUpdater &MSSAU, ScalarEvolution *SE) {
// Test if the value is already loop-invariant.
if (L->isLoopInvariant(I))
return true;
if (!isSafeToSpeculativelyExecute(I))
return false;
if (I->mayReadFromMemory())
return false;
// EH block instructions are immobile.
if (I->isEHPad())
return false;
// Don't hoist instructions with loop-variant operands.
for (Value *Operand : I->operands())
if (!makeLoopInvariant(L, Operand, Changed, InsertPt, MSSAU, SE))
return false;
// Hoist.
moveInstructionBefore(*I, *InsertPt, MSSAU, SE);
// There is possibility of hoisting this instruction above some arbitrary
// condition. Any metadata defined on it can be control dependent on this
// condition. Conservatively strip it here so that we don't give any wrong
// information to the optimizer.
I->dropUnknownNonDebugMetadata();
Changed = true;
return true;
}
static bool makeLoopInvariant(Loop *L, Value *V, bool &Changed, Instruction *InsertPt, MemorySSAUpdater &MSSAU, ScalarEvolution *SE) {
if (Instruction *I = dyn_cast<Instruction>(V))
return makeLoopInvariant(L, I, Changed, InsertPt, MSSAU, SE);
return true; // All non-instructions are loop-invariant.
}
struct JuliaLICM : public JuliaPassContext {
function_ref<DominatorTree &()> GetDT;
function_ref<LoopInfo &()> GetLI;
function_ref<MemorySSA *()> GetMSSA;
function_ref<ScalarEvolution *()> GetSE;
JuliaLICM(function_ref<DominatorTree &()> GetDT,
function_ref<LoopInfo &()> GetLI,
function_ref<MemorySSA *()> GetMSSA,
function_ref<ScalarEvolution *()> GetSE) :
GetDT(GetDT),
GetLI(GetLI),
GetMSSA(GetMSSA),
GetSE(GetSE) {}
bool runOnLoop(Loop *L, OptimizationRemarkEmitter &ORE)
{
// Get the preheader block to move instructions into,
// required to run this pass.
BasicBlock *preheader = L->getLoopPreheader();
if (!preheader)
return false;
BasicBlock *header = L->getHeader();
const llvm::DataLayout &DL = header->getModule()->getDataLayout();
initFunctions(*header->getModule());
// Also require `gc_preserve_begin_func` whereas
// `gc_preserve_end_func` is optional since the input to
// `gc_preserve_end_func` must be from `gc_preserve_begin_func`.
// We also hoist write barriers here, so we don't exit if write_barrier_func exists
if (!gc_preserve_begin_func && !write_barrier_func &&
!alloc_obj_func) {
LLVM_DEBUG(dbgs() << "No gc_preserve_begin_func or write_barrier_func or alloc_obj_func found, skipping JuliaLICM\n");
return false;
}
auto LI = &GetLI();
auto DT = &GetDT();
auto MSSA = GetMSSA();
auto SE = GetSE();
MemorySSAUpdater MSSAU(MSSA);
// Lazy initialization of exit blocks insertion points.
bool exit_pts_init = false;
SmallVector<Instruction*, 8> _exit_pts;
auto get_exit_pts = [&] () -> MutableArrayRef<Instruction*> {
if (!exit_pts_init) {
exit_pts_init = true;
SmallVector<BasicBlock*, 8> exit_bbs;
L->getUniqueExitBlocks(exit_bbs);
for (BasicBlock *bb: exit_bbs) {
_exit_pts.push_back(&*bb->getFirstInsertionPt());
}
}
return _exit_pts;
};
bool changed = false;
// Scan in the right order so that we'll hoist the `begin`
// before we consider sinking `end`.
LoopBlocksRPO worklist(L);
worklist.perform(LI);
for (auto *bb : worklist) {
for (BasicBlock::iterator II = bb->begin(), E = bb->end(); II != E;) {
auto call = dyn_cast<CallInst>(&*II++);
if (!call)
continue;
Value *callee = call->getCalledOperand();
assert(callee != nullptr);
// It is always legal to extend the preserve period
// so we only need to make sure it is legal to move/clone
// the calls.
// If all the input arguments dominates the whole loop we can
// hoist the `begin` and if a `begin` dominates the loop the
// corresponding `end` can be moved to the loop exit.
if (callee == gc_preserve_begin_func) {
bool canhoist = true;
for (Use &U : call->args()) {
// Check if all arguments are generated outside the loop
auto origin = dyn_cast<Instruction>(U.get());
if (!origin)
continue;
if (!DT->properlyDominates(origin->getParent(), header)) {
canhoist = false;
break;
}
}
if (!canhoist)
continue;
++HoistedPreserveBegin;
moveInstructionBefore(*call, *preheader->getTerminator(), MSSAU, SE);
LLVM_DEBUG(dbgs() << "Hoisted gc_preserve_begin: " << *call << "\n");
REMARK([&](){
return OptimizationRemark(DEBUG_TYPE, "Hoisted", call)
<< "hoisting preserve begin " << ore::NV("PreserveBegin", call);
});
changed = true;
}
else if (callee == gc_preserve_end_func) {
auto begin = cast<Instruction>(call->getArgOperand(0));
if (!DT->properlyDominates(begin->getParent(), header))
continue;
changed = true;
auto exit_pts = get_exit_pts();
if (exit_pts.empty()) {
++ErasedPreserveEnd;
eraseInstruction(*call, MSSAU);
continue;
}
++SunkPreserveEnd;
moveInstructionBefore(*call, *exit_pts[0], MSSAU, SE, MemorySSA::Beginning);
exit_pts[0] = call;
LLVM_DEBUG(dbgs() << "Sunk gc_preserve_end: " << *call << "\n");
REMARK([&](){
return OptimizationRemark(DEBUG_TYPE, "Sunk", call)
<< "sinking preserve end " << ore::NV("PreserveEnd", call);
});
for (unsigned i = 1; i < exit_pts.size(); i++) {
// Clone exit
auto CI = CallInst::Create(call, {}, exit_pts[i]);
exit_pts[i] = CI;
createNewInstruction(CI, call, MSSAU);
LLVM_DEBUG(dbgs() << "Cloned and sunk gc_preserve_end: " << *CI << "\n");
REMARK([&](){
return OptimizationRemark(DEBUG_TYPE, "Sunk", call)
<< "cloning and sinking preserve end" << ore::NV("PreserveEnd", call);
});
}
}
else if (callee == write_barrier_func) {
bool valid = true;
for (std::size_t i = 0; i < call->arg_size(); i++) {
if (!makeLoopInvariant(L, call->getArgOperand(i),
changed, preheader->getTerminator(),
MSSAU, SE)) {
valid = false;
LLVM_DEBUG(dbgs() << "Failed to hoist write barrier argument: " << *call->getArgOperand(i) << "\n");
break;
}
}
if (!valid) {
LLVM_DEBUG(dbgs() << "Failed to hoist write barrier: " << *call << "\n");
continue;
}
++HoistedWriteBarrier;
moveInstructionBefore(*call, *preheader->getTerminator(), MSSAU, SE);
changed = true;
REMARK([&](){
return OptimizationRemark(DEBUG_TYPE, "Hoist", call)
<< "hoisting write barrier " << ore::NV("GC Write Barrier", call);
});
}
else if (callee == alloc_obj_func) {
bool valid = true;
for (std::size_t i = 0; i < call->arg_size(); i++) {
if (!makeLoopInvariant(L, call->getArgOperand(i), changed,
preheader->getTerminator(), MSSAU, SE)) {
valid = false;
LLVM_DEBUG(dbgs() << "Failed to hoist alloc_obj argument: " << *call->getArgOperand(i) << "\n");
break;
}
}
if (!valid) {
LLVM_DEBUG(dbgs() << "Failed to hoist alloc_obj: " << *call << "\n");
continue;
}
LLVM_DEBUG(dbgs() << "Running escape analysis for " << *call << "\n");
jl_alloc::AllocUseInfo use_info;
jl_alloc::CheckInst::Stack check_stack;
jl_alloc::EscapeAnalysisRequiredArgs required{use_info, check_stack, *this, DL};
jl_alloc::runEscapeAnalysis(call, required, jl_alloc::EscapeAnalysisOptionalArgs().with_valid_set(&L->getBlocksSet()).with_optimization_remark_emitter(&ORE));
REMARK([&](){
std::string suse_info;
llvm::raw_string_ostream osuse_info(suse_info);
use_info.dump(osuse_info);
return OptimizationRemarkAnalysis(DEBUG_TYPE, "EscapeAnalysis", call) << "escape analysis for " << ore::NV("GC Allocation", call) << "\n" << ore::NV("UseInfo", osuse_info.str());
});
if (use_info.escaped) {
REMARK([&](){
return OptimizationRemarkMissed(DEBUG_TYPE, "Escape", call)
<< "not hoisting gc allocation " << ore::NV("GC Allocation", call)
<< " because it may escape";
});
continue;
}
if (use_info.addrescaped) {
REMARK([&](){
return OptimizationRemarkMissed(DEBUG_TYPE, "Escape", call)
<< "not hoisting gc allocation " << ore::NV("GC Allocation", call)
<< " because its address may escape";
});
continue;
}
if (use_info.refstore) {
// We need to add write barriers to any stores
// that may start crossing generations
REMARK([&](){
return OptimizationRemarkMissed(DEBUG_TYPE, "Escape", call)
<< "not hoisting gc allocation " << ore::NV("GC Allocation", call)
<< " because it may have an object stored to it";
});
continue;
}
REMARK([&](){
return OptimizationRemark(DEBUG_TYPE, "Hoist", call)
<< "hoisting gc allocation " << ore::NV("GC Allocation", call);
});
++HoistedAllocation;
moveInstructionBefore(*call, *preheader->getTerminator(), MSSAU, SE);
IRBuilder<> builder(preheader->getTerminator());
builder.SetCurrentDebugLocation(call->getDebugLoc());
// Note that this alignment is assuming the GC allocates at least pointer-aligned memory
auto align = Align(DL.getPointerSize(0));
auto clear_obj = builder.CreateMemSet(call, ConstantInt::get(Type::getInt8Ty(call->getContext()), 0), call->getArgOperand(1), align);
if (MSSAU.getMemorySSA()) {
auto clear_mdef = MSSAU.createMemoryAccessInBB(clear_obj, nullptr, clear_obj->getParent(), MemorySSA::BeforeTerminator);
MSSAU.insertDef(cast<MemoryDef>(clear_mdef), true);
}
changed = true;
}
}
}
if (changed && SE) {
#if JL_LLVM_VERSION >= 160000
SE->forgetLoopDispositions();
#else
SE->forgetLoopDispositions(L);
#endif
}
#ifdef JL_VERIFY_PASSES
assert(!verifyLLVMIR(*L));
#endif
return changed;
}
};
} //namespace
PreservedAnalyses JuliaLICMPass::run(Loop &L, LoopAnalysisManager &AM,
LoopStandardAnalysisResults &AR, LPMUpdater &U)
{
OptimizationRemarkEmitter ORE(L.getHeader()->getParent());
auto GetDT = [&AR]() -> DominatorTree & {
return AR.DT;
};
auto GetLI = [&AR]() -> LoopInfo & {
return AR.LI;
};
auto GetMSSA = [&AR]() {
return AR.MSSA;
};
auto GetSE = [&AR]() {
return &AR.SE;
};
auto juliaLICM = JuliaLICM(GetDT, GetLI, GetMSSA, GetSE);
if (juliaLICM.runOnLoop(&L, ORE)) {
#ifdef JL_DEBUG_BUILD
if (AR.MSSA)
AR.MSSA->verifyMemorySSA();
#endif
auto preserved = getLoopPassPreservedAnalyses();
preserved.preserveSet<CFGAnalyses>();
preserved.preserve<MemorySSAAnalysis>();
return preserved;
}
return PreservedAnalyses::all();
}