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llvm-project/llvm/lib/Target/AMDGPU/AMDGPUPromoteAlloca.cpp

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//===-- AMDGPUPromoteAlloca.cpp - Promote Allocas -------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass eliminates allocas by either converting them into vectors or
// by migrating them to local address space.
//
//===----------------------------------------------------------------------===//
#include "AMDGPU.h"
#include "AMDGPUSubtarget.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#define DEBUG_TYPE "amdgpu-promote-alloca"
using namespace llvm;
namespace {
class AMDGPUPromoteAlloca : public FunctionPass,
public InstVisitor<AMDGPUPromoteAlloca> {
static char ID;
Module *Mod;
const AMDGPUSubtarget &ST;
int LocalMemAvailable;
public:
AMDGPUPromoteAlloca(const AMDGPUSubtarget &st) : FunctionPass(ID), ST(st),
LocalMemAvailable(0) { }
bool doInitialization(Module &M) override;
bool runOnFunction(Function &F) override;
const char *getPassName() const override { return "AMDGPU Promote Alloca"; }
void visitAlloca(AllocaInst &I);
};
} // End anonymous namespace
char AMDGPUPromoteAlloca::ID = 0;
bool AMDGPUPromoteAlloca::doInitialization(Module &M) {
Mod = &M;
return false;
}
bool AMDGPUPromoteAlloca::runOnFunction(Function &F) {
const FunctionType *FTy = F.getFunctionType();
LocalMemAvailable = ST.getLocalMemorySize();
// If the function has any arguments in the local address space, then it's
// possible these arguments require the entire local memory space, so
// we cannot use local memory in the pass.
for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i) {
const Type *ParamTy = FTy->getParamType(i);
if (ParamTy->isPointerTy() &&
ParamTy->getPointerAddressSpace() == AMDGPUAS::LOCAL_ADDRESS) {
LocalMemAvailable = 0;
DEBUG(dbgs() << "Function has local memory argument. Promoting to "
"local memory disabled.\n");
break;
}
}
if (LocalMemAvailable > 0) {
// Check how much local memory is being used by global objects
for (Module::global_iterator I = Mod->global_begin(),
E = Mod->global_end(); I != E; ++I) {
GlobalVariable *GV = I;
PointerType *GVTy = GV->getType();
if (GVTy->getAddressSpace() != AMDGPUAS::LOCAL_ADDRESS)
continue;
for (Value::use_iterator U = GV->use_begin(),
UE = GV->use_end(); U != UE; ++U) {
Instruction *Use = dyn_cast<Instruction>(*U);
if (!Use)
continue;
if (Use->getParent()->getParent() == &F)
LocalMemAvailable -=
Mod->getDataLayout().getTypeAllocSize(GVTy->getElementType());
}
}
}
LocalMemAvailable = std::max(0, LocalMemAvailable);
DEBUG(dbgs() << LocalMemAvailable << "bytes free in local memory.\n");
visit(F);
return false;
}
static VectorType *arrayTypeToVecType(const Type *ArrayTy) {
return VectorType::get(ArrayTy->getArrayElementType(),
ArrayTy->getArrayNumElements());
}
static Value *
calculateVectorIndex(Value *Ptr,
const std::map<GetElementPtrInst *, Value *> &GEPIdx) {
if (isa<AllocaInst>(Ptr))
return Constant::getNullValue(Type::getInt32Ty(Ptr->getContext()));
GetElementPtrInst *GEP = cast<GetElementPtrInst>(Ptr);
auto I = GEPIdx.find(GEP);
return I == GEPIdx.end() ? nullptr : I->second;
}
static Value* GEPToVectorIndex(GetElementPtrInst *GEP) {
// FIXME we only support simple cases
if (GEP->getNumOperands() != 3)
return NULL;
ConstantInt *I0 = dyn_cast<ConstantInt>(GEP->getOperand(1));
if (!I0 || !I0->isZero())
return NULL;
return GEP->getOperand(2);
}
// Not an instruction handled below to turn into a vector.
//
// TODO: Check isTriviallyVectorizable for calls and handle other
// instructions.
static bool canVectorizeInst(Instruction *Inst) {
switch (Inst->getOpcode()) {
case Instruction::Load:
case Instruction::Store:
case Instruction::BitCast:
case Instruction::AddrSpaceCast:
return true;
default:
return false;
}
}
static bool tryPromoteAllocaToVector(AllocaInst *Alloca) {
Type *AllocaTy = Alloca->getAllocatedType();
DEBUG(dbgs() << "Alloca Candidate for vectorization \n");
// FIXME: There is no reason why we can't support larger arrays, we
// are just being conservative for now.
if (!AllocaTy->isArrayTy() ||
AllocaTy->getArrayElementType()->isVectorTy() ||
AllocaTy->getArrayNumElements() > 4) {
DEBUG(dbgs() << " Cannot convert type to vector");
return false;
}
std::map<GetElementPtrInst*, Value*> GEPVectorIdx;
std::vector<Value*> WorkList;
for (User *AllocaUser : Alloca->users()) {
GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(AllocaUser);
if (!GEP) {
if (!canVectorizeInst(cast<Instruction>(AllocaUser)))
return false;
WorkList.push_back(AllocaUser);
continue;
}
Value *Index = GEPToVectorIndex(GEP);
// If we can't compute a vector index from this GEP, then we can't
// promote this alloca to vector.
if (!Index) {
DEBUG(dbgs() << " Cannot compute vector index for GEP " << *GEP << '\n');
return false;
}
GEPVectorIdx[GEP] = Index;
for (User *GEPUser : AllocaUser->users()) {
if (!canVectorizeInst(cast<Instruction>(GEPUser)))
return false;
WorkList.push_back(GEPUser);
}
}
VectorType *VectorTy = arrayTypeToVecType(AllocaTy);
DEBUG(dbgs() << " Converting alloca to vector "
<< *AllocaTy << " -> " << *VectorTy << '\n');
for (std::vector<Value*>::iterator I = WorkList.begin(),
E = WorkList.end(); I != E; ++I) {
Instruction *Inst = cast<Instruction>(*I);
IRBuilder<> Builder(Inst);
switch (Inst->getOpcode()) {
case Instruction::Load: {
Value *Ptr = Inst->getOperand(0);
Value *Index = calculateVectorIndex(Ptr, GEPVectorIdx);
Value *BitCast = Builder.CreateBitCast(Alloca, VectorTy->getPointerTo(0));
Value *VecValue = Builder.CreateLoad(BitCast);
Value *ExtractElement = Builder.CreateExtractElement(VecValue, Index);
Inst->replaceAllUsesWith(ExtractElement);
Inst->eraseFromParent();
break;
}
case Instruction::Store: {
Value *Ptr = Inst->getOperand(1);
Value *Index = calculateVectorIndex(Ptr, GEPVectorIdx);
Value *BitCast = Builder.CreateBitCast(Alloca, VectorTy->getPointerTo(0));
Value *VecValue = Builder.CreateLoad(BitCast);
Value *NewVecValue = Builder.CreateInsertElement(VecValue,
Inst->getOperand(0),
Index);
Builder.CreateStore(NewVecValue, BitCast);
Inst->eraseFromParent();
break;
}
case Instruction::BitCast:
case Instruction::AddrSpaceCast:
break;
default:
Inst->dump();
llvm_unreachable("Inconsistency in instructions promotable to vector");
}
}
return true;
}
static bool collectUsesWithPtrTypes(Value *Val, std::vector<Value*> &WorkList) {
bool Success = true;
for (User *User : Val->users()) {
if(std::find(WorkList.begin(), WorkList.end(), User) != WorkList.end())
continue;
if (isa<CallInst>(User)) {
WorkList.push_back(User);
continue;
}
// FIXME: Correctly handle ptrtoint instructions.
Instruction *UseInst = dyn_cast<Instruction>(User);
if (UseInst && UseInst->getOpcode() == Instruction::PtrToInt)
return false;
if (!User->getType()->isPointerTy())
continue;
WorkList.push_back(User);
Success &= collectUsesWithPtrTypes(User, WorkList);
}
return Success;
}
void AMDGPUPromoteAlloca::visitAlloca(AllocaInst &I) {
IRBuilder<> Builder(&I);
// First try to replace the alloca with a vector
Type *AllocaTy = I.getAllocatedType();
DEBUG(dbgs() << "Trying to promote " << I << '\n');
if (tryPromoteAllocaToVector(&I))
return;
DEBUG(dbgs() << " alloca is not a candidate for vectorization.\n");
// FIXME: This is the maximum work group size. We should try to get
// value from the reqd_work_group_size function attribute if it is
// available.
unsigned WorkGroupSize = 256;
int AllocaSize =
WorkGroupSize * Mod->getDataLayout().getTypeAllocSize(AllocaTy);
if (AllocaSize > LocalMemAvailable) {
DEBUG(dbgs() << " Not enough local memory to promote alloca.\n");
return;
}
std::vector<Value*> WorkList;
if (!collectUsesWithPtrTypes(&I, WorkList)) {
DEBUG(dbgs() << " Do not know how to convert all uses\n");
return;
}
DEBUG(dbgs() << "Promoting alloca to local memory\n");
LocalMemAvailable -= AllocaSize;
Type *GVTy = ArrayType::get(I.getAllocatedType(), 256);
GlobalVariable *GV = new GlobalVariable(
*Mod, GVTy, false, GlobalValue::ExternalLinkage, 0, I.getName(), 0,
GlobalVariable::NotThreadLocal, AMDGPUAS::LOCAL_ADDRESS);
FunctionType *FTy = FunctionType::get(
Type::getInt32Ty(Mod->getContext()), false);
AttributeSet AttrSet;
AttrSet.addAttribute(Mod->getContext(), 0, Attribute::ReadNone);
Value *ReadLocalSizeY = Mod->getOrInsertFunction(
"llvm.r600.read.local.size.y", FTy, AttrSet);
Value *ReadLocalSizeZ = Mod->getOrInsertFunction(
"llvm.r600.read.local.size.z", FTy, AttrSet);
Value *ReadTIDIGX = Mod->getOrInsertFunction(
"llvm.r600.read.tidig.x", FTy, AttrSet);
Value *ReadTIDIGY = Mod->getOrInsertFunction(
"llvm.r600.read.tidig.y", FTy, AttrSet);
Value *ReadTIDIGZ = Mod->getOrInsertFunction(
"llvm.r600.read.tidig.z", FTy, AttrSet);
Value *TCntY = Builder.CreateCall(ReadLocalSizeY, {});
Value *TCntZ = Builder.CreateCall(ReadLocalSizeZ, {});
Value *TIdX = Builder.CreateCall(ReadTIDIGX, {});
Value *TIdY = Builder.CreateCall(ReadTIDIGY, {});
Value *TIdZ = Builder.CreateCall(ReadTIDIGZ, {});
Value *Tmp0 = Builder.CreateMul(TCntY, TCntZ);
Tmp0 = Builder.CreateMul(Tmp0, TIdX);
Value *Tmp1 = Builder.CreateMul(TIdY, TCntZ);
Value *TID = Builder.CreateAdd(Tmp0, Tmp1);
TID = Builder.CreateAdd(TID, TIdZ);
std::vector<Value*> Indices;
Indices.push_back(Constant::getNullValue(Type::getInt32Ty(Mod->getContext())));
Indices.push_back(TID);
Value *Offset = Builder.CreateGEP(GVTy, GV, Indices);
I.mutateType(Offset->getType());
I.replaceAllUsesWith(Offset);
I.eraseFromParent();
for (std::vector<Value*>::iterator i = WorkList.begin(),
e = WorkList.end(); i != e; ++i) {
Value *V = *i;
CallInst *Call = dyn_cast<CallInst>(V);
if (!Call) {
Type *EltTy = V->getType()->getPointerElementType();
PointerType *NewTy = PointerType::get(EltTy, AMDGPUAS::LOCAL_ADDRESS);
// The operand's value should be corrected on its own.
if (isa<AddrSpaceCastInst>(V))
continue;
// FIXME: It doesn't really make sense to try to do this for all
// instructions.
V->mutateType(NewTy);
continue;
}
IntrinsicInst *Intr = dyn_cast<IntrinsicInst>(Call);
if (!Intr) {
std::vector<Type*> ArgTypes;
for (unsigned ArgIdx = 0, ArgEnd = Call->getNumArgOperands();
ArgIdx != ArgEnd; ++ArgIdx) {
ArgTypes.push_back(Call->getArgOperand(ArgIdx)->getType());
}
Function *F = Call->getCalledFunction();
FunctionType *NewType = FunctionType::get(Call->getType(), ArgTypes,
F->isVarArg());
Constant *C = Mod->getOrInsertFunction((F->getName() + ".local").str(),
NewType, F->getAttributes());
Function *NewF = cast<Function>(C);
Call->setCalledFunction(NewF);
continue;
}
Builder.SetInsertPoint(Intr);
switch (Intr->getIntrinsicID()) {
case Intrinsic::lifetime_start:
case Intrinsic::lifetime_end:
// These intrinsics are for address space 0 only
Intr->eraseFromParent();
continue;
case Intrinsic::memcpy: {
MemCpyInst *MemCpy = cast<MemCpyInst>(Intr);
Builder.CreateMemCpy(MemCpy->getRawDest(), MemCpy->getRawSource(),
MemCpy->getLength(), MemCpy->getAlignment(),
MemCpy->isVolatile());
Intr->eraseFromParent();
continue;
}
case Intrinsic::memset: {
MemSetInst *MemSet = cast<MemSetInst>(Intr);
Builder.CreateMemSet(MemSet->getRawDest(), MemSet->getValue(),
MemSet->getLength(), MemSet->getAlignment(),
MemSet->isVolatile());
Intr->eraseFromParent();
continue;
}
default:
Intr->dump();
llvm_unreachable("Don't know how to promote alloca intrinsic use.");
}
}
}
FunctionPass *llvm::createAMDGPUPromoteAlloca(const AMDGPUSubtarget &ST) {
return new AMDGPUPromoteAlloca(ST);
}
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