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llvm-project/llvm/lib/Transforms/Scalar/InferAddressSpaces.cpp

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//===- InferAddressSpace.cpp - --------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// CUDA C/C++ includes memory space designation as variable type qualifers (such
// as __global__ and __shared__). Knowing the space of a memory access allows
// CUDA compilers to emit faster PTX loads and stores. For example, a load from
// shared memory can be translated to `ld.shared` which is roughly 10% faster
// than a generic `ld` on an NVIDIA Tesla K40c.
//
// Unfortunately, type qualifiers only apply to variable declarations, so CUDA
// compilers must infer the memory space of an address expression from
// type-qualified variables.
//
// LLVM IR uses non-zero (so-called) specific address spaces to represent memory
// spaces (e.g. addrspace(3) means shared memory). The Clang frontend
// places only type-qualified variables in specific address spaces, and then
// conservatively `addrspacecast`s each type-qualified variable to addrspace(0)
// (so-called the generic address space) for other instructions to use.
//
// For example, the Clang translates the following CUDA code
// __shared__ float a[10];
// float v = a[i];
// to
// %0 = addrspacecast [10 x float] addrspace(3)* @a to [10 x float]*
// %1 = gep [10 x float], [10 x float]* %0, i64 0, i64 %i
// %v = load float, float* %1 ; emits ld.f32
// @a is in addrspace(3) since it's type-qualified, but its use from %1 is
// redirected to %0 (the generic version of @a).
//
// The optimization implemented in this file propagates specific address spaces
// from type-qualified variable declarations to its users. For example, it
// optimizes the above IR to
// %1 = gep [10 x float] addrspace(3)* @a, i64 0, i64 %i
// %v = load float addrspace(3)* %1 ; emits ld.shared.f32
// propagating the addrspace(3) from @a to %1. As the result, the NVPTX
// codegen is able to emit ld.shared.f32 for %v.
//
// Address space inference works in two steps. First, it uses a data-flow
// analysis to infer as many generic pointers as possible to point to only one
// specific address space. In the above example, it can prove that %1 only
// points to addrspace(3). This algorithm was published in
// CUDA: Compiling and optimizing for a GPU platform
// Chakrabarti, Grover, Aarts, Kong, Kudlur, Lin, Marathe, Murphy, Wang
// ICCS 2012
//
// Then, address space inference replaces all refinable generic pointers with
// equivalent specific pointers.
//
// The major challenge of implementing this optimization is handling PHINodes,
// which may create loops in the data flow graph. This brings two complications.
//
// First, the data flow analysis in Step 1 needs to be circular. For example,
// %generic.input = addrspacecast float addrspace(3)* %input to float*
// loop:
// %y = phi [ %generic.input, %y2 ]
// %y2 = getelementptr %y, 1
// %v = load %y2
// br ..., label %loop, ...
// proving %y specific requires proving both %generic.input and %y2 specific,
// but proving %y2 specific circles back to %y. To address this complication,
// the data flow analysis operates on a lattice:
// uninitialized > specific address spaces > generic.
// All address expressions (our implementation only considers phi, bitcast,
// addrspacecast, and getelementptr) start with the uninitialized address space.
// The monotone transfer function moves the address space of a pointer down a
// lattice path from uninitialized to specific and then to generic. A join
// operation of two different specific address spaces pushes the expression down
// to the generic address space. The analysis completes once it reaches a fixed
// point.
//
// Second, IR rewriting in Step 2 also needs to be circular. For example,
// converting %y to addrspace(3) requires the compiler to know the converted
// %y2, but converting %y2 needs the converted %y. To address this complication,
// we break these cycles using "undef" placeholders. When converting an
// instruction `I` to a new address space, if its operand `Op` is not converted
// yet, we let `I` temporarily use `undef` and fix all the uses of undef later.
// For instance, our algorithm first converts %y to
// %y' = phi float addrspace(3)* [ %input, undef ]
// Then, it converts %y2 to
// %y2' = getelementptr %y', 1
// Finally, it fixes the undef in %y' so that
// %y' = phi float addrspace(3)* [ %input, %y2' ]
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/ValueMapper.h"
#include <cassert>
#include <iterator>
#include <limits>
#include <utility>
#include <vector>
#define DEBUG_TYPE "infer-address-spaces"
using namespace llvm;
static const unsigned UninitializedAddressSpace =
std::numeric_limits<unsigned>::max();
namespace {
using ValueToAddrSpaceMapTy = DenseMap<const Value *, unsigned>;
/// InferAddressSpaces
class InferAddressSpaces : public FunctionPass {
/// Target specific address space which uses of should be replaced if
/// possible.
unsigned FlatAddrSpace;
public:
static char ID;
InferAddressSpaces() : FunctionPass(ID) {}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addRequired<TargetTransformInfoWrapperPass>();
}
bool runOnFunction(Function &F) override;
private:
// Returns the new address space of V if updated; otherwise, returns None.
Optional<unsigned>
updateAddressSpace(const Value &V,
const ValueToAddrSpaceMapTy &InferredAddrSpace) const;
// Tries to infer the specific address space of each address expression in
// Postorder.
void inferAddressSpaces(ArrayRef<WeakTrackingVH> Postorder,
ValueToAddrSpaceMapTy *InferredAddrSpace) const;
bool isSafeToCastConstAddrSpace(Constant *C, unsigned NewAS) const;
// Changes the flat address expressions in function F to point to specific
// address spaces if InferredAddrSpace says so. Postorder is the postorder of
// all flat expressions in the use-def graph of function F.
bool rewriteWithNewAddressSpaces(
const TargetTransformInfo &TTI, ArrayRef<WeakTrackingVH> Postorder,
const ValueToAddrSpaceMapTy &InferredAddrSpace, Function *F) const;
void appendsFlatAddressExpressionToPostorderStack(
Value *V, std::vector<std::pair<Value *, bool>> &PostorderStack,
DenseSet<Value *> &Visited) const;
bool rewriteIntrinsicOperands(IntrinsicInst *II,
Value *OldV, Value *NewV) const;
void collectRewritableIntrinsicOperands(
IntrinsicInst *II,
std::vector<std::pair<Value *, bool>> &PostorderStack,
DenseSet<Value *> &Visited) const;
std::vector<WeakTrackingVH> collectFlatAddressExpressions(Function &F) const;
Value *cloneValueWithNewAddressSpace(
Value *V, unsigned NewAddrSpace,
const ValueToValueMapTy &ValueWithNewAddrSpace,
SmallVectorImpl<const Use *> *UndefUsesToFix) const;
unsigned joinAddressSpaces(unsigned AS1, unsigned AS2) const;
};
} // end anonymous namespace
char InferAddressSpaces::ID = 0;
namespace llvm {
void initializeInferAddressSpacesPass(PassRegistry &);
} // end namespace llvm
INITIALIZE_PASS(InferAddressSpaces, DEBUG_TYPE, "Infer address spaces",
false, false)
// Returns true if V is an address expression.
// TODO: Currently, we consider only phi, bitcast, addrspacecast, and
// getelementptr operators.
static bool isAddressExpression(const Value &V) {
if (!isa<Operator>(V))
return false;
switch (cast<Operator>(V).getOpcode()) {
case Instruction::PHI:
case Instruction::BitCast:
case Instruction::AddrSpaceCast:
case Instruction::GetElementPtr:
case Instruction::Select:
return true;
default:
return false;
}
}
// Returns the pointer operands of V.
//
// Precondition: V is an address expression.
static SmallVector<Value *, 2> getPointerOperands(const Value &V) {
const Operator &Op = cast<Operator>(V);
switch (Op.getOpcode()) {
case Instruction::PHI: {
auto IncomingValues = cast<PHINode>(Op).incoming_values();
return SmallVector<Value *, 2>(IncomingValues.begin(),
IncomingValues.end());
}
case Instruction::BitCast:
case Instruction::AddrSpaceCast:
case Instruction::GetElementPtr:
return {Op.getOperand(0)};
case Instruction::Select:
return {Op.getOperand(1), Op.getOperand(2)};
default:
llvm_unreachable("Unexpected instruction type.");
}
}
// TODO: Move logic to TTI?
bool InferAddressSpaces::rewriteIntrinsicOperands(IntrinsicInst *II,
Value *OldV,
Value *NewV) const {
Module *M = II->getParent()->getParent()->getParent();
switch (II->getIntrinsicID()) {
case Intrinsic::amdgcn_atomic_inc:
case Intrinsic::amdgcn_atomic_dec:
case Intrinsic::amdgcn_ds_fadd:
case Intrinsic::amdgcn_ds_fmin:
case Intrinsic::amdgcn_ds_fmax: {
const ConstantInt *IsVolatile = dyn_cast<ConstantInt>(II->getArgOperand(4));
if (!IsVolatile || !IsVolatile->isZero())
return false;
LLVM_FALLTHROUGH;
}
case Intrinsic::objectsize: {
Type *DestTy = II->getType();
Type *SrcTy = NewV->getType();
Function *NewDecl =
Intrinsic::getDeclaration(M, II->getIntrinsicID(), {DestTy, SrcTy});
II->setArgOperand(0, NewV);
II->setCalledFunction(NewDecl);
return true;
}
default:
return false;
}
}
// TODO: Move logic to TTI?
void InferAddressSpaces::collectRewritableIntrinsicOperands(
IntrinsicInst *II, std::vector<std::pair<Value *, bool>> &PostorderStack,
DenseSet<Value *> &Visited) const {
switch (II->getIntrinsicID()) {
case Intrinsic::objectsize:
case Intrinsic::amdgcn_atomic_inc:
case Intrinsic::amdgcn_atomic_dec:
case Intrinsic::amdgcn_ds_fadd:
case Intrinsic::amdgcn_ds_fmin:
case Intrinsic::amdgcn_ds_fmax:
appendsFlatAddressExpressionToPostorderStack(II->getArgOperand(0),
PostorderStack, Visited);
break;
default:
break;
}
}
// Returns all flat address expressions in function F. The elements are
// If V is an unvisited flat address expression, appends V to PostorderStack
// and marks it as visited.
void InferAddressSpaces::appendsFlatAddressExpressionToPostorderStack(
Value *V, std::vector<std::pair<Value *, bool>> &PostorderStack,
DenseSet<Value *> &Visited) const {
assert(V->getType()->isPointerTy());
// Generic addressing expressions may be hidden in nested constant
// expressions.
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
// TODO: Look in non-address parts, like icmp operands.
if (isAddressExpression(*CE) && Visited.insert(CE).second)
PostorderStack.push_back(std::make_pair(CE, false));
return;
}
if (isAddressExpression(*V) &&
V->getType()->getPointerAddressSpace() == FlatAddrSpace) {
if (Visited.insert(V).second) {
PostorderStack.push_back(std::make_pair(V, false));
Operator *Op = cast<Operator>(V);
for (unsigned I = 0, E = Op->getNumOperands(); I != E; ++I) {
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Op->getOperand(I))) {
if (isAddressExpression(*CE) && Visited.insert(CE).second)
PostorderStack.emplace_back(CE, false);
}
}
}
}
}
// Returns all flat address expressions in function F. The elements are ordered
// ordered in postorder.
std::vector<WeakTrackingVH>
InferAddressSpaces::collectFlatAddressExpressions(Function &F) const {
// This function implements a non-recursive postorder traversal of a partial
// use-def graph of function F.
std::vector<std::pair<Value *, bool>> PostorderStack;
// The set of visited expressions.
DenseSet<Value *> Visited;
auto PushPtrOperand = [&](Value *Ptr) {
appendsFlatAddressExpressionToPostorderStack(Ptr, PostorderStack,
Visited);
};
// Look at operations that may be interesting accelerate by moving to a known
// address space. We aim at generating after loads and stores, but pure
// addressing calculations may also be faster.
for (Instruction &I : instructions(F)) {
if (auto *GEP = dyn_cast<GetElementPtrInst>(&I)) {
if (!GEP->getType()->isVectorTy())
PushPtrOperand(GEP->getPointerOperand());
} else if (auto *LI = dyn_cast<LoadInst>(&I))
PushPtrOperand(LI->getPointerOperand());
else if (auto *SI = dyn_cast<StoreInst>(&I))
PushPtrOperand(SI->getPointerOperand());
else if (auto *RMW = dyn_cast<AtomicRMWInst>(&I))
PushPtrOperand(RMW->getPointerOperand());
else if (auto *CmpX = dyn_cast<AtomicCmpXchgInst>(&I))
PushPtrOperand(CmpX->getPointerOperand());
else if (auto *MI = dyn_cast<MemIntrinsic>(&I)) {
// For memset/memcpy/memmove, any pointer operand can be replaced.
PushPtrOperand(MI->getRawDest());
// Handle 2nd operand for memcpy/memmove.
if (auto *MTI = dyn_cast<MemTransferInst>(MI))
PushPtrOperand(MTI->getRawSource());
} else if (auto *II = dyn_cast<IntrinsicInst>(&I))
collectRewritableIntrinsicOperands(II, PostorderStack, Visited);
else if (ICmpInst *Cmp = dyn_cast<ICmpInst>(&I)) {
// FIXME: Handle vectors of pointers
if (Cmp->getOperand(0)->getType()->isPointerTy()) {
PushPtrOperand(Cmp->getOperand(0));
PushPtrOperand(Cmp->getOperand(1));
}
} else if (auto *ASC = dyn_cast<AddrSpaceCastInst>(&I)) {
if (!ASC->getType()->isVectorTy())
PushPtrOperand(ASC->getPointerOperand());
}
}
std::vector<WeakTrackingVH> Postorder; // The resultant postorder.
while (!PostorderStack.empty()) {
Value *TopVal = PostorderStack.back().first;
// If the operands of the expression on the top are already explored,
// adds that expression to the resultant postorder.
if (PostorderStack.back().second) {
if (TopVal->getType()->getPointerAddressSpace() == FlatAddrSpace)
Postorder.push_back(TopVal);
PostorderStack.pop_back();
continue;
}
// Otherwise, adds its operands to the stack and explores them.
PostorderStack.back().second = true;
for (Value *PtrOperand : getPointerOperands(*TopVal)) {
appendsFlatAddressExpressionToPostorderStack(PtrOperand, PostorderStack,
Visited);
}
}
return Postorder;
}
// A helper function for cloneInstructionWithNewAddressSpace. Returns the clone
// of OperandUse.get() in the new address space. If the clone is not ready yet,
// returns an undef in the new address space as a placeholder.
static Value *operandWithNewAddressSpaceOrCreateUndef(
const Use &OperandUse, unsigned NewAddrSpace,
const ValueToValueMapTy &ValueWithNewAddrSpace,
SmallVectorImpl<const Use *> *UndefUsesToFix) {
Value *Operand = OperandUse.get();
Type *NewPtrTy =
Operand->getType()->getPointerElementType()->getPointerTo(NewAddrSpace);
if (Constant *C = dyn_cast<Constant>(Operand))
return ConstantExpr::getAddrSpaceCast(C, NewPtrTy);
if (Value *NewOperand = ValueWithNewAddrSpace.lookup(Operand))
return NewOperand;
UndefUsesToFix->push_back(&OperandUse);
return UndefValue::get(NewPtrTy);
}
// Returns a clone of `I` with its operands converted to those specified in
// ValueWithNewAddrSpace. Due to potential cycles in the data flow graph, an
// operand whose address space needs to be modified might not exist in
// ValueWithNewAddrSpace. In that case, uses undef as a placeholder operand and
// adds that operand use to UndefUsesToFix so that caller can fix them later.
//
// Note that we do not necessarily clone `I`, e.g., if it is an addrspacecast
// from a pointer whose type already matches. Therefore, this function returns a
// Value* instead of an Instruction*.
static Value *cloneInstructionWithNewAddressSpace(
Instruction *I, unsigned NewAddrSpace,
const ValueToValueMapTy &ValueWithNewAddrSpace,
SmallVectorImpl<const Use *> *UndefUsesToFix) {
Type *NewPtrType =
I->getType()->getPointerElementType()->getPointerTo(NewAddrSpace);
if (I->getOpcode() == Instruction::AddrSpaceCast) {
Value *Src = I->getOperand(0);
// Because `I` is flat, the source address space must be specific.
// Therefore, the inferred address space must be the source space, according
// to our algorithm.
assert(Src->getType()->getPointerAddressSpace() == NewAddrSpace);
if (Src->getType() != NewPtrType)
return new BitCastInst(Src, NewPtrType);
return Src;
}
// Computes the converted pointer operands.
SmallVector<Value *, 4> NewPointerOperands;
for (const Use &OperandUse : I->operands()) {
if (!OperandUse.get()->getType()->isPointerTy())
NewPointerOperands.push_back(nullptr);
else
NewPointerOperands.push_back(operandWithNewAddressSpaceOrCreateUndef(
OperandUse, NewAddrSpace, ValueWithNewAddrSpace, UndefUsesToFix));
}
switch (I->getOpcode()) {
case Instruction::BitCast:
return new BitCastInst(NewPointerOperands[0], NewPtrType);
case Instruction::PHI: {
assert(I->getType()->isPointerTy());
PHINode *PHI = cast<PHINode>(I);
PHINode *NewPHI = PHINode::Create(NewPtrType, PHI->getNumIncomingValues());
for (unsigned Index = 0; Index < PHI->getNumIncomingValues(); ++Index) {
unsigned OperandNo = PHINode::getOperandNumForIncomingValue(Index);
NewPHI->addIncoming(NewPointerOperands[OperandNo],
PHI->getIncomingBlock(Index));
}
return NewPHI;
}
case Instruction::GetElementPtr: {
GetElementPtrInst *GEP = cast<GetElementPtrInst>(I);
GetElementPtrInst *NewGEP = GetElementPtrInst::Create(
GEP->getSourceElementType(), NewPointerOperands[0],
SmallVector<Value *, 4>(GEP->idx_begin(), GEP->idx_end()));
NewGEP->setIsInBounds(GEP->isInBounds());
return NewGEP;
}
case Instruction::Select:
assert(I->getType()->isPointerTy());
return SelectInst::Create(I->getOperand(0), NewPointerOperands[1],
NewPointerOperands[2], "", nullptr, I);
default:
llvm_unreachable("Unexpected opcode");
}
}
// Similar to cloneInstructionWithNewAddressSpace, returns a clone of the
// constant expression `CE` with its operands replaced as specified in
// ValueWithNewAddrSpace.
static Value *cloneConstantExprWithNewAddressSpace(
ConstantExpr *CE, unsigned NewAddrSpace,
const ValueToValueMapTy &ValueWithNewAddrSpace) {
Type *TargetType =
CE->getType()->getPointerElementType()->getPointerTo(NewAddrSpace);
if (CE->getOpcode() == Instruction::AddrSpaceCast) {
// Because CE is flat, the source address space must be specific.
// Therefore, the inferred address space must be the source space according
// to our algorithm.
assert(CE->getOperand(0)->getType()->getPointerAddressSpace() ==
NewAddrSpace);
return ConstantExpr::getBitCast(CE->getOperand(0), TargetType);
}
if (CE->getOpcode() == Instruction::BitCast) {
if (Value *NewOperand = ValueWithNewAddrSpace.lookup(CE->getOperand(0)))
return ConstantExpr::getBitCast(cast<Constant>(NewOperand), TargetType);
return ConstantExpr::getAddrSpaceCast(CE, TargetType);
}
if (CE->getOpcode() == Instruction::Select) {
Constant *Src0 = CE->getOperand(1);
Constant *Src1 = CE->getOperand(2);
if (Src0->getType()->getPointerAddressSpace() ==
Src1->getType()->getPointerAddressSpace()) {
return ConstantExpr::getSelect(
CE->getOperand(0), ConstantExpr::getAddrSpaceCast(Src0, TargetType),
ConstantExpr::getAddrSpaceCast(Src1, TargetType));
}
}
// Computes the operands of the new constant expression.
bool IsNew = false;
SmallVector<Constant *, 4> NewOperands;
for (unsigned Index = 0; Index < CE->getNumOperands(); ++Index) {
Constant *Operand = CE->getOperand(Index);
// If the address space of `Operand` needs to be modified, the new operand
// with the new address space should already be in ValueWithNewAddrSpace
// because (1) the constant expressions we consider (i.e. addrspacecast,
// bitcast, and getelementptr) do not incur cycles in the data flow graph
// and (2) this function is called on constant expressions in postorder.
if (Value *NewOperand = ValueWithNewAddrSpace.lookup(Operand)) {
IsNew = true;
NewOperands.push_back(cast<Constant>(NewOperand));
} else {
// Otherwise, reuses the old operand.
NewOperands.push_back(Operand);
}
}
// If !IsNew, we will replace the Value with itself. However, replaced values
// are assumed to wrapped in a addrspace cast later so drop it now.
if (!IsNew)
return nullptr;
if (CE->getOpcode() == Instruction::GetElementPtr) {
// Needs to specify the source type while constructing a getelementptr
// constant expression.
return CE->getWithOperands(
NewOperands, TargetType, /*OnlyIfReduced=*/false,
NewOperands[0]->getType()->getPointerElementType());
}
return CE->getWithOperands(NewOperands, TargetType);
}
// Returns a clone of the value `V`, with its operands replaced as specified in
// ValueWithNewAddrSpace. This function is called on every flat address
// expression whose address space needs to be modified, in postorder.
//
// See cloneInstructionWithNewAddressSpace for the meaning of UndefUsesToFix.
Value *InferAddressSpaces::cloneValueWithNewAddressSpace(
Value *V, unsigned NewAddrSpace,
const ValueToValueMapTy &ValueWithNewAddrSpace,
SmallVectorImpl<const Use *> *UndefUsesToFix) const {
// All values in Postorder are flat address expressions.
assert(isAddressExpression(*V) &&
V->getType()->getPointerAddressSpace() == FlatAddrSpace);
if (Instruction *I = dyn_cast<Instruction>(V)) {
Value *NewV = cloneInstructionWithNewAddressSpace(
I, NewAddrSpace, ValueWithNewAddrSpace, UndefUsesToFix);
if (Instruction *NewI = dyn_cast<Instruction>(NewV)) {
if (NewI->getParent() == nullptr) {
NewI->insertBefore(I);
NewI->takeName(I);
}
}
return NewV;
}
return cloneConstantExprWithNewAddressSpace(
cast<ConstantExpr>(V), NewAddrSpace, ValueWithNewAddrSpace);
}
// Defines the join operation on the address space lattice (see the file header
// comments).
unsigned InferAddressSpaces::joinAddressSpaces(unsigned AS1,
unsigned AS2) const {
if (AS1 == FlatAddrSpace || AS2 == FlatAddrSpace)
return FlatAddrSpace;
if (AS1 == UninitializedAddressSpace)
return AS2;
if (AS2 == UninitializedAddressSpace)
return AS1;
// The join of two different specific address spaces is flat.
return (AS1 == AS2) ? AS1 : FlatAddrSpace;
}
bool InferAddressSpaces::runOnFunction(Function &F) {
if (skipFunction(F))
return false;
const TargetTransformInfo &TTI =
getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
FlatAddrSpace = TTI.getFlatAddressSpace();
if (FlatAddrSpace == UninitializedAddressSpace)
return false;
// Collects all flat address expressions in postorder.
std::vector<WeakTrackingVH> Postorder = collectFlatAddressExpressions(F);
// Runs a data-flow analysis to refine the address spaces of every expression
// in Postorder.
ValueToAddrSpaceMapTy InferredAddrSpace;
inferAddressSpaces(Postorder, &InferredAddrSpace);
// Changes the address spaces of the flat address expressions who are inferred
// to point to a specific address space.
return rewriteWithNewAddressSpaces(TTI, Postorder, InferredAddrSpace, &F);
}
// Constants need to be tracked through RAUW to handle cases with nested
// constant expressions, so wrap values in WeakTrackingVH.
void InferAddressSpaces::inferAddressSpaces(
ArrayRef<WeakTrackingVH> Postorder,
ValueToAddrSpaceMapTy *InferredAddrSpace) const {
SetVector<Value *> Worklist(Postorder.begin(), Postorder.end());
// Initially, all expressions are in the uninitialized address space.
for (Value *V : Postorder)
(*InferredAddrSpace)[V] = UninitializedAddressSpace;
while (!Worklist.empty()) {
Value *V = Worklist.pop_back_val();
// Tries to update the address space of the stack top according to the
// address spaces of its operands.
LLVM_DEBUG(dbgs() << "Updating the address space of\n " << *V << '\n');
Optional<unsigned> NewAS = updateAddressSpace(*V, *InferredAddrSpace);
if (!NewAS.hasValue())
continue;
// If any updates are made, grabs its users to the worklist because
// their address spaces can also be possibly updated.
LLVM_DEBUG(dbgs() << " to " << NewAS.getValue() << '\n');
(*InferredAddrSpace)[V] = NewAS.getValue();
for (Value *User : V->users()) {
// Skip if User is already in the worklist.
if (Worklist.count(User))
continue;
auto Pos = InferredAddrSpace->find(User);
// Our algorithm only updates the address spaces of flat address
// expressions, which are those in InferredAddrSpace.
if (Pos == InferredAddrSpace->end())
continue;
// Function updateAddressSpace moves the address space down a lattice
// path. Therefore, nothing to do if User is already inferred as flat (the
// bottom element in the lattice).
if (Pos->second == FlatAddrSpace)
continue;
Worklist.insert(User);
}
}
}
Optional<unsigned> InferAddressSpaces::updateAddressSpace(
const Value &V, const ValueToAddrSpaceMapTy &InferredAddrSpace) const {
assert(InferredAddrSpace.count(&V));
// The new inferred address space equals the join of the address spaces
// of all its pointer operands.
unsigned NewAS = UninitializedAddressSpace;
const Operator &Op = cast<Operator>(V);
if (Op.getOpcode() == Instruction::Select) {
Value *Src0 = Op.getOperand(1);
Value *Src1 = Op.getOperand(2);
auto I = InferredAddrSpace.find(Src0);
unsigned Src0AS = (I != InferredAddrSpace.end()) ?
I->second : Src0->getType()->getPointerAddressSpace();
auto J = InferredAddrSpace.find(Src1);
unsigned Src1AS = (J != InferredAddrSpace.end()) ?
J->second : Src1->getType()->getPointerAddressSpace();
auto *C0 = dyn_cast<Constant>(Src0);
auto *C1 = dyn_cast<Constant>(Src1);
// If one of the inputs is a constant, we may be able to do a constant
// addrspacecast of it. Defer inferring the address space until the input
// address space is known.
if ((C1 && Src0AS == UninitializedAddressSpace) ||
(C0 && Src1AS == UninitializedAddressSpace))
return None;
if (C0 && isSafeToCastConstAddrSpace(C0, Src1AS))
NewAS = Src1AS;
else if (C1 && isSafeToCastConstAddrSpace(C1, Src0AS))
NewAS = Src0AS;
else
NewAS = joinAddressSpaces(Src0AS, Src1AS);
} else {
for (Value *PtrOperand : getPointerOperands(V)) {
auto I = InferredAddrSpace.find(PtrOperand);
unsigned OperandAS = I != InferredAddrSpace.end() ?
I->second : PtrOperand->getType()->getPointerAddressSpace();
// join(flat, *) = flat. So we can break if NewAS is already flat.
NewAS = joinAddressSpaces(NewAS, OperandAS);
if (NewAS == FlatAddrSpace)
break;
}
}
unsigned OldAS = InferredAddrSpace.lookup(&V);
assert(OldAS != FlatAddrSpace);
if (OldAS == NewAS)
return None;
return NewAS;
}
/// \p returns true if \p U is the pointer operand of a memory instruction with
/// a single pointer operand that can have its address space changed by simply
/// mutating the use to a new value. If the memory instruction is volatile,
/// return true only if the target allows the memory instruction to be volatile
/// in the new address space.
static bool isSimplePointerUseValidToReplace(const TargetTransformInfo &TTI,
Use &U, unsigned AddrSpace) {
User *Inst = U.getUser();
unsigned OpNo = U.getOperandNo();
bool VolatileIsAllowed = false;
if (auto *I = dyn_cast<Instruction>(Inst))
VolatileIsAllowed = TTI.hasVolatileVariant(I, AddrSpace);
if (auto *LI = dyn_cast<LoadInst>(Inst))
return OpNo == LoadInst::getPointerOperandIndex() &&
(VolatileIsAllowed || !LI->isVolatile());
if (auto *SI = dyn_cast<StoreInst>(Inst))
return OpNo == StoreInst::getPointerOperandIndex() &&
(VolatileIsAllowed || !SI->isVolatile());
if (auto *RMW = dyn_cast<AtomicRMWInst>(Inst))
return OpNo == AtomicRMWInst::getPointerOperandIndex() &&
(VolatileIsAllowed || !RMW->isVolatile());
if (auto *CmpX = dyn_cast<AtomicCmpXchgInst>(Inst))
return OpNo == AtomicCmpXchgInst::getPointerOperandIndex() &&
(VolatileIsAllowed || !CmpX->isVolatile());
return false;
}
/// Update memory intrinsic uses that require more complex processing than
/// simple memory instructions. Thse require re-mangling and may have multiple
/// pointer operands.
static bool handleMemIntrinsicPtrUse(MemIntrinsic *MI, Value *OldV,
Value *NewV) {
IRBuilder<> B(MI);
MDNode *TBAA = MI->getMetadata(LLVMContext::MD_tbaa);
MDNode *ScopeMD = MI->getMetadata(LLVMContext::MD_alias_scope);
MDNode *NoAliasMD = MI->getMetadata(LLVMContext::MD_noalias);
if (auto *MSI = dyn_cast<MemSetInst>(MI)) {
B.CreateMemSet(NewV, MSI->getValue(),
MSI->getLength(), MSI->getDestAlignment(),
false, // isVolatile
TBAA, ScopeMD, NoAliasMD);
} else if (auto *MTI = dyn_cast<MemTransferInst>(MI)) {
Value *Src = MTI->getRawSource();
Value *Dest = MTI->getRawDest();
// Be careful in case this is a self-to-self copy.
if (Src == OldV)
Src = NewV;
if (Dest == OldV)
Dest = NewV;
if (isa<MemCpyInst>(MTI)) {
MDNode *TBAAStruct = MTI->getMetadata(LLVMContext::MD_tbaa_struct);
B.CreateMemCpy(Dest, MTI->getDestAlignment(),
Src, MTI->getSourceAlignment(),
MTI->getLength(),
false, // isVolatile
TBAA, TBAAStruct, ScopeMD, NoAliasMD);
} else {
assert(isa<MemMoveInst>(MTI));
B.CreateMemMove(Dest, MTI->getDestAlignment(),
Src, MTI->getSourceAlignment(),
MTI->getLength(),
false, // isVolatile
TBAA, ScopeMD, NoAliasMD);
}
} else
llvm_unreachable("unhandled MemIntrinsic");
MI->eraseFromParent();
return true;
}
// \p returns true if it is OK to change the address space of constant \p C with
// a ConstantExpr addrspacecast.
bool InferAddressSpaces::isSafeToCastConstAddrSpace(Constant *C, unsigned NewAS) const {
assert(NewAS != UninitializedAddressSpace);
unsigned SrcAS = C->getType()->getPointerAddressSpace();
if (SrcAS == NewAS || isa<UndefValue>(C))
return true;
// Prevent illegal casts between different non-flat address spaces.
if (SrcAS != FlatAddrSpace && NewAS != FlatAddrSpace)
return false;
if (isa<ConstantPointerNull>(C))
return true;
if (auto *Op = dyn_cast<Operator>(C)) {
// If we already have a constant addrspacecast, it should be safe to cast it
// off.
if (Op->getOpcode() == Instruction::AddrSpaceCast)
return isSafeToCastConstAddrSpace(cast<Constant>(Op->getOperand(0)), NewAS);
if (Op->getOpcode() == Instruction::IntToPtr &&
Op->getType()->getPointerAddressSpace() == FlatAddrSpace)
return true;
}
return false;
}
static Value::use_iterator skipToNextUser(Value::use_iterator I,
Value::use_iterator End) {
User *CurUser = I->getUser();
++I;
while (I != End && I->getUser() == CurUser)
++I;
return I;
}
bool InferAddressSpaces::rewriteWithNewAddressSpaces(
const TargetTransformInfo &TTI, ArrayRef<WeakTrackingVH> Postorder,
const ValueToAddrSpaceMapTy &InferredAddrSpace, Function *F) const {
// For each address expression to be modified, creates a clone of it with its
// pointer operands converted to the new address space. Since the pointer
// operands are converted, the clone is naturally in the new address space by
// construction.
ValueToValueMapTy ValueWithNewAddrSpace;
SmallVector<const Use *, 32> UndefUsesToFix;
for (Value* V : Postorder) {
unsigned NewAddrSpace = InferredAddrSpace.lookup(V);
if (V->getType()->getPointerAddressSpace() != NewAddrSpace) {
ValueWithNewAddrSpace[V] = cloneValueWithNewAddressSpace(
V, NewAddrSpace, ValueWithNewAddrSpace, &UndefUsesToFix);
}
}
if (ValueWithNewAddrSpace.empty())
return false;
// Fixes all the undef uses generated by cloneInstructionWithNewAddressSpace.
for (const Use *UndefUse : UndefUsesToFix) {
User *V = UndefUse->getUser();
User *NewV = cast<User>(ValueWithNewAddrSpace.lookup(V));
unsigned OperandNo = UndefUse->getOperandNo();
assert(isa<UndefValue>(NewV->getOperand(OperandNo)));
NewV->setOperand(OperandNo, ValueWithNewAddrSpace.lookup(UndefUse->get()));
}
SmallVector<Instruction *, 16> DeadInstructions;
// Replaces the uses of the old address expressions with the new ones.
for (const WeakTrackingVH &WVH : Postorder) {
assert(WVH && "value was unexpectedly deleted");
Value *V = WVH;
Value *NewV = ValueWithNewAddrSpace.lookup(V);
if (NewV == nullptr)
continue;
LLVM_DEBUG(dbgs() << "Replacing the uses of " << *V << "\n with\n "
<< *NewV << '\n');
if (Constant *C = dyn_cast<Constant>(V)) {
Constant *Replace = ConstantExpr::getAddrSpaceCast(cast<Constant>(NewV),
C->getType());
if (C != Replace) {
LLVM_DEBUG(dbgs() << "Inserting replacement const cast: " << Replace
<< ": " << *Replace << '\n');
C->replaceAllUsesWith(Replace);
V = Replace;
}
}
Value::use_iterator I, E, Next;
for (I = V->use_begin(), E = V->use_end(); I != E; ) {
Use &U = *I;
// Some users may see the same pointer operand in multiple operands. Skip
// to the next instruction.
I = skipToNextUser(I, E);
if (isSimplePointerUseValidToReplace(
TTI, U, V->getType()->getPointerAddressSpace())) {
// If V is used as the pointer operand of a compatible memory operation,
// sets the pointer operand to NewV. This replacement does not change
// the element type, so the resultant load/store is still valid.
U.set(NewV);
continue;
}
User *CurUser = U.getUser();
// Handle more complex cases like intrinsic that need to be remangled.
if (auto *MI = dyn_cast<MemIntrinsic>(CurUser)) {
if (!MI->isVolatile() && handleMemIntrinsicPtrUse(MI, V, NewV))
continue;
}
if (auto *II = dyn_cast<IntrinsicInst>(CurUser)) {
if (rewriteIntrinsicOperands(II, V, NewV))
continue;
}
if (isa<Instruction>(CurUser)) {
if (ICmpInst *Cmp = dyn_cast<ICmpInst>(CurUser)) {
// If we can infer that both pointers are in the same addrspace,
// transform e.g.
// %cmp = icmp eq float* %p, %q
// into
// %cmp = icmp eq float addrspace(3)* %new_p, %new_q
unsigned NewAS = NewV->getType()->getPointerAddressSpace();
int SrcIdx = U.getOperandNo();
int OtherIdx = (SrcIdx == 0) ? 1 : 0;
Value *OtherSrc = Cmp->getOperand(OtherIdx);
if (Value *OtherNewV = ValueWithNewAddrSpace.lookup(OtherSrc)) {
if (OtherNewV->getType()->getPointerAddressSpace() == NewAS) {
Cmp->setOperand(OtherIdx, OtherNewV);
Cmp->setOperand(SrcIdx, NewV);
continue;
}
}
// Even if the type mismatches, we can cast the constant.
if (auto *KOtherSrc = dyn_cast<Constant>(OtherSrc)) {
if (isSafeToCastConstAddrSpace(KOtherSrc, NewAS)) {
Cmp->setOperand(SrcIdx, NewV);
Cmp->setOperand(OtherIdx,
ConstantExpr::getAddrSpaceCast(KOtherSrc, NewV->getType()));
continue;
}
}
}
if (AddrSpaceCastInst *ASC = dyn_cast<AddrSpaceCastInst>(CurUser)) {
unsigned NewAS = NewV->getType()->getPointerAddressSpace();
if (ASC->getDestAddressSpace() == NewAS) {
if (ASC->getType()->getPointerElementType() !=
NewV->getType()->getPointerElementType()) {
NewV = CastInst::Create(Instruction::BitCast, NewV,
ASC->getType(), "", ASC);
}
ASC->replaceAllUsesWith(NewV);
DeadInstructions.push_back(ASC);
continue;
}
}
// Otherwise, replaces the use with flat(NewV).
if (Instruction *I = dyn_cast<Instruction>(V)) {
BasicBlock::iterator InsertPos = std::next(I->getIterator());
while (isa<PHINode>(InsertPos))
++InsertPos;
U.set(new AddrSpaceCastInst(NewV, V->getType(), "", &*InsertPos));
} else {
U.set(ConstantExpr::getAddrSpaceCast(cast<Constant>(NewV),
V->getType()));
}
}
}
if (V->use_empty()) {
if (Instruction *I = dyn_cast<Instruction>(V))
DeadInstructions.push_back(I);
}
}
for (Instruction *I : DeadInstructions)
RecursivelyDeleteTriviallyDeadInstructions(I);
return true;
}
FunctionPass *llvm::createInferAddressSpacesPass() {
return new InferAddressSpaces();
}
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