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//===-- AMDGPUPromoteKernelArguments.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
//
//===----------------------------------------------------------------------===//
//
/// \file This pass recursively promotes generic pointer arguments of a kernel
/// into the global address space.
///
/// The pass walks kernel's pointer arguments, then loads from them. If a loaded
/// value is a pointer and loaded pointer is unmodified in the kernel before the
/// load, then promote loaded pointer to global. Then recursively continue.
//
//===----------------------------------------------------------------------===//
#include "AMDGPU.h"
#include "AMDGPUMemoryUtils.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/MemorySSA.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/InitializePasses.h"
#define DEBUG_TYPE "amdgpu-promote-kernel-arguments"
using namespace llvm;
namespace {
class AMDGPUPromoteKernelArguments : public FunctionPass {
MemorySSA *MSSA;
AliasAnalysis *AA;
Instruction *ArgCastInsertPt;
SmallVector<Value *> Ptrs;
void enqueueUsers(Value *Ptr);
bool promotePointer(Value *Ptr);
bool promoteLoad(LoadInst *LI);
public:
static char ID;
AMDGPUPromoteKernelArguments() : FunctionPass(ID) {}
bool run(Function &F, MemorySSA &MSSA, AliasAnalysis &AA);
bool runOnFunction(Function &F) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AAResultsWrapperPass>();
AU.addRequired<MemorySSAWrapperPass>();
AU.setPreservesAll();
}
};
} // end anonymous namespace
void AMDGPUPromoteKernelArguments::enqueueUsers(Value *Ptr) {
SmallVector<User *> PtrUsers(Ptr->users());
while (!PtrUsers.empty()) {
Instruction *U = dyn_cast<Instruction>(PtrUsers.pop_back_val());
if (!U)
continue;
switch (U->getOpcode()) {
default:
break;
case Instruction::Load: {
LoadInst *LD = cast<LoadInst>(U);
if (LD->getPointerOperand()->stripInBoundsOffsets() == Ptr &&
!AMDGPU::isClobberedInFunction(LD, MSSA, AA))
Ptrs.push_back(LD);
break;
}
case Instruction::GetElementPtr:
case Instruction::AddrSpaceCast:
case Instruction::BitCast:
if (U->getOperand(0)->stripInBoundsOffsets() == Ptr)
PtrUsers.append(U->user_begin(), U->user_end());
break;
}
}
}
bool AMDGPUPromoteKernelArguments::promotePointer(Value *Ptr) {
bool Changed = false;
LoadInst *LI = dyn_cast<LoadInst>(Ptr);
if (LI)
Changed |= promoteLoad(LI);
PointerType *PT = dyn_cast<PointerType>(Ptr->getType());
if (!PT)
return Changed;
if (PT->getAddressSpace() == AMDGPUAS::FLAT_ADDRESS ||
PT->getAddressSpace() == AMDGPUAS::GLOBAL_ADDRESS ||
PT->getAddressSpace() == AMDGPUAS::CONSTANT_ADDRESS)
enqueueUsers(Ptr);
if (PT->getAddressSpace() != AMDGPUAS::FLAT_ADDRESS)
return Changed;
IRBuilder<> B(LI ? &*std::next(cast<Instruction>(Ptr)->getIterator())
: ArgCastInsertPt);
// Cast pointer to global address space and back to flat and let
// Infer Address Spaces pass to do all necessary rewriting.
PointerType *NewPT =
PointerType::get(PT->getContext(), AMDGPUAS::GLOBAL_ADDRESS);
Value *Cast =
B.CreateAddrSpaceCast(Ptr, NewPT, Twine(Ptr->getName(), ".global"));
Value *CastBack =
B.CreateAddrSpaceCast(Cast, PT, Twine(Ptr->getName(), ".flat"));
Ptr->replaceUsesWithIf(CastBack,
[Cast](Use &U) { return U.getUser() != Cast; });
return true;
}
bool AMDGPUPromoteKernelArguments::promoteLoad(LoadInst *LI) {
if (!LI->isSimple())
return false;
LI->setMetadata("amdgpu.noclobber", MDNode::get(LI->getContext(), {}));
return true;
}
// skip allocas
static BasicBlock::iterator getInsertPt(BasicBlock &BB) {
BasicBlock::iterator InsPt = BB.getFirstInsertionPt();
for (BasicBlock::iterator E = BB.end(); InsPt != E; ++InsPt) {
AllocaInst *AI = dyn_cast<AllocaInst>(&*InsPt);
// If this is a dynamic alloca, the value may depend on the loaded kernargs,
// so loads will need to be inserted before it.
if (!AI || !AI->isStaticAlloca())
break;
}
return InsPt;
}
bool AMDGPUPromoteKernelArguments::run(Function &F, MemorySSA &MSSA,
AliasAnalysis &AA) {
if (skipFunction(F))
return false;
CallingConv::ID CC = F.getCallingConv();
if (CC != CallingConv::AMDGPU_KERNEL || F.arg_empty())
return false;
ArgCastInsertPt = &*getInsertPt(*F.begin());
this->MSSA = &MSSA;
this->AA = &AA;
for (Argument &Arg : F.args()) {
if (Arg.use_empty())
continue;
PointerType *PT = dyn_cast<PointerType>(Arg.getType());
if (!PT || (PT->getAddressSpace() != AMDGPUAS::FLAT_ADDRESS &&
PT->getAddressSpace() != AMDGPUAS::GLOBAL_ADDRESS &&
PT->getAddressSpace() != AMDGPUAS::CONSTANT_ADDRESS))
continue;
Ptrs.push_back(&Arg);
}
bool Changed = false;
while (!Ptrs.empty()) {
Value *Ptr = Ptrs.pop_back_val();
Changed |= promotePointer(Ptr);
}
return Changed;
}
bool AMDGPUPromoteKernelArguments::runOnFunction(Function &F) {
MemorySSA &MSSA = getAnalysis<MemorySSAWrapperPass>().getMSSA();
AliasAnalysis &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
return run(F, MSSA, AA);
}
INITIALIZE_PASS_BEGIN(AMDGPUPromoteKernelArguments, DEBUG_TYPE,
"AMDGPU Promote Kernel Arguments", false, false)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
INITIALIZE_PASS_END(AMDGPUPromoteKernelArguments, DEBUG_TYPE,
"AMDGPU Promote Kernel Arguments", false, false)
char AMDGPUPromoteKernelArguments::ID = 0;
FunctionPass *llvm::createAMDGPUPromoteKernelArgumentsPass() {
return new AMDGPUPromoteKernelArguments();
}
PreservedAnalyses
AMDGPUPromoteKernelArgumentsPass::run(Function &F,
FunctionAnalysisManager &AM) {
MemorySSA &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
AliasAnalysis &AA = AM.getResult<AAManager>(F);
if (AMDGPUPromoteKernelArguments().run(F, MSSA, AA)) {
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
PA.preserve<MemorySSAAnalysis>();
return PA;
}
return PreservedAnalyses::all();
}
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