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| //===-- AMDGPUAnnotateUniformValues.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 adds amdgpu.uniform metadata to IR values so this information
/// can be used during instruction selection.
//
//===----------------------------------------------------------------------===//
#include "AMDGPU.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/Analysis/LegacyDivergenceAnalysis.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.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-annotate-uniform"
using namespace llvm;
namespace {
class AMDGPUAnnotateUniformValues : public FunctionPass,
public InstVisitor<AMDGPUAnnotateUniformValues> {
LegacyDivergenceAnalysis *DA;
MemoryDependenceResults *MDR;
LoopInfo *LI;
DenseMap<Value*, GetElementPtrInst*> noClobberClones;
bool isKernelFunc;
public:
static char ID;
AMDGPUAnnotateUniformValues() :
FunctionPass(ID) { }
bool doInitialization(Module &M) override;
bool runOnFunction(Function &F) override;
StringRef getPassName() const override {
return "AMDGPU Annotate Uniform Values";
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<LegacyDivergenceAnalysis>();
AU.addRequired<MemoryDependenceWrapperPass>();
AU.addRequired<LoopInfoWrapperPass>();
AU.setPreservesAll();
}
void visitBranchInst(BranchInst &I);
void visitLoadInst(LoadInst &I);
bool isClobberedInFunction(LoadInst * Load);
};
} // End anonymous namespace
INITIALIZE_PASS_BEGIN(AMDGPUAnnotateUniformValues, DEBUG_TYPE,
"Add AMDGPU uniform metadata", false, false)
INITIALIZE_PASS_DEPENDENCY(LegacyDivergenceAnalysis)
INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_END(AMDGPUAnnotateUniformValues, DEBUG_TYPE,
"Add AMDGPU uniform metadata", false, false)
char AMDGPUAnnotateUniformValues::ID = 0;
static void setUniformMetadata(Instruction *I) {
I->setMetadata("amdgpu.uniform", MDNode::get(I->getContext(), {}));
}
static void setNoClobberMetadata(Instruction *I) {
I->setMetadata("amdgpu.noclobber", MDNode::get(I->getContext(), {}));
}
static void DFS(BasicBlock *Root, SetVector<BasicBlock*> & Set) {
for (auto I : predecessors(Root))
if (Set.insert(I))
DFS(I, Set);
}
bool AMDGPUAnnotateUniformValues::isClobberedInFunction(LoadInst * Load) {
// 1. get Loop for the Load->getparent();
// 2. if it exists, collect all the BBs from the most outer
// loop and check for the writes. If NOT - start DFS over all preds.
// 3. Start DFS over all preds from the most outer loop header.
SetVector<BasicBlock *> Checklist;
BasicBlock *Start = Load->getParent();
Checklist.insert(Start);
const Value *Ptr = Load->getPointerOperand();
const Loop *L = LI->getLoopFor(Start);
if (L) {
const Loop *P = L;
do {
L = P;
P = P->getParentLoop();
} while (P);
Checklist.insert(L->block_begin(), L->block_end());
Start = L->getHeader();
}
DFS(Start, Checklist);
for (auto &BB : Checklist) {
BasicBlock::iterator StartIt = (!L && (BB == Load->getParent())) ?
BasicBlock::iterator(Load) : BB->end();
auto Q = MDR->getPointerDependencyFrom(MemoryLocation(Ptr), true,
StartIt, BB, Load);
if (Q.isClobber() || Q.isUnknown())
return true;
}
return false;
}
void AMDGPUAnnotateUniformValues::visitBranchInst(BranchInst &I) {
if (DA->isUniform(&I))
setUniformMetadata(I.getParent()->getTerminator());
}
void AMDGPUAnnotateUniformValues::visitLoadInst(LoadInst &I) {
Value *Ptr = I.getPointerOperand();
if (!DA->isUniform(Ptr))
return;
auto isGlobalLoad = [&](LoadInst &Load)->bool {
return Load.getPointerAddressSpace() == AMDGPUAS::GLOBAL_ADDRESS;
};
// We're tracking up to the Function boundaries
// We cannot go beyond because of FunctionPass restrictions
// Thus we can ensure that memory not clobbered for memory
// operations that live in kernel only.
bool NotClobbered = isKernelFunc && !isClobberedInFunction(&I);
Instruction *PtrI = dyn_cast<Instruction>(Ptr);
if (!PtrI && NotClobbered && isGlobalLoad(I)) {
if (isa<Argument>(Ptr) || isa<GlobalValue>(Ptr)) {
// Lookup for the existing GEP
if (noClobberClones.count(Ptr)) {
PtrI = noClobberClones[Ptr];
} else {
// Create GEP of the Value
Function *F = I.getParent()->getParent();
Value *Idx = Constant::getIntegerValue(
Type::getInt32Ty(Ptr->getContext()), APInt(64, 0));
// Insert GEP at the entry to make it dominate all uses
PtrI = GetElementPtrInst::Create(
Ptr->getType()->getPointerElementType(), Ptr,
ArrayRef<Value*>(Idx), Twine(""), F->getEntryBlock().getFirstNonPHI());
}
I.replaceUsesOfWith(Ptr, PtrI);
}
}
if (PtrI) {
setUniformMetadata(PtrI);
if (NotClobbered)
setNoClobberMetadata(PtrI);
}
}
bool AMDGPUAnnotateUniformValues::doInitialization(Module &M) {
return false;
}
bool AMDGPUAnnotateUniformValues::runOnFunction(Function &F) {
if (skipFunction(F))
return false;
DA = &getAnalysis<LegacyDivergenceAnalysis>();
MDR = &getAnalysis<MemoryDependenceWrapperPass>().getMemDep();
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
isKernelFunc = F.getCallingConv() == CallingConv::AMDGPU_KERNEL;
visit(F);
noClobberClones.clear();
return true;
}
FunctionPass *
llvm::createAMDGPUAnnotateUniformValues() {
return new AMDGPUAnnotateUniformValues();
}
|