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//===- SIAnnotateControlFlow.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
/// Annotates the control flow with hardware specific intrinsics.
//
//===----------------------------------------------------------------------===//
#include "AMDGPU.h"
#include "GCNSubtarget.h"
#include "llvm/Analysis/LegacyDivergenceAnalysis.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/IntrinsicsAMDGPU.h"
#include "llvm/InitializePasses.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
#define DEBUG_TYPE "si-annotate-control-flow"
namespace {
// Complex types used in this pass
using StackEntry = std::pair<BasicBlock *, Value *>;
using StackVector = SmallVector<StackEntry, 16>;
class SIAnnotateControlFlow : public FunctionPass {
LegacyDivergenceAnalysis *DA;
Type *Boolean;
Type *Void;
Type *IntMask;
Type *ReturnStruct;
ConstantInt *BoolTrue;
ConstantInt *BoolFalse;
UndefValue *BoolUndef;
Constant *IntMaskZero;
Function *If;
Function *Else;
Function *IfBreak;
Function *Loop;
Function *EndCf;
DominatorTree *DT;
StackVector Stack;
LoopInfo *LI;
void initialize(Module &M, const GCNSubtarget &ST);
bool isUniform(BranchInst *T);
bool isTopOfStack(BasicBlock *BB);
Value *popSaved();
void push(BasicBlock *BB, Value *Saved);
bool isElse(PHINode *Phi);
bool hasKill(const BasicBlock *BB);
bool eraseIfUnused(PHINode *Phi);
bool openIf(BranchInst *Term);
bool insertElse(BranchInst *Term);
Value *
handleLoopCondition(Value *Cond, PHINode *Broken, llvm::Loop *L,
BranchInst *Term);
bool handleLoop(BranchInst *Term);
bool closeControlFlow(BasicBlock *BB);
public:
static char ID;
SIAnnotateControlFlow() : FunctionPass(ID) {}
bool runOnFunction(Function &F) override;
StringRef getPassName() const override { return "SI annotate control flow"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<LoopInfoWrapperPass>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<LegacyDivergenceAnalysis>();
AU.addPreserved<LoopInfoWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addRequired<TargetPassConfig>();
FunctionPass::getAnalysisUsage(AU);
}
};
} // end anonymous namespace
INITIALIZE_PASS_BEGIN(SIAnnotateControlFlow, DEBUG_TYPE,
"Annotate SI Control Flow", false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LegacyDivergenceAnalysis)
INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
INITIALIZE_PASS_END(SIAnnotateControlFlow, DEBUG_TYPE,
"Annotate SI Control Flow", false, false)
char SIAnnotateControlFlow::ID = 0;
/// Initialize all the types and constants used in the pass
void SIAnnotateControlFlow::initialize(Module &M, const GCNSubtarget &ST) {
LLVMContext &Context = M.getContext();
Void = Type::getVoidTy(Context);
Boolean = Type::getInt1Ty(Context);
IntMask = ST.isWave32() ? Type::getInt32Ty(Context)
: Type::getInt64Ty(Context);
ReturnStruct = StructType::get(Boolean, IntMask);
BoolTrue = ConstantInt::getTrue(Context);
BoolFalse = ConstantInt::getFalse(Context);
BoolUndef = PoisonValue::get(Boolean);
IntMaskZero = ConstantInt::get(IntMask, 0);
If = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if, { IntMask });
Else = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_else,
{ IntMask, IntMask });
IfBreak = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if_break,
{ IntMask });
Loop = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_loop, { IntMask });
EndCf = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_end_cf, { IntMask });
}
/// Is the branch condition uniform or did the StructurizeCFG pass
/// consider it as such?
bool SIAnnotateControlFlow::isUniform(BranchInst *T) {
return DA->isUniform(T) ||
T->getMetadata("structurizecfg.uniform") != nullptr;
}
/// Is BB the last block saved on the stack ?
bool SIAnnotateControlFlow::isTopOfStack(BasicBlock *BB) {
return !Stack.empty() && Stack.back().first == BB;
}
/// Pop the last saved value from the control flow stack
Value *SIAnnotateControlFlow::popSaved() {
return Stack.pop_back_val().second;
}
/// Push a BB and saved value to the control flow stack
void SIAnnotateControlFlow::push(BasicBlock *BB, Value *Saved) {
Stack.push_back(std::pair(BB, Saved));
}
/// Can the condition represented by this PHI node treated like
/// an "Else" block?
bool SIAnnotateControlFlow::isElse(PHINode *Phi) {
BasicBlock *IDom = DT->getNode(Phi->getParent())->getIDom()->getBlock();
for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
if (Phi->getIncomingBlock(i) == IDom) {
if (Phi->getIncomingValue(i) != BoolTrue)
return false;
} else {
if (Phi->getIncomingValue(i) != BoolFalse)
return false;
}
}
return true;
}
bool SIAnnotateControlFlow::hasKill(const BasicBlock *BB) {
for (const Instruction &I : *BB) {
if (const CallInst *CI = dyn_cast<CallInst>(&I))
if (CI->getIntrinsicID() == Intrinsic::amdgcn_kill)
return true;
}
return false;
}
// Erase "Phi" if it is not used any more. Return true if any change was made.
bool SIAnnotateControlFlow::eraseIfUnused(PHINode *Phi) {
bool Changed = RecursivelyDeleteDeadPHINode(Phi);
if (Changed)
LLVM_DEBUG(dbgs() << "Erased unused condition phi\n");
return Changed;
}
/// Open a new "If" block
bool SIAnnotateControlFlow::openIf(BranchInst *Term) {
if (isUniform(Term))
return false;
Value *Ret = CallInst::Create(If, Term->getCondition(), "", Term);
Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
return true;
}
/// Close the last "If" block and open a new "Else" block
bool SIAnnotateControlFlow::insertElse(BranchInst *Term) {
if (isUniform(Term)) {
return false;
}
Value *Ret = CallInst::Create(Else, popSaved(), "", Term);
Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
return true;
}
/// Recursively handle the condition leading to a loop
Value *SIAnnotateControlFlow::handleLoopCondition(
Value *Cond, PHINode *Broken, llvm::Loop *L, BranchInst *Term) {
if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
BasicBlock *Parent = Inst->getParent();
Instruction *Insert;
if (L->contains(Inst)) {
Insert = Parent->getTerminator();
} else {
Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
}
Value *Args[] = { Cond, Broken };
return CallInst::Create(IfBreak, Args, "", Insert);
}
// Insert IfBreak in the loop header TERM for constant COND other than true.
if (isa<Constant>(Cond)) {
Instruction *Insert = Cond == BoolTrue ?
Term : L->getHeader()->getTerminator();
Value *Args[] = { Cond, Broken };
return CallInst::Create(IfBreak, Args, "", Insert);
}
if (isa<Argument>(Cond)) {
Instruction *Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
Value *Args[] = { Cond, Broken };
return CallInst::Create(IfBreak, Args, "", Insert);
}
llvm_unreachable("Unhandled loop condition!");
}
/// Handle a back edge (loop)
bool SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
if (isUniform(Term))
return false;
BasicBlock *BB = Term->getParent();
llvm::Loop *L = LI->getLoopFor(BB);
if (!L)
return false;
BasicBlock *Target = Term->getSuccessor(1);
PHINode *Broken = PHINode::Create(IntMask, 0, "phi.broken", &Target->front());
Value *Cond = Term->getCondition();
Term->setCondition(BoolTrue);
Value *Arg = handleLoopCondition(Cond, Broken, L, Term);
for (BasicBlock *Pred : predecessors(Target)) {
Value *PHIValue = IntMaskZero;
if (Pred == BB) // Remember the value of the previous iteration.
PHIValue = Arg;
// If the backedge from Pred to Target could be executed before the exit
// of the loop at BB, it should not reset or change "Broken", which keeps
// track of the number of threads exited the loop at BB.
else if (L->contains(Pred) && DT->dominates(Pred, BB))
PHIValue = Broken;
Broken->addIncoming(PHIValue, Pred);
}
Term->setCondition(CallInst::Create(Loop, Arg, "", Term));
push(Term->getSuccessor(0), Arg);
return true;
}
/// Close the last opened control flow
bool SIAnnotateControlFlow::closeControlFlow(BasicBlock *BB) {
llvm::Loop *L = LI->getLoopFor(BB);
assert(Stack.back().first == BB);
if (L && L->getHeader() == BB) {
// We can't insert an EndCF call into a loop header, because it will
// get executed on every iteration of the loop, when it should be
// executed only once before the loop.
SmallVector <BasicBlock *, 8> Latches;
L->getLoopLatches(Latches);
SmallVector<BasicBlock *, 2> Preds;
for (BasicBlock *Pred : predecessors(BB)) {
if (!is_contained(Latches, Pred))
Preds.push_back(Pred);
}
BB = SplitBlockPredecessors(BB, Preds, "endcf.split", DT, LI, nullptr,
false);
}
Value *Exec = popSaved();
Instruction *FirstInsertionPt = &*BB->getFirstInsertionPt();
if (!isa<UndefValue>(Exec) && !isa<UnreachableInst>(FirstInsertionPt)) {
Instruction *ExecDef = cast<Instruction>(Exec);
BasicBlock *DefBB = ExecDef->getParent();
if (!DT->dominates(DefBB, BB)) {
// Split edge to make Def dominate Use
FirstInsertionPt = &*SplitEdge(DefBB, BB, DT, LI)->getFirstInsertionPt();
}
CallInst::Create(EndCf, Exec, "", FirstInsertionPt);
}
return true;
}
/// Annotate the control flow with intrinsics so the backend can
/// recognize if/then/else and loops.
bool SIAnnotateControlFlow::runOnFunction(Function &F) {
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
DA = &getAnalysis<LegacyDivergenceAnalysis>();
TargetPassConfig &TPC = getAnalysis<TargetPassConfig>();
const TargetMachine &TM = TPC.getTM<TargetMachine>();
bool Changed = false;
initialize(*F.getParent(), TM.getSubtarget<GCNSubtarget>(F));
for (df_iterator<BasicBlock *> I = df_begin(&F.getEntryBlock()),
E = df_end(&F.getEntryBlock()); I != E; ++I) {
BasicBlock *BB = *I;
BranchInst *Term = dyn_cast<BranchInst>(BB->getTerminator());
if (!Term || Term->isUnconditional()) {
if (isTopOfStack(BB))
Changed |= closeControlFlow(BB);
continue;
}
if (I.nodeVisited(Term->getSuccessor(1))) {
if (isTopOfStack(BB))
Changed |= closeControlFlow(BB);
if (DT->dominates(Term->getSuccessor(1), BB))
Changed |= handleLoop(Term);
continue;
}
if (isTopOfStack(BB)) {
PHINode *Phi = dyn_cast<PHINode>(Term->getCondition());
if (Phi && Phi->getParent() == BB && isElse(Phi) && !hasKill(BB)) {
Changed |= insertElse(Term);
Changed |= eraseIfUnused(Phi);
continue;
}
Changed |= closeControlFlow(BB);
}
Changed |= openIf(Term);
}
if (!Stack.empty()) {
// CFG was probably not structured.
report_fatal_error("failed to annotate CFG");
}
return Changed;
}
/// Create the annotation pass
FunctionPass *llvm::createSIAnnotateControlFlowPass() {
return new SIAnnotateControlFlow();
}