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//===- PhiValues.cpp - Phi Value Analysis ---------------------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "llvm/Analysis/PhiValues.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/IR/Instructions.h"
#include "llvm/InitializePasses.h"
using namespace llvm;
void PhiValues::PhiValuesCallbackVH::deleted() {
void PhiValues::PhiValuesCallbackVH::allUsesReplacedWith(Value *) {
// We could potentially update the cached values we have with the new value,
// but it's simpler to just treat the old value as invalidated.
bool PhiValues::invalidate(Function &, const PreservedAnalyses &PA,
FunctionAnalysisManager::Invalidator &) {
// PhiValues is invalidated if it isn't preserved.
auto PAC = PA.getChecker<PhiValuesAnalysis>();
return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>());
// The goal here is to find all of the non-phi values reachable from this phi,
// and to do the same for all of the phis reachable from this phi, as doing so
// is necessary anyway in order to get the values for this phi. We do this using
// Tarjan's algorithm with Nuutila's improvements to find the strongly connected
// components of the phi graph rooted in this phi:
// * All phis in a strongly connected component will have the same reachable
// non-phi values. The SCC may not be the maximal subgraph for that set of
// reachable values, but finding out that isn't really necessary (it would
// only reduce the amount of memory needed to store the values).
// * Tarjan's algorithm completes components in a bottom-up manner, i.e. it
// never completes a component before the components reachable from it have
// been completed. This means that when we complete a component we have
// everything we need to collect the values reachable from that component.
// * We collect both the non-phi values reachable from each SCC, as that's what
// we're ultimately interested in, and all of the reachable values, i.e.
// including phis, as that makes invalidateValue easier.
void PhiValues::processPhi(const PHINode *Phi,
SmallVectorImpl<const PHINode *> &Stack) {
// Initialize the phi with the next depth number.
assert(DepthMap.lookup(Phi) == 0);
assert(NextDepthNumber != UINT_MAX);
unsigned int RootDepthNumber = ++NextDepthNumber;
DepthMap[Phi] = RootDepthNumber;
// Recursively process the incoming phis of this phi.
TrackedValues.insert(PhiValuesCallbackVH(const_cast<PHINode *>(Phi), this));
for (Value *PhiOp : Phi->incoming_values()) {
if (PHINode *PhiPhiOp = dyn_cast<PHINode>(PhiOp)) {
// Recurse if the phi has not yet been visited.
unsigned int OpDepthNumber = DepthMap.lookup(PhiPhiOp);
if (OpDepthNumber == 0) {
processPhi(PhiPhiOp, Stack);
OpDepthNumber = DepthMap.lookup(PhiPhiOp);
assert(OpDepthNumber != 0);
// If the phi did not become part of a component then this phi and that
// phi are part of the same component, so adjust the depth number.
if (!ReachableMap.count(OpDepthNumber))
DepthMap[Phi] = std::min(DepthMap[Phi], OpDepthNumber);
} else {
TrackedValues.insert(PhiValuesCallbackVH(PhiOp, this));
// Now that incoming phis have been handled, push this phi to the stack.
// If the depth number has not changed then we've finished collecting the phis
// of a strongly connected component.
if (DepthMap[Phi] == RootDepthNumber) {
// Collect the reachable values for this component. The phis of this
// component will be those on top of the depth stack with the same or
// greater depth number.
ConstValueSet &Reachable = ReachableMap[RootDepthNumber];
while (true) {
const PHINode *ComponentPhi = Stack.pop_back_val();
for (Value *Op : ComponentPhi->incoming_values()) {
if (PHINode *PhiOp = dyn_cast<PHINode>(Op)) {
// If this phi is not part of the same component then that component
// is guaranteed to have been completed before this one. Therefore we
// can just add its reachable values to the reachable values of this
// component.
unsigned int OpDepthNumber = DepthMap[PhiOp];
if (OpDepthNumber != RootDepthNumber) {
auto It = ReachableMap.find(OpDepthNumber);
if (It != ReachableMap.end())
Reachable.insert(It->second.begin(), It->second.end());
} else
if (Stack.empty())
unsigned int &ComponentDepthNumber = DepthMap[Stack.back()];
if (ComponentDepthNumber < RootDepthNumber)
ComponentDepthNumber = RootDepthNumber;
// Filter out phis to get the non-phi reachable values.
ValueSet &NonPhi = NonPhiReachableMap[RootDepthNumber];
for (const Value *V : Reachable)
if (!isa<PHINode>(V))
NonPhi.insert(const_cast<Value *>(V));
const PhiValues::ValueSet &PhiValues::getValuesForPhi(const PHINode *PN) {
unsigned int DepthNumber = DepthMap.lookup(PN);
if (DepthNumber == 0) {
SmallVector<const PHINode *, 8> Stack;
processPhi(PN, Stack);
DepthNumber = DepthMap.lookup(PN);
assert(DepthNumber != 0);
return NonPhiReachableMap[DepthNumber];
void PhiValues::invalidateValue(const Value *V) {
// Components that can reach V are invalid.
SmallVector<unsigned int, 8> InvalidComponents;
for (auto &Pair : ReachableMap)
if (Pair.second.count(V))
for (unsigned int N : InvalidComponents) {
for (const Value *V : ReachableMap[N])
if (const PHINode *PN = dyn_cast<PHINode>(V))
// This value is no longer tracked
auto It = TrackedValues.find_as(V);
if (It != TrackedValues.end())
void PhiValues::releaseMemory() {
void PhiValues::print(raw_ostream &OS) const {
// Iterate through the phi nodes of the function rather than iterating through
// DepthMap in order to get predictable ordering.
for (const BasicBlock &BB : F) {
for (const PHINode &PN : BB.phis()) {
OS << "PHI ";
PN.printAsOperand(OS, false);
OS << " has values:\n";
unsigned int N = DepthMap.lookup(&PN);
auto It = NonPhiReachableMap.find(N);
if (It == NonPhiReachableMap.end())
OS << " UNKNOWN\n";
else if (It->second.empty())
OS << " NONE\n";
for (Value *V : It->second)
// Printing of an instruction prints two spaces at the start, so
// handle instructions and everything else slightly differently in
// order to get consistent indenting.
if (Instruction *I = dyn_cast<Instruction>(V))
OS << *I << "\n";
OS << " " << *V << "\n";
AnalysisKey PhiValuesAnalysis::Key;
PhiValues PhiValuesAnalysis::run(Function &F, FunctionAnalysisManager &) {
return PhiValues(F);
PreservedAnalyses PhiValuesPrinterPass::run(Function &F,
FunctionAnalysisManager &AM) {
OS << "PHI Values for function: " << F.getName() << "\n";
PhiValues &PI = AM.getResult<PhiValuesAnalysis>(F);
for (const BasicBlock &BB : F)
for (const PHINode &PN : BB.phis())
return PreservedAnalyses::all();
PhiValuesWrapperPass::PhiValuesWrapperPass() : FunctionPass(ID) {
bool PhiValuesWrapperPass::runOnFunction(Function &F) {
Result.reset(new PhiValues(F));
return false;
void PhiValuesWrapperPass::releaseMemory() {
void PhiValuesWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
char PhiValuesWrapperPass::ID = 0;
INITIALIZE_PASS(PhiValuesWrapperPass, "phi-values", "Phi Values Analysis", false,