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//===- AssumptionCache.cpp - Cache finding @llvm.assume calls -------------===//
// 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
// This file contains a pass that keeps track of @llvm.assume intrinsics in
// the functions of a module.
#include "llvm/Analysis/AssumeBundleQueries.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <utility>
using namespace llvm;
using namespace llvm::PatternMatch;
static cl::opt<bool>
VerifyAssumptionCache("verify-assumption-cache", cl::Hidden,
cl::desc("Enable verification of assumption cache"),
SmallVector<AssumptionCache::ResultElem, 1> &
AssumptionCache::getOrInsertAffectedValues(Value *V) {
// Try using find_as first to avoid creating extra value handles just for the
// purpose of doing the lookup.
auto AVI = AffectedValues.find_as(V);
if (AVI != AffectedValues.end())
return AVI->second;
auto AVIP = AffectedValues.insert(
{AffectedValueCallbackVH(V, this), SmallVector<ResultElem, 1>()});
return AVIP.first->second;
static void
findAffectedValues(CallBase *CI, TargetTransformInfo *TTI,
SmallVectorImpl<AssumptionCache::ResultElem> &Affected) {
// Note: This code must be kept in-sync with the code in
// computeKnownBitsFromAssume in ValueTracking.
auto AddAffected = [&Affected](Value *V, unsigned Idx =
AssumptionCache::ExprResultIdx) {
if (isa<Argument>(V)) {
Affected.push_back({V, Idx});
} else if (auto *I = dyn_cast<Instruction>(V)) {
Affected.push_back({I, Idx});
// Peek through unary operators to find the source of the condition.
Value *Op;
if (match(I, m_BitCast(m_Value(Op))) ||
match(I, m_PtrToInt(m_Value(Op))) || match(I, m_Not(m_Value(Op)))) {
if (isa<Instruction>(Op) || isa<Argument>(Op))
Affected.push_back({Op, Idx});
for (unsigned Idx = 0; Idx != CI->getNumOperandBundles(); Idx++) {
if (CI->getOperandBundleAt(Idx).Inputs.size() > ABA_WasOn &&
CI->getOperandBundleAt(Idx).getTagName() != IgnoreBundleTag)
AddAffected(CI->getOperandBundleAt(Idx).Inputs[ABA_WasOn], Idx);
Value *Cond = CI->getArgOperand(0), *A, *B;
CmpInst::Predicate Pred;
if (match(Cond, m_ICmp(Pred, m_Value(A), m_Value(B)))) {
if (Pred == ICmpInst::ICMP_EQ) {
// For equality comparisons, we handle the case of bit inversion.
auto AddAffectedFromEq = [&AddAffected](Value *V) {
Value *A;
if (match(V, m_Not(m_Value(A)))) {
V = A;
Value *B;
// (A & B) or (A | B) or (A ^ B).
if (match(V, m_BitwiseLogic(m_Value(A), m_Value(B)))) {
// (A << C) or (A >>_s C) or (A >>_u C) where C is some constant.
} else if (match(V, m_Shift(m_Value(A), m_ConstantInt()))) {
Value *X;
// Handle (A + C1) u< C2, which is the canonical form of A > C3 && A < C4,
// and recognized by LVI at least.
if (Pred == ICmpInst::ICMP_ULT &&
match(A, m_Add(m_Value(X), m_ConstantInt())) &&
match(B, m_ConstantInt()))
if (TTI) {
const Value *Ptr;
unsigned AS;
std::tie(Ptr, AS) = TTI->getPredicatedAddrSpace(Cond);
if (Ptr)
AddAffected(const_cast<Value *>(Ptr->stripInBoundsOffsets()));
void AssumptionCache::updateAffectedValues(AssumeInst *CI) {
SmallVector<AssumptionCache::ResultElem, 16> Affected;
findAffectedValues(CI, TTI, Affected);
for (auto &AV : Affected) {
auto &AVV = getOrInsertAffectedValues(AV.Assume);
if (llvm::none_of(AVV, [&](ResultElem &Elem) {
return Elem.Assume == CI && Elem.Index == AV.Index;
AVV.push_back({CI, AV.Index});
void AssumptionCache::unregisterAssumption(AssumeInst *CI) {
SmallVector<AssumptionCache::ResultElem, 16> Affected;
findAffectedValues(CI, TTI, Affected);
for (auto &AV : Affected) {
auto AVI = AffectedValues.find_as(AV.Assume);
if (AVI == AffectedValues.end())
bool Found = false;
bool HasNonnull = false;
for (ResultElem &Elem : AVI->second) {
if (Elem.Assume == CI) {
Found = true;
Elem.Assume = nullptr;
HasNonnull |= !!Elem.Assume;
if (HasNonnull && Found)
assert(Found && "already unregistered or incorrect cache state");
if (!HasNonnull)
erase_value(AssumeHandles, CI);
void AssumptionCache::AffectedValueCallbackVH::deleted() {
// 'this' now dangles!
void AssumptionCache::transferAffectedValuesInCache(Value *OV, Value *NV) {
auto &NAVV = getOrInsertAffectedValues(NV);
auto AVI = AffectedValues.find(OV);
if (AVI == AffectedValues.end())
for (auto &A : AVI->second)
if (!llvm::is_contained(NAVV, A))
void AssumptionCache::AffectedValueCallbackVH::allUsesReplacedWith(Value *NV) {
if (!isa<Instruction>(NV) && !isa<Argument>(NV))
// Any assumptions that affected this value now affect the new value.
AC->transferAffectedValuesInCache(getValPtr(), NV);
// 'this' now might dangle! If the AffectedValues map was resized to add an
// entry for NV then this object might have been destroyed in favor of some
// copy in the grown map.
void AssumptionCache::scanFunction() {
assert(!Scanned && "Tried to scan the function twice!");
assert(AssumeHandles.empty() && "Already have assumes when scanning!");
// Go through all instructions in all blocks, add all calls to @llvm.assume
// to this cache.
for (BasicBlock &B : F)
for (Instruction &I : B)
if (isa<AssumeInst>(&I))
AssumeHandles.push_back({&I, ExprResultIdx});
// Mark the scan as complete.
Scanned = true;
// Update affected values.
for (auto &A : AssumeHandles)
void AssumptionCache::registerAssumption(AssumeInst *CI) {
// If we haven't scanned the function yet, just drop this assumption. It will
// be found when we scan later.
if (!Scanned)
AssumeHandles.push_back({CI, ExprResultIdx});
#ifndef NDEBUG
assert(CI->getParent() &&
"Cannot register @llvm.assume call not in a basic block");
assert(&F == CI->getParent()->getParent() &&
"Cannot register @llvm.assume call not in this function");
// We expect the number of assumptions to be small, so in an asserts build
// check that we don't accumulate duplicates and that all assumptions point
// to the same function.
SmallPtrSet<Value *, 16> AssumptionSet;
for (auto &VH : AssumeHandles) {
if (!VH)
assert(&F == cast<Instruction>(VH)->getParent()->getParent() &&
"Cached assumption not inside this function!");
assert(match(cast<CallInst>(VH), m_Intrinsic<Intrinsic::assume>()) &&
"Cached something other than a call to @llvm.assume!");
assert(AssumptionSet.insert(VH).second &&
"Cache contains multiple copies of a call!");
AssumptionCache AssumptionAnalysis::run(Function &F,
FunctionAnalysisManager &FAM) {
auto &TTI = FAM.getResult<TargetIRAnalysis>(F);
return AssumptionCache(F, &TTI);
AnalysisKey AssumptionAnalysis::Key;
PreservedAnalyses AssumptionPrinterPass::run(Function &F,
FunctionAnalysisManager &AM) {
AssumptionCache &AC = AM.getResult<AssumptionAnalysis>(F);
OS << "Cached assumptions for function: " << F.getName() << "\n";
for (auto &VH : AC.assumptions())
if (VH)
OS << " " << *cast<CallInst>(VH)->getArgOperand(0) << "\n";
return PreservedAnalyses::all();
void AssumptionCacheTracker::FunctionCallbackVH::deleted() {
auto I = ACT->AssumptionCaches.find_as(cast<Function>(getValPtr()));
if (I != ACT->AssumptionCaches.end())
// 'this' now dangles!
AssumptionCache &AssumptionCacheTracker::getAssumptionCache(Function &F) {
// We probe the function map twice to try and avoid creating a value handle
// around the function in common cases. This makes insertion a bit slower,
// but if we have to insert we're going to scan the whole function so that
// shouldn't matter.
auto I = AssumptionCaches.find_as(&F);
if (I != AssumptionCaches.end())
return *I->second;
auto *TTIWP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>();
auto *TTI = TTIWP ? &TTIWP->getTTI(F) : nullptr;
// Ok, build a new cache by scanning the function, insert it and the value
// handle into our map, and return the newly populated cache.
auto IP = AssumptionCaches.insert(std::make_pair(
FunctionCallbackVH(&F, this), std::make_unique<AssumptionCache>(F, TTI)));
assert(IP.second && "Scanning function already in the map?");
return *IP.first->second;
AssumptionCache *AssumptionCacheTracker::lookupAssumptionCache(Function &F) {
auto I = AssumptionCaches.find_as(&F);
if (I != AssumptionCaches.end())
return I->second.get();
return nullptr;
void AssumptionCacheTracker::verifyAnalysis() const {
// FIXME: In the long term the verifier should not be controllable with a
// flag. We should either fix all passes to correctly update the assumption
// cache and enable the verifier unconditionally or somehow arrange for the
// assumption list to be updated automatically by passes.
if (!VerifyAssumptionCache)
SmallPtrSet<const CallInst *, 4> AssumptionSet;
for (const auto &I : AssumptionCaches) {
for (auto &VH : I.second->assumptions())
if (VH)
for (const BasicBlock &B : cast<Function>(*I.first))
for (const Instruction &II : B)
if (match(&II, m_Intrinsic<Intrinsic::assume>()) &&
report_fatal_error("Assumption in scanned function not in cache");
AssumptionCacheTracker::AssumptionCacheTracker() : ImmutablePass(ID) {
AssumptionCacheTracker::~AssumptionCacheTracker() = default;
char AssumptionCacheTracker::ID = 0;
INITIALIZE_PASS(AssumptionCacheTracker, "assumption-cache-tracker",
"Assumption Cache Tracker", false, true)