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llvm-mirror/unittests/Analysis/AliasAnalysisTest.cpp
Nikita Popov c2d5b85909 [BasicAA] Fix BatchAA results for phi-phi assumptions 
Change the way NoAlias assumptions in BasicAA are handled. Instead of
handling this inside the phi-phi code, always initially insert a
NoAlias result into the map and keep track whether it is used.
If it is used, then we require that we also get back NoAlias from
the recursive queries. Otherwise, the entry is changed to MayAlias.

Additionally, keep track of all location pairs we inserted that may
still be based on assumptions higher up. If it turns out one of those
assumptions is incorrect, we flush them from the cache.

The compile-time impact for the new implementation is significantly
higher than the previous iteration of this patch:
https://llvm-compile-time-tracker.com/compare.php?from=c0bb9859de6991cc233e2dedb978dd118da8c382&to=c07112373279143e37568b5bcd293daf81a35973&stat=instructions
However, it should avoid the exponential runtime cases we run into
if we don't cache assumption-based results entirely.

This also produces better results in some cases, because NoAlias
assumptions can now start at any root, rather than just phi-phi pairs.
This is not just relevant for analysis quality, but also for BatchAA
consistency: Otherwise, results would once again depend on query order,
though at least they wouldn't be wrong.

This ended up both more complicated and more expensive than I hoped,
but I wasn't able to come up with another solution that satisfies all
the constraints.

Differential Revision: https://reviews.llvm.org/D91936
2021-01-06 22:15:30 +01:00

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//===--- AliasAnalysisTest.cpp - Mixed TBAA unit tests --------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/BasicAliasAnalysis.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/AsmParser/Parser.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/IR/Module.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/SourceMgr.h"
#include "gtest/gtest.h"
using namespace llvm;
// Set up some test passes.
namespace llvm {
void initializeAATestPassPass(PassRegistry&);
void initializeTestCustomAAWrapperPassPass(PassRegistry&);
}
namespace {
struct AATestPass : FunctionPass {
static char ID;
AATestPass() : FunctionPass(ID) {
initializeAATestPassPass(*PassRegistry::getPassRegistry());
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AAResultsWrapperPass>();
AU.setPreservesAll();
}
bool runOnFunction(Function &F) override {
AliasAnalysis &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
SetVector<Value *> Pointers;
for (Argument &A : F.args())
if (A.getType()->isPointerTy())
Pointers.insert(&A);
for (Instruction &I : instructions(F))
if (I.getType()->isPointerTy())
Pointers.insert(&I);
for (Value *P1 : Pointers)
for (Value *P2 : Pointers)
(void)AA.alias(P1, LocationSize::beforeOrAfterPointer(), P2,
LocationSize::beforeOrAfterPointer());
return false;
}
};
}
char AATestPass::ID = 0;
INITIALIZE_PASS_BEGIN(AATestPass, "aa-test-pas", "Alias Analysis Test Pass",
false, true)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_END(AATestPass, "aa-test-pass", "Alias Analysis Test Pass",
false, true)
namespace {
/// A test customizable AA result. It merely accepts a callback to run whenever
/// it receives an alias query. Useful for testing that a particular AA result
/// is reached.
struct TestCustomAAResult : AAResultBase<TestCustomAAResult> {
friend AAResultBase<TestCustomAAResult>;
std::function<void()> CB;
explicit TestCustomAAResult(std::function<void()> CB)
: AAResultBase(), CB(std::move(CB)) {}
TestCustomAAResult(TestCustomAAResult &&Arg)
: AAResultBase(std::move(Arg)), CB(std::move(Arg.CB)) {}
bool invalidate(Function &, const PreservedAnalyses &) { return false; }
AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB,
AAQueryInfo &AAQI) {
CB();
return MayAlias;
}
};
}
namespace {
/// A wrapper pass for the legacy pass manager to use with the above custom AA
/// result.
class TestCustomAAWrapperPass : public ImmutablePass {
std::function<void()> CB;
std::unique_ptr<TestCustomAAResult> Result;
public:
static char ID;
explicit TestCustomAAWrapperPass(
std::function<void()> CB = std::function<void()>())
: ImmutablePass(ID), CB(std::move(CB)) {
initializeTestCustomAAWrapperPassPass(*PassRegistry::getPassRegistry());
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesAll();
AU.addRequired<TargetLibraryInfoWrapperPass>();
}
bool doInitialization(Module &M) override {
Result.reset(new TestCustomAAResult(std::move(CB)));
return true;
}
bool doFinalization(Module &M) override {
Result.reset();
return true;
}
TestCustomAAResult &getResult() { return *Result; }
const TestCustomAAResult &getResult() const { return *Result; }
};
}
char TestCustomAAWrapperPass::ID = 0;
INITIALIZE_PASS_BEGIN(TestCustomAAWrapperPass, "test-custom-aa",
"Test Custom AA Wrapper Pass", false, true)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(TestCustomAAWrapperPass, "test-custom-aa",
"Test Custom AA Wrapper Pass", false, true)
namespace {
class AliasAnalysisTest : public testing::Test {
protected:
LLVMContext C;
Module M;
TargetLibraryInfoImpl TLII;
TargetLibraryInfo TLI;
std::unique_ptr<AssumptionCache> AC;
std::unique_ptr<BasicAAResult> BAR;
std::unique_ptr<AAResults> AAR;
AliasAnalysisTest() : M("AliasAnalysisTest", C), TLI(TLII) {}
AAResults &getAAResults(Function &F) {
// Reset the Function AA results first to clear out any references.
AAR.reset(new AAResults(TLI));
// Build the various AA results and register them.
AC.reset(new AssumptionCache(F));
BAR.reset(new BasicAAResult(M.getDataLayout(), F, TLI, *AC));
AAR->addAAResult(*BAR);
return *AAR;
}
};
TEST_F(AliasAnalysisTest, getModRefInfo) {
// Setup function.
FunctionType *FTy =
FunctionType::get(Type::getVoidTy(C), std::vector<Type *>(), false);
auto *F = Function::Create(FTy, Function::ExternalLinkage, "f", M);
auto *BB = BasicBlock::Create(C, "entry", F);
auto IntType = Type::getInt32Ty(C);
auto PtrType = Type::getInt32PtrTy(C);
auto *Value = ConstantInt::get(IntType, 42);
auto *Addr = ConstantPointerNull::get(PtrType);
auto Alignment = Align(IntType->getBitWidth() / 8);
auto *Store1 = new StoreInst(Value, Addr, BB);
auto *Load1 = new LoadInst(IntType, Addr, "load", BB);
auto *Add1 = BinaryOperator::CreateAdd(Value, Value, "add", BB);
auto *VAArg1 = new VAArgInst(Addr, PtrType, "vaarg", BB);
auto *CmpXChg1 = new AtomicCmpXchgInst(
Addr, ConstantInt::get(IntType, 0), ConstantInt::get(IntType, 1),
Alignment, AtomicOrdering::Monotonic, AtomicOrdering::Monotonic,
SyncScope::System, BB);
auto *AtomicRMW = new AtomicRMWInst(
AtomicRMWInst::Xchg, Addr, ConstantInt::get(IntType, 1), Alignment,
AtomicOrdering::Monotonic, SyncScope::System, BB);
ReturnInst::Create(C, nullptr, BB);
auto &AA = getAAResults(*F);
// Check basic results
EXPECT_EQ(AA.getModRefInfo(Store1, MemoryLocation()), ModRefInfo::Mod);
EXPECT_EQ(AA.getModRefInfo(Store1, None), ModRefInfo::Mod);
EXPECT_EQ(AA.getModRefInfo(Load1, MemoryLocation()), ModRefInfo::Ref);
EXPECT_EQ(AA.getModRefInfo(Load1, None), ModRefInfo::Ref);
EXPECT_EQ(AA.getModRefInfo(Add1, MemoryLocation()), ModRefInfo::NoModRef);
EXPECT_EQ(AA.getModRefInfo(Add1, None), ModRefInfo::NoModRef);
EXPECT_EQ(AA.getModRefInfo(VAArg1, MemoryLocation()), ModRefInfo::ModRef);
EXPECT_EQ(AA.getModRefInfo(VAArg1, None), ModRefInfo::ModRef);
EXPECT_EQ(AA.getModRefInfo(CmpXChg1, MemoryLocation()), ModRefInfo::ModRef);
EXPECT_EQ(AA.getModRefInfo(CmpXChg1, None), ModRefInfo::ModRef);
EXPECT_EQ(AA.getModRefInfo(AtomicRMW, MemoryLocation()), ModRefInfo::ModRef);
EXPECT_EQ(AA.getModRefInfo(AtomicRMW, None), ModRefInfo::ModRef);
}
static Instruction *getInstructionByName(Function &F, StringRef Name) {
for (auto &I : instructions(F))
if (I.getName() == Name)
return &I;
llvm_unreachable("Expected to find instruction!");
}
TEST_F(AliasAnalysisTest, BatchAAPhiCycles) {
LLVMContext C;
SMDiagnostic Err;
std::unique_ptr<Module> M = parseAssemblyString(R"(
define void @f(i8* noalias %a, i1 %c) {
entry:
br label %loop
loop:
%phi = phi i8* [ null, %entry ], [ %a2, %loop ]
%offset1 = phi i64 [ 0, %entry ], [ %offset2, %loop]
%offset2 = add i64 %offset1, 1
%a1 = getelementptr i8, i8* %a, i64 %offset1
%a2 = getelementptr i8, i8* %a, i64 %offset2
%s1 = select i1 %c, i8* %a1, i8* %phi
%s2 = select i1 %c, i8* %a2, i8* %a1
br label %loop
}
)", Err, C);
Function *F = M->getFunction("f");
Instruction *Phi = getInstructionByName(*F, "phi");
Instruction *A1 = getInstructionByName(*F, "a1");
Instruction *A2 = getInstructionByName(*F, "a2");
Instruction *S1 = getInstructionByName(*F, "s1");
Instruction *S2 = getInstructionByName(*F, "s2");
MemoryLocation PhiLoc(Phi, LocationSize::precise(1));
MemoryLocation A1Loc(A1, LocationSize::precise(1));
MemoryLocation A2Loc(A2, LocationSize::precise(1));
MemoryLocation S1Loc(S1, LocationSize::precise(1));
MemoryLocation S2Loc(S2, LocationSize::precise(1));
auto &AA = getAAResults(*F);
EXPECT_EQ(NoAlias, AA.alias(A1Loc, A2Loc));
EXPECT_EQ(MayAlias, AA.alias(PhiLoc, A1Loc));
EXPECT_EQ(MayAlias, AA.alias(S1Loc, S2Loc));
BatchAAResults BatchAA(AA);
EXPECT_EQ(NoAlias, BatchAA.alias(A1Loc, A2Loc));
EXPECT_EQ(MayAlias, BatchAA.alias(PhiLoc, A1Loc));
EXPECT_EQ(MayAlias, BatchAA.alias(S1Loc, S2Loc));
BatchAAResults BatchAA2(AA);
EXPECT_EQ(NoAlias, BatchAA2.alias(A1Loc, A2Loc));
EXPECT_EQ(MayAlias, BatchAA2.alias(S1Loc, S2Loc));
EXPECT_EQ(MayAlias, BatchAA2.alias(PhiLoc, A1Loc));
}
TEST_F(AliasAnalysisTest, BatchAAPhiAssumption) {
LLVMContext C;
SMDiagnostic Err;
std::unique_ptr<Module> M = parseAssemblyString(R"(
define void @f(i8* %a.base, i8* %b.base, i1 %c) {
entry:
br label %loop
loop:
%a = phi i8* [ %a.next, %loop ], [ %a.base, %entry ]
%b = phi i8* [ %b.next, %loop ], [ %b.base, %entry ]
%a.next = getelementptr i8, i8* %a, i64 1
%b.next = getelementptr i8, i8* %b, i64 1
br label %loop
}
)", Err, C);
Function *F = M->getFunction("f");
Instruction *A = getInstructionByName(*F, "a");
Instruction *B = getInstructionByName(*F, "b");
Instruction *ANext = getInstructionByName(*F, "a.next");
Instruction *BNext = getInstructionByName(*F, "b.next");
MemoryLocation ALoc(A, LocationSize::precise(1));
MemoryLocation BLoc(B, LocationSize::precise(1));
MemoryLocation ANextLoc(ANext, LocationSize::precise(1));
MemoryLocation BNextLoc(BNext, LocationSize::precise(1));
auto &AA = getAAResults(*F);
EXPECT_EQ(MayAlias, AA.alias(ALoc, BLoc));
EXPECT_EQ(MayAlias, AA.alias(ANextLoc, BNextLoc));
BatchAAResults BatchAA(AA);
EXPECT_EQ(MayAlias, BatchAA.alias(ALoc, BLoc));
EXPECT_EQ(MayAlias, BatchAA.alias(ANextLoc, BNextLoc));
}
class AAPassInfraTest : public testing::Test {
protected:
LLVMContext C;
SMDiagnostic Err;
std::unique_ptr<Module> M;
public:
AAPassInfraTest()
: M(parseAssemblyString("define i32 @f(i32* %x, i32* %y) {\n"
"entry:\n"
" %lx = load i32, i32* %x\n"
" %ly = load i32, i32* %y\n"
" %sum = add i32 %lx, %ly\n"
" ret i32 %sum\n"
"}\n",
Err, C)) {
assert(M && "Failed to build the module!");
}
};
TEST_F(AAPassInfraTest, injectExternalAA) {
legacy::PassManager PM;
// Register our custom AA's wrapper pass manually.
bool IsCustomAAQueried = false;
PM.add(new TestCustomAAWrapperPass([&] { IsCustomAAQueried = true; }));
// Now add the external AA wrapper with a lambda which queries for the
// wrapper around our custom AA and adds it to the results.
PM.add(createExternalAAWrapperPass([](Pass &P, Function &, AAResults &AAR) {
if (auto *WrapperPass = P.getAnalysisIfAvailable<TestCustomAAWrapperPass>())
AAR.addAAResult(WrapperPass->getResult());
}));
// And run a pass that will make some alias queries. This will automatically
// trigger the rest of the alias analysis stack to be run. It is analagous to
// building a full pass pipeline with any of the existing pass manager
// builders.
PM.add(new AATestPass());
PM.run(*M);
// Finally, ensure that our custom AA was indeed queried.
EXPECT_TRUE(IsCustomAAQueried);
}
} // end anonymous namspace
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