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//===- BranchProbabilityInfoTest.cpp - BranchProbabilityInfo 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/BranchProbabilityInfo.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/AsmParser/Parser.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/DataTypes.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/raw_ostream.h"
#include "gtest/gtest.h"
namespace llvm {
namespace {
struct BranchProbabilityInfoTest : public testing::Test {
std::unique_ptr<BranchProbabilityInfo> BPI;
std::unique_ptr<DominatorTree> DT;
std::unique_ptr<LoopInfo> LI;
LLVMContext C;
BranchProbabilityInfo &buildBPI(Function &F) {
DT.reset(new DominatorTree(F));
LI.reset(new LoopInfo(*DT));
BPI.reset(new BranchProbabilityInfo(F, *LI));
return *BPI;
}
std::unique_ptr<Module> makeLLVMModule() {
const char *ModuleString = "define void @f() { exit: ret void }\n";
SMDiagnostic Err;
return parseAssemblyString(ModuleString, Err, C);
}
};
TEST_F(BranchProbabilityInfoTest, StressUnreachableHeuristic) {
auto M = makeLLVMModule();
Function *F = M->getFunction("f");
// define void @f() {
// entry:
// switch i32 poison, label %exit, [
// i32 0, label %preexit
// ... ;;< Add lots of cases to stress the heuristic.
// ]
// preexit:
// unreachable
// exit:
// ret void
// }
auto *ExitBB = &F->back();
auto *EntryBB = BasicBlock::Create(C, "entry", F, /*insertBefore=*/ExitBB);
auto *PreExitBB =
BasicBlock::Create(C, "preexit", F, /*insertBefore=*/ExitBB);
new UnreachableInst(C, PreExitBB);
unsigned NumCases = 4096;
auto *I32 = IntegerType::get(C, 32);
auto *Poison = PoisonValue::get(I32);
auto *Switch = SwitchInst::Create(Poison, ExitBB, NumCases, EntryBB);
for (unsigned I = 0; I < NumCases; ++I)
Switch->addCase(ConstantInt::get(I32, I), PreExitBB);
BranchProbabilityInfo &BPI = buildBPI(*F);
// FIXME: This doesn't seem optimal. Since all of the cases handled by the
// switch have the *same* destination block ("preexit"), shouldn't it be the
// hot one? I'd expect the results to be reversed here...
EXPECT_FALSE(BPI.isEdgeHot(EntryBB, PreExitBB));
EXPECT_TRUE(BPI.isEdgeHot(EntryBB, ExitBB));
}
TEST_F(BranchProbabilityInfoTest, SwapProbabilities) {
StringRef Assembly = R"(
define void @f() {
entry:
br label %loop
loop:
%iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
%iv.next = add i32 %iv, 1
%cond = icmp slt i32 %iv.next, 10
br i1 %cond, label %exit, label %loop
exit:
ret void
}
)";
LLVMContext Context;
SMDiagnostic Error;
auto M = parseAssemblyString(Assembly, Error, Context);
ASSERT_TRUE(M) << "Bad assembly?";
Function *F = M->getFunction("f");
auto *LoopHeaderBB = F->front().getSingleSuccessor();
ASSERT_TRUE(LoopHeaderBB != nullptr);
BranchInst *Branch = dyn_cast<BranchInst>(LoopHeaderBB->getTerminator());
ASSERT_TRUE(Branch != nullptr);
// Save the probabilities before successors swapping
BranchProbabilityInfo *BPI = &buildBPI(*F);
auto ProbEdge0 = BPI->getEdgeProbability(LoopHeaderBB, 0U);
auto ProbEdge1 = BPI->getEdgeProbability(LoopHeaderBB, 1U);
EXPECT_LT(ProbEdge0, ProbEdge1);
Branch->swapSuccessors();
BPI->swapSuccEdgesProbabilities(LoopHeaderBB);
// TODO: Check the probabilities are swapped as well as the edges
EXPECT_EQ(ProbEdge0, BPI->getEdgeProbability(LoopHeaderBB, 1U));
EXPECT_EQ(ProbEdge1, BPI->getEdgeProbability(LoopHeaderBB, 0U));
}
} // end anonymous namespace
} // end namespace llvm
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