1 //===- BranchProbabilityInfoTest.cpp - BranchProbabilityInfo unit tests ---===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "llvm/Analysis/BranchProbabilityInfo.h"
10 #include "llvm/Analysis/LoopInfo.h"
11 #include "llvm/AsmParser/Parser.h"
12 #include "llvm/IR/BasicBlock.h"
13 #include "llvm/IR/Constants.h"
14 #include "llvm/IR/Dominators.h"
15 #include "llvm/IR/Function.h"
16 #include "llvm/IR/Instructions.h"
17 #include "llvm/IR/LLVMContext.h"
18 #include "llvm/IR/Module.h"
19 #include "llvm/Support/DataTypes.h"
20 #include "llvm/Support/SourceMgr.h"
21 #include "llvm/Support/raw_ostream.h"
22 #include "gtest/gtest.h"
23 
24 namespace llvm {
25 namespace {
26 
27 struct BranchProbabilityInfoTest : public testing::Test {
28   std::unique_ptr<BranchProbabilityInfo> BPI;
29   std::unique_ptr<DominatorTree> DT;
30   std::unique_ptr<LoopInfo> LI;
31   LLVMContext C;
32 
33   BranchProbabilityInfo &buildBPI(Function &F) {
34     DT.reset(new DominatorTree(F));
35     LI.reset(new LoopInfo(*DT));
36     BPI.reset(new BranchProbabilityInfo(F, *LI));
37     return *BPI;
38   }
39 
40   std::unique_ptr<Module> makeLLVMModule() {
41     const char *ModuleString = "define void @f() { exit: ret void }\n";
42     SMDiagnostic Err;
43     return parseAssemblyString(ModuleString, Err, C);
44   }
45 };
46 
47 TEST_F(BranchProbabilityInfoTest, StressUnreachableHeuristic) {
48   auto M = makeLLVMModule();
49   Function *F = M->getFunction("f");
50 
51   // define void @f() {
52   // entry:
53   //   switch i32 undef, label %exit, [
54   //      i32 0, label %preexit
55   //      ...                   ;;< Add lots of cases to stress the heuristic.
56   //   ]
57   // preexit:
58   //   unreachable
59   // exit:
60   //   ret void
61   // }
62 
63   auto *ExitBB = &F->back();
64   auto *EntryBB = BasicBlock::Create(C, "entry", F, /*insertBefore=*/ExitBB);
65 
66   auto *PreExitBB =
67       BasicBlock::Create(C, "preexit", F, /*insertBefore=*/ExitBB);
68   new UnreachableInst(C, PreExitBB);
69 
70   unsigned NumCases = 4096;
71   auto *I32 = IntegerType::get(C, 32);
72   auto *Undef = UndefValue::get(I32);
73   auto *Switch = SwitchInst::Create(Undef, ExitBB, NumCases, EntryBB);
74   for (unsigned I = 0; I < NumCases; ++I)
75     Switch->addCase(ConstantInt::get(I32, I), PreExitBB);
76 
77   BranchProbabilityInfo &BPI = buildBPI(*F);
78 
79   // FIXME: This doesn't seem optimal. Since all of the cases handled by the
80   // switch have the *same* destination block ("preexit"), shouldn't it be the
81   // hot one? I'd expect the results to be reversed here...
82   EXPECT_FALSE(BPI.isEdgeHot(EntryBB, PreExitBB));
83   EXPECT_TRUE(BPI.isEdgeHot(EntryBB, ExitBB));
84 }
85 
86 } // end anonymous namespace
87 } // end namespace llvm
88