1 //===- BranchProbabilityInfoTest.cpp - BranchProbabilityInfo unit tests ---===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #include "llvm/Analysis/BranchProbabilityInfo.h"
11 #include "llvm/Analysis/LoopInfo.h"
12 #include "llvm/AsmParser/Parser.h"
13 #include "llvm/IR/BasicBlock.h"
14 #include "llvm/IR/Constants.h"
15 #include "llvm/IR/Dominators.h"
16 #include "llvm/IR/Instructions.h"
17 #include "llvm/IR/Function.h"
18 #include "llvm/IR/LLVMContext.h"
19 #include "llvm/IR/Module.h"
20 #include "llvm/Support/DataTypes.h"
21 #include "llvm/Support/SourceMgr.h"
22 #include "llvm/Support/raw_ostream.h"
23 #include "gtest/gtest.h"
24 
25 namespace llvm {
26 namespace {
27 
28 struct BranchProbabilityInfoTest : public testing::Test {
29   std::unique_ptr<BranchProbabilityInfo> BPI;
30   std::unique_ptr<DominatorTree> DT;
31   std::unique_ptr<LoopInfo> LI;
32   LLVMContext C;
33 
34   BranchProbabilityInfo &buildBPI(Function &F) {
35     DT.reset(new DominatorTree(F));
36     LI.reset(new LoopInfo(*DT));
37     BPI.reset(new BranchProbabilityInfo(F, *LI));
38     return *BPI;
39   }
40 
41   std::unique_ptr<Module> makeLLVMModule() {
42     const char *ModuleString = "define void @f() { exit: ret void }\n";
43     SMDiagnostic Err;
44     return parseAssemblyString(ModuleString, Err, C);
45   }
46 };
47 
48 TEST_F(BranchProbabilityInfoTest, StressUnreachableHeuristic) {
49   auto M = makeLLVMModule();
50   Function *F = M->getFunction("f");
51 
52   // define void @f() {
53   // entry:
54   //   switch i32 undef, label %exit, [
55   //      i32 0, label %preexit
56   //      ...                   ;;< Add lots of cases to stress the heuristic.
57   //   ]
58   // preexit:
59   //   unreachable
60   // exit:
61   //   ret void
62   // }
63 
64   auto *ExitBB = &F->back();
65   auto *EntryBB = BasicBlock::Create(C, "entry", F, /*insertBefore=*/ExitBB);
66 
67   auto *PreExitBB =
68       BasicBlock::Create(C, "preexit", F, /*insertBefore=*/ExitBB);
69   new UnreachableInst(C, PreExitBB);
70 
71   unsigned NumCases = 4096;
72   auto *I32 = IntegerType::get(C, 32);
73   auto *Undef = UndefValue::get(I32);
74   auto *Switch = SwitchInst::Create(Undef, ExitBB, NumCases, EntryBB);
75   for (unsigned I = 0; I < NumCases; ++I)
76     Switch->addCase(ConstantInt::get(I32, I), PreExitBB);
77 
78   BranchProbabilityInfo &BPI = buildBPI(*F);
79 
80   // FIXME: This doesn't seem optimal. Since all of the cases handled by the
81   // switch have the *same* destination block ("preexit"), shouldn't it be the
82   // hot one? I'd expect the results to be reversed here...
83   EXPECT_FALSE(BPI.isEdgeHot(EntryBB, PreExitBB));
84   EXPECT_TRUE(BPI.isEdgeHot(EntryBB, ExitBB));
85 }
86 
87 } // end anonymous namespace
88 } // end namespace llvm
89