unittests/Analysis/BranchProbabilityInfoTest.cpp

   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/Function.h"
  17 #include "llvm/IR/Instructions.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