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896c96fa1e
BPI may trigger signed overflow UB while computing branch probabilities for
cold calls or to unreachables. For example, with our current choice of weights,
we'll crash if there are >= 2^12 branches to an unreachable.
Use a safer BranchProbability constructor which is better at handling fractions
with large denominators.
Changes since the initial commit:
- Use explicit casts to ensure that multiplication operands are 64-bit
ints.
rdar://problem/29368161
Differential Revision: https://reviews.llvm.org/D27862
llvm-svn: 290022
89 lines
2.7 KiB
C++
89 lines
2.7 KiB
C++
//===- BranchProbabilityInfoTest.cpp - BranchProbabilityInfo unit tests ---===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/BranchProbabilityInfo.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/AsmParser/Parser.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Support/DataTypes.h"
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#include "llvm/Support/SourceMgr.h"
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#include "llvm/Support/raw_ostream.h"
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#include "gtest/gtest.h"
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namespace llvm {
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namespace {
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struct BranchProbabilityInfoTest : public testing::Test {
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std::unique_ptr<BranchProbabilityInfo> BPI;
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std::unique_ptr<DominatorTree> DT;
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std::unique_ptr<LoopInfo> LI;
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LLVMContext C;
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BranchProbabilityInfo &buildBPI(Function &F) {
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DT.reset(new DominatorTree(F));
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LI.reset(new LoopInfo(*DT));
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BPI.reset(new BranchProbabilityInfo(F, *LI));
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return *BPI;
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}
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std::unique_ptr<Module> makeLLVMModule() {
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const char *ModuleString = "define void @f() { exit: ret void }\n";
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SMDiagnostic Err;
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return parseAssemblyString(ModuleString, Err, C);
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}
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};
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TEST_F(BranchProbabilityInfoTest, StressUnreachableHeuristic) {
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auto M = makeLLVMModule();
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Function *F = M->getFunction("f");
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// define void @f() {
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// entry:
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// switch i32 undef, label %exit, [
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// i32 0, label %preexit
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// ... ;;< Add lots of cases to stress the heuristic.
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// ]
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// preexit:
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// unreachable
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// exit:
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// ret void
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// }
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auto *ExitBB = &F->back();
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auto *EntryBB = BasicBlock::Create(C, "entry", F, /*insertBefore=*/ExitBB);
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auto *PreExitBB =
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BasicBlock::Create(C, "preexit", F, /*insertBefore=*/ExitBB);
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new UnreachableInst(C, PreExitBB);
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unsigned NumCases = 4096;
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auto *I32 = IntegerType::get(C, 32);
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auto *Undef = UndefValue::get(I32);
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auto *Switch = SwitchInst::Create(Undef, ExitBB, NumCases, EntryBB);
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for (unsigned I = 0; I < NumCases; ++I)
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Switch->addCase(ConstantInt::get(I32, I), PreExitBB);
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BranchProbabilityInfo &BPI = buildBPI(*F);
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// FIXME: This doesn't seem optimal. Since all of the cases handled by the
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// switch have the *same* destination block ("preexit"), shouldn't it be the
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// hot one? I'd expect the results to be reversed here...
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EXPECT_FALSE(BPI.isEdgeHot(EntryBB, PreExitBB));
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EXPECT_TRUE(BPI.isEdgeHot(EntryBB, ExitBB));
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}
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} // end anonymous namespace
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} // end namespace llvm
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