diff --git a/lib/Analysis/ScalarEvolutionExpander.cpp b/lib/Analysis/ScalarEvolutionExpander.cpp index 86f714b930d..3ceda677ba6 100644 --- a/lib/Analysis/ScalarEvolutionExpander.cpp +++ b/lib/Analysis/ScalarEvolutionExpander.cpp @@ -187,8 +187,21 @@ Value *SCEVExpander::InsertBinop(Instruction::BinaryOps Opcode, // generated code. if (isa(IP)) ScanLimit++; + + // Conservatively, do not use any instruction which has any of wrap/exact + // flags installed. + // TODO: Instead of simply disable poison instructions we can be clever + // here and match SCEV to this instruction. + auto canGeneratePoison = [](Instruction *I) { + if (isa(I) && + (I->hasNoSignedWrap() || I->hasNoUnsignedWrap())) + return true; + if (isa(I) && I->isExact()) + return true; + return false; + }; if (IP->getOpcode() == (unsigned)Opcode && IP->getOperand(0) == LHS && - IP->getOperand(1) == RHS) + IP->getOperand(1) == RHS && !canGeneratePoison(&*IP)) return &*IP; if (IP == BlockBegin) break; } diff --git a/unittests/Analysis/ScalarEvolutionTest.cpp b/unittests/Analysis/ScalarEvolutionTest.cpp index e438e8af7aa..dffb68ac94f 100644 --- a/unittests/Analysis/ScalarEvolutionTest.cpp +++ b/unittests/Analysis/ScalarEvolutionTest.cpp @@ -1184,5 +1184,109 @@ TEST_F(ScalarEvolutionsTest, SCEVExpanderIsSafeToExpandAt) { EXPECT_TRUE(isSafeToExpandAt(AR, Post->getTerminator(), SE)); } +// Check that SCEV expander does not use the nuw instruction +// for expansion. +TEST_F(ScalarEvolutionsTest, SCEVExpanderNUW) { + /* + * Create the following code: + * func(i64 %a) + * entry: + * br false, label %exit, label %body + * body: + * %s1 = add i64 %a, -1 + * br label %exit + * exit: + * %s = add nuw i64 %a, -1 + * ret %s + */ + + // Create a module. + Module M("SCEVExpanderNUW", Context); + + Type *T_int64 = Type::getInt64Ty(Context); + + FunctionType *FTy = + FunctionType::get(Type::getVoidTy(Context), { T_int64 }, false); + Function *F = cast(M.getOrInsertFunction("func", FTy)); + Argument *Arg = &*F->arg_begin(); + ConstantInt *C = ConstantInt::get(Context, APInt(64, -1)); + + BasicBlock *Entry = BasicBlock::Create(Context, "entry", F); + BasicBlock *Body = BasicBlock::Create(Context, "body", F); + BasicBlock *Exit = BasicBlock::Create(Context, "exit", F); + + IRBuilder<> Builder(Entry); + ConstantInt *Cond = ConstantInt::get(Context, APInt(1, 0)); + Builder.CreateCondBr(Cond, Exit, Body); + + Builder.SetInsertPoint(Body); + auto *S1 = cast(Builder.CreateAdd(Arg, C, "add")); + Builder.CreateBr(Exit); + + Builder.SetInsertPoint(Exit); + auto *S2 = cast(Builder.CreateAdd(Arg, C, "add")); + S2->setHasNoUnsignedWrap(true); + auto *R = cast(Builder.CreateRetVoid()); + + ScalarEvolution SE = buildSE(*F); + const SCEV *S = SE.getSCEV(S1); + EXPECT_TRUE(isa(S)); + SCEVExpander Exp(SE, M.getDataLayout(), "expander"); + auto *I = cast(Exp.expandCodeFor(S, nullptr, R)); + EXPECT_FALSE(I->hasNoUnsignedWrap()); +} + +// Check that SCEV expander does not use the nsw instruction +// for expansion. +TEST_F(ScalarEvolutionsTest, SCEVExpanderNSW) { + /* + * Create the following code: + * func(i64 %a) + * entry: + * br false, label %exit, label %body + * body: + * %s1 = add i64 %a, -1 + * br label %exit + * exit: + * %s = add nsw i64 %a, -1 + * ret %s + */ + + // Create a module. + Module M("SCEVExpanderNSW", Context); + + Type *T_int64 = Type::getInt64Ty(Context); + + FunctionType *FTy = + FunctionType::get(Type::getVoidTy(Context), { T_int64 }, false); + Function *F = cast(M.getOrInsertFunction("func", FTy)); + Argument *Arg = &*F->arg_begin(); + ConstantInt *C = ConstantInt::get(Context, APInt(64, -1)); + + BasicBlock *Entry = BasicBlock::Create(Context, "entry", F); + BasicBlock *Body = BasicBlock::Create(Context, "body", F); + BasicBlock *Exit = BasicBlock::Create(Context, "exit", F); + + IRBuilder<> Builder(Entry); + ConstantInt *Cond = ConstantInt::get(Context, APInt(1, 0)); + Builder.CreateCondBr(Cond, Exit, Body); + + Builder.SetInsertPoint(Body); + auto *S1 = cast(Builder.CreateAdd(Arg, C, "add")); + Builder.CreateBr(Exit); + + Builder.SetInsertPoint(Exit); + auto *S2 = cast(Builder.CreateAdd(Arg, C, "add")); + S2->setHasNoSignedWrap(true); + auto *R = cast(Builder.CreateRetVoid()); + + ScalarEvolution SE = buildSE(*F); + const SCEV *S = SE.getSCEV(S1); + EXPECT_TRUE(isa(S)); + SCEVExpander Exp(SE, M.getDataLayout(), "expander"); + auto *I = cast(Exp.expandCodeFor(S, nullptr, R)); + EXPECT_FALSE(I->hasNoSignedWrap()); +} + } // end anonymous namespace } // end namespace llvm