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[SCEV] Fix for PR42397. SCEVExpander wrongly adds nsw to shl instruction.

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Change-Id: I76c9f628c092ae3e6e78ebdaf55cec726e25d692
llvm-svn: 365363
This commit is contained in:
Denis Bakhvalov 2019-07-08 18:03:43 +00:00
parent e52525bbb5
commit bdc34231f3
2 changed files with 47 additions and 2 deletions
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8
lib/Analysis/ScalarEvolutionExpander.cpp
View File

@ -838,9 +838,13 @@ Value *SCEVExpander::visitMulExpr(const SCEVMulExpr *S) {
if (match(W, m_Power2(RHS))) {
// Canonicalize Prod*(1<<C) to Prod<<C.
assert(!Ty->isVectorTy() && "vector types are not SCEVable");
auto NWFlags = S->getNoWrapFlags();
// clear nsw flag if shl will produce poison value.
if (RHS->logBase2() == RHS->getBitWidth() - 1)
NWFlags = ScalarEvolution::clearFlags(NWFlags, SCEV::FlagNSW);
Prod = InsertBinop(Instruction::Shl, Prod,
ConstantInt::get(Ty, RHS->logBase2()),
S->getNoWrapFlags(), /*IsSafeToHoist*/ true);
ConstantInt::get(Ty, RHS->logBase2()), NWFlags,
/*IsSafeToHoist*/ true);
} else {
Prod = InsertBinop(Instruction::Mul, Prod, W, S->getNoWrapFlags(),
/*IsSafeToHoist*/ true);

41
unittests/Analysis/ScalarEvolutionTest.cpp
View File

@ -1637,5 +1637,46 @@ TEST_F(ScalarEvolutionsTest, SCEVExpandInsertCanonicalIV) {
TestMatchingCanonicalIV(GetAR2, ARBitWidth);
}
TEST_F(ScalarEvolutionsTest, SCEVExpanderShlNSW) {
auto checkOneCase = [this](std::string &&str) {
LLVMContext C;
SMDiagnostic Err;
std::unique_ptr<Module> M = parseAssemblyString(str, Err, C);
assert(M && "Could not parse module?");
assert(!verifyModule(*M) && "Must have been well formed!");
Function *F = M->getFunction("f");
ASSERT_NE(F, nullptr) << "Could not find function 'f'";
BasicBlock &Entry = F->getEntryBlock();
LoadInst *Load = cast<LoadInst>(&Entry.front());
BinaryOperator *And = cast<BinaryOperator>(*Load->user_begin());
ScalarEvolution SE = buildSE(*F);
const SCEV *AndSCEV = SE.getSCEV(And);
EXPECT_TRUE(isa<SCEVMulExpr>(AndSCEV));
EXPECT_TRUE(cast<SCEVMulExpr>(AndSCEV)->hasNoSignedWrap());
SCEVExpander Exp(SE, M->getDataLayout(), "expander");
auto *I = cast<Instruction>(Exp.expandCodeFor(AndSCEV, nullptr, And));
EXPECT_EQ(I->getOpcode(), Instruction::Shl);
EXPECT_FALSE(I->hasNoSignedWrap());
};
checkOneCase("define void @f(i16* %arrayidx) { "
" %1 = load i16, i16* %arrayidx "
" %2 = and i16 %1, -32768 "
" ret void "
"} ");
checkOneCase("define void @f(i8* %arrayidx) { "
" %1 = load i8, i8* %arrayidx "
" %2 = and i8 %1, -128 "
" ret void "
"} ");
}
} // end anonymous namespace
} // end namespace llvm