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[ConstantRange] Add urem support

Add urem support to ConstantRange, so we can handle in in LVI. This
is an approximate implementation that tries to capture the most useful
conditions: If the LHS is always strictly smaller than the RHS, then
the urem is a no-op and the result is the same as the LHS range.
Otherwise the lower bound is zero and the upper bound is
min(LHSMax, RHSMax - 1).

Differential Revision: https://reviews.llvm.org/D60952

llvm-svn: 359019
This commit is contained in:
Nikita Popov 2019-04-23 18:00:17 +00:00
parent 9e41add586
commit b34570041b
3 changed files with 74 additions and 8 deletions

View File

@ -356,6 +356,11 @@ public:
/// \p Other.
ConstantRange udiv(const ConstantRange &Other) const;
/// Return a new range representing the possible values resulting
/// from an unsigned remainder operation of a value in this range and a
/// value in \p Other.
ConstantRange urem(const ConstantRange &Other) const;
/// Return a new range representing the possible values resulting
/// from a binary-and of a value in this range by a value in \p Other.
ConstantRange binaryAnd(const ConstantRange &Other) const;

View File

@ -794,6 +794,8 @@ ConstantRange ConstantRange::binaryOp(Instruction::BinaryOps BinOp,
return multiply(Other);
case Instruction::UDiv:
return udiv(Other);
case Instruction::URem:
return urem(Other);
case Instruction::Shl:
return shl(Other);
case Instruction::LShr:
@ -991,6 +993,19 @@ ConstantRange::udiv(const ConstantRange &RHS) const {
return getNonEmpty(std::move(Lower), std::move(Upper));
}
ConstantRange ConstantRange::urem(const ConstantRange &RHS) const {
if (isEmptySet() || RHS.isEmptySet() || RHS.getUnsignedMax().isNullValue())
return getEmpty();
// L % R for L < R is L.
if (getUnsignedMax().ult(RHS.getUnsignedMin()))
return *this;
// L % R is <= L and < R.
APInt Upper = APIntOps::umin(getUnsignedMax(), RHS.getUnsignedMax() - 1) + 1;
return getNonEmpty(APInt::getNullValue(getBitWidth()), std::move(Upper));
}
ConstantRange
ConstantRange::binaryAnd(const ConstantRange &Other) const {
if (isEmptySet() || Other.isEmptySet())

View File

@ -59,20 +59,19 @@ static void ForeachNumInConstantRange(const ConstantRange &CR, Fn TestFn) {
}
template<typename Fn1, typename Fn2>
static void TestUnsignedBinOpExhaustive(Fn1 RangeFn, Fn2 IntFn) {
static void TestUnsignedBinOpExhaustive(
Fn1 RangeFn, Fn2 IntFn,
bool SkipZeroRHS = false, bool CorrectnessOnly = false) {
unsigned Bits = 4;
EnumerateTwoConstantRanges(Bits, [&](const ConstantRange &CR1,
const ConstantRange &CR2) {
ConstantRange CR = RangeFn(CR1, CR2);
if (CR1.isEmptySet() || CR2.isEmptySet()) {
EXPECT_TRUE(CR.isEmptySet());
return;
}
APInt Min = APInt::getMaxValue(Bits);
APInt Max = APInt::getMinValue(Bits);
ForeachNumInConstantRange(CR1, [&](const APInt &N1) {
ForeachNumInConstantRange(CR2, [&](const APInt &N2) {
if (SkipZeroRHS && N2 == 0)
return;
APInt N = IntFn(N1, N2);
if (N.ult(Min))
Min = N;
@ -81,7 +80,18 @@ static void TestUnsignedBinOpExhaustive(Fn1 RangeFn, Fn2 IntFn) {
});
});
EXPECT_EQ(ConstantRange::getNonEmpty(Min, Max + 1), CR);
ConstantRange CR = RangeFn(CR1, CR2);
if (Min.ugt(Max)) {
EXPECT_TRUE(CR.isEmptySet());
return;
}
ConstantRange Exact = ConstantRange::getNonEmpty(Min, Max + 1);
if (CorrectnessOnly) {
EXPECT_TRUE(CR.contains(Exact));
} else {
EXPECT_EQ(Exact, CR);
}
});
}
@ -813,6 +823,42 @@ TEST_F(ConstantRangeTest, UDiv) {
EXPECT_EQ(Wrap.udiv(Wrap), Full);
}
TEST_F(ConstantRangeTest, URem) {
EXPECT_EQ(Full.urem(Empty), Empty);
EXPECT_EQ(Empty.urem(Full), Empty);
// urem by zero is poison.
EXPECT_EQ(Full.urem(ConstantRange(APInt(16, 0))), Empty);
// urem by full range doesn't contain MaxValue.
EXPECT_EQ(Full.urem(Full), ConstantRange(APInt(16, 0), APInt(16, 0xffff)));
// urem is upper bounded by maximum RHS minus one.
EXPECT_EQ(Full.urem(ConstantRange(APInt(16, 0), APInt(16, 123))),
ConstantRange(APInt(16, 0), APInt(16, 122)));
// urem is upper bounded by maximum LHS.
EXPECT_EQ(ConstantRange(APInt(16, 0), APInt(16, 123)).urem(Full),
ConstantRange(APInt(16, 0), APInt(16, 123)));
// If the LHS is always lower than the RHS, the result is the LHS.
EXPECT_EQ(ConstantRange(APInt(16, 10), APInt(16, 20))
.urem(ConstantRange(APInt(16, 20), APInt(16, 30))),
ConstantRange(APInt(16, 10), APInt(16, 20)));
// It has to be strictly lower, otherwise the top value may wrap to zero.
EXPECT_EQ(ConstantRange(APInt(16, 10), APInt(16, 20))
.urem(ConstantRange(APInt(16, 19), APInt(16, 30))),
ConstantRange(APInt(16, 0), APInt(16, 20)));
// [12, 14] % 10 is [2, 4], but we conservatively compute [0, 9].
EXPECT_EQ(ConstantRange(APInt(16, 12), APInt(16, 15))
.urem(ConstantRange(APInt(16, 10))),
ConstantRange(APInt(16, 0), APInt(16, 10)));
TestUnsignedBinOpExhaustive(
[](const ConstantRange &CR1, const ConstantRange &CR2) {
return CR1.urem(CR2);
},
[](const APInt &N1, const APInt &N2) {
return N1.urem(N2);
},
/* SkipZeroRHS */ true, /* CorrectnessOnly */ true);
}
TEST_F(ConstantRangeTest, Shl) {
ConstantRange Some2(APInt(16, 0xfff), APInt(16, 0x8000));
ConstantRange WrapNullMax(APInt(16, 0x1), APInt(16, 0x0));