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Implement constexpr __builtin_*_overflow
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As requested here:https://bugs.llvm.org/show_bug.cgi?id=37633
permit the __builtin_*_overflow builtins in constexpr functions.

Differential Revision: https://reviews.llvm.org/D48040

llvm-svn: 334650
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Erich Keane committed Jun 13, 2018
1 parent fbd450b commit 0095827
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118 changes: 118 additions & 0 deletions clang/lib/AST/ExprConstant.cpp
View file
Expand Up @@ -8155,6 +8155,124 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
case Builtin::BIomp_is_initial_device:
// We can decide statically which value the runtime would return if called.
return Success(Info.getLangOpts().OpenMPIsDevice ? 0 : 1, E);
case Builtin::BI__builtin_add_overflow:
case Builtin::BI__builtin_sub_overflow:
case Builtin::BI__builtin_mul_overflow:
case Builtin::BI__builtin_sadd_overflow:
case Builtin::BI__builtin_uadd_overflow:
case Builtin::BI__builtin_uaddl_overflow:
case Builtin::BI__builtin_uaddll_overflow:
case Builtin::BI__builtin_usub_overflow:
case Builtin::BI__builtin_usubl_overflow:
case Builtin::BI__builtin_usubll_overflow:
case Builtin::BI__builtin_umul_overflow:
case Builtin::BI__builtin_umull_overflow:
case Builtin::BI__builtin_umulll_overflow:
case Builtin::BI__builtin_saddl_overflow:
case Builtin::BI__builtin_saddll_overflow:
case Builtin::BI__builtin_ssub_overflow:
case Builtin::BI__builtin_ssubl_overflow:
case Builtin::BI__builtin_ssubll_overflow:
case Builtin::BI__builtin_smul_overflow:
case Builtin::BI__builtin_smull_overflow:
case Builtin::BI__builtin_smulll_overflow: {
LValue ResultLValue;
APSInt LHS, RHS;

QualType ResultType = E->getArg(2)->getType()->getPointeeType();
if (!EvaluateInteger(E->getArg(0), LHS, Info) ||
!EvaluateInteger(E->getArg(1), RHS, Info) ||
!EvaluatePointer(E->getArg(2), ResultLValue, Info))
return false;

APSInt Result;
bool DidOverflow = false;

// If the types don't have to match, enlarge all 3 to the largest of them.
if (BuiltinOp == Builtin::BI__builtin_add_overflow ||
BuiltinOp == Builtin::BI__builtin_sub_overflow ||
BuiltinOp == Builtin::BI__builtin_mul_overflow) {
bool IsSigned = LHS.isSigned() || RHS.isSigned() ||
ResultType->isSignedIntegerOrEnumerationType();
bool AllSigned = LHS.isSigned() && RHS.isSigned() &&
ResultType->isSignedIntegerOrEnumerationType();
uint64_t LHSSize = LHS.getBitWidth();
uint64_t RHSSize = RHS.getBitWidth();
uint64_t ResultSize = Info.Ctx.getTypeSize(ResultType);
uint64_t MaxBits = std::max(std::max(LHSSize, RHSSize), ResultSize);

// Add an additional bit if the signedness isn't uniformly agreed to. We
// could do this ONLY if there is a signed and an unsigned that both have
// MaxBits, but the code to check that is pretty nasty. The issue will be
// caught in the shrink-to-result later anyway.
if (IsSigned && !AllSigned)
++MaxBits;

LHS = APSInt(IsSigned ? LHS.sextOrSelf(MaxBits) : LHS.zextOrSelf(MaxBits),
!IsSigned);
RHS = APSInt(IsSigned ? RHS.sextOrSelf(MaxBits) : RHS.zextOrSelf(MaxBits),
!IsSigned);
Result = APSInt(MaxBits, !IsSigned);
}

// Find largest int.
switch (BuiltinOp) {
default:
llvm_unreachable("Invalid value for BuiltinOp");
case Builtin::BI__builtin_add_overflow:
case Builtin::BI__builtin_sadd_overflow:
case Builtin::BI__builtin_saddl_overflow:
case Builtin::BI__builtin_saddll_overflow:
case Builtin::BI__builtin_uadd_overflow:
case Builtin::BI__builtin_uaddl_overflow:
case Builtin::BI__builtin_uaddll_overflow:
Result = LHS.isSigned() ? LHS.sadd_ov(RHS, DidOverflow)
: LHS.uadd_ov(RHS, DidOverflow);
break;
case Builtin::BI__builtin_sub_overflow:
case Builtin::BI__builtin_ssub_overflow:
case Builtin::BI__builtin_ssubl_overflow:
case Builtin::BI__builtin_ssubll_overflow:
case Builtin::BI__builtin_usub_overflow:
case Builtin::BI__builtin_usubl_overflow:
case Builtin::BI__builtin_usubll_overflow:
Result = LHS.isSigned() ? LHS.ssub_ov(RHS, DidOverflow)
: LHS.usub_ov(RHS, DidOverflow);
break;
case Builtin::BI__builtin_mul_overflow:
case Builtin::BI__builtin_smul_overflow:
case Builtin::BI__builtin_smull_overflow:
case Builtin::BI__builtin_smulll_overflow:
case Builtin::BI__builtin_umul_overflow:
case Builtin::BI__builtin_umull_overflow:
case Builtin::BI__builtin_umulll_overflow:
Result = LHS.isSigned() ? LHS.smul_ov(RHS, DidOverflow)
: LHS.umul_ov(RHS, DidOverflow);
break;
}

// In the case where multiple sizes are allowed, truncate and see if
// the values are the same.
if (BuiltinOp == Builtin::BI__builtin_add_overflow ||
BuiltinOp == Builtin::BI__builtin_sub_overflow ||
BuiltinOp == Builtin::BI__builtin_mul_overflow) {
// APSInt doesn't have a TruncOrSelf, so we use extOrTrunc instead,
// since it will give us the behavior of a TruncOrSelf in the case where
// its parameter <= its size. We previously set Result to be at least the
// type-size of the result, so getTypeSize(ResultType) <= Result.BitWidth
// will work exactly like TruncOrSelf.
APSInt Temp = Result.extOrTrunc(Info.Ctx.getTypeSize(ResultType));
Temp.setIsSigned(ResultType->isSignedIntegerOrEnumerationType());

if (!APSInt::isSameValue(Temp, Result))
DidOverflow = true;
Result = Temp;
}

APValue APV{Result};
handleAssignment(Info, E, ResultLValue, ResultType, APV);
return Success(DidOverflow, E);
}
}
}

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84 changes: 84 additions & 0 deletions clang/test/SemaCXX/builtins-overflow.cpp
View file
@@ -1,6 +1,8 @@
// RUN: %clang_cc1 -fsyntax-only -std=c++17 -verify %s
// expected-no-diagnostics

#include <limits.h>

int a() {
const int x = 3;
static int z;
Expand All @@ -13,3 +15,85 @@ int a2() {
constexpr int *y = &z;
return []() { return __builtin_sub_overflow(x, x, y); }();
}

template<typename T>
struct Result {
bool B;
T Value;
constexpr bool operator==(const Result<T> &Other) {
return B == Other.B && Value == Other.Value;
}
};


template <typename RET, typename LHS, typename RHS>
constexpr Result<RET> add(LHS &&lhs, RHS &&rhs) {
RET sum{};
bool b = __builtin_add_overflow(lhs, rhs, &sum);
return {b, sum};
}

static_assert(add<short>(static_cast<char>(120), static_cast<char>(10)) == Result<short>{false, 130});
static_assert(add<char>(static_cast<short>(120), static_cast<short>(10)) == Result<char>{true, -126});
static_assert(add<unsigned int>(INT_MAX, INT_MAX) == Result<unsigned int>{false, static_cast<unsigned int>(INT_MAX) * 2u});
static_assert(add<int>(static_cast<unsigned int>(INT_MAX), 1u) == Result<int>{true, INT_MIN});

static_assert(add<int>(17, 22) == Result<int>{false, 39});
static_assert(add<int>(INT_MAX - 22, 24) == Result<int>{true, INT_MIN + 1});
static_assert(add<int>(INT_MIN + 22, -23) == Result<int>{true, INT_MAX});

template <typename RET, typename LHS, typename RHS>
constexpr Result<RET> sub(LHS &&lhs, RHS &&rhs) {
RET sum{};
bool b = __builtin_sub_overflow(lhs, rhs, &sum);
return {b, sum};
}

static_assert(sub<unsigned char>(static_cast<char>(0),static_cast<char>(1)) == Result<unsigned char>{true, UCHAR_MAX});
static_assert(sub<char>(static_cast<unsigned char>(0),static_cast<unsigned char>(1)) == Result<char>{false, -1});
static_assert(sub<unsigned short>(static_cast<short>(0),static_cast<short>(1)) == Result<unsigned short>{true, USHRT_MAX});

static_assert(sub<int>(17,22) == Result<int>{false, -5});
static_assert(sub<int>(INT_MAX - 22, -23) == Result<int>{true, INT_MIN});
static_assert(sub<int>(INT_MIN + 22, 23) == Result<int>{true, INT_MAX});

template <typename RET, typename LHS, typename RHS>
constexpr Result<RET> mul(LHS &&lhs, RHS &&rhs) {
RET sum{};
bool b = __builtin_mul_overflow(lhs, rhs, &sum);
return {b, sum};
}

static_assert(mul<int>(17,22) == Result<int>{false, 374});
static_assert(mul<int>(INT_MAX / 22, 23) == Result<int>{true, -2049870757});
static_assert(mul<int>(INT_MIN / 22, -23) == Result<int>{true, -2049870757});

constexpr Result<int> sadd(int lhs, int rhs) {
int sum{};
bool b = __builtin_sadd_overflow(lhs, rhs, &sum);
return {b, sum};
}

static_assert(sadd(17,22) == Result<int>{false, 39});
static_assert(sadd(INT_MAX - 22, 23) == Result<int>{true, INT_MIN});
static_assert(sadd(INT_MIN + 22, -23) == Result<int>{true, INT_MAX});

constexpr Result<int> ssub(int lhs, int rhs) {
int sum{};
bool b = __builtin_ssub_overflow(lhs, rhs, &sum);
return {b, sum};
}

static_assert(ssub(17,22) == Result<int>{false, -5});
static_assert(ssub(INT_MAX - 22, -23) == Result<int>{true, INT_MIN});
static_assert(ssub(INT_MIN + 22, 23) == Result<int>{true, INT_MAX});

constexpr Result<int> smul(int lhs, int rhs) {
int sum{};
bool b = __builtin_smul_overflow(lhs, rhs, &sum);
return {b, sum};
}

static_assert(smul(17,22) == Result<int>{false, 374});
static_assert(smul(INT_MAX / 22, 23) == Result<int>{true, -2049870757});
static_assert(smul(INT_MIN / 22, -23) == Result<int>{true, -2049870757});

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