r334650 - Implement constexpr __builtin_*_overflow
Evgenii Stepanov via cfe-commits
cfe-commits at lists.llvm.org
Tue Jul 3 13:00:24 PDT 2018
Discovered by MemorySanitizer, btw.
On Tue, Jul 3, 2018 at 12:59 PM, Evgenii Stepanov <eugeni.stepanov at gmail.com
> wrote:
> Hi,
>
> with this change, the following compiles to "ret i32 undef":
>
> int main(int argc, char **argv) {
>
> constexpr int x = 1;
>
> constexpr int y = 2;
>
> int z;
>
>
>
> __builtin_sadd_overflow(x, y, &z);
>
> return z;
>
> }
>
>
> On Wed, Jun 13, 2018 at 1:43 PM, Erich Keane via cfe-commits <
> cfe-commits at lists.llvm.org> wrote:
>
>> Author: erichkeane
>> Date: Wed Jun 13 13:43:27 2018
>> New Revision: 334650
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=334650&view=rev
>> Log:
>> Implement constexpr __builtin_*_overflow
>>
>> 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
>>
>> Modified:
>> cfe/trunk/lib/AST/ExprConstant.cpp
>> cfe/trunk/test/SemaCXX/builtins-overflow.cpp
>>
>> Modified: cfe/trunk/lib/AST/ExprConstant.cpp
>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ExprCo
>> nstant.cpp?rev=334650&r1=334649&r2=334650&view=diff
>> ============================================================
>> ==================
>> --- cfe/trunk/lib/AST/ExprConstant.cpp (original)
>> +++ cfe/trunk/lib/AST/ExprConstant.cpp Wed Jun 13 13:43:27 2018
>> @@ -8155,6 +8155,124 @@ bool IntExprEvaluator::VisitBuiltinCallE
>> 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);
>> + }
>> }
>> }
>>
>>
>> Modified: cfe/trunk/test/SemaCXX/builtins-overflow.cpp
>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/
>> builtins-overflow.cpp?rev=334650&r1=334649&r2=334650&view=diff
>> ============================================================
>> ==================
>> --- cfe/trunk/test/SemaCXX/builtins-overflow.cpp (original)
>> +++ cfe/trunk/test/SemaCXX/builtins-overflow.cpp Wed Jun 13 13:43:27 2018
>> @@ -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;
>> @@ -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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>
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