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[clang][bytecode] Allow right-shift of negative values #108987

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Merged
merged 1 commit into from
Sep 17, 2024
Merged

[clang][bytecode] Allow right-shift of negative values #108987

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35 changes: 19 additions & 16 deletions clang/lib/AST/ByteCode/Interp.h
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Original file line number Diff line number Diff line change
Expand Up @@ -159,8 +159,10 @@ bool CallBI(InterpState &S, CodePtr OpPC, const Function *Func,
bool CallPtr(InterpState &S, CodePtr OpPC, uint32_t ArgSize,
const CallExpr *CE);

enum class ShiftDir { Left, Right };

/// Checks if the shift operation is legal.
template <typename LT, typename RT>
template <ShiftDir Dir, typename LT, typename RT>
bool CheckShift(InterpState &S, CodePtr OpPC, const LT &LHS, const RT &RHS,
unsigned Bits) {
if (RHS.isNegative()) {
Expand All @@ -181,19 +183,21 @@ bool CheckShift(InterpState &S, CodePtr OpPC, const LT &LHS, const RT &RHS,
return false;
}

if (LHS.isSigned() && !S.getLangOpts().CPlusPlus20) {
const Expr *E = S.Current->getExpr(OpPC);
// C++11 [expr.shift]p2: A signed left shift must have a non-negative
// operand, and must not overflow the corresponding unsigned type.
if (LHS.isNegative()) {
S.CCEDiag(E, diag::note_constexpr_lshift_of_negative) << LHS.toAPSInt();
if (!S.noteUndefinedBehavior())
return false;
} else if (LHS.toUnsigned().countLeadingZeros() <
static_cast<unsigned>(RHS)) {
S.CCEDiag(E, diag::note_constexpr_lshift_discards);
if (!S.noteUndefinedBehavior())
return false;
if constexpr (Dir == ShiftDir::Left) {
if (LHS.isSigned() && !S.getLangOpts().CPlusPlus20) {
const Expr *E = S.Current->getExpr(OpPC);
// C++11 [expr.shift]p2: A signed left shift must have a non-negative
// operand, and must not overflow the corresponding unsigned type.
if (LHS.isNegative()) {
S.CCEDiag(E, diag::note_constexpr_lshift_of_negative) << LHS.toAPSInt();
if (!S.noteUndefinedBehavior())
return false;
} else if (LHS.toUnsigned().countLeadingZeros() <
static_cast<unsigned>(RHS)) {
S.CCEDiag(E, diag::note_constexpr_lshift_discards);
if (!S.noteUndefinedBehavior())
return false;
}
}
}

Expand Down Expand Up @@ -2394,7 +2398,6 @@ inline bool RVOPtr(InterpState &S, CodePtr OpPC) {
//===----------------------------------------------------------------------===//
// Shr, Shl
//===----------------------------------------------------------------------===//
enum class ShiftDir { Left, Right };

template <class LT, class RT, ShiftDir Dir>
inline bool DoShift(InterpState &S, CodePtr OpPC, LT &LHS, RT &RHS) {
Expand Down Expand Up @@ -2431,7 +2434,7 @@ inline bool DoShift(InterpState &S, CodePtr OpPC, LT &LHS, RT &RHS) {
}
}

if (!CheckShift(S, OpPC, LHS, RHS, Bits))
if (!CheckShift<Dir>(S, OpPC, LHS, RHS, Bits))
return false;

// Limit the shift amount to Bits - 1. If this happened,
Expand Down
1 change: 1 addition & 0 deletions clang/test/AST/ByteCode/shifts.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@

#define INT_MIN (~__INT_MAX__)

constexpr int a = -1 >> 3;

namespace shifts {
constexpr void test() { // ref-error {{constexpr function never produces a constant expression}} \
Expand Down
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