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[clang][bytecode] Implement bitcasts to composite types #114776

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Nov 4, 2024
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[clang][bytecode] Implement bitcasts to composite types #114776

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6 changes: 2 additions & 4 deletions clang/lib/AST/ByteCode/Compiler.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6467,10 +6467,8 @@ bool Compiler<Emitter>::emitBuiltinBitCast(const CastExpr *E) {
if (!this->visit(SubExpr))
return false;

if (!ToT || ToT == PT_Ptr) {
// Conversion to an array or record type.
assert(false && "Implement bitcast to pointers.");
}
if (!ToT || ToT == PT_Ptr)
return this->emitBitCastPtr(E);
assert(ToT);

const llvm::fltSemantics *TargetSemantics = nullptr;
Expand Down
10 changes: 10 additions & 0 deletions clang/lib/AST/ByteCode/Interp.h
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Expand Up @@ -3080,6 +3080,16 @@ inline bool BitCast(InterpState &S, CodePtr OpPC, bool TargetIsUCharOrByte,
return true;
}

inline bool BitCastPtr(InterpState &S, CodePtr OpPC) {
const Pointer &FromPtr = S.Stk.pop<Pointer>();
Pointer &ToPtr = S.Stk.peek<Pointer>();

if (!DoBitCastPtr(S, OpPC, FromPtr, ToPtr))
return false;

return true;
}

//===----------------------------------------------------------------------===//
// Read opcode arguments
//===----------------------------------------------------------------------===//
Expand Down
55 changes: 49 additions & 6 deletions clang/lib/AST/ByteCode/InterpBuiltinBitCast.cpp
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Expand Up @@ -48,9 +48,7 @@ using DataFunc =
} \
} while (0)

/// Float is a special case that sometimes needs the floating point semantics
/// to be available.
#define BITCAST_TYPE_SWITCH_WITH_FLOAT(Expr, B) \
#define BITCAST_TYPE_SWITCH_FIXED_SIZE(Expr, B) \
do { \
switch (Expr) { \
TYPE_SWITCH_CASE(PT_Sint8, B) \
Expand All @@ -61,10 +59,7 @@ using DataFunc =
TYPE_SWITCH_CASE(PT_Uint32, B) \
TYPE_SWITCH_CASE(PT_Sint64, B) \
TYPE_SWITCH_CASE(PT_Uint64, B) \
TYPE_SWITCH_CASE(PT_IntAP, B) \
TYPE_SWITCH_CASE(PT_IntAPS, B) \
TYPE_SWITCH_CASE(PT_Bool, B) \
TYPE_SWITCH_CASE(PT_Float, B) \
default: \
llvm_unreachable("Unhandled bitcast type"); \
} \
Expand Down Expand Up @@ -92,6 +87,12 @@ struct BitcastBuffer {

const std::byte *data() const { return Data.data(); }

std::byte *getBytes(unsigned BitOffset) const {
if (BitOffset % 8 == 0)
return const_cast<std::byte *>(data() + (BitOffset / 8));
assert(false && "hmm, how to best handle this?");
}

bool allInitialized() const {
// FIXME: Implement.
return true;
Expand Down Expand Up @@ -377,3 +378,45 @@ bool clang::interp::DoBitCast(InterpState &S, CodePtr OpPC, const Pointer &Ptr,

return Success;
}

bool clang::interp::DoBitCastPtr(InterpState &S, CodePtr OpPC,
const Pointer &FromPtr, Pointer &ToPtr) {
assert(FromPtr.isLive());
assert(FromPtr.isBlockPointer());
assert(ToPtr.isBlockPointer());

QualType FromType = FromPtr.getType();
QualType ToType = ToPtr.getType();

if (!CheckBitcastType(S, OpPC, FromType, /*IsToType=*/false))
return false;

if (!CheckBitcastType(S, OpPC, ToType, /*IsToType=*/true))
return false;

BitcastBuffer Buffer;
readPointerToBuffer(S.getContext(), FromPtr, Buffer,
/*ReturnOnUninit=*/false);

// Now read the values out of the buffer again and into ToPtr.
size_t BitOffset = 0;
bool Success = enumeratePointerFields(
ToPtr, S.getContext(),
[&](const Pointer &P, PrimType T, size_t _) -> bool {
BITCAST_TYPE_SWITCH_FIXED_SIZE(T, {
T &Val = P.deref<T>();

std::byte *M = Buffer.getBytes(BitOffset);

if (llvm::sys::IsBigEndianHost)
swapBytes(M, T::bitWidth() / 8);

Val = T::bitcastFromMemory(M, T::bitWidth());
P.initialize();
BitOffset += T::bitWidth();
});
return true;
});

return Success;
}
2 changes: 2 additions & 0 deletions clang/lib/AST/ByteCode/InterpBuiltinBitCast.h
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Expand Up @@ -19,6 +19,8 @@ class CodePtr;

bool DoBitCast(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
std::byte *Buff, size_t BuffSize, bool &HasIndeterminateBits);
bool DoBitCastPtr(InterpState &S, CodePtr OpPC, const Pointer &FromPtr,
Pointer &ToPtr);

} // namespace interp
} // namespace clang
Expand Down
2 changes: 2 additions & 0 deletions clang/lib/AST/ByteCode/Opcodes.td
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Expand Up @@ -847,3 +847,5 @@ def BitCast : Opcode {
let Args = [ArgBool, ArgUint32, ArgFltSemantics];
let HasGroup = 1;
}

def BitCastPtr : Opcode;
42 changes: 21 additions & 21 deletions clang/test/AST/ByteCode/builtin-bit-cast.cpp
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Expand Up @@ -287,7 +287,7 @@ struct int_splicer {

constexpr int_splicer splice(0x0C05FEFE, 0xCAFEBABE);

#if 0
#if 1
static_assert(bit_cast<unsigned long long>(splice) == (LITTLE_END
? 0xCAFEBABE0C05FEFE
: 0x0C05FEFECAFEBABE));
Expand All @@ -297,8 +297,8 @@ static_assert(bit_cast<int_splicer>(0xCAFEBABE0C05FEFE).x == (LITTLE_END
? 0x0C05FEFE
: 0xCAFEBABE));

static_assert(round_trip<unsigned long long>(splice));
static_assert(round_trip<long long>(splice));
static_assert(check_round_trip<unsigned long long>(splice));
static_assert(check_round_trip<long long>(splice));
#endif


Expand Down Expand Up @@ -340,13 +340,12 @@ void test_record() {
? 0xCAFEBABE0C05FEFE
: 0x0C05FEFECAFEBABE));

/// FIXME: Bit casts to composite types.
// static_assert(bit_cast<int_splicer>(0xCAFEBABE0C05FEFE).x == (LITTLE_END
// ? 0x0C05FEFE
// : 0xCAFEBABE));
static_assert(bit_cast<int_splicer>(0xCAFEBABE0C05FEFE).x == (LITTLE_END
? 0x0C05FEFE
: 0xCAFEBABE));

// static_assert(check_round_trip<unsigned long long>(splice));
// static_assert(check_round_trip<long long>(splice));
static_assert(check_round_trip<unsigned long long>(splice));
static_assert(check_round_trip<long long>(splice));

struct base2 {
};
Expand All @@ -368,13 +367,14 @@ void test_record() {
z == other.z && doublez == other.doublez;
}
};
// constexpr bases b = {{1, 2}, {}, {3}, 4};
// constexpr tuple4 t4 = bit_cast<tuple4>(b);
// static_assert(t4 == tuple4{1, 2, 3, 4});
// static_assert(round_trip<tuple4>(b));

// constexpr auto b2 = bit_cast<bases>(t4);
// static_assert(t4 == b2);
constexpr bases b = {{1, 2}, {}, {3}, 4};
constexpr tuple4 t4 = bit_cast<tuple4>(b);
static_assert(t4 == tuple4{1, 2, 3, 4});
static_assert(check_round_trip<tuple4>(b));

/// FIXME: We need to initialize the base pointers in the pointer we're bitcasting to.
// constexpr auto b2 = bit_cast<bases>(t4);
// static_assert(t4 == b2);
}

void test_partially_initialized() {
Expand Down Expand Up @@ -411,16 +411,16 @@ void bad_types() {
};
static_assert(__builtin_bit_cast(int, X{0}) == 0); // both-error {{not an integral constant expression}} \
// both-note {{bit_cast from a union type is not allowed in a constant expression}}
#if 0
#if 1

struct G {
int g;
};
// expected-error@+2 {{constexpr variable 'g' must be initialized by a constant expression}}
// expected-note@+1 {{bit_cast from a union type is not allowed in a constant expression}}
// both-error@+2 {{constexpr variable 'g' must be initialized by a constant expression}}
// both-note@+1 {{bit_cast from a union type is not allowed in a constant expression}}
constexpr G g = __builtin_bit_cast(G, X{0});
// expected-error@+2 {{constexpr variable 'x' must be initialized by a constant expression}}
// expected-note@+1 {{bit_cast to a union type is not allowed in a constant expression}}
// both-error@+2 {{constexpr variable 'x' must be initialized by a constant expression}}
// both-note@+1 {{bit_cast to a union type is not allowed in a constant expression}}
constexpr X x = __builtin_bit_cast(X, G{0});
#endif
struct has_pointer {
Expand Down
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