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[Clang] Add __builtin_bswapg #162433

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[Clang] Add __builtin_bswapg #162433

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92466f3
[Clang] Add __builtin_bswapg
clingfei Oct 8, 2025
d4ea868
handle special case 8 in interp__builtin_bswap and fix extra space in…
clingfei Oct 9, 2025
fa016a1
add dependent check for argument
clingfei Oct 9, 2025
c0d0f3c
fix bswapg codegen and add c++ tests
clingfei Oct 10, 2025
1e9895c
fix test for builtin-bswapg
clingfei Oct 10, 2025
bca24f2
add failure tests and reference tests, and adjust checks according to…
clingfei Oct 12, 2025
ba83b56
add tests for arrays, pointers, enums, class, nullptr_t
clingfei Oct 15, 2025
a2a6191
add release notes
clingfei Oct 15, 2025
dfd3385
Merge branch 'main' into builtin
clingfei Oct 15, 2025
6afe334
add support and test cases for _BitInt
clingfei Oct 18, 2025
ed8c33a
remove extra spaces
clingfei Oct 18, 2025
6333668
add more test cases for _BitInt
clingfei Oct 19, 2025
2b4e009
add CodeGen tests for _BitInt
clingfei Oct 19, 2025
42301e8
remove the assumption 'Val.getActiveBits <= 64' in interp__builtin_bs…
clingfei Oct 19, 2025
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6 changes: 6 additions & 0 deletions clang/include/clang/Basic/Builtins.td
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Original file line number Diff line number Diff line change
Expand Up @@ -755,6 +755,12 @@ def BSwap : Builtin, Template<["unsigned short", "uint32_t", "uint64_t"],
let Prototype = "T(T)";
}

def BSwapg : Builtin {
let Spellings = ["__builtin_bswapg"];
let Attributes = [NoThrow, Const, Constexpr, CustomTypeChecking];
let Prototype = "int(...)";
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Suggested change
let Prototype = "int(...)";
let Prototype = "T(T)";

Should this match the other generic ones?

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No, this will cause a build error:
llvm-project/clang/include/clang/Basic/Builtins.td:761:7: error: Not a template
let Prototype = "T(T)";
^

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IIRC T(T) assumes an explicit set of type mappings. In principle I think this could be labeled as T(T) with the customtypechecking flag. That would be more correct than int(..), and the Sema work is already doing the custom checking.

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I wonder whether we should have a CustomTypeCheckingBuiltin that doesn't ask for a prototype. I don't think that would work without any modification to Clang though. Some builtins might assume the return type is correct and won't set it again during custom type checking.

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I think it would be nice if we could automate type checking for truly template/generic builtins. I feel like builtins using CustomTypeChecking should have an accurate prototype, but I agree that no prototype is better than a fake one.

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Yeah, some more infrastructure for this would be nice, especially since we seem to go in the direction of "all the builtins are generic".

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IIRC T(T) assumes an explicit set of type mappings. In principle I think this could be labeled as T(T) with the customtypechecking flag. That would be more correct than int(..), and the Sema work is already doing the custom checking.

In fact, at first I attempted to use T(T) with an explicit set of type mappings, but the automatically generated builtin functions are bswapg16, bswapg32, etc., rather than a single generic bswapg. I'm not sure if I can use T(T) without making more modifications to clang. It would be nice if that worked.

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sorry, missed this reply - yeah it exists to automate the bindings for multiple types rather than just specifying a generic function :-/

}

def Bitreverse : BitInt8_16_32_64BuiltinsTemplate, Builtin {
let Spellings = ["__builtin_bitreverse"];
let Attributes = [NoThrow, Const, Constexpr];
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8 changes: 5 additions & 3 deletions clang/lib/AST/ByteCode/InterpBuiltin.cpp
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Expand Up @@ -1004,8 +1004,10 @@ static bool interp__builtin_bswap(InterpState &S, CodePtr OpPC,
const CallExpr *Call) {
const APSInt &Val = popToAPSInt(S, Call->getArg(0));
assert(Val.getActiveBits() <= 64);

pushInteger(S, Val.byteSwap(), Call->getType());
if (Val.getBitWidth() == 8)
pushInteger(S, Val, Call->getType());
else
pushInteger(S, Val.byteSwap(), Call->getType());
return true;
}

Expand Down Expand Up @@ -3288,7 +3290,7 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const CallExpr *Call,
case Builtin::BI__builtin_elementwise_ctzg:
return interp__builtin_elementwise_countzeroes(S, OpPC, Frame, Call,
BuiltinID);

case Builtin::BI__builtin_bswapg:
case Builtin::BI__builtin_bswap16:
case Builtin::BI__builtin_bswap32:
case Builtin::BI__builtin_bswap64:
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9 changes: 9 additions & 0 deletions clang/lib/AST/ExprConstant.cpp
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Expand Up @@ -13982,6 +13982,15 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,

return Success(Val.reverseBits(), E);
}
case Builtin::BI__builtin_bswapg: {
APSInt Val;
if (!EvaluateInteger(E->getArg(0), Val, Info))
return false;
if (Val.getBitWidth() == 8)
return Success(Val, E);

return Success(Val.byteSwap(), E);
}

case Builtin::BI__builtin_bswap16:
case Builtin::BI__builtin_bswap32:
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1 change: 1 addition & 0 deletions clang/lib/CodeGen/CGBuiltin.cpp
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Expand Up @@ -3622,6 +3622,7 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
Builder.CreateArithmeticFence(ArgValue, ConvertType(ArgType)));
return RValue::get(ArgValue);
}
case Builtin::BI__builtin_bswapg:
case Builtin::BI__builtin_bswap16:
case Builtin::BI__builtin_bswap32:
case Builtin::BI__builtin_bswap64:
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30 changes: 30 additions & 0 deletions clang/lib/Sema/SemaChecking.cpp
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Expand Up @@ -2200,6 +2200,32 @@ static bool BuiltinCpu(Sema &S, const TargetInfo &TI, CallExpr *TheCall,
return false;
}

/// Checks that __builtin_bswapg was called with a single argument, which is an
/// unsigned integer, and overrides the return value type to the integer type.
static bool BuiltinBswapg(Sema &S, CallExpr *TheCall) {
if (S.checkArgCount(TheCall, 1))
return true;
ExprResult ArgRes = S.DefaultLvalueConversion(TheCall->getArg(0));
if (ArgRes.isInvalid())
return true;

Expr *Arg = ArgRes.get();
TheCall->setArg(0, Arg);
if (Arg->isTypeDependent())
return false;

QualType ArgTy = Arg->getType();

if (!ArgTy->isIntegerType()) {
S.Diag(Arg->getBeginLoc(), diag::err_builtin_invalid_arg_type)
<< 1 << /* scalar */ 1 << /* unsigned integer ty */ 1 << /* no fp */ 0
<< ArgTy;
return true;
}
TheCall->setType(ArgTy);
return false;
}

/// Checks that __builtin_popcountg was called with a single argument, which is
/// an unsigned integer.
static bool BuiltinPopcountg(Sema &S, CallExpr *TheCall) {
Expand Down Expand Up @@ -3448,6 +3474,10 @@ Sema::CheckBuiltinFunctionCall(FunctionDecl *FDecl, unsigned BuiltinID,
}
break;
}
case Builtin::BI__builtin_bswapg:
if (BuiltinBswapg(*this, TheCall))
return ExprError();
break;
case Builtin::BI__builtin_popcountg:
if (BuiltinPopcountg(*this, TheCall))
return ExprError();
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4 changes: 4 additions & 0 deletions clang/test/AST/ByteCode/builtin-functions.cpp
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Expand Up @@ -824,6 +824,10 @@ namespace bswap {
int h3 = __builtin_bswap16(0x1234) == 0x3412 ? 1 : f();
int h4 = __builtin_bswap32(0x1234) == 0x34120000 ? 1 : f();
int h5 = __builtin_bswap64(0x1234) == 0x3412000000000000 ? 1 : f();
int h6 = __builtin_bswapg(0x12) == 0x12 ? 1 : f();
int h7 = __builtin_bswapg(0x1234) == 0x3412 ? 1 : f();
int h8 = __builtin_bswapg(0x00001234) == 0x34120000 ? 1 : f();
int h9 = __builtin_bswapg(0x0000000000001234) == 0x3412000000000000 ? 1 : f();
}

#define CFSTR __builtin___CFStringMakeConstantString
Expand Down
2 changes: 1 addition & 1 deletion clang/test/CodeGen/builtins.c
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Expand Up @@ -130,7 +130,7 @@ int main(void) {
P(object_size, (s0, 3));

// Whatever

P(bswapg, (N));
P(bswap16, (N));
P(bswap32, (N));
P(bswap64, (N));
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4 changes: 4 additions & 0 deletions clang/test/Sema/constant-builtins-2.c
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Expand Up @@ -479,6 +479,10 @@ int h0 = __builtin_types_compatible_p(int, float);
int h3 = __builtin_bswap16(0x1234) == 0x3412 ? 1 : f();
int h4 = __builtin_bswap32(0x1234) == 0x34120000 ? 1 : f();
int h5 = __builtin_bswap64(0x1234) == 0x3412000000000000 ? 1 : f();
int h6 = __builtin_bswapg((char)(0x12)) == (char)(0x12) ? 1 : f();
int h7 = __builtin_bswapg((short)(0x1234)) == (short)(0x3412) ? 1 : f();
int h8 = __builtin_bswapg(0x00001234) == 0x34120000 ? 1 : f();
int h9 = __builtin_bswapg(0x0000000000001234ULL) == 0x3412000000000000 ? 1 : f();
extern long int bi0;
extern __typeof__(__builtin_expect(0, 0)) bi0;

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5 changes: 4 additions & 1 deletion clang/test/Sema/constant-builtins.c
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Expand Up @@ -25,7 +25,10 @@ int h0 = __builtin_types_compatible_p(int,float);
int h3 = __builtin_bswap16(0x1234) == 0x3412 ? 1 : f();
int h4 = __builtin_bswap32(0x1234) == 0x34120000 ? 1 : f();
int h5 = __builtin_bswap64(0x1234) == 0x3412000000000000 ? 1 : f();

int h6 = __builtin_bswapg((char)0x12) == (char)0x12 ? 1 : f();
int h7 = __builtin_bswapg((short)(0x1234)) == (short)(0x3412) ? 1 : f();
int h8 = __builtin_bswapg(0x00001234) == 0x34120000 ? 1 : f();
int h9 = __builtin_bswapg(0x0000000000001234ULL) == 0x3412000000000000 ? 1 : f();
short somefunc(void);

short t = __builtin_constant_p(5353) ? 42 : somefunc();
Expand Down
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