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[Clang] Fix __builtin_fpclassify #190848

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[Clang] Fix __builtin_fpclassify #190848

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7e4320f
[Clang] Implement __builtin_fpclassify
YeonguChoe Apr 7, 2026
b13bbd7
Change FileCheck test code that uses fpclassify
YeonguChoe Apr 7, 2026
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88 changes: 43 additions & 45 deletions clang/lib/CodeGen/CGBuiltin.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4415,60 +4415,58 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,

case Builtin::BI__builtin_fpclassify: {
CodeGenFunction::CGFPOptionsRAII FPOptsRAII(*this, E);
// FIXME: for strictfp/IEEE-754 we need to not trap on SNaN here.

Value *NanLiteral = EmitScalarExpr(E->getArg(0));
Value *InfiniteLiteral = EmitScalarExpr(E->getArg(1));
Value *NormalLiteral = EmitScalarExpr(E->getArg(2));
Value *SubnormalLiteral = EmitScalarExpr(E->getArg(3));
Value *ZeroLiteral = EmitScalarExpr(E->getArg(4));
Value *V = EmitScalarExpr(E->getArg(5));
llvm::Type *Ty = ConvertType(E->getArg(5)->getType());

// Create Result
BasicBlock *Begin = Builder.GetInsertBlock();
BasicBlock *End = createBasicBlock("fpclassify_end", this->CurFn);
BasicBlock *Entry = Builder.GetInsertBlock();
BasicBlock *NotNan = createBasicBlock("fpclassify_not_nan", CurFn);
BasicBlock *NotInfinite =
createBasicBlock("fpclassify_not_infinite", CurFn);
BasicBlock *NotNormal = createBasicBlock("fpclassify_not_normal", CurFn);
BasicBlock *NotSubnormal =
createBasicBlock("fpclassify_not_subnormal", CurFn);
BasicBlock *End = createBasicBlock("fpclassify_end", CurFn);

// End Block
Builder.SetInsertPoint(End);
PHINode *Result =
Builder.CreatePHI(ConvertType(E->getArg(0)->getType()), 4,
"fpclassify_result");
PHINode *Result = Builder.CreatePHI(ConvertType(E->getArg(0)->getType()), 5,
"fpclassify_result");

// if (V==0) return FP_ZERO
Builder.SetInsertPoint(Begin);
Value *IsZero = Builder.CreateFCmpOEQ(V, Constant::getNullValue(Ty),
"iszero");
Value *ZeroLiteral = EmitScalarExpr(E->getArg(4));
BasicBlock *NotZero = createBasicBlock("fpclassify_not_zero", this->CurFn);
Builder.CreateCondBr(IsZero, End, NotZero);
Result->addIncoming(ZeroLiteral, Begin);

// if (V != V) return FP_NAN
Builder.SetInsertPoint(NotZero);
Value *IsNan = Builder.CreateFCmpUNO(V, V, "cmp");
Value *NanLiteral = EmitScalarExpr(E->getArg(0));
BasicBlock *NotNan = createBasicBlock("fpclassify_not_nan", this->CurFn);
// Entry Block
Builder.SetInsertPoint(Entry);
Value *IsNan = Builder.createIsFPClass(V, FPClassTest::fcNan);
Result->addIncoming(NanLiteral, Entry);
Builder.CreateCondBr(IsNan, End, NotNan);
Result->addIncoming(NanLiteral, NotZero);

// if (fabs(V) == infinity) return FP_INFINITY
// NotNan Block
Builder.SetInsertPoint(NotNan);
Value *VAbs = EmitFAbs(*this, V);
Value *IsInf =
Builder.CreateFCmpOEQ(VAbs, ConstantFP::getInfinity(V->getType()),
"isinf");
Value *InfLiteral = EmitScalarExpr(E->getArg(1));
BasicBlock *NotInf = createBasicBlock("fpclassify_not_inf", this->CurFn);
Builder.CreateCondBr(IsInf, End, NotInf);
Result->addIncoming(InfLiteral, NotNan);

// if (fabs(V) >= MIN_NORMAL) return FP_NORMAL else FP_SUBNORMAL
Builder.SetInsertPoint(NotInf);
APFloat Smallest = APFloat::getSmallestNormalized(
getContext().getFloatTypeSemantics(E->getArg(5)->getType()));
Value *IsNormal =
Builder.CreateFCmpUGE(VAbs, ConstantFP::get(V->getContext(), Smallest),
"isnormal");
Value *NormalResult =
Builder.CreateSelect(IsNormal, EmitScalarExpr(E->getArg(2)),
EmitScalarExpr(E->getArg(3)));
Value *IsInfinite = Builder.createIsFPClass(V, FPClassTest::fcInf);
Result->addIncoming(InfiniteLiteral, NotNan);
Builder.CreateCondBr(IsInfinite, End, NotInfinite);

// NotInfinite Block
Builder.SetInsertPoint(NotInfinite);
Value *IsNormal = Builder.createIsFPClass(V, FPClassTest::fcNormal);
Result->addIncoming(NormalLiteral, NotInfinite);
Builder.CreateCondBr(IsNormal, End, NotNormal);

// NotNormal Block
Builder.SetInsertPoint(NotNormal);
Value *IsSubnormal = Builder.createIsFPClass(V, FPClassTest::fcSubnormal);
Result->addIncoming(SubnormalLiteral, NotNormal);
Builder.CreateCondBr(IsSubnormal, End, NotSubnormal);

// NotSubnormal Block
Builder.SetInsertPoint(NotSubnormal);
Result->addIncoming(ZeroLiteral, NotSubnormal);
Builder.CreateBr(End);
Result->addIncoming(NormalResult, NotInf);

// return Result
// End Block
Builder.SetInsertPoint(End);
return RValue::get(Result);
}
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