================
@@ -2922,7 +2922,7 @@ static bool handleFloatFloatBinOp(EvalInfo &Info, const
BinaryOperator *E,
// If during the evaluation of an expression, the result is not
// mathematically defined [...], the behavior is undefined.
// FIXME: C++ rules require us to not conform to IEEE 754 here.
- if (LHS.isNaN()) {
+ if (!Info.getLangOpts().CPlusPlus23 && LHS.isNaN()) {
----------------
AaronBallman wrote:
I think we're potentially misinterpreting the standard here regarding NANs. CC
@jcranmer-intel @hubert-reinterpretcast
https://eel.is/c++draft/basic.fundamental#13 is the interesting bit (I think),
and I believe it's saying that if the floating-point representation you use has
a way to represent a mathematical value then that value is "representable in
that type". e.g., if your fp format can support positive/negative infinity,
then a positive/negative infinity is considered representable. Note 10 says
that more explicitly as: "Since negative and positive infinity are
representable in ISO/IEC/IEEE 60559 formats, all real numbers lie within the
range of representable values of a floating-point type adhering to ISO/IEC/IEEE
60559."
NANs are representable within ISO/IEC 60559 and are a mathematical result of an
operation such as zero divided by zero. So I believe NANs are valid in a
constant expression.
MSVC, Clang, and GCC all agree that they're not, but EDG believes they are:
https://godbolt.org/z/cxPcKGvP3
https://github.com/llvm/llvm-project/pull/88978
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