rsmith requested changes to this revision.
rsmith added inline comments.
================
Comment at: clang/lib/AST/ExprConstant.cpp:9612
+ case Builtin::BIlround:
+ case Builtin::BI__builtin_lround: {
----------------
It's non-conforming to accept calls to these non-`__builtin` functions in
constant expression evaluation, but it's fine to constant-fold them. Please
issue a `CCEDiag` diagnostic for them (take a look at what we do for
`Builtin::BIstrlen` or `Builtin::BIstrcmp` for an example; it would probably be
reasonable to factor out a local lambda to issue suitable diagnostics for this
case).
(For example, we are required to produce a diagnostic for `constexpr long n =
lround(1.2);`, but we are permitted to constant-fold `long n = lround(1.2);`
and emit it with static initialization.)
================
Comment at: clang/lib/AST/ExprConstant.cpp:9616
+ return EvaluateFloat(E->getArg(0), Val, Info) &&
+ Success(lround(Val.convertToDouble()), E);
+ }
----------------
This assumes that the host `double` has the same behavior as the target
`double`, which is not true in general. Generally the right thing to do is to
implement the relevant functionality on `APFloat`, taking care to produce the
right answer for the floating-point model being used by that `APFloat`. This
also assumes that the host `long` is the same size as the target `long`, which
again is not true in general. Finally, you need to catch the case where the
`APFloat` does not fit into the target type; in that case, the best response is
probably to treat the evaluation as non-constant and leave it to the runtime
library to implement whatever error response it chooses.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D66862/new/
https://reviews.llvm.org/D66862
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