[PATCH] D134859: [clang][Interp] Implement basic support for floating point values

[Timm Bäder via Phabricator via cfe-commits]

tbaeder added a comment.

In D134859#3945709 <https://reviews.llvm.org/D134859#3945709>, @sepavloff wrote:

> In D134859#3943926 <https://reviews.llvm.org/D134859#3943926>, @tbaeder wrote:
>
>> FYI, I noticed the way the floating values are serialized doesn't work if the `APFloat` heap-allocated anything; those values aren't preserved through (de)serialization of course.
>>
>> Reproducer:
>>
>>   constexpr double foo() {
>>     return __LDBL_MIN__;
>>   }
>
> The return statement returns a value of type `long double` while the function returns `double`. If `long double` is wider than `double`, truncation occurs, may be this is the reason?

It also happens when the function returns a `long double`.

I tracked the problem down to the way we emit byte code into a `std::vector`. It's simply `reintepret_cast'`ed to `const char *`, so that won't work for `APFloat`.

This change seems to fix the problem:

  diff --git a/clang/lib/AST/Interp/ByteCodeEmitter.cpp b/clang/lib/AST/Interp/ByteCodeEmitter.cpp
  index ff2136d34872..61e9662013c3 100644
  --- a/clang/lib/AST/Interp/ByteCodeEmitter.cpp
  +++ b/clang/lib/AST/Interp/ByteCodeEmitter.cpp
  @@ -163,8 +163,15 @@ static void emit(Program &P, std::vector<char> &Code, const T &Val,
     }
  
     if constexpr (!std::is_pointer_v<T>) {
  -    const char *Data = reinterpret_cast<const char *>(&Val);
  -    Code.insert(Code.end(), Data, Data + Size);
  +     if constexpr (std::is_trivially_copyable_v<T>) {
  +      const char *Data = reinterpret_cast<const char *>(&Val);
  +      Code.insert(Code.end(), Data, Data + Size);
  +     } else {
  +       // Construct the value directly into our storage vector.
  +       size_t ValPos = Code.size();
  +       Code.resize(Code.size() + Size);
  +       new (Code.data() + ValPos) T(Val);
  +     }
     } else {
       uint32_t ID = P.getOrCreateNativePointer(Val);
       const char *Data = reinterpret_cast<const char *>(&ID);




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  https://reviews.llvm.org/D134859/new/

https://reviews.llvm.org/D134859