<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/64823>64823</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Miscompilation/Assertion "FPConstrained should be enabled on entire function"' failed with FENV_ACCESS and default function argument
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang:codegen,
            miscompilation,
            floating-point
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          hubert-reinterpretcast
      </td>
    </tr>
</table>

<pre>
    With the following source, asserts-enabled builds of Clang hit an assertion:
```
/root/llvm-project/clang/lib/CodeGen/CodeGenFunction.cpp:161: void clang::CodeGen::CodeGenFunction::CGFPOptionsRAII::ConstructorHelper(clang::FPOptions): Assertion `(CGF.CurFuncDecl == nullptr || CGF.Builder.getIsFPConstrained() || isa<CXXConstructorDecl>(CGF.CurFuncDecl) || isa<CXXDestructorDecl>(CGF.CurFuncDecl) || (NewExceptionBehavior == llvm::fp::ebIgnore && NewRoundingBehavior == llvm::RoundingMode::NearestTiesToEven)) && "FPConstrained should be enabled on entire function"' failed.
```

If it is accepted that the pragma state at the point where code is lexically present is to be respected when the code is evaluated, then the non-asserts builds miscompile the code (as can be seen by inspecting the assembly obtained with `-O`; the call to `foo` is not generated).

https://godbolt.org/z/5PKqY5nfa

```cpp
#include <float.h>
struct ChangeRounding {
  ChangeRounding();
 ~ChangeRounding();
};
int foo(), bar();

#pragma STDC FENV_ACCESS ON

struct Ex {
  Ex() = default;
  Ex(const Ex &, int = (ChangeRounding(), (float)0xFFFFFFFF != (float)0x100000000 ? foo() : bar()));
};

#pragma STDC FENV_ACCESS OFF
void q(const Ex &e) { Ex e2(e); }
```

Clang version info:
```
clang version 18.0.0 (https://github.com/llvm/llvm-project.git 6eb0332e72e5d9c5db1f89bac28770bc6f0725c2)
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJykVc2O2zYQfhr6MlhBHq4t-eCDV7bSRZFNkARteiooaiSxoEmFpPanhz57QclaO9vdFkEFwRY5_x_nGwrvVWuItmx1w1b7hRhCZ922Gypy4cqRMoFc7yhI4cOisvXT9lcVOggdQWO1tg_KtODt4CQxLEB4Ty74KzKi0lRDNShde7ANFFqYFjoVQJiTmrKG8R1L9yzdsXV6eqclls7awLDU-v541Tv7B8m4lNFN3FYVw7KwNb0jc_4qByOj30T2PeO75XrJ-A7uraphsuQ7xnez2eVitjxtvis_fujj2n_a3d7OmsYHN8hg3U-ke3IM8wuvzxYMNzHqbi4SYlmYF-_KpBhcDLQnqYHxPeN7MIPWfXDAsoJlBUStm4gauaSlcOvLj1NcoQzVDHOGm1lXecF4UXz9epFZdM344Z_xXrPb04-YMczv6OHwKGms84Y6ca-smwuJJzUh0fTTP1W3rbGOgOGa4Rru6OGTHUytTPu28azx3tY07dyRcOTDF0X-iz3cx_PejGlNXhnidxiB7-yga6gI5ja0BsgE5Qia-ZgRGWbQCKWpTl7vwfH3tgEVQHkQMtZNNYROhJEAvRPtUYAPIhDMe1aZAA8dOQJpa4qWmh6VFFo_Qe_IkxndBRsTdOR7ktHrQ0dm9DBb0b3QgwjxzIsomKTGmqsTyWZyHZWX9tgrTWd7hrnwIIWJQTyRgeoJlBmDRcZGxejmWOknsFWYgHuI1Gbr9OpDBIHfTP6E1jFbtk4ba9k6jckZG6AlQ25KcJNcQtaF0Pt4dFgyLFtbV1aHxLrI2z8ZlquPP3_7bWUacWn0DH5k7mkGcGWkHmI5vGi0FSHpYo-O0qlxoeiEaWnuGWDZzSSGF5KJOIzP4r_-Vcyy_fN3PM9Y-KSBBVTCvVSf8z11xOcv-wLKw90vv--K4vD5M3y4u1Q8pX54vEz38Dhzm--hpkYMOpzTncQyNvloFzu_gJhaVI-sfa0cHDk7Isdwkz6WpwcYLk92Z-EyPT3AeHmuGOIoO5c8va_h9N8glOWkM47jby_qoWnQ3MQlIcOcpkAQY7xNz-lauSfn46BVprFvXSnyO81lnqRJGhF40a0qdEOVSHs83T0vrqCkVQHWVKWcI2VIq3ojV3W1bPJNJSTmWZZWct2kGa4kxgq-T2VRb3m94RuxoO1yvcHrJS5Tvui2FfI8T1cyX1G-zBqBosb0WlJG1YqjpIXaYoo8zZebFDFHnqy4EBlvUK6vq2XaVOw6paNQOonpRrYtlPcDbdfXOfKFFhVpP17ziPOlFUdFS9MsLBji8yQRzyMybo89okx7NQ63uL3aL9x2hKUaWs-uU6188OfIQQVN2_cv3JUXN-L_ntnTsLrsL2HqmTjPJiBcOxzJhMXg9PbHjpphOSLoGZYjiH8HAAD__z_q0Os">