[PATCH] D88498: [FPEnv] Evaluate initializers in constant rounding mode

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith requested changes to this revision.
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================
Comment at: clang/lib/Parse/ParseDecl.cpp:2290
+          // rounding mode.
+          if (VD->isFileVarDecl() || VD->isConstexpr() ||
+              (!getLangOpts().CPlusPlus && VD->isStaticLocal())) {
----------------
It's far from clear to me that this is correct in C++. In principle, for a dynamic initializer, the rounding mode could have been set by an earlier initializer.

Perhaps we can make an argument that, due to the permission to interleave initializers from different TUs, every dynamic initializer must leave the program in the default rounding mode, but I don't think even that makes this approach correct, because an initializer could do this:

```
double d;
double e = (fesetround(...), d = some calculation, fesetround(...default...), d);
```

I think we can only do this in C and will need something different for C++.

(I think this also has problems in C++ due to constexpr functions: it's not the case that all floating point operations that will be evaluated as part of the initializer lexically appear within it.)


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https://reviews.llvm.org/D88498