[PATCH] D62825: [C++2a] Add __builtin_bit_cast, used to implement std::bit_cast
JF Bastien via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon Jun 3 17:21:33 PDT 2019
jfb added inline comments.
================
Comment at: clang/lib/AST/ExprConstant.cpp:5447
+
+ case APValue::LValue: {
+ LValue LVal;
----------------
rsmith wrote:
> This will permit bitcasts from `nullptr_t`, providing a zero value. I think that's wrong; the bit representation of `nullptr_t` is notionally uninitialized (despite strangely having pointer size and alignment).
>
> I think this is a specification bug: `bit_cast<intptr_t>(nullptr)` should be non-constant (it won't necessarily be `0` at runtime) but the current wording doesn't seem to permit us to treat it as non-constant.
You brought this up in ABQ, the outcome was... poor notes so I have no idea what Core decided...
Repository:
rC Clang
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D62825/new/
https://reviews.llvm.org/D62825
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