[PATCH] D130058: [Clang] Diagnose ill-formed constant expression when setting a non fixed enum to a value outside the range of the enumeration values

[Erich Keane via Phabricator via cfe-commits]

erichkeane added inline comments.


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Comment at: clang/lib/AST/Decl.cpp:4609
+
+  if (NumNegativeBits) {
+    unsigned NumBits = std::max(NumNegativeBits, NumPositiveBits + 1);
----------------
How does this work if both NumNegativeBits and NumPositiveBits are 0?  Based on my reading of the standard, an empty enum should have the valid values 0 and 1, so a 'bitwidth' of 1.


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Comment at: clang/test/SemaCXX/constant-expression-cxx11.cpp:2409
+// Empty but as-if it had a single enumerator with value 0
+enum EEmpty {};
+
----------------
Would also like to see `enum E4 {e41=0};`, which should have the values 0 and 1.


================
Comment at: clang/test/SemaCXX/constant-expression-cxx11.cpp:2429
+  constexpr EEmpty x7 = static_cast<EEmpty>(1); // expected-error {{must be initialized by a constant expression}}
+  // expected-note at -1 {{store of value outside of the range of unscoped enum, valid values 0 to 0}}
+
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Ok, so I think '1' should be valid here based on my reading.  

An empty should be the exact same case as the proposed `E4` above, and I believe we can never allow 'zero' bits.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D130058/new/

https://reviews.llvm.org/D130058