[PATCH] D76323: [AST] Fix handling of long double and bool in __builtin_bit_cast

[Erik Pilkington via Phabricator via cfe-commits]

erik.pilkington created this revision.
erik.pilkington added reviewers: rsmith, ldionne, jfb.
Herald added subscribers: ributzka, dexonsmith, jkorous.

On x86, `long double` has 6 unused trailing bytes. This patch changes the constant evaluator to treat them as though they were padding bytes, so reading from them results in an indeterminate value, and nothing is written for them. Also, fix a similar bug with bool, but instead of treating the unused bits as padding, enforce that they're zero.

Fixes a bug Louis pointed out in: https://reviews.llvm.org/D75960


https://reviews.llvm.org/D76323

Files:
  clang/include/clang/Basic/DiagnosticASTKinds.td
  clang/lib/AST/ExprConstant.cpp
  clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp

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