Merge pull request #8560 from liamwhite/bitfield-may-alias

common: fix bitfield aliasing on GCC/Clang

1 files changed, 9 insertions, 0 deletions

diff --git a/src/common/bit_field.h b/src/common/bit_field.h
index 16d805694..7e1df62b1 100644
--- a/src/common/bit_field.h
+++ b/src/common/bit_field.h
@@ -146,7 +146,16 @@ public:
     }
 
     constexpr void Assign(const T& value) {
+#ifdef _MSC_VER
         storage = static_cast<StorageType>((storage & ~mask) | FormatValue(value));
+#else
+        // Explicitly reload with memcpy to avoid compiler aliasing quirks
+        // regarding optimization: GCC/Clang clobber chained stores to
+        // different bitfields in the same struct with the last value.
+        StorageTypeWithEndian storage_;
+        std::memcpy(&storage_, &storage, sizeof(storage_));
+        storage = static_cast<StorageType>((storage_ & ~mask) | FormatValue(value));
+#endif
     }
 
     [[nodiscard]] constexpr T Value() const {