[PATCH] D80055: Diagnose union tail padding

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

rsmith added a comment.

In D80055#2055151 <https://reviews.llvm.org/D80055#2055151>, @jfb wrote:

> I was wondering if any of the tests were surprising to you, or if the behavior described was as expected?


I've highlighted one case where the test expectation doesn't match the standard rules.



================
Comment at: clang/test/CodeGen/union-tail-padding.c:42
+#elif __cplusplus < 201703
+Front front6 = Front(); // expected-warning {{Initializing union 'Front' field 'i' only initializes the first 4 of 8 bytes, leaving the remaining 4 bytes undefined}}
+Front front7 = Front{}; // expected-warning {{Initializing union 'Front' field 'i' only initializes the first 4 of 8 bytes, leaving the remaining 4 bytes undefined}}
----------------
This warning appears to be incorrect. Value-initialization of a union with a trivial default constructor performs zero-initialization, which does zero out padding bits.


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