Fwd: [X-POST] Alignas broken when used with constexpr array data member for structure

Alec Teal a.teal@warwick.ac.uk
Tue Jan 9 13:39:00 GMT 2018


Per recommendation asking on GCC help



-------- Forwarded Message --------
Subject: 	Alignas broken when used with constexpr array data member for 
structure
Date: 	Tue, 9 Jan 2018 13:15:37 +0000
From: 	Alec Teal <a.teal@warwick.ac.uk>
To: 	gcc@gcc.gnu.org <gcc@gcc.gnu.org>



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Hi there,

In GCC 4.8.4 I have something like the following:

constexpr int x = 5;

constexpr int y = 4;

struct alignas(y) my_data_block {

    char data[x];

};


And it causes some weird errors to the tune of "size of array ‘data’ is
not an integral constant-expression" in the presence of the alignas

This is a pretty nasty bug and means it's not implemented as I thought.
I don't know the front-ends (but I do actually know GIMPLE-low and below
quite well, love the pattern matching) and I'd like to dig more, it's
almost certainly fixed - this is just for personal curiosity.

Where would I look? A 1 line reply with a directory would be a great
start; even if it's just a guess.

I did ask in #gcc on freenode - it didn't go so well, sorry to ping you
all for this.


Alec



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