[Bug c++/79085] New: ICE with placement new to unaligned location

["thopre01 at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79085

            Bug ID: 79085
           Summary: ICE with placement new to unaligned location
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: thopre01 at gcc dot gnu.org
                CC: jason at gcc dot gnu.org
  Target Milestone: ---

Created attachment 40517
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40517&action=edit
Placement new to unaligned location

Hi,

The attached file ICE when compiled with -Os. The ICE is due to the assert in
assign_temp when called from expand_call because TREE_ADDRESSABLE(type) is
true. This is set from the C++ frontend in finish_struct_bits because there is
a non default constructor and expand_call calls assign_temp because the
location in which the return value optimization is not sufficiently aligned.

Due to the check to SLOW_UNALIGNED_ACCESS in expand_call, this does not affect
all targets. I was able to reproduce the bug can be reproduced on
alpha-linux-gnu by adapting size_t and ptrdiff_t accordingly.

Setting the component to C++ based on the comment regarding the assertion of
TREE_ADDRESSABLE in assign_temp.