Re: [PATCH] Fix ms_struct/-mms-bitfields structure layout (PR target/52991)

[JonY <10walls at gmail dot com>]

On 02/28/2018 12:26 AM, Jakub Jelinek wrote:
> Hi!
> 
> The following patch fixes the reported ms_struct/-mms-bitfields structure
> layout issues from PR52991.
> 
> There are multiple issues, two of them introduced by the
> https://gcc.gnu.org/ml/gcc-patches/2006-04/msg01064.html -mms-bitfields
> revamp from Eric and follow-up fix r114552, the rest has been introduced
> later when the known_align < desired_align case has been enabled for the ms
> bitfield layout.
> 
> The first 2 hunks fix alignment of packed non-bitfield fields, we can't
> ignore all the alignment updates for them, just should use only
> desired_align which takes DECL_PACKED into account, rather than
> MAX (type_align, desired_align).  Similarly, the last hunk in stor-layout.c
> makes sure that for DECL_PACKED fields we use BITS_PER_UNIT alignment rather
> than the type alignment.
> 
> The rest attempts to unbreak r184409 which enabled known_align < desired_align
> case; doing that if rli->prev_field and ms layout is wrong, we first need to
> deal with the bitfield packing and if we are within a bitfield word, we
> shouldn't do any realignment, only in between them.
> 
> The patch reverts changes to bf-ms-layout{,-2}.c tests done in 2012, which
> were done just to match the r184409 changes, and adds 2 new tests.  All of
> these 4 I've tested (slightly tweaked, so that it compiles with VC) with
> the online VC compiler http://rextester.com/l/c_online_compiler_visual .
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> 

No objections.

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