Re: [patch] Fix PR middle-end/92071

[Richard Biener <richard.guenther@gmail.com>]

On Fri, Mar 13, 2020 at 8:37 AM Eric Botcazou <ebotcazou@adacore.com> wrote:
>
> Hi,
>
> this is a regression present on the mainline for the ARM in the form of an
> assertion failure at -O2 in the back-end, which rightfully refuses to generate
> a load from an unaligned memory location (the ARM target is strict-alignment).
>
> It comes from a __builtin_memcpy generating:
>
> MEM <unsigned char[8]> [(char * {ref-all})&b] = MEM <unsigned char[8]> [(char
> * {ref-all})a.0_1];
>
> in the .optimized dump, where b is a small union.  As a result, store_field is
> invoked with:
>
> (gdb) p debug_rtx(target)
> (reg/v:DI 113 [ b ])
>
> and sends:
>
> (gdb) p debug_rtx(temp)
> (mem:BLK (reg/f:SI 115) [0 MEM <unsigned char[8]> [(char * {ref-all})a.0_1]+0
> S8 A8])
>
> to store_bit_field with 64 bits and BLKmode.  The unaligned memory reference
> is then generated by store_integral_bit_field, which does:
>
> rtx value_word = operand_subword_force (value, wordnum, value_mode);
>
> thus creating an unaligned word mode (SImode) load.
>
> store_integral_bit_field is ready to handle BLKmode fields, there is even a
> subtlety with their handling on big-endian targets, see PR middle-end/50325,
> but not if they are unaligned, so the fix is simply to call extract_bit_field
> for them in order to generate an unaligned load.  As a bonus, this subsumes
> the big-endian specific path that was added under PR middle-end/50325.
>
> Bootstrapped/regtested on x86-64/Linux and SPARC/Solaris, OK for mainline?

OK.

Thanks,
Richard.

>
> 2019-03-13  Eric Botcazou  <ebotcazou@adacore.com>
>
>         PR middle-end/92071
>         * expmed.c (store_integral_bit_field): For fields larger than a word,
>         call extract_bit_field on the value if the mode is BLKmode.  Remove
>         specific path for big-endian targets and tidy things up a little bit.
>
>
> 2019-03-13  Eric Botcazou  <ebotcazou@adacore.com>
>
>         * gcc.c-torture/compile/20200313-1.c: New test.
>
> --
> Eric Botcazou