netronome/nfp/bpf/jit.c cannot be build with -O3

[Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>]

Hi.

Obligatory disclaimer: building the kernel with -O3 is a non-standard 
thing done via this patch [1], but I've asked people in #kernelnewbies, 
and it was suggested that the issue should be still investigated.

So, with v5.1 kernel release I cannot build the kernel with -O3 anymore. 
It fails as shown below:

===
  CC      drivers/net/ethernet/netronome/nfp/bpf/jit.o
In file included from ./include/asm-generic/bug.h:5,
                 from ./arch/x86/include/asm/bug.h:83,
                 from ./include/linux/bug.h:5,
                 from drivers/net/ethernet/netronome/nfp/bpf/jit.c:6:
In function ‘__emit_shf’,
    inlined from ‘emit_shf.constprop’ at 
drivers/net/ethernet/netronome/nfp/bpf/jit.c:364:2,
    inlined from ‘shl_reg64_lt32_low’ at 
drivers/net/ethernet/netronome/nfp/bpf/jit.c:379:2,
    inlined from ‘shl_reg’ at 
drivers/net/ethernet/netronome/nfp/bpf/jit.c:2506:2:
./include/linux/compiler.h:344:38: error: call to 
‘__compiletime_assert_341’ declared with attribute error: BUILD_BUG_ON 
failed: (((0x001f0000000ULL) + (1ULL << 
(__builtin_ffsll(0x001f0000000ULL) - 1))) & (((0x001f0000000ULL) + (1ULL 
<< (__builtin_ffsll(0x001f0000000ULL) - 1))) - 1)) != 0
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
                                      ^
./include/linux/compiler.h:325:4: note: in definition of macro 
‘__compiletime_assert’
    prefix ## suffix();    \
    ^~~~~~
./include/linux/compiler.h:344:2: note: in expansion of macro 
‘_compiletime_assert’
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
  ^~~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:39:37: note: in expansion of macro 
‘compiletime_assert’
 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^~~~~~~~~~~~~~~~~~
./include/linux/bitfield.h:57:3: note: in expansion of macro 
‘BUILD_BUG_ON_MSG’
   BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ?  \
   ^~~~~~~~~~~~~~~~
./include/linux/bitfield.h:89:3: note: in expansion of macro 
‘__BF_FIELD_CHECK’
   __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: "); \
   ^~~~~~~~~~~~~~~~
drivers/net/ethernet/netronome/nfp/bpf/jit.c:341:3: note: in expansion 
of macro ‘FIELD_PREP’
   FIELD_PREP(OP_SHF_SHIFT, shift) |
   ^~~~~~~~~~
make[1]: *** [scripts/Makefile.build:276: 
drivers/net/ethernet/netronome/nfp/bpf/jit.o] Error 1
make: *** [Makefile:1726: drivers/net/ethernet/netronome/nfp/bpf/jit.o] 
Error 2
===

Needless to say, with -O2 this file is built just fine. My compiler is:

===
$ gcc --version
gcc (GCC) 8.3.0
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is 
NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR 
PURPOSE.
===

I had no issues with -O3 before, so, maybe, this deserves a peek.

I'm open to testing patches and providing more info if needed.

Thanks.

[1] 
https://gitlab.com/post-factum/pf-kernel/commit/7fef93015ff1776d08119ef3d057a9e9433954a9

--
  Oleksandr Natalenko (post-factum)