[Bug lto/99828] inlining failed in call to ‘always_inline’ ‘memcpy’: --param max-inline-insns-auto limit reached

["rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99828

--- Comment #9 from rguenther at suse dot de <rguenther at suse dot de> ---
On Wed, 31 Mar 2021, marxin at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99828
> 
> --- Comment #8 from Martin Liška <marxin at gcc dot gnu.org> ---
> All right, I vanished the test-case:
> 
> $ cat 1.i
> inline __attribute__((__always_inline__)) __attribute__((gnu_inline)) void *
> memcpy();
> void *apply_relocate_add_write = memcpy;
> 
> $ touch 2.s
> $ cat 3.i
> enum { false, true } * __memcpy();

??  obviously bad reduction.

> _Bool kasan_check_range();
> void *memcpy(void *dest, void *src, long len) {
>   if (kasan_check_range(len, false, 0) || kasan_check_range(len, true, 0))
>     return __memcpy(dest, src, len);
> }
> 
> long LZ4_decompress_generic_dst_restSize;
> char LZ4_decompress_generic_dst_lowPrefix;
> void LZ4_decompress_generic_dst() {
>   __builtin_memcpy(LZ4_decompress_generic_dst,
>                    &LZ4_decompress_generic_dst_lowPrefix,
>                    LZ4_decompress_generic_dst_restSize);

I wonder if this use of __builtin_memcpy intends to not use the
kernels always-inline memcpy but GCCs own inline expansion?
This obviously doesn't work, not with LTO at least.

It looks like with kasan enabled (and memcpy "wrapped") the
memcpy declaration should _not_ have the always-inline (since
the implementation is no longer always-inline).  That would be
a fix on the kernel side, but I'd also diagnose any such
always-inline "mismatch" we get to at WPA.