[Bug middle-end/110052] useless local variable not optimized away

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110052

--- Comment #4 from Bernhard Reutner-Fischer <aldot at gcc dot gnu.org> ---
(In reply to Bernhard Reutner-Fischer from comment #3)
> Note that in this particular case myrealloc() is static, maybe i should have
> omitted the noipa attribute for it was only meant to simplify analysis and
> there is no such attribute in the original code.
> Furthermore, i would have hoped that given the placement of the definition
> of myrealloc() before the typedef foo_t, it should be unlikely that the
> usage of *foo would invalidate such an optimisation _in this particular
> case_. While the original code unfortunately does not mark *foo as restrict,
> adding restrict would hopefully make it clear that myrealloc() has no
> business in comparing foo's struct members, i'd hope?
> 
> When i drop the noipa attribute in the v1 testcase to make it similar to the
> motivating case, i get:

Correction: When i replace noipa with noinline,noclone (and drop
-ffunction-sections -fdata-sections to improve readability), i get:
    10: 0000000000000030    52 FUNC    GLOBAL DEFAULT    1 bloat
    10: 0000000000000030    21 FUNC    GLOBAL DEFAULT    1 ok

0000000000000030 <bloat>:
  30:   53                      push   %rbx
  31:   48 89 fb                mov    %rdi,%rbx
  34:   48 83 ec 10             sub    $0x10,%rsp
  38:   8b 47 14                mov    0x14(%rdi),%eax
  3b:   48 83 7f 08 00          cmpq   $0x0,0x8(%rdi)
  40:   89 44 24 0c             mov    %eax,0xc(%rsp)
  44:   75 11                   jne    57 <bloat+0x27>
  46:   48 8d 54 24 0c          lea    0xc(%rsp),%rdx
  4b:   be 00 01 00 00          mov    $0x100,%esi
  50:   31 ff                   xor    %edi,%edi
  52:   e8 a9 ff ff ff          callq  0 <myrealloc>
  57:   8b 44 24 0c             mov    0xc(%rsp),%eax
  5b:   89 43 14                mov    %eax,0x14(%rbx)
  5e:   48 83 c4 10             add    $0x10,%rsp
  62:   5b                      pop    %rbx
  63:   c3                      retq   

0000000000000030 <ok>:
  30:   48 83 7f 08 00          cmpq   $0x0,0x8(%rdi)
  35:   75 0d                   jne    44 <ok+0x14>
  37:   48 8d 57 14             lea    0x14(%rdi),%rdx
  3b:   be 00 01 00 00          mov    $0x100,%esi
  40:   31 ff                   xor    %edi,%edi
  42:   eb bc                   jmp    0 <myrealloc>
  44:   c3                      retq