[Bug middle-end/113164] New: [missed optimization] struct fields should not alias

[Bug middle-end/113164] New: [missed optimization] struct fields should not alias

[powerboat9.gamer at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113164

            Bug ID: 113164
           Summary: [missed optimization] struct fields should not alias
           Product: gcc
           Version: 13.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: powerboat9.gamer at gmail dot com
  Target Milestone: ---

I have the following code

> struct sss {
>     int a;
>     int b;
> };
> 
> int foo(struct sss *a, struct sss *b) {
>     return &a->a == &b->b;
> }

When I compile it with

> gcc -c -O3 -Wall -Wextra test.c

I get

> 0000000000000000 <foo>:
>    0:	48 83 c6 04          	add    $0x4,%rsi
>    4:	31 c0                	xor    %eax,%eax
>    6:	48 39 fe             	cmp    %rdi,%rsi
>    9:	0f 94 c0             	sete   %al
>    c:	c3                   	ret

, but GCC should be able to infer that the two pointers being compared can not
alias.

[Bug middle-end/113164] [missed optimization] struct fields should not alias

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113164

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
           Keywords|                            |alias, missed-optimization

[Bug middle-end/113164] [missed optimization] struct fields should not alias

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113164

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2024-01-08
     Ever confirmed|0                           |1
                 CC|                            |hubicka at gcc dot gnu.org,
                   |                            |rguenth at gcc dot gnu.org
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
This would rely on TBAA btw, with -fno-strict-aliasing we allow *a and *b
to overlap, aka

 a = &b->b;

confirmed.  I think we have all the bits in aliasing_component_refs_p and
friends, it just would need to be factored/wired up for addresses.

[Bug middle-end/113164] [missed optimization] struct fields should not alias

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113164
Bug 113164 depends on bug 13962, which changed state.

Bug 13962 Summary: [tree-ssa] make "fold" use alias information to optimize pointer comparisons
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=13962

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED