[Bug tree-optimization/107502] New: GCC fails to detect foo(first_const,last)-first_const+first pattern

[Bug tree-optimization/107502] New: GCC fails to detect foo(first_const,last)-first_const+first pattern

[unlvsur at live dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107502

            Bug ID: 107502
           Summary: GCC fails to detect
                    foo(first_const,last)-first_const+first pattern
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: unlvsur at live dot com
  Target Milestone: ---

GCC fails to detect foo(first_const,last)-first_const+first pattern.

This is to use C++ std::contiguous_iterator interfaces with char const*
foo(char const* first, char const* last) noexcept; like APIs. However, GCC
fails to detect they are the same in IR and make them tail calls.

See godbolt:

https://godbolt.org/z/67PvYPar8

[Bug tree-optimization/107502] GCC fails to detect foo(first_const,last)-first_const+first pattern

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107502

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Created attachment 53817
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53817&action=edit
testcase

[Bug tree-optimization/107502] GCC fails to detect foo(first_const,last)-first_const+first pattern

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107502

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Your testcase has no return in it.
So there is a __builtin_unreachable added at the end of each function without
returns.
<source>: In function 'char* test(char*, char*)':
<source>:34:1: warning: no return statement in function returning non-void
[-Wreturn-type]
   34 | }
      | ^
<source>: In function 'std::vector<char>::iterator
test2(std::vector<char>::iterator, std::vector<char>::iterator)':
<source>:40:1: warning: no return statement in function returning non-void
[-Wreturn-type]
   40 | }
      | ^
ASM generation compiler returned: 0
<source>: In function 'char* test(char*, char*)':
<source>:34:1: warning: no return statement in function returning non-void
[-Wreturn-type]
   34 | }
      | ^
<source>: In function 'std::vector<char>::iterator
test2(std::vector<char>::iterator, std::vector<char>::iterator)':
<source>:40:1: warning: no return statement in function returning non-void
[-Wreturn-type]
   40 | }
      | ^

[Bug tree-optimization/107502] GCC fails to detect foo(first_const,last)-first_const+first pattern

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107502

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I filed PR 107503 with the reduced testcase for the test2 case (after having
fixed the return issue).

[Bug tree-optimization/107502] GCC fails to detect foo(first_const,last)-first_const+first pattern

[unlvsur at live dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107502

--- Comment #4 from cqwrteur <unlvsur at live dot com> ---
(In reply to Andrew Pinski from comment #3)
> I filed PR 107503 with the reduced testcase for the test2 case (after having
> fixed the return issue).

sorry about that. it should be vector case
https://godbolt.org/z/f9TYMxb7c

[Bug tree-optimization/107502] GCC fails to detect foo(first_const,last)-first_const+first pattern

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107502

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to cqwrteur from comment #4)
> (In reply to Andrew Pinski from comment #3)
> > I filed PR 107503 with the reduced testcase for the test2 case (after having
> > fixed the return issue).
> 
> sorry about that. it should be vector case
> https://godbolt.org/z/f9TYMxb7c

Right, PR 107503 has the reduced testcase for your vector (test2 function)
testcase.