[Bug middle-end/30314] optimize multiply-by-constant overflow (wrap) test

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=30314

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2021-08-11
           Assignee|unassigned at gcc dot gnu.org      |pinskia at gcc dot 
gnu.org

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
starting in GCC 11, we produce:
        movl    $140, %edx
        movq    %rdi, %rax
        mulq    %rdx
        jo      .L11

Which corresponds to this gimple:
  _7 = .MUL_OVERFLOW (num_3(D), 140);
  _8 = IMAGPART_EXPR <_7>;
  if (_8 != 0)

So it is definitely better than before.

BUT this is not the best code, clang produces (for 64bit):
        movabsq $131762457669353941, %rax       # imm = 0x1D41D41D41D41D5
        cmpq    %rax, %rdi
        jb      .LBB0_2

So basically ULONGMAX/140 as described.

So something like:
(simplify
 (imagpart (IFN_MUL_OVERFLOW:s @0 INTEGER_CST@1))
 (if (TREE_CODE (TYPE_MAX_VALUE (type)) == INTEGER_CST)
  (convert (le @0 (trunc_div { TYPE_MAX_VALUE (type); } @1))))