[Bug tree-optimization/88841] Missed optimization transforming cascading ||s into a bit select

[Bug tree-optimization/88841] Missed optimization transforming cascading ||s into a bit select

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88841

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
   Last reconfirmed|2019-01-15 00:00:00         |2021-12-17

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Here is the full testcase where all three functions should produce the same
assembly code, right now _2 and _3 produce the same and the best code:

bool isspc_1(char c)
{
    return c == ' '
        || c == '\n'
        || c == '\r'
        || c == '\t';
}

bool isspc_2(char c)
{
    return c == ' '
        || c == '\r'
        || c == '\n'
        || c == '\t';
}

bool isspc_3(char c)
{
    switch(c)
    {
        case ' ':
        case '\r':
        case '\n':
        case '\t':
            return 1;
    }
    return 0;
}

[Bug tree-optimization/88841] Missed optimization transforming cascading ||s into a bit select

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88841

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
For the trunk for _2, if_to_switch can convert that one to:

;; Canonical GIMPLE case clusters: 9-10 13 32 
;; BT can be built: BT:9-32 
Removing basic block 3
Expanded into a new gimple STMT: switch (c_6(D)) <default: <L6> [INV], case 9
... 10: <L5> [INV], case 13: <L5> [INV], case 32: <L5> [INV]>

For _1, we get the following IR (because fold-const decided to convert the ||
to | in some cases already):
  _1 = c_8(D) == 32;
  _2 = c_8(D) == 10;
  _3 = _1 | _2;
  if (_3 != 0)
    goto <bb 4>; [INV]
  else
    goto <bb 3>; [INV]

  <bb 3> :
  _4 = c_8(D) == 13;
  _5 = c_8(D) == 9;
  _6 = _4 | _5;