[Bug tree-optimization/95408] New: Failure to optimize bitwise and with negated conditional using the same operand to conditional with decremented operand

[Bug tree-optimization/95408] New: Failure to optimize bitwise and with negated conditional using the same operand to conditional with decremented operand

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95408

            Bug ID: 95408
           Summary: Failure to optimize bitwise and with negated
                    conditional using the same operand to conditional with
                    decremented operand
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

bool f(int x)
{
    return x & -((unsigned)x < some_constant);
}

This can be optimized to `return (unsigned)(x - 1) < (some_constant - 1);`.
This transformation is done by LLVM, but not by GCC.

[Bug tree-optimization/95408] Failure to optimize bitwise and with negated conditional using the same operand to conditional with decremented operand

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95408

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

[Bug tree-optimization/95408] Failure to optimize bitwise and with negated conditional using the same operand to conditional with decremented operand

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95408

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |pinskia at gcc dot gnu.org
   Last reconfirmed|                            |2023-05-13
             Status|UNCONFIRMED                 |ASSIGNED

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
For unsigned x (to simplify things first).
In forwardprop4 we have
  _1 = x_4(D) <= 121211;
  _3 = _1 ? x_4(D) : 0;
  _5 = _3 != 0;

This could be done as:
x_4(D) <= 121211 ? x_4(D) != 0 : 0

Which then would be:
(x_4(D) <= 121211 & x_4(D) != 0) 
((x_4(D) - 1) <= 121210)

So I have a patch which does the second step into the 3rd expression (there is
another bug or 2 about it). the 3rd expression into the final is already done.
It is just the first that needs to happen to written up.

Something like this for the first step.
(for op (tcc_comparison)
/* (c ? a : CST0) op CST1  -->  c ? (a op CST1) : (CST0 op CST1) */
 (simplify
  (op (cond:s @0 @1 CONSTANT_CLASS_P@2) CONSTANT_CLASS_P@3)
  (cond! @0 (op @1 @3) (op @2 @4)))

So mine.

[Bug tree-optimization/95408] Failure to optimize bitwise and with negated conditional using the same operand to conditional with decremented operand

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95408

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
In forwprop1 we have:
  _2 = x.0_1 <= 121210;
  _3 = (int) _2;
  _4 = _3 * x_5(D);
  _6 = _4 != 0;

since _3 is zero_one_valued we could do instead:
```
(for cmp   (ne      eq     )
     bitop (bit_and bit_ior)
 (simplify
  (cmp (mult zero_one_valued_p@0 @1) integer_zerop@2)
  (bitop! (convert @0) (ne @1 @2))))
```
And we should be able to get it earlier on.

Still mine and I will look into the above.

[Bug tree-optimization/95408] Failure to optimize bitwise and with negated conditional using the same operand to conditional with decremented operand

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95408

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                URL|                            |https://gcc.gnu.org/piperma
                   |                            |il/gcc-patches/2023-Septemb
                   |                            |er/630651.html
           Keywords|                            |patch

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I was looking for this one when I wrote
https://gcc.gnu.org/pipermail/gcc-patches/2023-September/630651.html .