[Bug tree-optimization/107052] Range of __builtin_popcount can be improved with nonzerobits

["aldyh at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107052

Aldy Hernandez <aldyh at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-09-27
                 CC|                            |amacleod at redhat dot com
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #2 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
Don't you mean the only values for popcount are 0-2?  I mean, there are only
two bits that could be 1 with a mask of 0x300.  Or am I missing something?

Either way, your check is for b > 3, and we should be able to fold that away.

There are two problems here.  The cast of a_4 to a.0_1 dropped the nonzero
mask.  I would've expected that a cast to a number of the same precision would
keep the 0x300 mask, instead we have:

a.0_1 : [irange] unsigned int [0, 768] NONZERO 0x3ff

If we had the 0x300 mask available in cfn_popcount::fold_range(), then we could
fold it.  The second problem is that cfn_popcont, does not look at the nonzero
bits at all.

=========== BB 2 ============
Imports: a_3(D)  
Exports: a.0_1  a_3(D)  a_4  b_5  
         a.0_1 : a_3(D)(I)  a_4  
         a_4 : a_3(D)(I)  
         b_5 : a.0_1  a_3(D)(I)  a_4  
a_3(D)  [irange] int VARYING
    <bb 2> :
    a_4 = a_3(D) & 768;
    a.0_1 = (unsigned int) a_4;
    b_5 = __builtin_popcount (a.0_1);
    if (b_5 > 3)
      goto <bb 3>; [INV]
    else
      goto <bb 4>; [INV]

a.0_1 : [irange] unsigned int [0, 768] NONZERO 0x3ff
a_4 : [irange] int [0, 768] NONZERO 0x300
b_5 : [irange] int [0, 10] NONZERO 0xf
2->3  (T) a.0_1 :       [irange] unsigned int [0, 768] NONZERO 0x3ff
2->3  (T) a_4 :         [irange] int [0, 768] NONZERO 0x300
2->3  (T) b_5 :         [irange] int [4, 10] NONZERO 0xf
2->4  (F) a.0_1 :       [irange] unsigned int [0, 768] NONZERO 0x3ff
2->4  (F) a_4 :         [irange] int [0, 768] NONZERO 0x300
2->4  (F) b_5 :         [irange] int [0, 3] NONZERO 0x3