[Bug rtl-optimization/21643] New: GCC fails to merge ranges in comparison.

[Bug rtl-optimization/21643] New: GCC fails to merge ranges in comparison.

[dwmw2 at infradead dot org]

I'd expect the result of compiling these two functions to be identical, but it
isn't:

int fish1(unsigned char c)
{
        if (c =='"' || c == 0x20 || c < 0x20)
                return 1;
}
int fish2(unsigned char c)
{
        if (c == '"' || c <= 0x20)
                return 1;
}

If I remove the 'c == '"' ||' from each, I do get the expected results.
$ gcc -O2 -S asd.c -o /dev/stdout
        .file   "asd.c"
        .section        ".text"
        .align 2
        .p2align 4,,15
        .globl fish1
        .type   fish1, @function
fish1:
        mr 0,3
        li 3,1
        cmpwi 7,0,34
        cmpwi 6,0,32
        beqlr 7
        cmplwi 7,0,31
        beqlr 6
        blelr 7
        blr
        .size   fish1,.-fish1
        .align 2
        .p2align 4,,15
        .globl fish2
        .type   fish2, @function
fish2:
        mr 0,3
        li 3,1
        cmpwi 7,0,34
        cmplwi 6,0,32
        beqlr 7
        blelr 6
        blr
        .size   fish2,.-fish2
        .ident  "GCC: (GNU) 4.0.0 20050512 (Red Hat 4.0.0-5)"
        .section        .note.GNU-stack,"",@progbits

-- 
           Summary: GCC fails to merge ranges in comparison.
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dwmw2 at infradead dot org
                CC: gcc-bugs at gcc dot gnu dot org,jakub at redhat dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21643

[Bug rtl-optimization/21643] GCC fails to merge ranges in comparison.

[dwmw2 at infradead dot org]

------- Additional Comments From dwmw2 at infradead dot org  2005-05-18 12:33 -------
Happens with gcc 3.4 too, and also on i386.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21643

[Bug tree-optimization/21643] GCC fails to merge ranges in comparison.

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-05-18 12:38 -------
Confirmed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
          Component|rtl-optimization            |tree-optimization
     Ever Confirmed|                            |1
           Keywords|                            |missed-optimization
   Last reconfirmed|0000-00-00 00:00:00         |2005-05-18 12:38:44
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21643

[Bug tree-optimization/21643] GCC fails to merge ranges in comparison.

[trt at acm dot org]

------- Additional Comments From trt at acm dot org  2005-05-18 17:21 -------
This is because fold-const.c only does ad-hoc re-association.
Here is an example for fold_truthop (approx line 8805)

      /* Check for the possibility of merging component references.  If our
         lhs is another similar operation, try to merge its rhs with our
         rhs.  Then try to merge our lhs and rhs.  */
      if (TREE_CODE (arg0) == code
          && 0 != (tem = fold_truthop (code, type,
                                       TREE_OPERAND (arg0, 1), arg1)))
        return fold_build2 (code, type, TREE_OPERAND (arg0, 0), tem);

A similar hack could be done for fold_range_test.

(I wrote a helper fold_assoc (f, x, code, type, op1, op2) that does this in a
more general way, but it in turn needed `find_assoc_p' and `commutes_p'
functions, and handling EXPR_MINUS was onerous.  It might be too slow for
general use.  Basically, it needs a fast way to check for common subexpressions
to avoid pointless recursions.)

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21643

[Bug tree-optimization/21643] GCC fails to merge ranges in comparison.

[trt at acm dot org]

------- Additional Comments From trt at acm dot org  2005-05-18 17:28 -------
Here is a equivalent case that gcc also misses (but beyond scope of
fold-const.c). By the way, since there is a missing final return, can't gcc just
simplify all three functions into "return 1;" :-)

int fish3(unsigned char c)
{
        if (c =='"') return 1;
        if (c == 0x20) return 1;
        if (c < 0x20) return 1;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21643