[Bug tree-optimization/14495] [tree-ssa] Propagate range info into a switch statement

[wouter dot vermaelen at pi dot be]

------- Comment #5 from wouter dot vermaelen at pi dot be  2006-04-20 10:58 
-------
I think something similar happens for the following code. 

  int f(int a) {
    switch (a & 7) {
      case 0: return  2;
      case 1: return  3;
      case 2: return  5;
      case 3: return  7;
      case 4: return 11;
      case 5: return 13;
      case 6: return 17;
      case 7: return 19;
    }
  }

Part of the generated code looks like this:

        movl    8(%ebp), %eax
        andl    $7, %eax
        cmpl    $7, %eax
        jbe     .L15
        popl    %ebp
        ret
        .p2align 4,,15
.L15:
        jmp     *.L11(,%eax,4)


The test for values bigger than 7 is clearly not needed here.

I don't know much about compiler technologie, but maybe this specific case is
easier to solve with some peephole optimization?


I have seen real code (Z80 emulator or HQ2x scaler algorithm) that does a
switch on a unsigned char and handles all 256 cases. Code like that would
benefit from this optimization.

Thanks.


-- 

wouter dot vermaelen at pi dot be changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |wouter dot vermaelen at pi
                   |                            |dot be


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14495